Wilcom Inc.
Wilcom
MODEL T136BGMZW
CIRCUIT TEST SET
Operating Instructions
T136BGM Current Test Set
Operating Instructions
811-233-010
February 2007
Copyright (c) 2007 Wilcom
All Rights reserved
Wilcom reserves the right to make changes to the material contained
herein without notice and shall not be liable for errors contained
herein or for incidental, consequential damage in connection with the
furnishing, performance or use of this material.
This document may not be copied or duplicated in part or in whole for
any purpose without the express written permission of Wilcom.
i
Table of Contents
Page
Introduction....................................................................... 1
Specifications..................................................................... 6
Circuit Description........................................................... 9
Input Circuit..................................................................... 9
Measuring Circuit Input Section....................................... 9
Circuit Measuring............................................................. 10
Batteries & PUSH to MEAS............................................ 11
Operating the T136BGM................................................ 12
Operating Procedure....................................................... 12
Applications...................................................................... 14
Performance Limits........................................................ 14
Measurements at the Subscriber’s Location................... 14
Measurements at the C.O. Main Frame.......................... 15
Balance Measurements.................................................. 16
Maintenance.................................................................... 17
Battery Replacement..................................................... 17
Service and Repair......................................................
18
Warranty............................................................................ 19
Figures
1. T136BGM Circuit Test Set.........................................
5
2. C-Message Weighting Characteristics.............................. 8
3. Data Pad...........................................................................13
ii
M
Introduction
odels T136BGMZW is portable, compact combination level
and noise measuring set designed to facilitate circuit and noise
measurements by installers and repair persons without using elaborate
or expensive equipment. The T136BGMZW measures current from
the ring lead to ground. This measurement allows the station ground
integrity to be evaluated. Since the office battery potential, loop
length, station ground resistance and other variables will affect the
magnitude of current to ground, it is difficult to determine ground
resistance exactly, The data pads used with the T136BGMZW include
a table to facilitate determining if the station ground is faulty. In
addition to measuring current from the ring lead to ground, these units
are designed to measure loop current, circuit loss, noise metallic and
noise to ground, each over a range which includes the normally
acceptable limits. Meter scale colors indicate normally acceptable,
marginal and unacceptable divisions of measurements.
GND mA measurement indicates the dc current drawn by a resistance
of approximately 700 Ω for the T136BGMZW connected between the
ring lead and the station ground.
LOOP mA (DC loop current) measurement indicates the dc current
drawn by a resistance of approximately
430 Ω connected across the line.
Provisions have been made for dialing and holding a remote line. In
the DIAL & BATT TEST position of the FUNCTION switch, the line
connectors are switched through to a pair of square terminal posts for
connecting a dial telephone hand set. In all other positions of the
FUNCTION switch, a hold coil is connected across the line. The hold
circuitry has a dc resistance of approximately 430Ω with ac impedance high enough to have no significant effect on measurements.
1
Introduction
The FUNCTION switch position called CKT LOSS provides terminated level measurement of a tone from -15 dBm to +1 dBm.
Measurement response characteristics are flat from 300 Hz to 15
kHz; 60 Hz is attenuated more than 25 dB as input impedance is 600
Ω.
The FUNCTION switch position designated CKT NOISE provides
additional sensitivity and frequency weighting for measuring noise
metallic on a C-Message basis as input impedance is 600 Ω.
The FUNCTION switch position designated PWR INFL (Power
Influence) measures noise voltages between a circuit and ground on
a C-Message weighted basis. The input circuit in this position has an
impedance of 100,000 Ω between either input terminal and ground.
In most conventional measuring sets, the reference level for noise-toground measurement is 40 dB above the 600 Ω dBrn reference
voltage. The PWR INFL scale of the T136BGMZW is calibrated to
give a direct reading in dBrnC (600 Ω voltage equivalent) so that
balance measurements can be made directly with no need for the
conventional 40 dB correction.
