Measure very low current

[Simon Tew]

Hi Everyone,

I have a project to perform V/I measurement of device.

The device need to be applied i.e.DC500V~6KV meanwhile measure mA range of current flow through the device by LabVIEW. What hardware do you recommend? Precision and high speed measurement is required since arcing detection is needed during high voltage step up gradually.

How to detect arcing condition if using programmable HV power supply?

Seem like I need a HV programmable DC power supply with high speed current read back function meanwhile limit the output current when arcing occur. Which manufacturer can provide this kind of HV power supply? I search but can not find!

Or

Currently looking at NI DMM PCI card, but can DMM card withstand DC6KV appear at its input terminal probe? Will such high voltage damage DMM card?

Thanks.

[Henrik_Volkers]

6kV with mA current is a serious task. (Say, it can be at least painfull :womanmad: )  

Dealing with voltages in that range and energy can be LETAL !! The choice of elements used is critical ...  

Insert HIGH VOLTAGE DISCLAIMER here

One way of current measurement is a shunt resistor on the low side (  to ground) with some additional protecting devices, fast (clamping) diodes and maybe additional limiting resistors.

Assuming a higher output impedance of your source you can detect the voltage drop of the arcing with a capacitive decoupling. I just build something similar for a Geiger-Müller tube counter (400V).

An arc will result in a high dI/dt, so another way would be a (RF) current transformer in the supply wire with the benefit of a galvanic decoupling 🙂 

Companies that build High-voltage EndOfLine-Testers (ELABO, but there are a lot more) 

Kepco build high voltage sources

Start looking here or here  to get the names of some companies and than contact the application engineers

.. and a look under my desk GLASSMANN HIGH VOLTAGE INC

(-100kV 40mA, 3 phase connector, the right toy for the grown up boy 😉 )

[Simon Tew]

Hi Henrik,

Thanks for your reply. I will keep in mind.

I intend to use standard DC programmable power supply to perform such test. I look into the manual and found that the unit is built in safety feature like overload trip etc. So will this unit trip under arcing condition? If yes, I can read back the current & voltage before and after tripping and use software to determine the "arcing" occurrance. Is it possible?

Thanks. 

[Simon Tew]

Hi All,

The generation of HV is not issue anymore since I can use standard HV power supply.

If I using the NI DMM module to measure the low current range it should work but can DMM withstand DC6000V bare wire voltage? Any suggestion to measure 10uA ~ 2mA current with such high voltage?

Please advise.

Thanks.

[AnalogKid2DigitalMan]

Google "DC Hipot tester".

They are off the shelf units specifically made for applying high voltages and detecting arcing and breakdown with automatic current limiting or removal of voltage. Units are available with interfaces to a computer (RS-232, USB, GPIB, analog outputs/inputs). Plus they provide inherent safety measures and typically electrical isolation to the computer interface.

-AK2DM

[Simon Tew]

Thanks for your reply. I will keep in mind your suggestion.