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Insulation Resistance Measurements

Former Community Member
Former Community Member
Hello,


We have a Insulation Resistance measurement unit from Hioki - ST5520.

We are using this to measure multiple devices controlled through a relay matrix as shown in the figure. The positive and negative terminals of the ST5520 is multiplexed through the relay matrix to the 64 pins of the connector. There are 7 pcb's each containing 20 relays.

The individual board testing from ST5520 to the connector is giving a open condition result with a high value of insulation resistance of 9.90Gohm @1000V, when there is no load at the connector output, it is left open.

But the when the whole system is wired and tested with the 7 pcb's(all 32 channels), the value fluctuates and starts with a value from 100Mohm and eventually reaches open condition value.

Is there a problem with this process of multiple channel testing? or this is the expected behaviour? the open condition value(9.90Gohm@1000V) is maintained once it reaches this value and further tests result in this same value. 

Once the system is left OFF for a period of a day, then the testing is resumed again, the same behaviour of starting from 100Mohm to open condition value repeats. Is this to be expected or i am understanding/ doing something wrong?

Any help with this is much appreciated. Thanks in advance.
0d3eb1e11f9f4ba9176cae1b22dc1e68-huge-insulation-measurement.png
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  • 0
    starts with a value from 100Mohm and eventually reaches open condition value.

    :

    Once the system is left OFF for a period of a day, then the testing is resumed again, the same behaviour of starting from 100Mohm to open condition value repeats.

    sounds to me that either there's some damp in the system that's being dried out by the test voltage (probably unlikely) or that all the PCBs and relays are acting as a reasonably large capacitor that takes time a charge up from the limited IR meter test current (possibly more likely). If it were the latter problem I might expect the 'slow ramp up' problem to return immediately if the IR meter's +ve and -ve leads were reversed (all presuming it's a DC test current).


        - Andy.
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  • 0
    starts with a value from 100Mohm and eventually reaches open condition value.

    :

    Once the system is left OFF for a period of a day, then the testing is resumed again, the same behaviour of starting from 100Mohm to open condition value repeats.

    sounds to me that either there's some damp in the system that's being dried out by the test voltage (probably unlikely) or that all the PCBs and relays are acting as a reasonably large capacitor that takes time a charge up from the limited IR meter test current (possibly more likely). If it were the latter problem I might expect the 'slow ramp up' problem to return immediately if the IR meter's +ve and -ve leads were reversed (all presuming it's a DC test current).


        - Andy.
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