2
Introduction
The T136BGMZW has four separate meter scales:
LOOP mA
Range:
0 to 100 mA (GND or LOOP as determined by FUNCTION switch)
Color Segments:
Red
Yellow
Green
below 20 mA
20 mA to 23 mA
23 mA to 100 mA
CKT LOSS
Range:
+1 dBm full scale, calibrated in 1 dB increments to -15 dBm
Color Segments:
Red
Yellow
Green
Yellow
below -10 dBm
-10 dBm to -8 dBm
-8 dBm to 0 dBm
0 dBm to +1 dBm
CKT NOISE (Noise Metallic)
Range:
+33 dBrnC full scale, calibrated in 1 dB increments to 15 dBrnC
Color Segments:
Green
Yellow
Red
below 20 dBrnC
20 dBrnC to 30 dBrnC
30 dBrnC to 33 dBrnC
PWR INFL (Noise-to-Ground)
Range:
+93 dBrnC (600
Ω voltage equivalent) full scale; calibrated in
1 dB increments to 75 dBrnC
Color Segments:
Green
Yellow
Red
below 80 dBrnC
80 dBrnC to 90 dBrnC
90 dBrnC to 93 dBrnC
3
Introduction
The 136BGMZW has two momentary push button RANGE
EXTENDER switches, arranged so that the PUSH TO MEAS
button and one RANGE EXTENDER button can be operated
together with one finger. The RANGE EXTENDER button above
the PUSH TO MEAS button on the panel extends the measuring
range by 10 dB. It is designated + 10 dB because its use requires
that 10 dB be added to the meter scale reading. Similarly, the
RANGE EXTENDER button below the PUSH TO MEAS button
reduces sensitivity by 20 dB.
When the FUNCTION switch is in any measure position, the DIAL
posts enable the tester to listen to the signals being measured without
interfering with the measurements.
A non-locking push button switch is used to supply power to the
measuring circuits from two small 9 volt batteries. No current is
supplied by the batteries until the switch is depressed to take a reading.
Consequently, the useful life of the batteries can approach shelf life
because the ON period is usually very short.
4
Introduction
Figure 1. The T136BGMZW Circuit Test Set
5
Specifications
Measuring Ranges
DC current (GND mA):
DC current (LOOP mA):
0 to 100 mA, through 700 Ωand diode bridge
between ring and ground. Measurements may be
made with either polarity DC on the line.
0 to 100 mA, through 430 Ωand diode bridge.
Measurements may be made with either polarity DC
on the line.
Signal level (CKT LOSS):
Scale with log graduation, -15 dBm to +1 dBm with
1 dB divisions.
Noise Metallic (CKT NOISE):
Scale graduated from 15 to 33 dBrnC with 1 dB
divisions.
Noise-to-Ground (PWR INFL):
Range Extension:
Scale graduated from 75 dBrnC (600 Ω voltage
equivalent) to 93 dBrnC with 1 dB divisions.
Add +10 dB and + 20 dB push button switches.
Range extension applies to all level and noise
measurements.
Input Circuits
Impedance
CKT LOSS and CKT NOISE meas:
PWR INFL measurement:
Frequency Response:
600 Ω AC; 430 Ω DC.
100 kΩ tip/ring to ground.
CKT LOSS measurement, range from 300 Hz to
15 kHz. Attenuation at 60 Hz is more than 25 dB.
CKT NOISE and PWR INFL measurements, CMSG weighting. Refer to Figure 2.
Hold Impedance
DC Resistance:
430 Ω over a range of 0 - 120 mA
6
Specifications
Controls and Connections
Switches:
Multi-position FUNCTION switch.
Push button PUSH TO MEAS switch.
Push button +10 dB range extender.
Push button + 20 dB range extender.
Connections:
DIAL terminals: square clip-on type.
LEADS: three 4 foot leads with test clips and
colored: Green for Tip, Red for Ring, and Yellow
for Ground
Power
Battery Type:
Battery operation, two 9 volt batteries, Eveready
216 or equivalent NEDA No. 1604.
Physical
Height:
Width:
Length:
Weight (with batteries):
5 7/8 in. (15.0 cm)
4 3/8 in. (11.2 cm)
6 3/8 in. (16.2 cm)
3 lbs. 4 oz. (1.47 kg)
7
Figure 2. C-message Weighting Characteristic
Specifications
8
Circuit Description
T
he Model T136BGMZW is a basic transmission measurement
set providing loop testing in accordance with industry standards. The
following subsections of this manual describe the T136BGMZW
measurement operation.
