Elenco Electronics M-1006K Instruction manual

DIGITAL MULTIMETER KIT
MODEL M-1006K
Assembly and Instruction Manual
Elenco Electronics, Inc.
Copyright © 2001 Elenco Electronics, Inc.
753096
PARTS LIST
If you are a student, and any parts are missing or damaged, please see instructor or bookstore.
If you purchased this meter kit from a distributor, catalog, etc., please contact Elenco Electronics
(address/phone/e-mail is at the back of this manual) for additional assistance, if needed. DO NOT contact your
place of purchase as they will not be able to help you.
RESISTORS (Parts mounted on card.)
Qty.
Symbol
1
R9
1
R8
1
R7
1
R13
1
R6
1
R5
1
R17
1
R12
1
R14
1
R4
1
R15
1
R3
1
R25
3
R10, R11, R24
1
R2
5
R18 - R22
1
R1
1
R23
Placed in bag with carded parts.
1
R16
Value
.01Ω
.99Ω .5% 1/4W
9Ω .5% 1/4W
100Ω 5% 1/4W
100Ω .5% 1/4W
900Ω .5% 1/4W
910Ω 1% 1/4W
1kΩ 5% 1/2W
4.7kΩ 5% 1/4W
9kΩ .5% 1/4W
30kΩ 1% 1/4W
90kΩ .5% 1/4W
100kΩ 5% 1/4W
220kΩ 5% 1/4W
352kΩ .5% 1/2W
470kΩ 5% 1/4W
548kΩ .5% 1/2W
1MΩ 5% 1/4W
Color Code
Shunt Wire
black-white-white-silver-green
white-black-black-silver-green
brown-black-brown-gold
brown-black-black-black-green
white-black-black-black-green
white-brown-black-black-brown
brown-black-brown-gold
yellow-violet-red-gold
white-black-black-brown-green
orange-black-black-red-brown
white-black-black-red-green
brown-black-yellow-gold
red-red-yellow-gold
orange-green-red-orange-green
yellow-violet-yellow-gold
green-yellow-gray-orange-green
brown-black-green-gold
Part #
100161
109930
119000
131000
131050
139050
139130
141000
144700
149050
153030
159050
161000
162200
163551
164700
165451
171000
200Ω (201)
Potentiometer
191310
Qty.
1
4
1
Symbol
C1
C2, C3, C4, C6
C5
Value
100pF (101)
.1µF (104)
.1µF (104)
Qty.
1
Symbol
D1
Value
1N4007
CAPACITORS
Description
Disc
Mylar (small yellow)
Mylar
Part #
221017
251017S
251017
SEMICONDUCTORS
Description
Diode (mounted on resistor card)
Part #
314007
MISCELLANEOUS
Qty.
1
2
1
1
1
1
1
1
1
1
3
Description
LCD
Zebra
PC Board IC Installed
Fuse 0.2A, 250V
Battery 9V
Battery Snap
Selector Knob
Case Top (Black)
Case Bottom (Black)
Zebra Frame
Screw 2mm x 6mm
Qty.
2
2
1
3
2
6
2
1
1
1
1
Part #
351115
500006
516101
533002
590009
590098
622104
623113
623209
629012
643439
Description
Part #
Screw 2mm x 10mm
643447
Fuse Holder Clips
663100
Socket Transistor
664007
Input Socket
664101
Ball Bearing
666400
Slide Contact
680013
Spring 1/4” (Selector Knob)
680014
Label Front
724012
Grease
790004
Solder Tube
9ST4
Test Lead Set
RWTL1000B
NOTE:
Not used but printed on PC board: R26 - R29, T1
The 7106 IC1 is already installed on the PC board. This type of installation is called C.O.B. (chip on
board). The IC is tested after it is installed on the PC board.
-1-
PARTS IDENTIFICATION
Battery Snap
Resistors
PC Board with IC
Transistor
Test Socket
LCD Assembly
Zebras/LCD/Frame/Cover
Zebras
Shunt Wire
Selector Knob
Potentiometer
Fuse
Clip
Zebra
Frame
Slide
Contact
Fuse
Input Socket
LCD
Ball Bearing
Capacitors
Diode
C5
Mylar
Discap
IDENTIFYING RESISTOR VALUES
Use the following information as a guide in properly identifying the value of resistors.
4 Bands
1 2
Multiplier
Tolerance
5 Bands
1
2 3 Multiplier
Tolerance
IDENTIFYING CAPACITOR VALUES
Capacitors will be identified by their capacitance value in pF (picofarads), nF (nanofarads), or µF (microfarads). Most
capacitors will have their actual value printed on them. Some capacitors may have their value printed in the following
manner. The maximum operating voltage may also be printed on the capacitor.
Second Digit
103K
100V
Multiplier
For the No.
