TM-11-6625-298-14
TM
T E C H N I C A L
O P E R A T O R ’ S ,
S U P P O R T ,
11-6625-298-14
M A N U A L
O R G A N I Z A T I O N A L ,
A N D
G E N E R A L
M A I N T E N A N C E
OHMMETER
D I R E C T
S U P P O R T
M A N U A L
ZM-21/U
( NSN 5950-00-645-2191 ),
OHMMETER
ZM-21A/U
(NSN 6625-00-643-1030),
AND
OHMMETER
ZM-21B/U
( NSN 6625-00-581-2466)
HEADQUARTERS,
DEPARTMENT
OF
13
THE
JANUARY
ARMY
1977
WARNING
DANGEROUS VOLTAGES EXIST IN THIS EQUIPMENT
Do not come in contact with test leads or terminals during operation. Potentials as high as 500 volts
exist during operation,
DON’T TAKE CHANCES!
*TM 11-6625-298-14
TECHNICAL MANUAL
No. 11-6625-298-14
HEADQUARTERS
DEPARTMENT OF THE ARMY
W ASHINGTON , D. C., 13 January 1977
}
OPERATOR’S, ORGANIZATIONAL, DIRECT SUPPORT, AND GENERAL SUPPORT
MAINTENANCE MANUAL
OHMMETER ZM-21/U (NSN 5950-00-645-2191),
OHMMETER ZM-21A/U (NSN 6625-00-643-1030),
AND
OHMMETER ZM-21B/U (NSN 6625-00-581-2466)
REPORTING OF ERRORS
You can improve this manual by recommending improvements using DA
Form 2028-2 (Test ) located in the back of the manual. Simply tear out the
self-addressed form, fill it out as shown on the sample, fold it where shown,
and drop it in the mail.
If there are no blank DA Form 2028-2 (Test) forms in the back of your
manual, use the standard DA Form 2028 (Recommended Changes to
Publications and Blank Forms) and forward to the Commander, US Army
Electronics Command, ATTN: DRSEL-MA-Q, Fort Monmouth, NJ 07703.
In either case, a reply will be furnished direct to you.
Paragraph
C
H A P T E R
1-1–1-5
1-6–1-9
1-1
1-1
2-1,2-2
2-3,2-4
2-1
2-3
3-1
I. Controls and instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
II. Operation under usual conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2–3-19
III. Operation under unusual conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20–3-23
3-1
3-1
3-10
I. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Section
II. Description and data . . . . . . . . . . . . . . . . . . . . . . . . . .
C
H A P T E R
Section
2 . SERVICE UPON RECEIPT AND INSTALLATION
I. Service upon receipt of materiel . . . . . . . . . . . . . . . . . . . . . . . . . . . .
II. Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3. OPERATING INSTRUCTIONS
CHAPTER
Section
C
HAPTER
4.
OPERATOR AND ORGANIZATIONAL MAINTENANCE INSTRUCTIONS
Section I. Tools and equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
II. Preventive maintenance checks and services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
III. Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IV. Maintenance of ohmmeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C
HAPTER
Page
1 . INTRODUCTION
5.
FUNCTIONING OF EQUIPMENT.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-1
4-2,4-3
4-4
4-5,4-6
4-1
4-1
4-2
4-2
5-1–5-7
5-1
i
TM 11-6625-298-14
Paragraph Page
6. GENERAL SUPPORT MAINTENANCE INSTRUCTIONS
Section I. Tools and equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6-1,6-2
6-1
II. Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3-6-5
6-1
III. Maintenance of ohmmeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6-6-17 6-6
IV. General support testing procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6-16,6-19 6-8
A PPENDIX A . REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A-1
B. BASIC ISSUE ITEMS LIST AND ITEMS TROOP INSTALLED OR AUTHORIZED LIST
(not applicable)
C. MAINTENANCE ALLOCATION
Section
I
N
D
E
X
I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
II. Maintenance allocation chart..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C-1
C-3
Index 1
LIST OF ILLUSTRATIONS
Figure
1-1
1-2
2-1
3-1
3-2
3-3
3-4
3-5
5-1
5-2
5-3
5-4
5-6
5-6
6-1
6-2
6-3
6-4
ii
Title
Page
Ohmmeter ZM-21B/U . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Ohmmeter ZM-21(*)/U, exterior view. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Packaging of Ohmmeter ZM-21(*)/U . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . a.c
. . or
. . d.c.
. . rotating
. . ...........
. . . . .... . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . .
Connections for testing
machines
Connections for testing transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Connections for testing capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Connections for cable testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Connections for measuring one cable conductor to ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Generator drive assembly, Ohmmeter ZM-21A/U and ZM-21B/-U . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Generator drive assembly, Ohmmeter ZM-21A/U . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Ohmmeter ZM-21/U (and some early model ZM-21A/U), schematic diagram . . . . . . . . . . . . . . . . . . . . . . . .
Ohmmeter ZM-21A/U and ZM-21B/U, schematic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Meter assembly, Ohmmeter AM-21B/U . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Ohmmeter, side of chassis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Interior view and housing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
End shield and chassis assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Meter scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1-0
1-2
2-2
3-3
3-4
3-5
3-6
3-7
5-1
5-2
5-3
5-3
5-4
5-5
6-2
6-3
6-4
6-7
TM 11-6625-298-14
Figure 1-1. Ohmmeter ZM-21B/U.
1-0
TM 11-6625-298-14
CHAPTER 1
INTRODUCTION
Section I. GENERAL
1-1. Scope
a. This manual describes Ohmmeter ZM-21/U,
ZM-21A/U, and ZM-21B/U (ZM-21 (*)/U) and its
functioning;
operation,
and
operator,
organizational, and general support maintenance.
There is no direct support maintenance authorized
for this equipment.
b. A list of references is contained in appendix
A.
c. The maintenance allocation Chart (MAC)
appears in appendix C.
1-2. Indexes of Publications
a. DA Pam 310-4. Refer to the latest issue of
DA Pam 310-4 to determine whether there are new
editions, changes, or additional publications
pertaining to this equipment.
b. DA Pam 310-7. Refer to DA Pam 310-7 to
determine whether there are modification work
orders (MWOs) pertaining to this equipment.
1-3. Forms and Records
a. Reports of Maintenance and Unsatisfactory
Equipment. Maintenance forms, records, and
reports which are to be used by maintenance
personnel at all maintenance levels are listed in
and prescribed by TM 38-750.
b. Report of Packaging and Handling
Deficiencies. Fill out and forward DD Form 6
(Packaging Improvement Report) as prescribed in
AR 700-58/NAVSUPINST 4030.29/AFR 7113/MCO P4030.29A, and DSAR 4145.8.
c. Discrepancy in Shipment Report (DISREP)
(SF361). Fill out and forward Discrepancy in
Shipment Report (DISREP) (SF 361) as prescribed
in AR 55-38/NAVSUPINST 4610.33A/AFR 7518/MCO P4610.19B, and DSAR 4500.15.
1-4. Administrative Storage
For procedures, forms, records, and inspections
required during administrative storage of this
equipment, refer to TM 740-90-1.
1-5. Destruction of Army Materiel
Demolition and destruction of electronic equipment
will be under the direction of the commander and
in accordance with TM 750-244-2.
Section II. DESCRIPTION AND DATA
1-6. Description
a. Ohmmeter ZM-21/U, ZM-21A/U, and ZM21B/U (fig. 1-1) are a self-contained, portable,
constant-voltage, insulation-resistance measuring
sets (hereinafter referred to as ohmmeter). Figure
1-1 illustrates ZM-21B/U, all other models are
similar in outward appearances. The ohmmeter
consists of a high-range ohmmeter of special
design, a hand-operated, direct current (dc)
generator, a controller (controller in ZM-21A and
ZM-21B only), and a resistance network housed in
a bakelite case. Three terminals are provided for
external connections. On the top is a handle and a
hinged protective cover for the meter window
glass. Printed on the back of the hinged protective
cover are condensed instructions for operation.
b. The test leads that come with the ohmmeter
are six feet long with spade clips at one end and
spring clips at the other end. The spring clips are
covered with rubber covers, one black and one red.
c. The carrying case is a gray, enamel-painted
metal box (ZM-21/U and ZM-21A/U) with a
webbed carrying strap and two latches the
carrying case for the ZM-21B/U is made of plastic.
1-1
TM 11-6625-298-14
Figure 1-2. Ohmmeter ZM-21(*)/U, exterior view.
1-7. Purpose and Use
a. Ohmmeter (fig. 1-2) is used to determine the
insulation condition of telephone cables, of transformers, between windings and ground of rotating
equipment, and of all other types of electrical
equipment for which insulation resistance is an
important factor.
b. The ohmmeter applies a high potential to
equipment under test in order to detect low insulation resistance which may not indicate
satisfactorily on a low potential ohmmeter.
c. Regular use of the ohmmeter can minimize
failure in circuits or equipment caused by faulty
insulation. A sudden lowering of insulation
resistance indicates a fault that should be investigated immediately.
Table 1-1
1-2
1-8. Tabulated Data
Resistance range . . . . . . . . 0 through 1,000 megohms.
Test potential..................... 500 volts dc ±5 percent (when
measuring values below 2
megohms, the voltage drops
materially).
Accuracy . . . . . . . . .. Within 1 percent of any cardinal calibration point.
NOTE
Insulation resistance above 1,000 megohms
is indicated by a point marked infinity
on the meter scale.
