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Contents
General ..................................................... 4
Function description .............................. 4
Safety regulations ...................... 5
Control panels ......................................... 6
Control panel for MOM200A ........................ 6
Control panel for MOM600A ........................ 6
Operating instructions ............................ 7
External Measuring Instrument ............ 8
Troubleshooting ............................................. 8
Application examples ............................. 9
Measuring resistance in a breaker ............... 9
Measuring resistance at bus-bar joints ..... 10
Expanded measuring range ....................... 11
Application example ............................ 11
Specifications ........................................ 12
MOM200A .................................................... 12
Outputs ................................................. 12
Input ...................................................... 12
Measuring section ............................... 12
Other ..................................................... 12
MOM600A (115 V) ....................................... 12
Outputs ................................................. 12
Input ...................................................... 12
Measuring section ............................... 12
Other ..................................................... 12
MOM600A (230 V) ....................................... 13
Outputs ................................................. 13
Input ...................................................... 13
Measuring Section ............................... 13
Other ..................................................... 13 4
General
This manual is for the MOM200A, and MOM600A
microohmmeters.
The microohmmeter is designed to measure the
resistances of breaker contacts, bus-bar joints,
contact elements in bus-bars and other high-current
links.
When contact resistance rises because of oxidation,
loosened or improperly tightened threaded joints,
temperatures rise abnormally at the points of
contact. This abnormal heating reduces conductivity
thereby accelerating the rise in temperature and
this often leads to serious trouble.
The microohmmeter can be used to detect such
problems early so that they can be remedied long
before trouble starts. Checking contact resistance at
regular intervals provides a clear indication of the
state of your system.
Function description
Connect the instrument to the object being tested.
After you have adjusted the instrument to provide
the desired current through the test object (100 A
for example), the actual voltage drop across the test
object will be measured automatically, and all you
have to do is press a button to display the actual
resistance.
High current is generated and sent out by the
instrument during measurement. A miniature circuit
breaker and a thermal cut-out are provided to make
certain this current doesnt generate excessive heat
inside the instrument.
The instrument is equipped with a device that
guards against induction. A relay short-circuits the
sensing input when the instruments ON/OFF switch
is off and also when the instrument is in the m
mode. To protect against external overvoltages, both
the current output and the sensing input are
decoupled to ground.
MOM200A is used for currents up to 200 A.
MOM600A can provide an output current of up to
600 A, and it can be set to six different measuring
ranges.
Full-wave rectified current is used for measuring. 5
Safety regulations
voltage. If you attempt to service the
instrument yourself the warranty is no
longer valid.
Do not use any accessories that are not
intended for use together with the
instrument.
Disconnect the instrument from the
mains before cleaning. Use a damp cloth
for cleaning. Do not use liquid cleaners or
aerosol cleaners.
Important!
Use only approved mains detachable
cable set with the instrument. Main
supply cables shall be rated for the
maximum current for the equipment and
the cable shall meet the requirements of
IEC 60227 or IEC 60245. Mains supply
cables certified or approved by a recog-
nized testing authority are regarded as
meeting this requirement.
Refer all servicing to Programma
authorized personnel.
If you need to return the instrument,
please use either the original crate or one
of equivalent strength.
Important!
Read the manual and comply with the
following instructions before using the
micromhmeter
Always comply with local safety regula-
tions.
Warning!
Before measuring resistances in circuit
breakers or disconnecting switches (isola-
tors), always check to see that the object
being tested is closed and grounded on one
side.
If there is a current transformer in the
current circuit, the protective relay equip-
ment that is connected to it must be
blocked to prevent actuation. After complet-
ing your measurements, you can follow the
normal procedures that are used to demag-
netize current transformer cores after DC
has passed through their current trans-
former.
Never open a circuit breaker while a
microohmmeter is connected to it.
Current continues to flow for a while after
the microohmmeter is turned off. How long
it continues depends on the ratio of the
components in the L/R circuit.
Warning!
Always connect protective earth (ground).
Always use safety connecting leads.
Always turn the equipment off before
connecting.
High voltage/current on input/output
terminals.
Never leave the instrument unattended
while it is turned on and in the high-
current mode.
Unplug the instrument from the mains
supply when it is left unattended or not in
use.
Do not attempt to service the
instrument yourself. Opening or removing
covers may expose you to dangerous 6
Fig. 1
Control panels
Control panel for
MOM600A
1.
Positive current output
2.
Negative current output
3.
Sensing terminal
4.
Resistance button
5.
LED, resistance
6.
LED, current
7.
LED, thermal cut-out
8.
Current-shunt terminal
9.
Sensing current push buttons
10. Miniature circuit breaker, 17 A (MOM600
115 V only)
11. Miniature circuit breaker for mains
12. Pointer instrument for current
13. Grounding terminal
14. ON/OFF switch
15. Mains inlet
16 Variable transformer
Control panel for
MOM200A
1.
Positive current output
2.
Negative current output
3.
Sensing terminal
4.
Resistance button
5.
LED, resistance
6.
LED, current
7.
LED, thermal cut-out
8.
Current-shunt terminal
9.
Current range switch
10. Resistance range switch
11. Miniature circuit breaker for mains
12. Miniature circuit breaker for variable
transformer
13. Grounding terminal
14. ON/OFF switch
15. Mains inlet
16. Variable transformer
Fig. 2
1
2
3
4
8
5
6
7
11
12
14
15
9
10
13
16
1
2
3
4
9
8
7
13
12
15
14
16
5
6
10
11 7
Operating instructions
1.
Keep the microohmmeter disconnected
from the mains while making connections.
2.
Ground one side of the test object.
3.
Ground the microohmmeter.
4.
Connect the two current cables on two
sides of the test object.
5.
Connect the two sensing cables (using the
same polarities as those used for the current
cables) on two sides of the test object and
as close to the test object as possible.
Important!
The sensing cables must be connected
inside the current cables. Otherwise the
test data may be incorrect. See Fig.3.
Fig. 3
6.
Connect the microohmmeter to the mains.
7.
Turn on the ON/OFF switch.
8.
MOM200A: Select the desired current
range using the "Current range switch".
MOM600A: Select the desired current
range using the proper "Sensing current
push button".
9.
Clear, 0-set, the instrument by turning the
knob (16) on the variable transformer down
to "0", whereupon it will enter the current-
generation mode and LED (6) will light up.
10. Now turn the knob (16) on the variable
transformer to the right until the current
rises to the desired value. Check the value
on the digital measurement instrument.
The analog instrument (on MOM 600A)
provides only an approximate current
reading. To obtain the best microohm
Important!
Read the manual and comply with the
Safety regulations, see page 5, before
using the micromhmeter.
Always comply with local safety regulations.
Note! Operating this equipment near sources
of strong electric fields may cause it to
display erroneous current values.
Note! Since power consumption is high, the
instrument requires a 16 A fuse.
Note! On the MOM200A model, you must set
the decimal point selector so that the
decimal point is located correctly for the
measuring range. If the display shows
an "1" to the far left the current