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insulation resistance tester for capacitor

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kiransbaddi

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Hi i m designing insulation resistance tester for the capacitor. insulation resistance value is in the range from 30000Mega ohms and above. how to detect such a large resistance and/or small current ? I m able to detect up to 500Meg Ohms
 

Hi,

Did you look for related documents in the internet?
Like this: https://www.murata.com/support/faqs/products/capacitor/mlcc/char/0003

There are some parameters:
* applied DC voltage
* time
* leakage current.

Without knowing your applied voltage... we don't know what current you want to measure.
Another parameter to know is the range of the DUT capacitance.

Current measurement usually is done with a TIA. Choose a suitable Opamp and suitable low leakage protection diodes.

Klaus
 

Thanks for your quick response here are some details.

Applied DC voltage is 100V
time 50sec
a range of DUT capacitance is 0.001uF to 5uF

capacitor type: polyester and polypropelyne
 

Hi,

100V, 30GOhms: I = 3.3nA.
Not impossible. But needs careful circuit and PCB design. I recommend guarding of sensitive signals.

Maybe consider to measure with positive as well as negative voltage. With this you can cancel out offset errors.
Use analog and/or digital filter to supress noise.
Integrating/averaging (digitally) for the time of a full wave of mains will cancel out mains pickup.

Show your design.

Klaus
 

This is simple resistance detection circuit

IR.PNG
 

Hi,

No TIA.
And not very much information.

A lot of questions?

C2 is the DUT?
What´s the use of R2, R3, R6?
Why U1 has low gian and U2 high gain. Usually it´s the other way round.
What type of OPAMPs?

Please try to redesign the circuit and try to give all informations at once.

Klaus
 

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