0
1
2
3
Multiply By
1
10
100
1k
Tolerance*
Maximum Working Voltage
10µF 16V
First Digit
Multiplier
4
5
8
10k 100k .01
9
0.1
Note: The letter “R” may be used at times to
signify a decimal point; as in 3R3 = 3.3
* The letter M indicates a tolerance of +20%
The value is 10 x 1,000 =
10,000pF or .01µF 100V
The letter K indicates a tolerance of +10%
The letter J indicates a tolerance of +5%
METRIC UNITS AND CONVERSIONS
Abbreviation
p
n
µ
m
–
k
M
Means
pico
nano
micro
milli
unit
kilo
mega
Multiply Unit By
.000000000001
.000000001
.000001
.001
1
1,000
1,000,000
Or
10-12
10-9
10-6
10-3
100
103
106
-2-
1,000 pico units = 1 nano unit
1,000 nano units = 1 micro unit
1,000 micro units = 1 milli unit
1,000 milli units
= 1 unit
1,000 units
1,000 kilo units
= 1 kilo unit
= 1 kilo unit
CONSTRUCTION
Introduction
The most important factor in assembling your M-1006K Digital Multimeter Kit is good soldering techniques.
Using the proper soldering iron is of prime importance. A small pencil type soldering iron of 25 - 40 watts is
recommended. The tip of the iron must be kept clean at all times and well tinned.
Safety Procedures
• Wear eye protection when soldering.
• Locate soldering iron in an area where you do not have to go around it or reach over it.
• Do not hold solder in your mouth. Solder contains lead and is a toxic substance. Wash your hands
thoroughly after handling solder.
• Be sure that there is adequate ventilation present.
Assemble Components
In all of the following assembly steps, the components must be installed on the top side of the PC board unless
otherwise indicated. The top legend shows where each component goes. The leads pass through the
corresponding holes in the board and are soldered on the foil side.
Use only rosin core solder of 63/37 alloy.
DO NOT USE ACID CORE SOLDER!
What Good Soldering Looks Like
Types of Poor Soldering Connections
A good solder connection should be bright, shiny,
smooth, and uniformly flowed over all surfaces.
1.
Solder all components from
the copper foil side only.
Push the soldering iron tip
against both the lead and
the circuit board foil.
1. Insufficient heat - the
solder will not flow onto the
lead as shown.
Soldering Iron
Component Lead
Foil
Soldering iron positioned
incorrectly.
Circuit Board
2.
3.
4.
Apply a small amount of
solder to the iron tip. This
allows the heat to leave the
iron and onto the foil.
Immediately apply solder to
the opposite side of the
connection, away from the
iron.
Allow the heated
component and the circuit
foil to melt the solder.
Allow the solder to flow
around the connection.
Then, remove the solder
and the iron and let the
connection cool.
The
solder should have flowed
smoothly and not lump
around the wire lead.
Rosin
2. Insufficient solder - let the
solder flow over the
connection until it is
covered. Use just enough
solder
to
cover
the
connection.
Soldering Iron
Solder
Foil
Solder
Gap
Component Lead
Solder
3. Excessive solder - could
make connections that you
did not intend to between
adjacent foil areas or
terminals.
Soldering Iron
Solder
Foil
4. Solder bridges - occur
when solder runs between
circuit paths and creates a
short circuit. This is usually
caused by using too much
solder.
To correct this,
simply drag your soldering
iron across the solder
bridge as shown.
Here is what a good solder
connection looks like.
-3-
Soldering Iron
Foil
Drag
ASSEMBLY INSTRUCTIONS
Identify and install the following parts as shown. After soldering each part, mark a check
Be sure that solder has not bridged to an adjacent pad.
C1 - 100pF (101) Discap
in the box provided.
R20 - 470kΩ 5% 1/4W Resistor
(yellow-violet-yellow-gold)
(see Figure A)
C2 - .1µF (104) Mylar (small yellow)
R22 - 470kΩ 5% 1/4W Resistor
(yellow-violet-yellow-gold)
(see Figure A)
C5 - .1µF (104) Mylar
R24 - 220kΩ 5% 1/4W Resistor
(red-red-yellow-gold)
(see Figure A)
R21 - 470kΩ 5% 1/4W Resistor
(yellow-violet-yellow-gold)
(see Figure A)
C4 - .1µF (104) Mylar (small yellow)
R25 - 100kΩ 5% 1/4W Resistor
(brown-black-yellow-gold)
(see Figure A)
C3 - .1µF (104) Mylar (small yellow)
R23 - 1MΩ 5% 1/4W Resistor
(brown-black-green-gold)
(see Figure A)
R15 - 30kΩ 1% 1/4W Resistor
(orange-black-black-red-brown)
(see Figure A)
R6 - 100Ω .5% 1/4W Resistor
(brown-black-black-black-green)
(see Figure A)
R16 - 200Ω (201) Potentiometer
(see Figure B)
R5 - 900Ω .5% 1/4W Resistor
(white-black-black-black-green)
(see Figure A)
R17 - 910Ω 1% 1/4W Resistor
(white-brown-black-black-brown)
(see Figure A)
R4 - 9kΩ .5% 1/4W Resistor
(white-black-black-brown-green)
(see Figure A)
R14 - 4.7kΩ 5% 1/4W Resistor
(yellow-violet-red-gold)
(see Figure A)
R3 - 90kΩ .5% 1/4W Resistor
(white-black-black-red-green)
(see Figure A)
R13 - 100Ω 5% 1/4W Resistor
(brown-black-brown-gold)
(see Figure A)
R19 - 470kΩ 5% 1/4W Resistor
R18 - 470kΩ 5% 1/4W Resistor
(yellow-violet-yellow-gold)
(see Figure A)
Figure A
Figure B
Stand resistor on end as
shown. Solder and cut
off the excess leads.