1-9. Items Comprising an Operable Ohmmeter ZM21(*)/U
Refer to table 1-1 for items comprising an operable
Ohmmeter ZM-21(*)/U.
TM 11-6625-298-14
CHAPTER 2
SERVICE UPON RECEIPT AND INSTALLATION
Section I. SERVICE UPON RECEIPT OF MATERIEL
2-1. Unpacking.
a. Refer to figure 2-1, and follow the steps below
when unpacking the ohmmeter.
(1) Break and fold back the metal straps.
(2) Remove the nails from the top of the
wooden packing crate with a nail-puller, and
remove the top. Do not attempt to pry off the
sides or top; such action may damage the
equipment.
(3) Remove the packaged equipment and cut
the tape that seals the carton.
(4) Cut the barrier material along the seam,
and remove the inner corrugated carton.
(5) Open the inner corrugated carton, and
remove the ohmmeter in its carrying case, the two
test leads, and the technical publication.
(6) Open the carrying case, remove the ohmmeter and desiccant bags and check the
equipment , as specified in paragraph 2-2.
b. The ohmmeter may be received as a domestic
shipment, without a wooden crate. The unpacking
instructions given in a above apply also to unpacking domestic shipments. If heavy wrapping
paper has been used in lieu of cartons, remove it
carefully and check the contents as in paragraph 2-
2.
2-1
TM 11-6625-298-14
Figure 2-1. Packaging of Ohmmeter ZM-21/U.
2-2
TM 11-6625-298-14
2.2. Checking Unpacked Equipment
a. Inspect the equipment for damage incurred
during shipment. If the equipment has been
damaged, report the damage on DD Form 6, as in
paragraph 1-3.
b. Check the equipment against the component
listing in table 1-1 and on the packing slip to see if
the shipment is complete. Report all discrepancies
in accordance with paragraph 1-3. The equipment
should be placed in service even though a minor
assembly or part that does not affect proper
functioning is missing.
c. Check to see whether the equipment has been
modified. Equipment which has been modified will
have the MWO number on the front panel, near
the nomenclature plate.) Check also to see whether
all currently applicable MWOs have been applied.
(Current MWOs applicable to the equipment are
listed in DA Pam 310-7).
Section II. INSTALLATION
2-3. Tools, Test Equipment, and Materials
Required for Installation
Since Ohmmeter ZM-21(*)/U is intended primarily
for field use, there are no installation procedures
requiring tools or equipment.
2-4. Preliminary Adjustment of Equipment
a. Perform the following preoperational
procedures:
(l) Unfold the hand generator crank to bring
it to its proper operating position.
(2) Connect the spade-type terminals of the
test leads to the line and ground terminals.
b. For a simple check of the equipment, proceed
as follows:
NOTE
The ohmmeter should be operated while at
rest on a firm level surface,with the in-
dicator in a horizontal plane. Do not place
it in or near a strong magnetic field.
(1) With the equipment prepared as in a
above, turn the hand generator crank at operating
speed (approx 160 rpm). With the leads disconnected the ohmmeter should indicate an infinite
resistance.
(2) Short circuit the test leads by clipping
them together, and turn the hand generator crank
at operating speed. The ohmmeter should indicate
zero resistance.
(3) If a further check is desired, and a resistor
of known value is available, connect it between the
test leads and turn the hand generator crank. The
ohmmeter should indicate the known value of the
resistor.
2-3
TM 11-6625-298-14
CHAPTER 3
OPERATING INSTRUCTIONS
Section I. CONTROLS AND INSTRUMENTS
3-1. General
The ohmmeter controls and instruments used by
the operator are illustrated in figures 1-1 and 1-2
and the function of each control or instrument is
listed in table 3-1.
Table 3-1. Controls and Instruments
Control or instrument
Function
GROUND terminal . . . . . . . . . . . . . . . . . . . . .. Provides common ground connection between component being
tested and test equipment case.
LINE terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..Used when taking readings of external resistance or insulation
resistances connected across line and ground terminals.
GUARD terminal . . . . . . ......................................Used to guard against surface leakage resistance. Prevents
leakage from entering resistance measuring circuit.
Handcrank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . When rotated at approximately 160 rpm, generator produces
500 vdc.
Meter scale ZERO to INFINITY.
Provides a visual indication of resistance value under test.
Carrying handle . . . . . . ..........................................................................Used when carrying test equipment.
Test leads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Used to provide connections between test equipment and
component being tested.
Section Il. OPERATION UNDER USUAL CONDITIONS
3-2. General
Make all measurements with the hand generator
crank rotated clockwise fast enough (at approximately 160 revolutions per minute (rpm)) to
cause the centrifugal clutch to slip. When the
clutch slips, maximum steady voltage is being
delivered. The position of the pointer on the scale
indicates insulation resistance values in megohms.
Be careful to read the scale directly above the
pointer and the scale, otherwise, readings may be
in error because of parallax.The tests described in
paragraphs 3-6 through 3-16 are general and cover
equipment of all types and designs. Before testing
the insulation of any equipment refer to the
technical manual covering the specific equipment
under test for definite insulation resistance values
and voltage ratings.
3-3. Preoperational Check
Before connecting the ohmmeter to the equipment
to be tested, make the following checks to
determine whether the ohmmeter is operating
properly.
a. Full Scale Check. With no connection to the
ohmmeter terminals, crank the hand generator at
operating speed. The pointer will indicate IN-
FINITY if the test set is in good operating condition.
b. Zero Check. Short the LINE and GROUND
terminals by connecting them and turn the hand
generator crank at operating speed. The pointer
will indicate ZERO if the ohmmeter is in good
operating condition.
3-4. Guard Connection
a. To obtain a true resistance value of the insulation under test, both the insulation and the
measuring instrument must be protected against
surface leakage to eliminate possible errors. The
ohmmeter has an internal protective or guard
system for this purpose. The guard system is
connected to the GUARD terminal so that
protection against surface leakage can be extended
to the insulation under test. Any leakage current
between the base of the insulator and its terminal
will recarried back to the test set through the
GUARD terminal, and the internal guard circuit of
the test set will prevent this leakage from entering
the measuring circuit.
b. When using guarded connections, readings
are of the insulation resistance only and do not
take into account the parallel shunting resistance
3-1
TM 11-6625-298-14
of surface conditions. A measurement taken with a
GUARD connection and compared to a
measurement of the same equipment taken without
a GUARD connection will establish whether low
insulation resistance readings are caused by poor
insulation or bad surface conditions. If readings
taken with guarded connections are higher than
those without guarded connections, the surface of
the equipment has a low resistance.
3-5. Insulation Resistance
All tests shall be made with the hand generator
crank rotated at approximately 160 revolutions per
minute. Since the meter scale is calibrated in
megohms, the position of the pointer on the scale
indicates insulation resistance values directly in
megohms. Indications shall be read with the eyes
directly above the pointer and the scale to prevent
errors. Types of operation described in subsequent
paragraphs are necessarily general to cover
equipment of all types and designs. Before testing
any specific equipment, refer to the technical
manual covering the equipment for definite insulation resistance standards.
a. Unit of Measurement. Insulation resistance is
that property of an insulating material which
opposes the passage of electrical current. It is
expressed in ohms or megohms. Insulation
resistance increases as the thickness of the insulating material increases but decreases as the
area of material under test increases. For example,
if an insulating material covering a given surface
and having a resistance of 100 megohms is extended to 10 times its area, the insulation
resistance will drop to 10 megohms. Thus, one mile
Of* spinal-four cable may measure 1,000 megohms
but 10 miles will measure 100 megohms. If the
insulating material is doubled in thickness,
however, the area having an insulation resistance
of 100 megohms now will have a resistance of 200
megohms, and the area having an insulation
resistance of 10 megohms will have a resistance of
20 megohms.
b. Conditions Affecting Insulation Resistance.
(1) Temperature. The temperature coefficient
3-2
of the resistance of an insulating material is
negative and numerically large. Therefore, even a
small increase in temperature will cause a
relatively large decrease in insulation resistance.
Always make measurements at the same temperature, if possible, because insulation resistance
drops at high temperatures. For example, the
insulation resistance between the stator winding of
a slow-speed generator and the frame is 100
megohms at 80° F., but falls to 10 megohms at
140° F.
(2) Moisture and humidity. Chemically pure
water is a non conductor; however, the impurities
that water absorbs from the atmosphere and other
sources cause it to be partially conductive.
Therefore, moisture will become a conductor in
parallel with the insulation and will cause a
decided drop in insulation resistance. This is a
temporary condition and may be remedied by
drying the equipment.
(3) Chemical fumes. Strong acid or alkali
fumes attack insulation and permanently lower its
insulation resistance.
(4) Surface conditions. Dirt, especially when
mixed with oil, or with a copper or carbon dust,
forms a low-resistance path across the insulation,
lowering its resistance.
c. Values of Insulation Resistance. Since insulation resistance is affected by varying conditions (b above), no constant rules can be
established to govern its value. Certain minimum
values have, however, been established arbitrarily
for different types of cable and equipment (para 312). Actual values of insulation resistance are not
as important as changes in insulation resistance.
Periodic tests should be made and the results
recorded together with information regarding
climatic conditions at the time tests are made.
3-6. Insulation Test of Ac and Dc Rotating
Machines Rated 600 Volts or Less
a. Connect a test lead from the LINE terminal
of the ohmmeter to a lead, an exposed conductor,
or the commutator of the machine (fig. 3-1).
