OT:Instrument Use

We have one of these in our tool cabinet http://www.mitchellinstrument.com/aemc-model-6250-advanced-micro-ohmmeter-cat-212981.html

But no one knows what it is used for. There is a description at the bottom of the page that says it can be use to check cable resistance and breaker and other types of contacts but can't you just do that with your standard fluke DMM?

Where would you really need this?

Just as a yardstick could be used for distance (it's about a foot long) a fine micrometer is used when very precise measurements are needed (it's .00035 inches). This meter bears the same relationship to your Fluke DMM. Both are useful but for different purposes. If you don't need the the very fine, very precise resistance measurements then the DMM is appropriate.

For general stuff like checking contactor contact resistance for signs of arcing or burning is the dmm ok or would something like in the link be better?

Your DMM uses 1 mA to check resistance. The higher amperage tests on this meter would be better. From the posted link:

Typical Applications:
- Winding of motors and transformers
- Bonding verification on ground systems
- Weld joint integrity verification
- Contact resistance of breakers or switchgear
- Aircraft and rail bonding checks
- Battery strap resistance checks
- Cable joint and bus bar connection checks

Note the units, micro and milli, in the descriptive name of the instrument: micro ohmmeter or milli-ohmmeter

Agree with keithkyll.

The DLRO (Digital Low Resistance Ohmmeter) is very useful in diagnosing connection problems. These are usually 4 leads that perform the measurement - 2 which supply the current and 2 which measure the potential difference. The correct placement of the leads is necessary to get the proper reading. They work by sending the rated (or selected) known current through a connection and then measuring the voltage drop across that connection. In your case, it would be 10 amps. Using Ohms law allows a very accurate resistance to be calculated.

I've used these in mostly the power industry looking at the contact resistance across large breakers. These are also good for checking ground connections at substations and for bus ducts. They can not be used on anything powered.

DMM have their place for troubleshooting, but for verifying the intergrity of a power system connection, I wouldn't use them at all.

Read the instructions and understand all the safety aspects before you use this. You have a pretty nice instrument there.