Mount the potentiometer to the PC board as shown.
-4-
ASSEMBLY INSTRUCTIONS
Identify and install the following parts as shown. After soldering each part, mark a check
Be sure that solder has not bridged to an adjacent pad.
in the box provided.
C6 - .1µF (104) Mylar (small yellow)
R1 - 548kΩ .5% 1/2W Resistor
(green-yellow-gray-orange-green)
R7 - 9Ω .5% 1/4W Resistor
(white-black-black-silver-green)
R2 - 352kΩ .5% 1/2W Resistor
(orange-green-red-orange-green)
R8 - .99Ω .5% 1/4W Resistor
(black-white-white-silver-green)
R11 - 220kΩ 5% 1/4W Resistor
(red-red-yellow-gold)
(see Figure A)
R12 - 1kΩ 5% 1/2W Resistor
(brown-black-brown-gold)
R10 - 220kΩ 5% 1/4W Resistor
(red-red-yellow-gold)
(see Figure A)
Figure C
D1 - 1N4007 Diode
(see Figure C)
Stand diode on end. Mount
with band as shown on the top
legend.
Band
Install the following parts. Then, mark a check
in the box provided.
Insert the narrow end of the three input sockets into the PC board from the solder side, as shown in Figure D.
Solder the sockets to the PC board on the component side only. The solder should extend completely around
the socket (see Figure D).
Insert the shunt wire (R9) into the PC board holes from the component side as shown in Figure D. Adjust
the wire so that it sticks out the other (solder) side of the PC board 3/16 of an inch. Solder the wire to the
PC board on the component side only.
Be sure that the 8-pin transistor socket will slide easily through its hole in the top case from either direction.
If it does not, carefully slide it through the hole several times in each direction to remove any burrs. Do not
push on the socket leads or they may be damaged.
Insert the socket into the PC board holes from the solder side as shown in Figure D. Be sure that the tab
lines up with the hole as shown in the figure. Solder the socket to the PC board on the component side of
the PC board as shown in the figure and cut off excess leads.
Feed the battery snap wires up through the holes in the PC board from the solder side as shown in Figure D.
Insert the red wire into the hole marked (9V+) and black wire into hole marked (9V–) as shown. Solder the
wires to the PC board.
Insert the two fuse clips into the PC board holes as shown in Figure D. Be sure that the tabs are on the
outside as shown in the figure. Solder the clips to the PC board.
-5-
Fuse Clips
Solder Side
Tab
Shunt Wire
Solder
Solder Side
Input Sockets
Red Wire
Battery Snap
Transistor
Socket
Black Wire
Close-up view of the
transistor socket and
PC board.
Figure D
Remove the clear protective film from the front of the LCD (Note:
DO NOT remove the silver backing). Place the LCD, zebra frame,
and zebras into the top case as shown in Figure E. Be sure that
the LCD tab is in the same direction as shown in the figure.
Zebras
Cut open the plastic envelope containing the grease and put a
small amount of grease in each spring hole of the selector knob
as shown in Figure F. Then, insert a 1/4” spring into each hole as
shown in the figure.
Zebra Frame
LCD
Tab
1/4” Springs
Top Case
Clear Protective Film
Spring Holes
Figure E
Figure F
-6-
Put the bearings into two opposite indents in the case top as shown in Figure G.
Place the six slide contactors on the selector knobs as shown in Figure G.
Place the selector knob into the case top so that the springs fit over the bearings as shown in Figure G.
Place the PC board over the selector knob. Be sure that the 8-pin socket slides into its hole. Then fasten
the PC board with two 6mm screws as shown in Figure G.
Insert the 0.25A, 250V fuse into the fuse clips. Your fuse may be unmarked.
Peel the backing off of the front label and place it on the case top.
Connect a 9V battery to the battery snap.