TM 11-6625-298-14
Figure 3-1. Connections for testing a.c. or d.c. rotating machines.
b. Connect another test lead from the GROUND
terminal to the shaft or frame of the equipment
under test. Be sure that the surface to which the
connection is made is free of paint or any other
substance that is a nonconductor.
c. Turn the hand generator crank at operating
speed. If the machine is cold, the indication should
be between 1 and 10 megohms. If the machine is
warm, the indication will be lower. Also, a large
machine will have a lower insulation resistance
than a small machine.
d. If all the circuits in the machine are not
interconnected as in separately excited generators,
measure each circuit individually.
3-7. Insulation Test of Ac and Dc Rotating
Machines Rated Over 800 Volts
a. Connect the equipment and test as directed
for machines at 600 volts or less (para 3-6 above).
b. Turn the hand generator crank at operating
speed. If the machine is cold, readings should
range between 10 and 100 megohms. Readings will
be lower if the equipment is warm.
c. Direct current (dc) fields on ac machines
should indicate between 1 and 10 megohms.
3-8. Insulation Test of Transformers
a. Connect a test lead from the GROUND
terminal of the ohmmeter to the core or case of the
transformer (fig. 3-2).
3-3
TM 11-6625-298-14
Figure 3-2. Connection for testing transformers.
b. Measure the high- and low-voltage windings
separately. Connect a test lead from the LINE
terminal of the ohmmeter, first to the low-voltage
windings and then to the high-voltage windings.
c. Measure between windings by connecting the
GROUND lead from the ohmmeter to one winding
of the transformer, and another test lead from the
LINE terminal of the ohmmeter to the other
winding.
d. Turn the hand generator crank at operating
speed. Indications for all measurements should be
100 megohms or more on air core transformer.
Indications on oil-filled transformer will be
3-4
considerably lower. Extremely low readings indicate the presence of moisture in the oil and
indicate that the oil should be changed.
3-9. Insulation Test of Capacitors
WARNING
Discharge the capacitor after an insulation
resistance test has been made, or
disconnect the leads one at a time. Short
out the capacitor. Contact with a fully
charged capacitor can cause a dangerous
shock.
TM 11-6625-298-14
CAUTION
Do not exceed the voltage rating of the
capacitor under test.
a. Connect a test lead from the GROUND
terminal of the ohmmeter to the case of the
capacitor (fig. 3-3).
b. Connect another lead from the LINE terminal
of the ohmmeter to one of the terminals of the
capacitor.
c. Turn the hand generator at operating speed.
The indication obtained is the insulation between
the capacitor and its case. The indication should be
500 megohms or more.
d. Remove the GROUND lead from the case of
the capacitor and connect it to the remaining
terminal of the capacitor.
NOTE
The ohmmeter pointer will dip toward zero
when the crank is first turned, but will
move up the scale as the capacitor becomes
charged with the test potential. The
capacitor must be fully charged with the
test potential before a reading may be
taken. To be sure that the capacitor is fully
charged, turn the generator crank for one
minute.
e. Turn the crank handle at operating speed. The
insulation reading should be 500 megohms or
greater.
Figure 3-3. Connections for testing capacitors.
3-10. Insulation Test of Insulating Bushings
a. Connect a test lead from the GROUND
terminal of the ohmmeter to the base of the
bushing.
b. Connect another test lead from the LINE
terminal of the ohmmeter to the bushing terminal.
c. Turn the hand generator crank at operating
speed. If the bushing under test is the dry type,
the reading should be INFINITY or near INFINITY. If the bushing under test is the filled
type, the reading should be near 1,000 megohms.
d. If the reading is lower than near INFINITY
for a dry-type bushing or 1,000 megohms for a
filled-type bushing, connect the third test lead to
3-5
TM 11-6625-298-14
the GUARD terminal of the ohmmeter and to a
point approximately at the center of the bushing.
Make this connection by wrapping the bushing
with tinfoil or with a cloth saturated with salt
water and connecting the test clip to the tinfoil or
cloth.
e. Operate the hand generator crank. If the
Žreading taken with the GUARD terminal connected is approximately the same as the first
reading, the low resistance is caused by a fault in
the bushing. If the reading is considerably higher,
the low resistance formerly observed is caused by
surface leakage. When low resistance is caused by
surface leakage, the bushing is serviceable but
should be cleaned.
CAUTION
Use the GUARD connection if insulation
tests are made on a damp or humid day.
Surface leakage always will be high under
such conditions.
Figure 3-4. Connections for cable testing.
3-11. Insulation Test of Power Cables and Wires
NOTE
Disconnect equipment from the powerline
while insulation resistance measurements
are being made.
a Power Cables.
(1) Connections for measurement of one
conductor to all other conductors.
(a) Connect a test lead from the LINE
terminals of the ohmmeter to the conductor to be
measured (fig. 3-5).
(b) Tie all other conductors together, and
connected them to the GROUND terminal of the ohmmeter.
(c) Connect a teat lead from the GUARD
terminal to the cable sheath. Use of the GUARD
terminal prevents error caused by parallel ground
leakage.
(2) Connections for measurement of one
conductor to ground.
3-6
(a) Connect a test lead from the LINE
terminal of the ohmmeter to the conductor to be
measured (fig. 3-5).
(b) Connect a test lead from the GROUND
terminal to the shield of the cable.
(c) Tie all other conductors together and
connect them to the GUARD terminal. Use of the
GUARD terminal prevents error caused by leakage
in the parallel circuits.
(3) Operation.
(a) Turn the hand generator crank at
operating speed. A short length of cable usually
will have an insulation resistance value of 1,000
megohms or more. The insulation resistance value
of a long cable usually will be considerably lower
than that of a short cable.
NOTE
When testing the insulation of a long
cable, operate the hand generator for
approximately 1 minute before taking a
TM 11-6625-298-14
reading. This will eliminate any error that
might be caused by the electrostatic
capacity of the cable.
(b) After all measurements are completed,
discharge the cable by grounding all conductors.
Figure 3-5. Connections for measuring one cable conductor to ground.
b. Power Wires. Test the insulation of individual
power wires in the same manner as cable conductors (a above). Make the GROUND connection
to the outer sheath, or jacket, of the wire.
3-12. Insulation Test of Telephone Cables
and Wires and Minimum Insulation Resistance values
a. Testing Insulation Resistance.
(1) Test the insulation of exchange cables in
the same manner as power cables (para 3-11a
above). The conductors of these cables, when new,
should have an insulation resistance of at least 500
megohm-miles.
NOTE
A conductor is said to have an insulation
resistance value of 500 megohm-miles when
the insulation resistance of a 1-mile length
is 500 megohms. Because short cables
usually have a higher insulation resistance
value, a 2-mile length will have en insulation resistance of 250 megohms, a 10mile length will have an insulation
resistance of 50 megohms, etc.
(2) When testing the insulation resistance of
large exchange cables, divide the pairs into
bunches of 25 to 100 pairs per bunch. Test each
bunch as a single conductor of a power cable.
(3) If the insulation resistance of a bunch is
not lower than a single pair, assume that the
insulation resistance of all pairs in that bunch is
satisfactory.
(4) If the insulation resistance of a bunch is
less than that given in the table 3-2 below,
separate the wires and measure each separately
against all other wires grounded to that sheath.
3-7
TM 11-6625-298-14
Each wire should give a reading as high as that
given in the table.
(5) If the insulation resistance of any individual wire is less than that given in the table,
disconnect all other bunches from the sheath and
measure the wire against these bunches and
against the sheath. This will determine if the
trouble is between wires, or between the wire and
the sheath, or both.
(6) After testing all the bunches, measure a
few wires of each bunch against the remaining
wires of the bunch to determine whether any of the
conductors have a low insulation resistance.
b. Insulation Resistance Requirements for
Telephone Cables. Table 3-2 below gives the insulation resistance requirements for telephone
cables based on a standard required insulation
resistance of 500 megohms per mile of cable. Given
values are the minimum insulation between one
wire and the sheath, with all other wires of the
cable grounded to the sheath at a temperature of
60° F.
NOTE
The set shall be operated for one minute
before readings are taken.
Table 3-2. Required Insulation Resistance for Telephone Cables
Length
of
cable ( ft )
500 . . . . . . . . . . . . . . . . ...
1,000 . . . . . . . . . . .
1,500 . . . . . . . . . . . . . . . . . .
2,000 . . . . . . . . . . . . . . . . . .
3,000 ................................
4,000 . . . . . . . . . . . . . . . . . .
5,000 . . . . . . . . . . . . . . . . . .
6,000 . . . . . . . . . . . . . . . . . .
7,000 . . . . . . . . . . . . . . . . . .
8,000 . . . . . . . . . . . . . . . . . .
9,000 . . . . . . . . . . . . . . . . . .
10,000. . . . . . . .
Required
insulation
resistance (meg)
5,250 . . . . . . . . . . . . . . . . . . . .
1 . . . . . . . . . . . . . . .
2,640 . . . . . . . . . . . . . . . . .
2.......................
1,760 . . . . . . . . . . . .
3 . . . . . . . . . .
1,230 . . . . . . . . . . . . . . . 4 . . . . . . . . . . . . . . . . . .
880. . . . . . . . . . . . . . . . . . . . .
5
660 . . . . . . . . . . . . . . . . . . . . . 6
528 . . . . . . . . . . . . . . . . . . 7
.
.
.
.
.
.
440 . . . . . . . . . . . . . . . . .
8.......................
377 . . . . . . . . . . . .
9 . . . . . . . .
330 . . . . . . . . . . . . . . . . .
