Hioki Resistance Check - Fluctuation

[pssriram16]

I am using a Hioki 3540 tester to measure resistance across 18 AWG copper wires. To verify that the tester works fine I measured known resistances ranging from 10 ohm to 300 ohm and it seems to work fine. But when I measured the resistance across my circuit (which has two relays) then I seem to have trouble reading values accurately. The issue I see is wide fluctuation of the resistance values in the display screen ranging from 0 ohm to OL and this keeps cycling. I verified the contacts of the relays and there seems to be no issues and also I verified continuity across the entire circuit, seems to have no issues. But why is the hioki tester reading such a wide fluctuation of values? Need help.

 

[john monks]

Are you sure the circuit is off?
Are you sure you are not putting any voltage into your tester?

 

[pssriram16]

Hi John. I am able to verify continuity between the positive and the negative source/sense connections when the relay contact closes. Also I don't see any voltage induced into the circuit.

My suspicion is whether there is a winding some where in the coil that is causing the inductance effect.

 

[john monks]

I'm stumped. But now I'm growing more curious. Maybe you could put an oscilloscope across the same points you are measuring and see what is happening. Maybe your Hioki 3540 has problems with inductive circuits. Maybe a connection is not quite tight and the voltage increases until it finally conducts then drops off again. Are you sure your device is totally disconnected from all other power sources?

 

[davenn]

Hi John. I am able to verify continuity between the positive and the negative source/sense connections when the relay contact closes. Also I don't see any voltage induced into the circuit.

My suspicion is whether there is a winding some where in the coil that is causing the inductance effect.

thats not what john asked....

he asked, do you have power on the circuit that you are trying to measure the resistance on ? you cant do resistance measurements when the power is connected
Across the relay coil you will measure the resistance of the relay which should be marked on the relay ( NO POWER ON CIRCUIT) A diode across the coil will change the resistance measured

Dave

 

[duke37]

My digital meter does its nut when trying to measure the resistance of an inductance. I presume that this is because it uses a short pulse of current. I use an analog meter for this purpose.

 

[pssriram16]

Thanks John and Davenn. Looks like the relay was the issue here. I bypassed the relay contacts and the resistance displayed right away without much issues, but only in the comparator mode in Auto Range. (Comparator mode is when I set the high limit and the low limit). Thanks all for the guidance, very much appreciate it.