6mm Screws
PC Board
Selector Knob
Rib
Slide Contactor
Close-up View
Case Top
Bearings
Battery Compartment
Figure G
-7-
TESTING, CALIBRATION, AND TROUBLESHOOTING
TESTING OF LCD
With no test leads connected to the meter, move the selector switch around the dial. You should obtain the following
readings. A (–) sign may also be present or blinking.
1) ACV Range:
750
200
0 0.0
000
2) DCA,10A Ranges:
200µ
2000µ
20m
200m
10A
0 0.0
000
0.0 0
0 0.0
0.0 0
3) Ohms, Diode and hFE Ranges: B indicates blank.
hFE
000
Diode (
)
1BBB
200
1 B B.B
4) DCV Range:
2000
20k
200k
2000k
1BBB
1 B.B B
1 B B.B
1BBB
200m
2000m
20
200
1000
0 0.0
000
0.0 0
0 0.0
000
If any of these tests fail:
a) Check that the battery is good.
b) Check the values of resistors R14, R15, R19, R20, R23 - R25.
c) Check the values of capacitors C1 - C6.
d) Check the PC board for solder bridges and bad solder connections.
e) Check that the slide contactors are seated correctly.
f ) Check that the LCD and zebras are seated correctly.
CALIBRATION
Refer to the METER OPERATION section for test lead connections and measurement procedure.
A/D CONVERTER CALIBRATION
Turn the range selector switch to the 20V position and connect the test leads. Using another meter of known accuracy,
measure a DC voltage of less than 20 volts (such as a 9V battery). Calibrate the kit meter by measuring the same voltage
and adjusting R16 until the kit meter reads the same as the accurate meter (do not use the kit meter to measure its own
battery). When the two meters agree, the kit meter is calibrated. Turn the knob to the OFF position and remove the voltage
source.
SHUNT WIRE CALIBRATION
To calibrate the shunt wire, you will need a 5 amp current source such as a
5V power supply and a 1 ohm, 25 watt resistor. If a 5 amp source is not
available, you can use a lower current (2 amps). If no supply is available, it is
not important to do this test. Set the range switch to the 10A position and
connect the test leads as shown in Figure H. If the meter reads higher than
5A, resolder the shunt wire so that there is less wire between the 10A DC and
COM sockets.
If the meter reads low, resolder the shunt wire so that there is more wire
between the sockets.
123
Power Supply
5VDC –
+
1Ω
25 Watts
10A DC
VΩmA
COM
If the calibration fails:
a) Check the PC board for solder bridges and bad solder connections.
b) Check the value of resistors R7 - R9, R23, and capacitor C3.
-8-
Figure H
DC VOLTS TEST
1) If you have a variable power supply, set the supply to about the midpoint of each of the DCV ranges and compare the
kit meter reading to a meter known accuracy.
2) If you do not have a variable power supply, make the following two tests:
a) Set the range switch to 2000mV and measure the voltage across the 100 ohm resistor of Figure Ia. You should get
about 820mV. Compare the reading to a meter of known accuracy.
b) Set the range switch to 200mV and measure the voltage across the 100 ohm resistor of Figure Ib. You should get
about 90mV. Compare the reading to a meter of known accuracy.
If any of these tests fail:
123
123
10A DC
10A DC
a) Recheck the meter
calibration.
b) Check the value and the
soldering of resistors R1R6, R12-R17, R21-R24,
and capacitor C3.
VΩmA
VΩmA
1kΩ
9V
COM
10kΩ
COM
9V
100Ω
100Ω
Figure Ia
Figure Ib
AC VOLTS TEST
To test the ACV ranges, we will need a source of AC voltage. The AC power line is the most convenient.
CAUTION: Be very careful when working with 120VAC. Be sure that the range switch is in the 200 or 750VAC
position before connecting the test leads to 120VAC.
1) Set the range to 200VAC and measure the AC power line. The voltage should be about 120VAC. Compare
the reading to a meter of known accuracy.
2) Set the range to 750VAC and measure the AC power line. The voltage should be about 120VAC. Compare
the reading to a meter of known accuracy.
If either if the above tests fail:
a) Check the values and the soldering of resistors R1 - R6, R22.
b) Check that diode D1 is mounted as shown in the assembly instructions.
DC AMPS TEST
1) Set the range switch to 200µA and connect the meter as in Figure J. With RA equal to 100kΩ the current
should be about 90µA. Compare the reading to a known accurate meter.
2) Set the range switch and RA as in the following table. Read the currents shown and compare to a known
accurate meter.
Range Switch
2000µA
20mA
200mA
RA
10kΩ
1kΩ
470Ω
Current (approx.)
900µA
9mA
19mA
123
9V
RA
10A DC
VΩmA
If any of the above tests fail:
a) Check the fuse.
b) Check the value and soldering of resistors R7, R8, and R9.