10
293 . . . . . . . . . . . . . . . . . . . .
11
264 . . . . . . . . . . . . . . . . . . . . . 12 . . . . . . . .
c. Insulation Resistance Requirements for
Spiral-Four Cable.
(1) General. Spiral-four cable consists of four
individually insulated conductors in a braided
metal sheath. Cable WC-548 has a heavy rubber
jacket; Cable WF-8/G has a polyethylene plastic
covering. For a complete test of the insulation
resistance of spiral-four cable, measure each
conductor in turn with the other three conductors
connected to the braid. Thus a complete test can
be made in four measurements.
(2) Cable WC-548.
(a) Insulation resistance requirements for
various lengths of new cable WC-548 are as
follows:
Cable length (mi)
Insulation resistance(meg)
¼ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...750
1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...200
25 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1O
(b) In the case of working cable, the insulation resistance of one 1/4-mile Cable Assembly
CC-358 should not drop below 10 megohms, and
the insulation resistance of a 25-to 30-mile repeater
section should not drop below 1 megohm.
(3) Cable WF-8/G.
(a) New Cable WF-8/G, either in 1/4-mile
lengths of Cable Assembly CX-1065/G of four
cable assemblies coupled together during initial
3-8
Length
of
cable (mi)
Required
insulation
resistance ( meg)
500
250
167
125
100
88.3
71.3
62.5
55.5
50
45.4
41.7
installation, should show an insulation resistance
above 1,000 megohms. For lengths greater than 1
mile, the minimum insulation resistance can be
found by dividing 1,000 by the number of miles in
the cable. For example, if a 10-mile length of Cable
WF-8/G is to be tested– 1,000 ÷ 10 = 100
megohms, the minimum insulation resistance for
10 miles.
NOTE
Manufacturing specifications require a
minimum resistance of 5,000 megohms per
1,000 feet. Insulation resistance above
1,000 megohms is indicated by INFINITY
on the meter scale of the ohmmeter.
(b) A cable line may develop low insulation
resistance and deteriorate to a point where it can
no longer be useful. When this happens, the cause
of the drop in insulation resistance to below one
megohm must be located and removed.
d. Computing Minimum Insulation Resistance. The minimum insulation resistance for any
length or size of cable may be found as follows:
(1) The required minimum insulation
resistance between one wire, one foot long and the
cable sheath is 2,640,000 megohms. To find the
required minimum insulation resistance for one
insulated conductor of any length, divide 2,640,000
by the length of the conductor expressed in feet.
TM 11-6625-298-14
For example, to find the required insulation
resistance between one conductor and the cable
sheath of a cable 672 feet long:
2,640,000 ÷ 672 = 3,928.57 megohms.
(2) In the case of a multiple-pair cable, to find
the minimum insulation resistance of the entire
cable to the cable sheath, divide the requirement
for one conductor by the total number of conductors in the cable. For example, the total
number of conductors in a 51-pair cable would be
51 x 2 or 102 conductors. Thus, the minimum
insulation ressitance requirement for a 51-pair
cable 672 feet long ( (1) above) would be:
3,928.57 ÷ 102 = 38.51 megohms.
3-13. Test of Wiring Installations.
Wiring systems are tested to see whether they are
free from short circuits and grounds. Remove fuses
and open switches before making tests.
a. Testing for G. ounds.
(1) Connect the GROUND terminal of the
ohmmeter to a good ground.
(2) Connect the LINE terminal to a wire of
the wiring system that is being checked for
grounds. Measure one wire at a time. A low
reading indicates that the wire is grounded. A
high reading indicates that there is no ground and
that the insulation is good.
b. Testing for Short Circuits.
(1) Connect the LINE terminal of the ohm-
meter to one wire of the wiring system.
(2) Connect the GROUND terminal to the
other wire.
(3) Wire circuits of No. 12 or No. 14 AWG
wire should have a resistance of approximately 1
megohm. The insulation resistance of wires of
larger gauge is based on current capacity and
should read approximately as follows:
NOTE
Circuits with a current capacity above 100
amperes cannot be measured on the ohmmeter. The lowest calibration point of the
ohmmeter is 100,000 ohms (0. 1 megohm).
3-14. Test of Electrical Instruments
The insulation resistance between all connected
electrical circuits of an electrical instrument and
the case should be no lower than 20 megohms. If
the instrument has both a current and a voltage
circuit, the insulation resistance between the
current circuit and the voltage circuit should be no
lower than 5 megohms.
3-15. Insulation Test of Tools and Appliances
The insulation resistance values of tools and appliances should be approximately the same as the
insulation resistance value of the wiring system to
which they are attached. Tests for short circuits
and grounds are made in the same manner as tests
of wiring installations (para 3-13).
3-16. Measurement of Resistors
The resistance value of resistors can be found with
the ohmmeter if within the megohm range. The
resistor must be disconnected from its circuit and
all power turned off. Connect the LINE terminal to
one side of the resistor and connect the GROUND
terminal to the other side. Operate the ohmmeter.
The reading will be directly in megohms.
3-17. Insulation Resistance Values of Equipment
Under Test
Whenever possible, take minimum insulation
resistance values of equipment being tested from
the specifications covering such equipment. If
specifications are not available, use table 3-3 which
consists of accepted minimum requirements.
Table 3-3
3-9
TM 11-6625-298-14
Table 3-3
3-18. Locating Low Insulation
a. General. The ohmmeter may be used to
locate low cable insulation caused by moisture.
Such a trouble can be burned in by applying high
voltage directly across the fault. This breaks down
the insulation at the fault and permits the bare
wires to make metallic contact. When a solid
ground or short circuit has developed, the fault can
be located with a Wheatstone bridge test set or by
using tone and an exploring coil.
b. Procedure. To burn in trouble using the ohmmeter, proceed as follows:
(1) Connect the wire under test to the
GUARD terminal of the ohmmeter.
(2) Connect the cable sheath to the GROUND
terminal.
(3) Turn the hand generator crank at
operating speed. Full generator voltage (500 volts)
is applied directly across the fault. The current
ballast resistors are not in the circuit and there
will be no reading on the ohmmeter scale.
3-19. Stopping Procedure
When measurements have been completed,
disconnect all test leads from the ohmmeter and
from the equipment being tested. Close the hinged
cover; place the ohmmeter and leads in the
carrying case.
Section III. OPERATION UNDER UNUSUAL CONDITIONS
3-20. General
When operating the ohmmeter in regions where
extreme cold, heat, humidity, moisture, or sand
conditions prevail, special precautions must be
taken to keep the equipment in operating condition
at all times. Paragraphs 3-21 through 3-23 contain
instructions for minimizing the effect of these
unusual operating conditions.
3-21. Operation in Arctic Climates
Because the ohmmeter is intended for both indoor
and outdoor use, the equipment may be exposed to
extreme cold in actual operation as well as in
storage and in transport. When operated at extremely low temperature, the hand generator crank
will not operate as easily as at normal room
temperatures. The generator drive assembly parts
may break. If the ohmmeter is operated in a warm
place after exposure to the cold, moisture will
condense on the equipment until the equipment
reaches room temperature. This condition also
arises when the equipment warms up during the
day after a cold night. When the ohmmeter has
reached room temperature, dry it thoroughly.
Perform preventive maintenance operations (para
4-3) frequently to keep the unit as moisture-free as
possible.
3-10
3-22. Operation in Desert Climates
The main problem when operating the ohmmeter in
desert climates is to prevent dirt, dust, and sand
from filtering into the equipment. Keep the
equipment in the carrying case with the lid closed
and latched at all times when not in use, and cover
with canvas or other material.
3-23. Operation in Tropical Climates
The main difficulty encountered in the operation of
the ohmmeter in tropical climates is high relative
humidity. Although it is sealed against humidity,
moisture still will condense on the outside of the
instrument case whenever its temperature becomes
lower than the temperature of the air. Mositure
collecting between the binding posts lowers the
resistance between them and will cause faulty
readings. Dry the case with a dry cloth before
attempting to make teats with the equipment.
Inspect the equipment frequently to keep it free
from rust, corrosion, and fungus growth. Perform
preventive maintenance operations (para 4-3)
frequently to keep the unit as moisture-free as
possible.
TM 11-6625-298-14
CHAPTER 4
OPERATOR AND ORGANIZATIONAL MAINTENANCE INSTRUCTIONS
Section l. TOOLS AND EQUIPMENT
4-1. General
Tools and test equipment authorized for use by
the operator and organizational technician are
listed in appendix C.
Section II. PREVENTIVE MAINTENANCE CHECKS AND SERVICES
deficiencies together with the corrective action
4-2. General
taken as prescribed in TM 38-750.
To be sure that the ZM-21(*)/U is always ready
for operation, it must be inspected systematically
4-3. Preventive Maintenance Checks and Services
so that defects may be discovered and corrected
Periods
before they result in serious damage or failure. The
Preventive maintenance checks and services of the
necessary preventive maintenance checks and
ZM-21(*)/U are required daily, weekly, monthly,
services to be performed are listed and described in
and quarterly. In addition, the weekly preventive
tables 4-1 and 4-2. The item numbers indicate the
maintenance checks and services must be persequence of minimum inspection requirements.
formed under the following conditions:
Defects discovered during operation of the unit will
a. Upon initial receipt.
be noted for future correction to be made as soon
b. Upon return from higher category mainas operation has ceased. Stop operation imtenance.
mediately if a deficiency is noted during operation
which would damage the equipment. Record all
Table 4-1. Operator/Crew Preventive Maintenance Checks and Services.
w- Weekly
D–Daily
Time required: 0.4
Time required: 0.2
ITEM TO BE INSPECTED
Interval
Worktime
and
(T/ H)
sequence No.
