Micro Ohm Meter
The Micro Ohm Cable Tester measures from 3 to 2000 micro ohms and can be used to measure the resistance of secondary weld circuit components. These include kickless cables, water cooled jumpers, laminated shunts, air cooled jumpers, weld gun castings, weld tips joints, weld transformers, oxidation in joints, connectors, or any component that can increase in resistance. This meter is a tool that can be used for both preventive maintenance and for troubleshooting the secondary welding circuit.
A stable 2.5 Amp Current source is incorporated into the meter providing high accuracy measurements to be displayed on a large 3 ½ digit LCD display.
Milli-Ohm Meter also available. The Milli Ohm Cable Tester (MOCT7600) measures from 0.3 to 200 milli ohms and can be used to measure the resistance of primary (440 volt) weld circuit components. These include the primary supply cable, circuit breakers, crimped lugs, bolted joints or any component that can increase in resistance.
How the Micro Ohm Meter Works
The Micro Ohm Meter Tester uses a 4-wire Kelvin probe system. Each probe passes test current through the outer points of the probe and the voltage is sensed by the center pin. With this method, errors caused by the resistance of the leads and the contact resistance are eliminated.
Operation
Connect both meter cables to the connectors on the right side of the box. Press one probe to each end of the component being tested. The meter senses the continuity of the component being tested and turns itself on. If the sample under test is totally open the meter will not turn itself on.
After the meter is turned on, the current source circuit is activated to maintain 2.5 amps. When the current is stable at 2.5 amps the “Display Hold” indicator goes off and resistance readings are displayed. If the sample under the test has a resistance greater than the capacity of the meter, the “Display Hold” indicator will stay on and no numbers will be displayed.
When a stable reading is displayed the probes can be removed. (NOTE: Holding the probes tightly against the component being tested will aid in stabilizing the reading). Remove the probes quickly so as not to bounce the probes. The “Display Hold” indicator will come on and the display will hold the last reading momentarily.
After the hold period, the meter will automatically turn off and the display will go blank.
Using Your Micro Ohm Meter for Troubleshooting
1. Take a ‘base’ resistance reading when all components are known to be good i.e. new, clean, well-tightened connections. The complete secondary circuit can be measured at the gun from tip to tip; separate components can be measured without removing them from the secondary circuit. This resistance reading should be recorded and stored for when a problem arises.
2. When a problem arises, take another resistance reading and compare this reading with a ‘base’ reading. If it is significantly high enough to have caused the problem, proceed to the next step. If it is not high enough, then the problem may not lie with the secondary weld loop.
3. If you get a high resistance reading from the complete loop, you must then take resistance reading for each component that could be causing the problem. The components do not need to be taken out of the circuit and indeed should not be taken out of the circuit as the problem may be a loose bolt and this would not be found if components are removed. Note: More stable readings will be obtained if the area where the probe is placed is cleaned with an abrasive cleansing pad prior to the reading being taken.
4. Once the problem-causing component is found, take the appropriate actions to remedy the problem.
Monitor cable resistance in the secondary weld circuit on a periodic basis. When the resistance has reached a level that would result in a defective weld, the cable should be changed. The resistance level at which you change the cable should be determined on a case by case or plant by plant basis because of the multitude of factors affecting cable life, weld schedules, inspection intervals, etc.
Micro Ohm Meter Specs
| Property | Value |
|---|---|
|
Measuring Range |
3-1999 µΩ |
|
Accuracy |
|
|
Relative accuracy |
<1% of F.S. |
|
Absolute accuracy |
<2% of F.S. |
|
Measuring Current |
2.5 Amps |
|
Power Supply |
|
|
Measuring Current & Display |
12 Volt Rechargeable "C" size batteries |
|
Display |
|
|
Type |
LCD |
|
Digits |
3 ½ |
|
Height |
0.7" (18mm) |
|
Est. Battery Life |
|
|
Current on |
1.25 hours |
|
Number of checks (10 sec.) |
450 |
|
Dimensions |
|
|
Length |
8 ¼" |
|
Width |
7" |
|
Depth |
3 ¾" |
WARNING: ALL PRIMARY POWER MUST BE TURNED OFF AND DISCONNECTED BEFORE USING THE METER ON PRIMARY OR SECONDARY COMPONENTS! ADDITIONALLY, ANY CAPACITORS OR POWER STORAGE DEVICES MUST BE DISCONNECTED BEFORE USING THE METER!
NOTE: DO NOT PLACE THE PROBES ON A CIRCUIT THAT HAS VOLTAGE ON IT. THIS COULD CAUSE PERMANENT DAMAGE TO THE INPUT CIRCUITRY.
Resources
Battery – 12 Volt Rechargeable
When the word “BAT” is displayed this indicates that the “12 Volt” battery voltage is running low and will soon need to be recharged.
To recharge the “12 Volt” battery, plug the 18 Volt power supply into the battery connector. The LED will come on and stay on until battery is charged, about 6 hours. When the LED light goes off the charging unit goes to a lower voltage to maintain the charge.
Battery – Replacement “C”
When the word “BAT” is displayed this indicates that the battery voltage is running low and will soon need to be replaced.
Replace old batteries with new “C” batteries using the alignment stickers as a guide.
Using Your Meter
The Flex-Cable Micro Ohm Meter may be used to measure the resistance of very high conductivity conductors such as copper cables, laminated shunts and copper buss bars.
Because of its capability of detecting increases in resistance of these items, the meter may be used for troubleshooting problems with the secondary circuit of a resistance welder. An increase in resistance is one criterion that has been used effectively to eliminate downtime attributed to cables.
Description Part Number
Micro Ohm Meter MOCT7550
Milli Ohm Meter MOCT7600
Carrying Strap 250-7878-36
Lead & Probe Assemblies (Pair 4ft) 250-7253-48
Probe Leads (Pair 4ft) 600-8023-48
Probe Leads (Pair 6ft) 600-8023-72
Probe Leads (Custom Length) Please Call (423) 894-6234
Probes (Pair) 250-7702-00
Shrink Tube (Pair for Leads) 250-0301-00
Clamping Probe & Lead (Single 6ft) 250-2519-72
Pistol Probes & Leads (Pair 4ft) 250-7478-48
Pistol Probe Leads (Pair 4ft) 250-7783-48
Pistol Probe Leads (Custom Length) Please Call (423) 894-6234
Rechargeable 12 Volt Battery/Charger 250-7274-12
Replacement Charger 250-7324-18