-9-
COM
Figure J
Accurate
Meter
RESISTANCE/DIODE TEST
1) Measure a resistor of about half of the full scale value of each resistance range. Compare the kit meter
readings to those from a meter of known accuracy.
2) Measure the voltage drop of a good silicon diode. You should read about 700mV. Power diodes and the
base to emitter junction of power transistors may read less.
If any of these tests fail:
a) Check the values and the soldering of resistors R1 - R6, and R12.
hFE
1) Set the range switch to hFE and insert a small transistor into the appropriate NPN or PNP holes in the
transistor socket.
2) Read the hFE of the transistor. The hFE of transistors varies over a wide range, but you will probably get a
reading between 100 and 300.
If this check fails:
a) Check that the transistor socket is aligned according to Figure D.
b) Check the value and soldering of resistors R10, R11, and R29.
FINAL ASSEMBLY
Snap the case bottom onto the case top and fasten with the two 10mm screws as shown in Figure K.
Screws
Case
Bottom
Battery
Case Top
Figure K
-10-
THEORY OF OPERATION
A block diagram of the M-1006K is shown in Figure 1. Operation centers around a custom LSI chip. This chip
contains a dual slope A/D (analog to digital) converter, display latches, seven segment decoder and display
drivers. A block diagram of the IC functions is shown in Figure 2. The input voltage or current signals are
conditioned by the selector switches to produce an output DC voltage with a magnitude between 0 and 199mV.
If the input signal is 100VDC, it is reduced to 100mVDC by selecting a 1000:1 divider. Should the input be
100VAC, it is first rectified and then divided down to 100mVDC. If current is to be read, it is converted to a DC
voltage by internal shunt resistors.
DC
Analog
Data
V
Input
Selector
Switches
AC
Converter
V
Ohms
Converter
Ω
Voltage
Divider
V
A/D
Converter
& Display
Driver
Selector
Switches
Decimal
Figure 1
Current
Shunt
I
Point
Display
For resistance measurements, an internal voltage source drives the test resistor in series with a known resistor.
The ratio of the test resistor voltage to the known resistor voltage is used to determine the value of the test
resistor.
The input of the 7106 IC is fed to an A/D converter. Here the DC voltage is changed to a digital format. The
resulting signals are processed in the decoders to light the appropriate LCD segments.
Timing for the overall operation of the A/D converter is derived from an external oscillator whose frequency is
selected to be 25kHz. In the IC, this frequency is divided by four before it clocks the decade counters. It is then
further divided to form the three convert-cycles phases. The final readout is clocked at about two readings per
second.
The digitized measurements are presented to the display as four decoded digits (seven segments) plus polarity.
The decimal point position on the display is determined by the selector switch setting.
A/D CONVERTER
A simplified circuit diagram of the analog portion of the A/D converter is shown in Figure 3. Each of the switches
shown represent analog gates which are operated by the digital section of the A/D converter. The basic timing
for switch operation is keyed by the external oscillator. The conversion process is continuously repeated. A
complete cycle is shown in Figure 3.
Any given measurement cycle performed by the A/D converter can be divided into three consecutive time
periods, autozero (AZ), integrate (INTEG) and read. A counter determines the length of the time periods. The
integrate period is fixed at 1,000 clock pulses. The read period is a variable time that is proportional to the
unknown input voltage. It can vary from zero counts for zero input voltage to 2,000 counts for a full scale input
voltage. The autozero period varies from 1,000 to 3,000 counts. For an input voltage less than full scale
autozero gets the unused portion of the read period. The value of the voltage is determined by counting the
number of clock pulses that occur during the read period.
During autozero a ground reference is applied as an input to the A/D converter. Under ideal conditions, the
output of the comparator would also go to zero. However, input-offset-voltage errors accumulate in the amplifier
loop and appear at the comparator output as an error voltage. This error is impressed across the AZ capacitor
where it is stored for the remainder of the measurement cycle. The stored level is used to provide offset voltage
correction during the integrate and read periods.
-11-
The integrate period begins at the end of the autozero period. As the period begins, the AZ switch opens and
the INTEG switch closes. This applies the unknown input voltage to the input of the A/D converter. The voltage
is buffered and passed on to the integrator to determine the charge rate (slope) on the INTEG capacitor At the
end of the fixed integrate period, the capacitor is charged to a level proportional to the unknown input voltage.
During the read period, this voltage is translated to a digital indication by discharging the capacitor at a fixed
rate and counting the number of clock pulses that occur before it returns to the original autozero level.
As the read period begins, the INTEG switch opens and the read switch closes. This applies a known reference
voltage to the input to the A/D converter. The polarity of this voltage is automatically selected to be opposite
that of the unknown input voltage, thus causing the INTEG capacitor to discharge at a fixed rate (slope). This
rate is determined by the known reference voltage. When the charge is equal to the initial starting point
(autozero level), the read period is ended. Since the discharge slope is fixed during the read period, the time
required for discharge is proportional to the unknown input voltage. Specifically, the digital reading displayed is
1000 (VIN / VREF).