PROCEDURE
D
W
1
1
COMPLETENESS
Check to see that the ZM-21(*)/U is complete against the component listing
in paragraph 1-9.
0.1
2
EXTERIOR SURFACES
Check to see that exterior is clean and free from dust, dirt, fungus, rust, and
corrosion.
0.1
3
HARDWARE
Check to be sure that all screws and handles are securely fastened.
0.1
4
TEST LEADS
Check for loose clips and terminals, cleanliness of terminals, and breaks in
the insulation.
5
OPERATION
While the ZM-21(*)/U is in operation, be alert for symptoms of trouble.
2
0.1
4-1
TM 11-6625-298-14
Table 4-2. Organisational Preventive Maintenance Checks and Services
Q–Quarterly
M–Monthly
Time required:
Time required: 0.2
0.3
ITEM TO BE INSPECTED
PROCEDURE
M
Worktime
(T/H)
Q
INTERIOR OF UNIT
Carefully withdraw the chassis from case and check for loose connections,
defective insulation, and cleanliness.
0.2
METER
Check meter stop and pointer for damage.
CARRYING CASE
Check for chipped paint, dirt, dust, grease fungus, and corrosion. Check also
that the foam rubber lining is fastened securely.
0.1
1
PUBLICATIONS
See that all publications are complete, serviceable, and current. Refer to DA
Pam 310-4.
0.1
2
MODIFICATIONS
Check to see if the equipment has been modified. Refer to DA Pam 310-7.
0.1
Section Ill. TROUBLESHOOTING.
4-4. General
At the organizational level, the troubleshooting of
this equipment is limited to the operational check
described in paragraph 2-4b. If the pointer fails to
indicate the proper resistances, forward the
equipment to general support personnel for
complete troubleshooting and repair.
Section IV. MAINTENANCE OF OHMMETER
4-5. Cleaning
Inspect the exterior of the ZM21(*)/U. The
surface should be clean and free of dust, dirt,
grease, and fungus.
a. Remove dust and loose dirt with a clean, soft
cloth.
WARNING
The fumes of trichloroethane are toxic.
Provide thorough ventilation whenever
used. DO NOT use near an open flame.
Trichloroethane is not flammable, but
exposure of the fumes to an open flame or
hot metal forms highly toxic phosgene
gases.
b. Remove grease, fungus, and ground-in dirt
from metal parts with a cloth dampened (not wet)
with trichloroethane.
c. Remove dust or dirt from terminals with a
soft brush.
4-2
CAUTION
Do not press on the meter face when
cleaning. Damage to the equipment may
result.
d. Clean the cables, meter glass, and exterior
surface with a clean, soft cloth. Dampen the cloth
with water, using mild detergent, if necessary, for
more effective cleaning.
4-6. Touchup Painting
The bakelite case of the ZM-21(*) /U does not
require painting. If the metal parts show signs of
rust or corrosion, remove it with fine sandpaper.
Brush two thin coats of paint on the bare metal to
Protect it from further corrosion. Refer to TB 430118 for more detailed refinishing information.
TM 11-6625-298-14
CHAPTER 5
FUNCTIONING OF EQUIPMENT
5-1. Function
Ohmmeter ZM-21(*) /U measures high values of
insulation resistance of all types of electrical
equipment and wiring. The resistance across the
input terminals is in series with the generator lead
to the meter, thus affecting the current flow
through the meter. A hand crank on the ohmmeter
drives the dc generator with voltage being
maintained at a constant level by an electronic
controller circuit. The resistance range of the ohmmeter is from O through 1,000 megohms. The
resistance is indicated by a meter of special design,
and the indication given is as near as possible to a
true representation of the insulation resistance of
the equipment, wire, or cable under test.
5-2. Hand Generator
a. The dc hand generator consists essentially of
a rotating armature in a fixed magnetic field. The
armature has a 39-bar commutator running be-
tween two carbon brushes. When the armature is
rotated in the magnetic field, an armature voltage
is generated that is led out to the ohmmeter
terminals through the carbon brushes. With the
generator rotating at the proper speed, the
predominant ripple frequency is approximately
1,200 hertz (Hz) with a peak-to-peak ripple voltage
of approximately 6 volts. Because of the low ac
component, no capacitor is required across the
output of the generator.
b. The generator drive assembly of ohmmeter is
shown in figure 5-1. The generator is driven by a
hand-operated crank through a gear train and
clutch assembly. The clutch assembly is adjusted
so that it will not slip. On, earlier models of the
ohmmeter (fig. 5-2) when the crank reaches an
operating speed of approximately 160 rpm, centrifugal force disengages the clutch shoes from the
hub in order to maintain constant voltage.
Figure 5-1. Generator drive assembly, Ohmmeter ZM-21A/U and ZM-21B/U
5-1
TM 11-6625-298-14
Figure 5-2. Generator drive assembly, Ohmmeter ZM-21/U.
5-3. Controller
The controller (fig. 5-3) is an electronic circuit
contained in a sealed plastic box which limits the
output voltage of the generator to 525 volts. It is
5-2
actually a series voltage regulator with terminal 1
as the input, terminal 2 as the output, and terminal 3 as the common. The controller is used in
some models of ZM-21A/U and all of ZM-21B/U.
TM 11-6625-298-14
Figure 5-3. Ohmmeter ZM-21/U (and some earlier model ZM-21A/U). schematic diagram.
Figure 5-4. Ohmmeter ZM-21A/U and ZM-21B/U, schematic diagram.
5-4. Resistance Network
The resistance network of Ohmmeter ZM-21B/U
consists of one 90,000 ohm resistor, R1, and two
250,000-ohnm resistors R2 and R3 (fig. 5-4). The
two 250,000-ohm resistors are connected in series
between one side of meter potential coil L2 of the
ohmmeter and the positive side of the generator
(through the controller). Resistor R1 is connected
between one side of meter current coil L1 of the
ohmmeter and the LINE terminal and acts as a
protective resistance to guard against damage
caused by excessive current flowing in coil L1.
5-5. Meter Movement
a. The meter movement is shown in figure 5-5.
The indicating instrument consists of two coils,
potential coil L2, and current coil L1. These coils,
mounted on a common axis and connected so that
they oppose each other in a definite ratio, rotate
between two pole pieces in a magnetic field. One
force tends to move the indicating pointer toward
ZERO on the ohmmeter scale; the other force
tends to move the pointer toward INFINITY.
b. Current flows to the indicator through
flexible ligaments of practically zero torque which
5-3
TM 11-6625-298-14
connect the ohmmeter terminals to the moving coil
assembly. The position at which the pointer finally
comes to rest on the scale is determined by the
Figure 5-5. Meter assembly,
5-6. Working Circuit
a. The working circuit of the insulation
resistance measuring set is designated in heavy
lines in figure 5-6. The crank of the hand generator
operated at a speed of 160 rpm rotates generator
G1 at approximately 6,000 rpm. The generator
output voltage is limited to 525 volts dc by the
controller. With no connections made to the ohmmeter terminals, current flows from the negative
(–) terminal of generator G1, through potential
coil L2 of the meter, and through the resistors R2
and R3 (through the controller) to the positive (+)
terminal of the generator. The magnetic field set
up by potential coil L2 reacts with the field set up
by the permanent magnet in such a way that the
coil assembly and the pointer move in a counterclockwise direction until the pointer indicates
infinity.
5-4
resultant of the two opposing forces that move the
coil assembly.
Ohmmeter ZM-21B/U.
b. An unknown resistor connected between the
line terminal and the ground terminal provide a
another path for current flow. This path is from
negative (–) terminal of generator G 1, through
current coil L1 of the meter, resistor R1, the line
terminal, and the ground terminal to the positive
(+) side of generator G1 through the controller.
The magnetic field set up by current coil L1 tends
to move the coil assembly and the pointer in a
clockwise direction. If the unknown resistance is
low, most of the current flows through coil L1 and
the pointer indicates a reading close to zero. If the
value of the resistance is high, less current flows
through coil L1 and the pointer moves from the
zero end of the scale to indicate a point nearer
infinity.
TM 11-6625-298-14
Figure 5-6. Functional diagram.
5-7. Guard Circuit
The guard circuit as shown in figure 5-6 increases
the accuracy of the instrument by preventing
leakage when making measurements over 100
megohms. The guard circuit consists of a metal
ring around the line terminal and metal plates on
which resistor R1, R2, and R3 are mounted. A
brass tube connects the ring and plates together.
The guard circuit prevents leakage current along
the surface of the instrument case between the
ground terminal and the line terminal from affecting the meter readings. Leakage current to the
line terminal is picked up by the guard ring and
led directly to the generator without going through
resistor R1 and the meter coils.
5-5
TM 11-6625-298-14
CHAPTER 6
GENERAL SUPPORT MAINTENANCE INSTRUCTIONS
Section l. TOOLS AND EQUIPMENT
6-1. General
This chapter contains instructions for general
support of Ohmmeter ZM-21*) /U. The types of
repair that can be performed by units having
general support responsibilities is limited only by
the tools and test equipment available and by the
skill of the technician.
6-2. Tools and Equipment
For a listing of tools and test equipment needed
for general support maintenance, see appendix C.
Section Il. TROUBLESHOOTING
6-3. Organization of Troubleshooting Procedures
a. General. The first step in servicing a
defective ohmmeter is to sectionalize the fault.