Input Circuit
The input switching circuit connects the input leads to the selected
measurement circuitry.
a. The GND mA, the ring (RED) lead is connected through a total
impedance of 700 Ω to the ground (YELLOW) lead.
b. In DIAL & BATT TEST, the T and R leads are connected to the
square DIAL terminals.
c. In LOOP mA, the T and R leads are connected through a
combined impedance of 430 Ω.
d. In both CKT LOSS and CKT NOISE the line is connected
through dc blocking capacitors to the terminating resistance and
input circuity, while the 430 Ω hold impedance is shunted across
the line to draw dc holding current.
e. In PWR INFL, each side of the line is connected through a
series 100 kΩ resistor to a blocking capacitor to ground. This
provides the longitudinal path with proper attenuation for
noise-to-ground measurement.
Measuring Circuit Input Section
The function of the measuring circuit input section is to provide
isolation and line impedance matching.
9
Circuit Description
The Measuring Circuit DC input consists of a series/parallel circuit
switched through additional poles of the FUNCTION switch to a
shunt capacitor, series resistor and the meter itself. The PUSH TO
MEAS switch need not be used for DC measurements.
The CKT LOSS and CKT NOISE input is DC blocked for 100 volts.
The DC shunt effect of the 430 Ω impedance prevents the voltage
across the line from ever exceeding this value, even when loop
extenders are used. Following the DC blocking, the line is connected
to a 600 Ω precision impedance.
Circuit Measurements
All measurements taken using the T136BGMZW are referenced to
600 Ω, 1 mW. In the CKT LOSS mode this means a tone at .775 volts
will result in a 0 dBm response. All other readings are scaled to this
according to the following formula:
dB = 20 log Vmes/.775
where Vmes = the amplitude of the signal measured in volts.
NOISE MEASUREMENTS are referenced to 600 Ω, -90 dBm which
is equivalent to 0 dBrn and then weighted via the C-Message curve
(see Figure 2). A signal of .775 mV will produce a meter reading of
30 dBrnC. All readings are referenced to the formula:
dBm = 90 - 20 log Vmes/.775
POWER INFLUENCE levels are calculated in the same manner as
CKT NOISE, except voltages between tip and ring to ground are
measured. The preceding formula applies.
10
Circuit Description
Batteries and PUSH TO MEAS Switch
The measuring set is powered by a pair of 9-volt batteries. Since the
batteries supply power only while the PUSH TO MEAS switch is
held, battery life approaches shelf life.
Battery voltage is connected to the positive and negative supply
busses of the measuring set through transistors which are normally cut
off. Pressing the PUSH TO MEAS switch turns on both transistors,
supplying positive and negative voltages simultaneously.
With the FUNCTION switch in BATT TEST position, pushing the
PUSH TO MEAS switch supplies power to the measuring circuits to
load the batteries. At the same time it connects positive and negative
voltages through to the meter to test for satisfactory battery voltage.
11
Operation
C
onnections to the circuit to be tested are made with the clip leads
on the end of the red, green and yellow leads which represent ring, tip
and ground, respectively.
CAUTION: GROUND should be connected first.
A lineman’s dial telephone set is connected by clipping to the
terminals marked DIAL.
Operating Procedure
Place the FUNCTION switch in the GND mA position . Record this
measurement. Select LOOP mA and note the current. The station
ground may be evaluated by evaluating the plotting measurements on
the optional T136 data pad (Wilcom part number 06800015). See
Figure 3. Readings above the scale indicate ground references of 25
Ω or less. Readings below the scale indicate higher ground resistances.
Consult company practices for further investigation.
Turn the FUNCTION switch to the CKT LOSS position and press the
PUSH TO MEAS button. This turns the set on; it must be held in
place until the measurement has been made. Readings are made on the
CKT LOSS scale of the meter.