The autozero period and thus a new measurement cycle begins at the end of the read period. At the same time
the counter is released for operation by transferring its contents (the previous measurement value) to a series of
latches. This stored data is then decoded and buffered before being used to drive the LCD display.
-12-
a
f
a
b
g
b
e
c
d
BACKPLANE
28
LCD PHASE DRIVER
7 Segment
Decode
7 Segment
Decode
TYPICAL SEGMENT OUTPUT
V+
7 Segment
Decode
200
0.5mA
LATCH
Segment
Output
2mA
Thousand
Tens
Hundreds
Units
Internal Digital Ground
To Switch Drivers
From Comparator Output
V+
CLOCK
6.2V
LOGIC CONTROL
-4
*
3
TEST
Internal Digital Ground
1V
500Ω
* Three inverters.
One inverter shown for clarity.
8
7
6
OSC 3
OSC 2
OSC 1
CREF
CREF+
42
V+
44
43
A-Z &
Z1
41
A-Z &
Z1
1
+
2.8V
CINT
37
INT
INTEGRATOR
6.2V
35
+
+
A-Z
COMPARATOR
Z1
DE (-)
+
DE (+)
ANALOG SECTION of 7106
DE (-)
40
38
A-Z & DE(+)
& Z1
INT
34
V
Read
To
Digital
Control
Logic
AZ
+ REF
(Flying
Capacitor)
Integ.
Integ.
Unknown
Input
Voltage +
AZ
AZ
Integ.
AZ
Read
+.20
.15
.10
.05
0
Counter Output
Figure 3
TO
DIGITAL
SECTION
DE (+)
A-Z
IN LO
ZERO
CROSSING
DETECTOR
POLARITY
FLIP/FLOP
39
IN HI
Figure 2
7106 IC Functions
CAZ
AUTO
ZERO
V+
36
10µA
INT
COMMON
DIGITAL SECTION
RINT
REF LO CREF BUFFER
REF HI
V
4
0
1000
160ms
0
500
1000
1500
DUAL SLOPE A/D CONVERTER
-13-
2000
DC VOLTAGE MEASUREMENT
200mV
Figure 4 shows a simplified diagram of the DC voltage
measurement function. The input voltage divider resistors
add up to 1 megaohm. Each step down divides the voltage
by a factor of ten. The divider output must be within the
range –0.199 to +0.199 volts or the overload indicator will
function. The overload indication consists of a 1 in the most
significant digit and blanks in the remaining digits.
Volts
900kΩ
2V
Low Pass
Filter
90kΩ
20V
9kΩ
7106
100mV
REF
200V
900Ω
1kV
100Ω
Common
Figure 4
Simplified DC Voltage Measurement Diagram
AC VOLTAGE MEASUREMENT
Figure 5 shows a simplified diagram of the AC voltage
measurement function. The AC voltage is first rectified and
passed through a low pass filter to smooth out the
waveform. A scaler reduces the voltage to the DC value
required to give the correct RMS reading.
Rectifier
Volts
Low Pass
Filter
Low Pass
Filter - Scaler
7106
200V
100mV
REF
900Ω
750V
100Ω
Common
Figure 5
Simplified AC Voltage Measurement Diagram
CURRENT MEASUREMENT
Figure 6 shows a simplified diagram of the current
measurement function. Internal shunt resistors convert the
current to between –0.199 to +0.199 volts which is then
processed in the 7106 IC to light the appropriate LCD
segments. When current in the range of 10A is to be read,
it is fed to the 10A input and does not pass through the
selector switch.
200µA
900Ω
2000µA
100Ω
2000µA
A
Low Pass
Filter
200µA
20mA
200mA
10A
10A
9Ω
20mA
200mA
10A
100mV
REF
7106
.99Ω
.01Ω
Common
Figure 6
-14-
Simplified DC Amps Measurement Diagram
RESISTANCE MEASUREMENT
Figure 7 shows a simplified diagram of the resistance measurement
function. A simple series circuit is formed by the voltage source, a
reference resistor from the voltage divider (selected by the selector
switches), and the test (unknown) resistor. The ratio of the two resistors
is equal to the ratio of their respective voltage drops. Therefore, since
the value of one resistor is known, the value of the second can be
determined by using the voltage drop across the known resistor as a
reference. This determination is made directly by the A/D converter.
