Monitor down to 0.1uA

Hi,

Anyone got a circuit whereby I can monitor a DC current down to 0.1uA without putting in a shunt resistor?

I was thinking about a circuit that goes inline, gives creates a voltage 1,000,000 X larger so you can read it with a meter or even put a small 4 digit display on the circuit..

Anything anyone?

Steve

without a shunt? you need to have some kind of sensing for it to get a voltage that you can amplify.... if it's AC you could use a toroid core. the wire with a current to be sensed goes through the hole, then you have windings as a secondary that go to your amplifier. for DC, you could place a hall effect sensor next to the wire carrying the current, or have it go through a toroid core with a gap cut in it, and put the hall effect sensor in the gap. magnetic sensing is the best way to sense current without a shunt resistor.

Or an op-amp I to V converter.

Monitoring down to 0.1 uA makes big difference if the signal is 1,000 Amps or 100 uA.

So, there isn't enough info. OP amp I-V converters are normally used. The insertion loss can be in the uV range easily.

More info

Sorry for the lack of info

OK, the very low current id produced by a flame rectification probe, a AC voltage is placed on the probe and if a flame is present a measurable DC current can be detected. however this is small 0.5uA - 10uA I wanted to place something inline with the "flame rectification probe" and amplify it to make it easier to read or display in either A or V. however whatever is placed in line must either not effect the DC current produced by the flame or replace it (what I mean by replace is if the device placed inline alters the DC current + or - it somehow compensates for this)

Well hope this gives enough info for someone to help and sorry again for not being clear initially.

Steve

I'm aware of that application. Fluke makes some meters that have that function built in. e.g. **broken link removed**

You can make one with a handful of parts. An OP amp, 9V battery and a rail splitter and the usual junk (case, bypass caps, 9 V battery clip, case etc) You can make 1 V out = 10 uA.

The first figure here: https://www.diyaudio.com/forums/diyaudio-com-articles/172983-zen-i-v-converter.html is the basic design. Vos is the critical parameter for the OP amp. I'd probably use a low power, low bandwidth,Rail to rail OP amp. If you use a rail splitter, then the minimum voltage +-4.5 or more like +-3V would make sense.

Things like an indicator and a low bat indicator might make it more versatile.

You can probably make RC = 1/2*PI*f where f = 1 kHz.

R = 1/10ua. You can figure out C. Just make it close.

I actually made one for work using two 9V batteries for measuring light intensity, The currents were a bit higher, though.