Noise measurements are made by placing the FUNCTION switch in
the DIAL position (dial tone should be heard in the lineman’s
handset); and then dialing the number of the quiet (or balance)
termination at the Central Office. When a connection has been
established, turn the FUNCTION switch to the CKT NOISE position
12
Operation
Station Ground evaluation
The station ground may be evaluated by evaluating the plotting
measurements on the optional T136BGM data pad (Wilcom part
number 06800015).
Rear of Pad
Front of Pad
Figure 3.
T136BGM Data Pad
13
Operation
and press the PUSH TO MEAS button. The reading on the CKT
NOISE scaleon the meter is the noise metallic on the line. If the meter
should read off scale, operate the RANGE EXTENDER switch to
bring the reading on scale. If the RANGE EXTENDER switch is
used, the appropriate correction must be added to the meter reading.
PWR INFL, or noise to ground measurements, are made while
connected to the quiet termination at the C.O; turn the FUNCTION
switch to the PWR INFL position. The PWR INFL meter scale is
calibrated to read the noise to ground directly in dBrnC (600 Ω voltage
equivalent). If the meter should read off-scale, the range extender
switch may be used as before.
It is possible to listen to the signal by connecting an earphone to the
DIAL posts.
A battery test may be made by turning the FUNCTION switch to the
BATT TEST position and pressing the PUSH TO MEAS button. If
the meter does not read in the GOOD area, the batteries should be
replaced in accordance with instructions in the Maintenance section.
WARNING: This test is NOT designed to be used with voltages
in excess of ringing voltage.
14
Applications
T
he following describes the applications for which the
T136BGMZW Circuit Test Set is useful, including noise measurements at the subscriber and C.O. locations, and balance measurements.
Performance Limits
The measurement ranges of the T136BGMZW has been designed to
be within the normally acceptable limits of circuit loss, noise metallic
and noise to ground. The colored segments of the meter scale indicate
the various degrees of performance acceptability when direct readings
are made on the meter (i.e., when the range extender switch is not
used). The significance of each color is as follows:
GREEN:
YELLOW:
RED:
Acceptable performance.
Marginal performance. Investigation of
potential troubles should be initiated.
Unacceptable performance. Immediate
corrective action required.
If reading is off-scale high, without using range extender switch, when
measuring CKT NOISE or PWR INFL, unacceptable performance is
indicated.
Measurements at the Subscriber’s Location
Measurements may be made from the terminal block or protection
block at the customer’s premises. It is not necessary to disconnect the
customer’s equipment, but the equipment must be in the ON HOOK
condition when measurements are made. The leads on the
T136BGMZW is connected to Tip, Ring and Ground as outlined in the
15
Applications
Operation section. A good ground, preferably the ground at the
protector block, must be available to make power influence measurements.
Measurements at the C.O. Main Frame
Noise measurements may be made at the main frame in the C.O.
toward the subscriber or toward the
office equipment.
To Subscriber — meaningful noise measurements can only be made
toward the subscriber when there is a termination at the far end. The
heat coils should be removed for the test. If a section of the
subscriber’s loop is to be measured, a termination should be connected at the far end of the section. Unterminated measurements will
not provide useful data for analyzing noise problems; however, if a
large number of unterminated loops aretested, useful statistical information can be compiled on the extent of noise problems on loops out
of a C.O. A 900 Ω resistor in series with a 2 µF capacitor is a common
termination used at the subscriber end.
To C.O. Equipment — it may be desirable to determine how much
noise originates in the C.O. and the balance of the office equipment.
Remove the heat coils and connect the Green and Red leads to the Tip
and Ring terminals toward the office equipment — connect the
Yellow lead to C.O. ground bus. Dial the quiet termination and make
CKT NOISE and PWR INFL measurements.
16
Applications
If the induced longitudinal voltage is low, it may not be possible to
make power influence measurements. It is then necessary to introduce
an external longitudinal voltage at a fixed frequency; any signal
source between 500 Hz and 1000 Hz is satisfactory.
The Wilcom Model T279 is useful for providing a balanced terminating circuit to which a longitudinal voltage source can be connected.
Balance Measurements
Circuit balance can be determined from the CKT NOISE and PWR
INFL measurements both made with the T136BGMZW.