Low Pass
Filter
Ω
100Ω
Test
Resistor
Reference
Voltage
900Ω
2000Ω/Dio
9kΩ
20kΩ
7106
200Ω
90kΩ 200kΩ
2000kΩ
Common
900kΩ
Voltage
Source
Figure 7
Overall operation of the A/D converter during a resistance
measurement is basically as described earlier with one exception. The
reference voltage present during a voltage measurement is replaced by
the voltage drop across the reference resistor. This allows the voltage
across the unknown resistor to be read during the read period.
hFE MEASUREMENT
Figure 8 shows a simplified diagram of the hFE measurement function.
Internal circuits in the 7106 IC maintain the COMMON line at 2.8 volts
below V+. When a PNP transistor is plugged into the transistor socket,
base to emitter current flows through resistor R10. The voltage drop in
resistor R10 due to the collector current is fed to the 7106 and indicates
the hFE of the transistor. For an NPN transistor, the emitter current
through R11 indicates the hFE of the transistor.
Simplified Resistance Measurement Diagram
V+
PNP
NPN
E
C
B
B
C
E
R11
220kΩ
Low Pass
Filter
R10
220kΩ
100mV
Ref.
7106
R23
10Ω
Common
Figure 8
SPECIFICATIONS
GENERAL
DC CURRENT
DISPLAY
OVERRANGE INDICATION
MAXIMUM COMMON MODE
VOLTAGE
STORAGE ENVIRONMENT
TEMPERATURE COEFFICIENT
POWER
DIMENSIONS
3 1/2 digit LCD, with polarity
3 least significant digits blanked.
RANGE
200µA
2000µA
20mA
200mA
10A
500V peak.
–15OC to 50OC.
(0OC to 18OC and 28OC to 50OC)
less than 0.1 x applicable accuracy
specification per OC.
9V alkaline or carbon zinc battery.
128 x 75 x 24mm.
OVERLOAD PROTECTION
RESOLUTION
0.1mV
1mV
10mV
100mV
1V
MAXIMUM ALLOWABLE INPUT
INPUT IMPEDANCE
ACCURACY
+1% rdg + 2d
+1% rdg + 2d
+1% rdg + 2d
+1.2% rdg + 2d
+2% rdg + 3d
.25A/250V fuse (mA input only).
AC VOLTAGE
RANGE
200V
750V
DC VOLTAGE
RANGE
200mV
2000mV
20V
200V
1000V
RESOLUTION
0.1µA
1µA
10µA
100µA
10mA
ACCURACY
+0.5% rdg + 2d
+0.5% rdg + 2d
+0.5% rdg + 2d
+0.5% rdg + 2d
+0.5% rdg + 2d
RESOLUTION
100mV
1V
ACCURACY
+1.2% rdg + 10d
+1.2% rdg + 10d
MAXIMUM ALLOWABLE INPUT
FREQUENCY
750Vrms.
45 - 450Hz.
RESISTANCE
RANGE
200Ω
2000Ω
20kΩ
200kΩ
2000kΩ
1000VDC or peak AC.
1MΩ.
RESOLUTION
0.1Ω
1Ω
10Ω
100Ω
1kΩ
ACCURACY
+0.8% rdg + 2d
+0.8% rdg + 2d
+0.8% rdg + 2d
+0.8% rdg + 2d
+1% rdg + 2d
MAXIMUM OPEN CIRCUIT VOLTAGE
2.8V.
DIODE CHECK
RANGE
DIODE
RESOLUTION
1mV
MAX TEST CURRENT
1.4mA
MAX OPEN CIRCUIT VOLTAGE
2.8V
TEST RANGE
0 - 1000
TEST CURRENT
Ib = 10µA
TEST VOLTAGE
Vce 3V
TRANSISTOR hFE TEST
RANGE
NPN/PNP
-15-
METER OPERATION
PRECAUTIONS AND PREPARATIONS FOR MEASUREMENT
1) Be sure the battery is connected to the battery snap and correctly placed in the battery compartment.
2) Before connecting the test leads to the circuit, be sure the range switch is set to the correct position.
3) Be sure that the test leads are connected to the correct meter terminals before connecting them to the
circuit.
4) Before changing the range switch, remove one of the test leads from the circuit.
5) Operate the instrument only in temperatures between 0 and 50OC and in less than 80% RH.
6) Pay careful attention to the maximum rated voltage of each range and terminal.
7) When finished making measurements, set the switch to OFF. Remove the battery when the instrument will
not be used for a long period of time.
8) Do not use or store the instrument in direct sunlight or at high temperature or humidity.
VOLTAGE MEASUREMENTS
1) Connect the black test lead to the “COM” terminal.
2) Connect the red test lead to the “VΩMA” terminal.
3) Set the range switch to the desired “V
the switch to the highest range.
” or “V~” position. If the magnitude of the voltage is not known, set
4) Connect the leads across the points to be measured and read the display. If the range switch is too high,
reduce it until a satisfactory reading is obtained.
DCA MEASUREMENTS
HIGH CURRENTS (200mA to 10A)
1) Connect the black test lead to the “COM” terminal.
