Current Meter

[TK5EP]

Hi All,

i also need to measure some current but on a HV supply, with about 500V DC above ground. Current can flow in both direction, negative and positive with a max of 50 mA.

Any idea how i can do this in a safe way ??

Thanks for any feedback.

[Squibcakes]

Wow, those Allegro Hall Sensors look really good. I have order a couple to test them out.

As for measuring the HV supply, I've only ever used a HV probe connected to a DVM. Sorry, no other idea how to do that.

Cheers

[Charles Linquis]

I have used the Allegro Hall-effect sensors extensively. Bi-directional, great isolation. Good accuracy.

[TK5EP]

Hi all,

I looked the datasheet of the ACS704 which is the smallest device by Allegro (+/- 5A) and it shows a 133mV/A sensitivity.
I think it's a bit low for measuring 50 mA max scale....

An application note for the MAX4172 in a amplified high voltage sensor gives 10mV/mA, which seems to be more adequate, but unfortunately it's not bidirectionnal !

Other possibility is to use an amplified Hall effect sensor, but it needs an ground insolated low voltage supply on the sensor side, which is another problem !

Still looking for the right solution....

[Acetronics2]

Hi, TK5

The best for that voltage levels ( !!! ) is to use a little shunt, an AOP and a V/F converter, then drive an opto-isolator or better an opto-fiber coupler ... remember only CNY21 like HV optocouplers are safe, here ...

on the other side Freq = Current, so it's easy for a PIC to display that !!!

Alain

[TK5EP]

Hi Alain,

Maybe.... but the name problem is to insulate all the circuit from the high voltage side. The OPamp has to be supplied on this HV side, so you need low voltage supply which MUST be HV insulated.

Maybe the Alegro can be adequate if its output is amplified to a level that can be handled by the PIC?

Corsican greetings ...

Hi, TK5

The best for that voltage levels ( !!! ) is to use a little shunt, an AOP and a V/F converter, then drive an opto-isolator or better an opto-fiber coupler ... remember only CNY21 like HV optocouplers are safe, here ...

on the other side Freq = Current, so it's easy for a PIC to display that !!!

Alain

[sougata]

Hi there,

Sorry to catch this thread late. I manufacture series of PIC controlled thyristor based battery charger. For low cost designs I use a piece of wire acting as a shunt in the negative line and then a LM358 for the amplification. It is safe to use it in a HV line also as long as it is referenced to ground. You can use a programmable gain IA like AD620 for your differential measurement needs and couple it to a linear optocoupler like the Vishay IL300. This gives far accurate results than the V/F approach and is cheaper. The only problem is you need another supply. Consider using the IRF PVI series of optos to make a 5ma supply isolated DC-DC converter as well as linear output opto. Maxim has got a very good appnote on high side current measurement (1KV).

Whew! Enough gyans...

If you could post a specific issue with detailed electrical parameter then I might find something on my Hard drive.

BTW I always use a PIC with 10bits res. If thats enough then go on.

Regards

Sougata