Measuring Earth Bondage and Insulation Resistance

[bdiesel]

Good Day All,

I am building a data acquisition system for a test rig.  Two of the tests that need to be performed one the test unit are Earth Bondage (in the order of mOhm) and Insulation Resistance (in the order of MOhm).  Does anybody know if there are signal conditioning units that would enable these measurements using CompactRIO?

Bruce

[Henrik_Volkers]

If it part of a end of line test unit for main voltage units it's a bit more than signal conditionig 😉

'Earth Bondage' requires usually currents in the 1 to 10A range (depents on the DUT)

Isolation tests usually voltages in >500V range

For a  EOL test these units need traceability

I would look for a professional E-test unit. You can get them with all kind of communication/control interfaces, so you can talk to them with LabVIEW.

[bdiesel]

Hi Henrik,

No, it isn't for testing EOL equipment.  It is for testing hydraulic valves for aircraft.  I need to be able to test the earth bonding and insulation of the electrical components of the valve.

Bruce

[Henrik_Volkers]

EOL = End Of Line

doesn't matter what product.

In your case it's easy, aircraft parts needs to be tested  according to standards and the equipment needs to be traceable according to standards.  This holds for every quality relevant test! 

Spoiler

Or you passed the audits in very exclusive resorts instead of the floor 😄

So, what are your requirements for both tests?

[bdiesel]

Hi Henrik,

I am trying to find the exacts standards that these tests need to show compliance with.  But in the meantime, here are examples of each of the test specifications.

Regards,

  Bruce

[Henrik_Volkers · Accepted solution]

Isolation:

Apply 50V dc and measure the current  with 1Meg current shunt to GND (this is sometimes the rated input impedance of volt meter, or get a good 1M resistor). If the  voltage is higher than 125mV the isolation is lower than 400MOhm.  (Assuming all is perfekt) All uncertaincy involved will lower that 125mV boundary to avoid false pass and add to false fail. (thermoelectric, drift, settle time ...)

Get a some calibrated 390M, 400M, .... resistors for a on side verification (starting with daily verification, and extend periode according to results)  and a calibrated voltmeter for the 50V.... and a voltage divider for continous 50V checking isn't that bad 😉

 Some input protection will be needed !

Earth bondage:

Test current is not specified. Get a current source of ~1A  and a 20mOhm four terminal resistor (vishay?) . Do a four terminal contact resistor measurement on your valves.

Put your DUT and the 20mOhm resistor in series , apply current, diffrentially measure the two voltages across both (~20mV @1A)

Again: A calibrated 20mOhm resistor would be nice for validation.

I expect the four terminal contacting of your DUT as the tricky part...

So I would look for a two (more switching) or four channel simultanious sampling unit with a ~200mV range.   You can match the isolation measure shunt (1M) and the current (~1A) to the input range of your DAQ.  The Thermocouplereading units have nice low input ranges and good line noise filters 😉

Always a good idea to ask a NI-Application engineer. Maybe a SMU is a good starting point for earth bondage.... 

Another route: Ask Keithley .. they are known to have good units for high and low Ohms and currents.

[bdiesel]

Thanks for your valuable input Henrik.  Very much appreciated!!