Sectionalization means tracing the fault to one of
the major circuits responsible for the abnormal
operation. The second step is to localize the fault.
Localization means tracing the fault to a particular
stage or network within one of the major circuits.
The third step is to isolate the fault. Isolation
means tracing the fault to the defective part
responsible for the abnormal condition. Some
faults, such as burned-out resistors, arcing, and
shorted transformers often can be located by sight,
smell, and hearing. The majority of faults,
however, must be isolated by checking voltages
and resistances.
b. Component Sectionalization, Localization,
and Isolation. Listed below is a group of tests
arranged to simplify and to reduce unnecessary
work and to aid in tracing a trouble to a specific
component. Follow the procedure in the sequence
given. A technician must be careful not to cause
further damage to the ohmmeter while it is being
serviced.
(1) Visual inspection. The purpose of visual
inspection is to locate faults without testing or
measuring circuits. All visual signs should be
observed and an attempt made to sectionalize the
fault to a particular function.
(2) Operational tests. Operational tests
frequently indicate the general location of trouble.
In many instances, the tests will help in determining the exact nature of the fault.
(3) Troubleshooting
table. Troubleshooting
table 6-1 lists symptoms of common troubles and
gives (or references) corrective measures. Such a
table obviously cannot include all trouble symptoms that may occur. The technician should use
this chart as a guide in analyzing symptoms that
may not be listed.
(4) Intermittent troubles. In all the tests, the
possibility of intermittent troubles should not be
overlooked. If present, this type of trouble often
may be made to appear by tapping or jarring the
equipment. It is possible that some external
connections may cause trouble. Test wiring for
loose connections; move wires and components
with an insulated tool, such as a pencil or fiber
rod. This may show where a faulty connection or
component is located.
c. Ohmmeter. A knowledge of the functioning of
the ohmmeter is necessary for the technician. See
paragraphs 5-1 through 5-7 for pertinent information. To supplement the troubleshooting
table and to locate parts, refer to the following
illustrations:
(1) Schematic diagram (fig. 5-5).
(2) Functional diagram (fig. 5-6).
(3) Illustrations showing location of parts (fig.
5-1, 5-5, 6-1, and 6-2).
6-1
TM 11-6625-298-14
Figure 6-1.
6-2
TM 11-6625-298-14
Figure 6-2. Interior view and housing.
6-4. Prelininary Inspection
a. Removal of Chassis.
(1) Break the wax seal covering the screw in
the lower right hand corner of the end shield.
(2) Remove this screw and the other three
screws that secure the end shield-chassis assembly
to the case.
(3) Extend the hand generator crank until it is
at right angles to the end shield.
CAUTION
Be careful not to damage the meter
pointer.
(4) Grasp the crank and withdraw the end
shield-chassis assembly from the case.
6-3
TM 11-6625-298-14
Figure 6-3. End shield and chassis assembly.
b. Removal of Chassis Cover.
(1) Remove the screw in the chassis directly
in front of the small recessed portion of the chassis
cover (fig. 6-3).
NOTE
Older models have a cover secured by four
small screws.
(2) Gently pry up the cover on one side. The
cover will snap out of the chassis.
c. Inspection. Make a preliminary inspection of
the equipment to determine the extent of repair
necessary.
(1) Inspect for broken insulation connections
to terminals and other parts.
(2) Check for defective soldered connections.
(3) Examine wiring to see that no bare wire is
touching other wires or chassis.
(4) Test operation of the hand generator by
turning the crank; the shaft should move freely
and smoothly.
6-4
(5) Inspect for loose or missing screws.
(6) Operate the unit according to the
procedure paragraph 2-4b. This should provide
an indication as to any trouble which might be
present.
d. Reassembly of Equipment.
(1) Replace the chassis cover by pushing it
gently into place.
(2) Replace the screws on the chassis in front
of the chassis cover.
(3) Seat the gasket on the ridge on the inside
face of the end shield. If the gasket is damaged
replace it with a new one.
(4) Grasp the crank handle and carefully
insert the chassis into the case.
(5) Replace the four screws on the end shield
and tighten them securely.
Table 6-1
TM 11-6625-298-14
6-5
TM 11-6625-298-14
6-5. Isolating Trouble
a. Indicator Scale Test. The indicator scale test
may localize a faulty meter indication to the indicating instrument. Proceed as follows:
(1) Connect LINE and GROUND terminals to
known resistances.
(2) Operate hand generator crank. Note any
deviation between the known resistance values and
the values indicated on the test set.
(3) The deviation from any marked point
should not exceed 1/32 inch.
b. Output Voltage Test. The output voltage
test may show that the generator is defective or
that the controller requires replacement. Proceed
as follows:
(1) Connect Multimeter ME-26/U to the
ground and guard terminals.
(2) Turn hand generator crank until maximum
voltage is obtained Note the output voltage.
(3) The output voltage of the generator should
be between 500 and 550 volts dc.
(a) If the multimeter reading is above 550
volts dc; replace the controller.
(b) If the multimeter indicates less than 500
volts dc, check the output directly at the
generator. If the output is still below 500 volts dc,
replace the generator.
NOTE
Low output voltage that cannot be adjusted may be caused by an open current
coil in the indicating instrument.
(c) If generator output is above 500 volts
dc, replace the controller.
c. Resistance Network Test. Disconnect the
three resistors R1, R2, and R3 (fig. 5-4) and Check
each separately with Multimeter ME-26/U. The
resistors should check to within one percent of
their marked values. Normal values are given in
figure 5-4.
d. Continuity Test. Check the continuity of the
circuit, point-to-point, with Multimeter ME-26/U.
Check for possible short circuits in the same
manner.
e. Intermittent Trouble. In all tests, the
possibility of intermittent trouble should not be
overlooked. If present, this type of trouble may
often be made to appear by tapping or jarring the
equipment.
Section Ill. MAINTENANCE OF OHMMETER
6-6. Replacement of Parts
a. Repair of Ohmmeter ZM-21(*) /U shall be
accomplished by competent personnel supplied
with proper tools and equipment (listed in ap
pendix C).
b. All parts are easily reached when the chassis
assembly is removed from the case.
c. When removing wiring from terminals, tag
each wire to be sure of correct reassembly.
d. Take care not to damage adjacent parts when
removing, installing, or connecting new parts.
e. Replacement parts shall be identical to the
original parts and shall be installed in the same
physical position as the original.
f. When replacing wiring, each new piece of wire
shall be the same length as the wire being
replaced.
6-6
6-7. Replacement of Meter
a. Remove the chassis from the case according
to instructions in paragraph 6-4a.
b. Unsolder the connections to the meter terminals (fig. 5-5); tag the wires so that they may be
replaced properly.
c. Remove the mounting screws and bushings
from the meter magnet, and remove the meter (fig.
5-5).
d. Install a new meter, using the same screws
and bushings that were used to mount the old
instrument. Resolder the equipment wiring to the
meter terminals.
e. Replace the meter scale plate (fig. 6-2) with a
blank scale plate. Calibrate and mark the new scale
plate as shown in figure 6-4 according to directions
given in paragraph 6-16.
TM 11-6625-298-14
Figure 6-4. Meter scale.
6-8. Replacement of controller
a. Remove the chassis (para 6-4a).
b. Disconnect and tag the three wires leading to
the controller.
c. Remove the two screws holding the controller
to the chassis.
d. Reconnect the wires to the replacement
controller and replace the screws that fasten the
controller to the chassis.
6-9. Replacement of Hand Generator
a. Remove the chassis and chassis cover.
b. Remove the two snap buttons on the underside of the chassis.
c. Disconnect the leads from the generator
brush-holder terminals.
d. Remove the self-locking nuts, two of which
can be reached from the top of the chassis and the
other two through the holes on the underside of
the chassis from which the snap buttons have been
removed.
e. Withdraw the generator from the chassis.
f. Knock out the taper pin that retains the
clutch driven hub (fig. 5-1), and remove the hub.
g. Install the clutch hub and the new generator
by drilling the generator shaft and pinning the hub
to the shaft.
h. Place the new generator on the chassis, and
replace the self-locking nuts. On the underside of
the chassis, return the snap button to the holes
from which they were removed.
i. Reconnect the leads to the generator brushholder terminals.
6-10. Replacement of Meter Armature
a. Remove the meter (para 6-7).
b. Disconnect the ligaments and terminal from
the moving coil assembly (fig. 5-5).
CAUTION
Be careful not to damage the coil pivots or
the pointer.
c. Back off the upper jewelled bearing, and
carefully withdrew the armature from the magnet.
d. Install a new armature, and replace the upper
jewelled bearing. Reconnect the ligaments and
terminals to the moving coil assembly.
e. Replace the meter and meter scale (pars 6-7).
Calibrate and mark the new meter scale according
to instructions given in paragraph 6-16.
6-11. Replacement of Hand Generator Armature
a. Remove the generator (para 6-9).
b. Remove the generator brush caps (fig. 6-3)
and remove the brushes.
c. Remove the two self-locking nuts at the front
end of the generator (fig. 6-1).
d. Withdraw the armature, and replace it with a
new one.
e. Place the end bell in position, and replace the
self-locking nuts.
f. Replace the generator brushes and brush
cape.
g. Reinstall the generator as instructed in
paragraph 6-9.
6-12. Replacement of Terminals
When replacing terminals be sure to install all
washers and insulator bushings in the order in
which they were originally installed. Observe this
precaution especially in the case of the line terminal; this is the terminal on which the guard ring
is mounted.