2) Connect the red test lead to the 10ADC terminal.
3) Set the range switch to the 10A
position.
4) Open the circuit to be measured and connect the leads in series with the load to be measured.
5) Read the display. If the display read less than 200mA, follow the low current procedure below.
6) Turn off all of the power to the circuit being tested and discharge all of the capacitors before disconnecting
the test leads.
LOW CURRENTS (less than 200mA)
7) Connect the black test lead to the “COM” terminal.
8) Connect the red test lead to the VΩMA terminal.
9) Set the range switch to the desired A position. If the magnitude of the current is not known, set the switch
to the highest position.
10) Open the circuit to be measured and connect the leads in series with the load to be measured.
11) Read the display. If the range switch is too high, reduce it until a satisfactory reading is obtained.
12) Turn off all power to the circuit being tested and discharge all capacitors before disconnecting the test leads.
-16-
RESISTANCE MEASUREMENTS
1)
2)
3)
4)
Connect the black test lead to the “COM” terminal.
Connect the red test lead to the “VΩMA” terminal.
Set the range switch to the desired “Ω” position.
If the resistance being measured is connected to a circuit, turn off the power to the circuit being tested and
discharge all of the capacitors.
5) Connect the leads across the resistor to be measured and read the display. When measuring high
resistance, be sure not to contact adjacent points even if insulated. Some insulators have relatively low
resistance and will cause the measured resistance to be lower than the actual resistance.
DIODE CHECK
1) Connect the black test lead to the “COM” terminal.
2) Connect the red test lead to the “VΩMA” terminal.
3) If the diode being measured is connected to a circuit, turn off all power to the circuit and discharge all
capacitors.
4) Set the range switch to “
”.
Forward Voltage Check
5) Connect the red lead to the anode and the black lead to the cathode of the diode. Normally the forward
voltage drop of a good silicon diode reads between 450 and 900mV.
Reverse Voltage Check
6) Reverse the leads to the diode. If the diode is good, an overrange indication is given (a 1 in the most
significant digit and blanks in the remaining digits). If the diode is bad, “000” or some other value is
displayed.
hFE MEASUREMENTS
1) Set the range switch to hFE and insert the test transistor into the appropriate NPN or PNP
holes in the transistor socket.
2) Read the hFE of the transistor.
BATTERY & FUSE REPLACEMENT
If “ + ” appears on the display, it indicates that the battery should be replaced.
To replace battery and fuse (250mA/250V), remove the 2 screws in the bottom of the case.
Simply remove the old fuse/battery and replace with a new fuse/battery.
QUIZ
1. The function of the A/D converter is to . . .
A) convert digital to analog.
B) divide the analog signal by 2.
C) convert analog to digital.
D) convert AC to DC.
2. The divider used for DC voltage measurements is a . . .
A) divide by 20.
B) capacitance divider.
C) divide by 5.
D) resistor divider.
3. When the AC voltage is measured, it is first . . .
A) divided by 2.
B) rectified.
C) divided by 100.
D) sent to a high pass filter.
4. When measuring current, the shunt resistors convert the
current to . . .
A) –0.199 to +0.199 volts.
B) –1.199 to +1.199 volts.
C) –0.099 to +0.099 volts.
D) –199 to +199 volts.
5. The DC voltage divider resistors add up to . . .
A) 100Ω.
B) 1000Ω.
C) 100kΩ.
D) 1MΩ.
6. Resistance measurements are made by . . .
A) comparing voltage drops in the unknown resistor and a
reference resistor.
B) measuring the current in the unknown resistor.
C) measuring the current in the reference resistor.
D) equalizing the voltage drops in the unknown and the
reference resistors.
7. The measurement cycle performed by the A/D converter can be
divided into time periods known as . . .
A) long and short.
B) autozero, integrate and read.
C) zero, read and interphase.
D) convert, integrate and display.
8. A resistor with the band colors green-black-green-brown-green is . . .
A) 50.5kΩ +5%.
B) 5.15kΩ +10%.
C) 5.05kΩ +.5%.
D) 5.05kΩ +1%.
9. The M-1005K has . . .
A) A 3 digit display.
B) A 3 1/2 digit display.
C) A 4 1/2 digit display.
D) None of the above.
10.When measuring 450mA, the meter leads should be connected to . . .
A) COM and VΩmA.
B) COM and 10A.
C) 10A and VΩmA.
D) COM and Building GND.
-17-
Answers: 1. C, 2. D, 3. B, 4. A,
5. D, 6. A, 7. B, 8. C, 9. B, 10. B
SCHEMATIC DIAGRAM
-18-
Elenco Electronics, Inc.
150 W. Carpenter Avenue
Wheeling, IL 60090
(847) 541-3800
www.elenco.com
e-mail: elenco@elenco.com