Balance (dB) = PWR INFL - CKT NOISE
The balance of a circuit will determine how susceptible it is to the
induction of noise. The following Balance values provide a guide for
determining acceptable balance:
BALANCE
Over 60 dB
50-60 dB
40-50 dB
Under 40 dB
CONDITION
Excellent
Good
Fair
Poor
Usually any balance under 50 dB requires improvement, particularly
when the power influence is high (i.e., over 75 dBrnC as measured on
the T136BGMZW). If power influence is low, a greater degree of
unbalance can be tolerated; however, if the power influence should
increase, the practice is to get as high a balance as possible.
17
T
Maintenance
he T136BGMZW should require little, if any, maintenance
except for replacing the batteries. If any difficulties arise in the
performance condition, please contact Wilcom Products, Inc. for
further information.
Battery Replacement
The T136BGMZW only draws current when the PUSH TO MEAS
switch is pressed; consequently, the batteries will have close to shelf
life. The batteries should be checked periodically by placing the
FUNCTION switch in the BATT TEST position and pressing the
PUSH TO MEAS button. If the meter does not read in the GOOD
segment, the batteries should be replaced.
If a battery replacement is indicated, rotate the four fasteners on the
bottom of the case 1/4 turn counter clockwise and lift the panel from
the case. Disconnect the batteries, pull the batteries out, insert new
batteries and reconnect the terminals. Use Eveready No. 216 or
equivalent; the NEDA No. is 1604. Replace the case hatch, press
down and turn the screw fasteners 1/4 turn clockwise
Repair
Should the T136BGMZW require service, the unit may be sent to
Wilcom at the address at the front of this manual, in accordance with
the warranty instructions.
Should technical assistance be necessary, contact our Applications
Engineers at the following number:
1-800-222-1898.
18
Service and Repair
For service or repair follow the procedure below:
1. Call Wilcom Customer Service. Support personnel will determine if the
equipment requires service, repair or calibration.
2. If the equipment must be returned to Wilcom for service, Wilcom
Customer Service will issue a Return Material Authorization (RMA) number
and the following address for return:
Wilcom
73 Daniel Webster Highway
Belmont, NH 03220
TEL (800) 222-1898 (USA only) or (603) 524-2622
FAX (603) 524-3735
www.wilcominc.com
IMPORTANT
Never send any equipment back to Wilcom without a Return
Material Authorization (RMA) number.
3. Pack the equipment in its original shipping material. Be sure to include a
statement or report fully detailing the defect and conditions under which it
was observed. Also be sure to include a contact name and telephone
number.
4. Return the equipment, prepaid, to the above address. Be sure to write the
RMA on the shipping slip. Wilcom will refuse and return any package that
does not bear the RMA.
Ordering Information
Orders for any of the Wilcom products and any of their optional accessories
should be directed to the address shown above.
19
Warranty
All products are warranted against defects in materials and workmanship. This warranty applies for a period of two (2) years from
date of delivery, except for Fiber Optic instrumentation and equipment which have a one (1) year warranty on parts and two (2) years
on labor. (The only exception in the digital testing equipment is the
D550 Shark, which has a warranty of one (1) year from date of delivery.) Wilcom's obligation under this warranty is limited to servicing
or adjusting each instrument returned to its factory within the warranty period, and to replace any components found to be defective.
If determined that the defective condition is a result of misuse or
abnormal operation, repairs will be billed.
LIMITATION OF WARRANTY
The foregoing warranties are the exclusive warranties provided by
Wilcom. Wilcom will not be liable for any special, indirect, incidental or consequential damages whatsoever resulting from loss of use,
loss of data or loss of profits arising out of or in connection with the
use or performance of the product, even if Wilcom has been informed
of the possibility of such damages in advance. All implied warranties, including without limitation warranties of merchantability and
fitness for a particular purpose, as well as warranties arising from a
course of dealing or usage of trade are expressly disclaimed.
PROPRIETARY INFORMATION
The information contained in this manual is the proprietary material
of Wilcom, and may not be reproduced, used for manufacturing purposes, or disclosed to others for any use without written permission
from Wilcom.
20
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