6-13. Replacement of Meter Window Glass
a. Remove the rectangular nickel-plated bezel
from the top surface of the meter window.
6-7
TM 11-6625-298-14
b. Lift out the old meter window glass and clean
away old insulating compound from around the
meter scale aperture.
c. Spread new insulating compound around the
scale aperture and press the new meter window
glass in place.
d. Press the bezel down firmly over the glass.
6-14. Replacement of Meter Window Cover
a. Remove the four screws that hold the pillow
blocks in place (fig. 1-2).
b. Lift off the pillow blocks.
c. Lift the old cover out of the recess above the
meter window into which it fits.
d. Install a new cover and replace the pillow
blocks.
6-15. Lubrication of the Ohmmeter
a. General. The generator ball bearings and the
drive assembly gear train are lubricated by the
manufacturer and ordinarily will require no further
lubrication. When the generator is disassembled
for repair, however, the following lubrication shall
be performed at the general support maintenance
level.
b. Disassembly. The ohmmeter shall be
disassembled, inspected, and cleaned in accordance
with instructions given in paragraphs 4-5 and 6-4.
Remove four screws which hold chassis to the end
shield. The chassis and end shield may now be
separated, exposing all gearing. The internal or
ring-gear will remain within the end shield (fig. 5-1
and 5-2).
CAUTION
Do not lubricate any portion of the clutch
mechanism or the drive shaft and lock pin.
This also applies to the ratchet and drive
spring of older models.
c. Lubrication. Apply a small amount of grease
(Aircraft and Instruments-GL) to the generator
ball bearings and the entire drive assembly gear
train. Wipe off excess with a clean, lint-free cloth.
Grease (GL) is an all-weather lubricant; no special
precautions are necessary when it is used in extreme climates.
6-16. Calibration and Marking of Meter Scale
a. Equipment Required. In addition to
Multimeter
required.
(1) Ten
(2) Ten
(3) Ten
(4) Ten
ME-26/U the following resistors are
resistors, 0.1 megohm, ± prercent.
resistors, 1 megohm ± percent.
resistors, 10 megohms ± percent.
resistors, 100 megohms ± percent.
NOTE
Before calibrating a new meter scale, check
the output voltage of the ohmmeter (para
6-5 b). If the output voltage is above 550
volts or below 500 volts, replace the
controller.
b. Calibration. To calibrate a blank meter scale,
proceed as follows:
(1) Connect the line and ground terminals
together and turn the hand generator crank at
operating speed. The meter pointer should deflect
to the right-hand end of the blank scale plate. This
point is zero calibration on the scale; mark the
point in pencil.
(2) Remove the connector between the line
and ground terminals and again turn the hand
generator crank at operating speed. The pointer
should deflect to the opposite end of the blank
scale plate. This is the infinity point on the scale;
mark this point in pencil.
(3) Connect resistors (a above), singly or in
series, to obtain the various values of resistance
such as were indicated on the original scale (fig. 64). Connect the resistors between the line and
ground terminals of the ohmmeter. Turn the hand
generator crank at operating speed each time.
Mark each resistance value on the blank scale plate
in pencil.
c. Marking. Remove the meter scale plate from
its bracket and draw in the new points of
calibration with India ink. Use a straightedge and
a draftsman’s ruling pen.
6-17. Adjustment of Clutch
The clutch should be tightened all the way down to
prevent slipping. The operating voltage is
maintained by the controller, not by the clutch.
Section IV. GENERAL SUPPORT TESTING PROCEDURES
6-18. General
This section contains references for use by general
support maintenance personnel to determine
whether the performance of the repaired equipment
is satisfactory for return to the users.
6-8
6-19. Test Procedure
Perform the tests in paragraph 6-5a and 6-5b.
TM 11-6625-298-14
APPENDIX A
REFERENCES
DA Pam 310-4
DA Pam 310-7
TB 9-6625-975-35
TB 43-0118
TM 11-6625-203-12
TM 11-6625-298-34P
TM 38-750
TM 740-90-1
TM 750-244-2
Index of Technical manuals, Technical Bulletins, Supply Manuals (types 7,
8, and 9), Supply Bulletins, and Lubrications Orders.
US Army Equipment Index of Modification Work Orders.
Calibration Procedure for Ohmmeters I-48, I-48-B, ZM-21A/U, ZM-21B/U
(Winslow Model 5G1000), and Biddle Models 7676-1, 7679, 7679-1, and
7679-R.
Field Instruction for Painting and Preserving Electronics Command
Equipment Including Camouflage Pattern Painting of Electrical Equipment Shelters.
Operator and Organizational Maintenance: Multimeters AN/URM-105 and
AN/URM-105C Including Multimeters ME-77/U and ME-77C/U.
Direct Support and General Support Maintenance Repair Parts and Special
Tools Lists (Including Depot Maintenance Repair Parts and Special
Tools): Ohmmeters ZM-21/U, ZM-21A/U, and ZM-21B/U, Test Sets
1-48-A and 1-48-B (FSN 6625-581-2466.)
The Army Maintenance Management System (TAMMS).
Administrative Storage of Equipment.
Procedures for Destruction of Electronics Materiel to Prevent Enemy Use
(Electronics Command).
A-1
TM 11-6625-298-14
APPENDIX C
MAINTENANCE ALLOCATION
Section I. INTRODUCTION
C-1. General
This appendix provides a summary of the maintenance operations for ZM-21/U, ZM-21A/U, and
ZM-21B/U. It authorizes categories of maintenance for specific maintenance functions on
repairable items and components and the tools and
equipment required to perform each function. This
appendix may be used as an aid in planning
maintenance operations.
C-2. Maintenance Function
Maintenance functions will be limited to and
defined as follows:
a. Inspect. To determine the serviceability of an
item by comparing its physical, mechanical, and/or
electrical characteristics with established standards
through examination.
b. Test. To verify serviceability and to detect
incipient failure by measuring the mechanical or
electrical characteristics of an item and comparing
those characteristics with prescribed standards.
c. Service. Operations required periodically to
keep an item in proper operating condition; i.e., to
clean, preserve, drain, paint, or to replenish
fuel/lubricants/hydraulic fluids or compressed air
supplies.
d. Adjust. Maintain within prescribed limits by
bringing into proper or exact position, or by
setting the operating characteristics to the
specified parameters.
e. Align. To adjust specified variable elements
of an item to about optimum or desired performance.
f. Calibrate. To determine and cause corrections
to be made or to be adjusted on instruments or
test measuring and diagnostic equipment used in
precision measurement. Consists of the comparison
of two instruments, one of which is a certified
standard of known accuracy, to detect and adjust
any discrepancy in the accuracy of the instrument
being compared.
g. Install. The act of emplacing, seating, or
fixing into position an item, part, module (component or assembly) in a manner to allow the
proper functioning of the equipment/system.
h. Replace. The act of substituting a serviceable like-type part, subassembly, model
(component or assembly) for an unserviceable
counterpart.
i. Repair. The application of maintenance
services (inspect, test, service, adjust, align,
claibrate, replace) or other maintenance actions
(welding, grinding, riveting, straightening, facing,
remachining, or resurfacing) to restore serviceability to an item by correcting specific
damage, fault malfunction, or failure in a part,
subassembly, module/component/assembly, end
item or system. This function does not include the
trial and error replacement of running spare type
items such as fuses, lamps, or electron tubes.
j. Overhaul. That periodic maintenance effort
(service/action) necessary to restore an item to a
completely serviceable/operational condition as
prescribed by maintenance standards (e.g., DMR)
in appropriate technical publications. Overhaul is
normally the highest degree of maintenance performed by the Army. Overhaul does not normally
return an item to like-new condition.
k. Rebuild. Consists of. those services/actions
necessary for the restoration of unserviceable
equipment to a like-new condition in accordance
with original manufacturing standards. Rebuild is
the highest degree of material maintenance applied
to Army equipment. The rebuild operation includes
the act of returning to zero those age
measurements (hours, miles, etc. ) considered in
classifying Army equipment/components.
C-3. Column Entries
a. Column 1, Group Number. Column 1 lists
group numbers, the purpose of which is to identify
components,
assemblies,
subassemblies, and
modules with the next higher assembly.
b. Column 2, Component/Assembly. Column 2
contains, the noun names of components, assemblies, subassemblies, and modules for which
maintenance is authorized.
c. Column 3, Maintenance Functions. Column 3
lists the functions to be performed on the item
listed in column 2. When items are listed without
maintenance functions, it is solely for purpose of
having the group numbers in the MAC and RPSTL coincide.
d. Column 4, Maintenance Category. Column 4
C-1
TM 11-6625-298-14
specifies, by the listing of a “worktime” figure in
the appropriate subcolumn(s), the lowest level of
maintenance authorized to perform the function
listed in column 3. This figure represents the
active time required to perform that maintenance
function at the indicated category of maintenance.
If the number or complexity of the tasks within
the listed maintenance function vary at different
maintenance categories, appropriate “worktime”
figures will be shown for each category. The
number of task-hours specified by the “worktime”
figure represents the average time required to
restore an item (assembly, subassembly, component, module, end item or system) to a serviceable condition under typical field operating
conditions. This time includes preparation time,
troubleshooting time and quality assurance/quality
control time in addition to the time required to
perform the specific tasks identified for the
maintenance functions authorized in the maintenance allocation chart. Subcolumns of column 4
are as follows:
C–Operator/crew
O–Organizational
F–Direct support
H-General support
D–Depot
e. Column 5, Tools and Equipment. Column 5
specifies by code, those common tool sets (not
individual tools) and special tools, test, and
support equipment required to perform the
designated function.
