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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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    davezawadi (David Stone):

    If you allow it to auto-range it will take ages to settle on some very high figure which is of no value to you. 


    You have to decide if you are go/no go testing, where you set the parameters and the green light comes on or that when you exceed your minimum requirement everything is okay, so you sign the item under test as safe or if you want to keep a record of readings as part of a maintenance regime to detect deterioration of the insulation, for which you need a accurate test result to know what the starting point was.


    Someone who scribbles the infinity symbol or writes OL in the test result box on a certificate is not being particularly helpful if you don’t know what the upper limit of the range is on their test meter if you are trying to determine the rate of deterioration at a later time.


     Andy Betteridge 


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  • 0
    davezawadi (David Stone):

    If you allow it to auto-range it will take ages to settle on some very high figure which is of no value to you. 


    You have to decide if you are go/no go testing, where you set the parameters and the green light comes on or that when you exceed your minimum requirement everything is okay, so you sign the item under test as safe or if you want to keep a record of readings as part of a maintenance regime to detect deterioration of the insulation, for which you need a accurate test result to know what the starting point was.


    Someone who scribbles the infinity symbol or writes OL in the test result box on a certificate is not being particularly helpful if you don’t know what the upper limit of the range is on their test meter if you are trying to determine the rate of deterioration at a later time.


     Andy Betteridge 


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