C-4. Tool and Test Equipment Requirements
(Table 1)
a. Tool or Test Equipment Reference Code. The
numbers in this column coincide with the numbers
used in the tools and equipment column of the
MAC. The number indicate the applicable tool or
test equipment for the maintenance functions.
b. Maintenance Category. The codes in this
column indicate the maintenance category allocated
the tool or test equipment.
c. Nomenclature. This column lists the noun
name and nomenclature of the tools and test
equipment required to perform the maintenance
functions.
d. National/NATO Stock Number. This column
lists the National/NATO stock number of the
specific tool or test equipment.
e. Tool Number. This column lists the
manufactures part number of the tool followed by
the Federal Supply Code for Manufacturers (5digit) in parentheses.
(Next printed page is C-3)
C-2
TM 11-6625-298-14
SECTION II
MAINTENANCE
FOR
ALLOCATION
CHART
OHNMET2R Z!&21/U, ZM-21A/U, Am ZM-21B/U
—
(2)
(1)
GROUP
NUMBER
COMPONENT/ASSEMBLY
(3)
(4)
MAINTENANCE
FLINCTION
MAINTENANCE
c
o
F
(5)
~TEWRY
H
TOOLS AND
EQUIPMENT
D
2HK?41?TER Z!!-211hJ
01
02
03
CASE
CARL!Ei
oRmsml?R
9.1
Inspect
Service
Eep:ace
0.2
Inspee t
Service
Replace
Repair
0.1
0.2
0.5
Inspect
Service
rest
.Service
Adjust
Calibrate
Replace
Overhaul
0.1
!3.2
C.!4
1
0.5
1
0.5
0.2
0.2
0.9
1.5
2,5,6,’?,8
1
2,5,6,7,8
1
2.5
1-8
C-3
TM 11-6625-298-14
TABLE 1.
TOOL AND TEST EQUIPMENT REQUIREMENTS
FOR
OIBMETER 2M-21/U, 2N-2L4/U, AND ZN-21B/U
‘QOL OR TES1
EQUIPMENT
REF COOE
I
MAINTENANCE
CATEGORY
I
NOMENCLATURE
TK.101/G
1
H,D
2
D
hRILTIMSTER ME-26/U
3
D
DC MICRCNZTER, O-5 UA (WESTUN MDD 622)
TOOL KIT, ELECTRONIC EQUIPMENT
[email protected]
STOCK NUM6ER
180.00.064 -S178
62 S.00-646-9409
62 S.00.669.0266
4
D
s
H,D
RESISTOR, FIXED, FIiM
6
H,D
RESISTI.?R, FIXED,
7
H,O
RESISTOR, FIXED, FIIAI 10 t4EGOHN :1% (10 required)
905-00 -065 -058s
8
H,D
IRESISTDR, FIXED, mm 100 NEGIYiN :1% (10 required)
90S.00.049.8618
C-4
RESISTANCE, OECADE 2N-16/U
0.1 MEGDIM :1% (10 required)
FILN 1 MMCNW :1$ (10 rpquired)
905.00.683.6672
905.00-433.9267
TOOL lWMBER
TM 11-6625-298-14
Paragraph
Adjustment of clutch . . . . . . . . . . . . . . . . . . . . . ...6-17
Administrative storage... . . . . . . . . . . . . . . . . . . ...1-4
Calibration and marking
Of meter scale . . . . . . . . . . . . . . . . . . . . . . . . . . ...6-16
Clacking unpacked equipment . . . . . . . . . . . . . . ...2-2
Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...4-5
Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...5-3
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...1-6
Destruction of Army material . . . . . . . . . . . . . . . ...1-5
Forms and records . . . . . . . . . . . . . . . . . . . . . . . . . ...1-3
Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...5-1
Guard circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...5-7
Hand generator . . . . . . . . . . . . . . . . . . . . . . . . . . . ...5-2
Insulation resistance:
Conditions affecting . . . . . . . . . . . . . . . . . . . . . ..3-5b
Unit of measurement . . . . . . . . . . . . . . . . . . . ...3-5a
Values of . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...3-5c
Insulation resistance values
of equipment under test . . . . . . . . . . . . . . . . . . . ..3-17
Insulation test of:
A.c. and d.c. rotating machines
over 600 volts. . . . . . . . . . . . . . . . . . . . . . . ...3-7
A.c. and d.c. rotating machines
600 volts or less . . . . . . . . . . . . . . . . . . . . . ...3-6
Capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...3-9
Miscellaneous units . . . . . . . . . . . . . . . . . . . ...3-14
Power cables and wires . . . . . . . . . . . . . . . . . ...3-11
Telephones cables and wires . . . . . . . . . . . . ...3-12
Transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8
Wiring installations . . . . . . . . . . . . . . . . . . . . ...3-13
Isolating trouble:
Continuity test . . . . . . . . . . . . . . . . . . . . . . . . ..6-5d
Indicator scale test . . . . . . . . . . . . . . . . . . ...6-5a
Intermittent trouble . . . . . . . . . . . . . . . . . . . ..6-5e
Output voltage test . . . . . . . . . . . . . . . . . . . ...6-5b
Resistance network test . . . . . . . . . . . . . . . . ..6-5c
Locating low insulation . . . . . . . . . . . . . . . . . . . . . ..3-18
Lubrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-15
6-8
1-1
6-8
2-3
4-2
5-2
1-1
1-1
1-1
5-1
5-5
5-1
3-2
3-2
3-2
3-9
3-3
3-2
3-4
3-9
3-6
3-7
3-3
3-9
6-6
6-6
6-6
6-6
6-6
3-10
6-6
Paragraph
Maintenance forms end records . . . . . . . . . . . . . . ...1-3
Measurement of resistors . . . . . . . . . . . . . . . . . . ...3-16
Meter movement . . . . . . . . . . . . . . . . . . . . . . . . . . ...5-5
Minimum insulation resistance values . . . . . . . . . 3-12d
Operation under unusual condition:
Arctic climates . . . . . . . . . . . . . . . . . . . . . . . ...3-21
Desert climates . . . . . . . . . . . . . . . . . . . . . . . ...3-22
Tropical climates . . . . . . . . . . . . . . . . . . . . . ...3-23
Organizational troubleshooting,
general . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..4-4
Painting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...4-6
Preliminary adjustment . . . . . . . . . . . . . . . . . . . . ...2-4
Preventive maintenance
checks end services:
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...4-2
Period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...4-3
Purpose and use . . . . . . . . . . . . . . . . . . . . . . . . . . . ...1-7
Replacement of
Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..6-8
Hand generator . . . . . . . . . . . . . . . . . . . . . . . ...6-9
Hand generator armature . . . . . . . . . . . . . . . ..6-11
Meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-7
Meter armature . . . . . . . . . . . . . . . . . . . . . . ...6-10
Meter window cover . . . . . . . . . . . . . . . . . . . ...6-14
Meter window glass . . . . . . . . . . . . . . . . . . . ...6-13
Terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...6-12
Replacement of parts, general . . . . . . . . . . . . . . . ...6-6
Resistance network . . . . . . . . . . . . . . . . . . . . . . . . ...5-4
Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-1
Stopping procedure . . . . . . . . . . . . . . . . . . . . . . . . ...3-19
Tabulated data . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...1-8
Troubleshooting:
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..6-3
Preliminary inspection . . . . . . . . . . . . . . . . . ...6-4
Unpacking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...2-1
Working circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6
Page
1-1
3-9
5-3
3-8
3-10
3-10
3-10
4-2
4-2
2-3
4-1
4-1
1-2
6-7
6-7
6-7
6-8
6-7
6-8
6-7
6-7
6-6
5-3
1-1
3-10
1-2
6-1
6-3
2-1
5-4
Index 1
TM 11-6625-298-14
By Order of the Secretary of the Army:
BERNARD W. ROGERS
General, United States Army
Chief of Staff
Official:
PAUL T. SMITH
Major General, United States Army
The Adjutant General
Distribution:
Active Army:
USASA (2)
COE (1)
TSG (1)
USAARENBD (1)
DARCOM (1)
TRADOC (2)
OS Maj Cmd (4)
LOGCOMDS (3)
MICOM (2)
TECOM (2)
USACC (4)
MDW (1)
Armies (2)
Caps (2)
HISA (Ft Monmouth) (33)
Svc Colleges (1)
USASIGS (5)
USAADS (2)
USAFAS (2)
USAARMS (2)
USAIS (2)
USAES (2)
USAICS (3)
MAAG (1)
USARMIS (1)
Instls (2) except
Ft. Gordon (10)
Ft Huachuca (10)
Ft Carson (5)
Ft Richardson (ECOM Ofc) (2)
LBAD (14)
SAAD (30)
TOAD (14)
SHAD (3)
Ft Gillem (10)
Sig FLDMS (1)
USAERDAA (1)
USAERDAW (1)
Units org under fol T0E
(1 copy each unit):
7
11-16
11-18
11-500(AA-AC)
17
44-445
44-535
44-537
44-545
44-547
55-217
NG: State AG (3).
USAR: None.
For explanation of abbreviations used, see AR 310-60.
U.S.
GOVERNMENT
PRINTING
OFFICE:
1986
-
652-032/45422
THE METRIC SYSTEM AND EQUIVALENTS
PIN: 012171-000
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