Hello,
I have an engineering challenge of measuring a very small current produced by microbes... it may be about 10 or 100 pA of current that I need to measure.
The measurement doesn't have to be super-accurate, but accuracy is desirable. Basically, I have to be able to discern between no current and some current, and the ability to quantify the current to the nearest 10 pA would be excellent.
I have found this TI part OPA129, which is a DiFET input for 100 femtoAmp input bias current! The offset error is 2 mV max, but I think that will be okay because my scheme to charge up an extremely low leakage capacitor and read the voltage from it, buffered by this femtoAmp op amp.
I was just reading a Bob Pease essay on capacitor leakage... he is showing that polypropylene capacitors have extremely low leakage, such that they will drop a few mV per year.
The microbes that I want to gain electricity from can probably produce 0.4V or so, and at least 0.1V, so if I can see that capacitors are charging up to 0.1V when connected to the microbes, and do not charge up when everything is the same but there are no microbes, then perhaps this is good enough proof in the pudding.
What I am wondering here are people's input about doing extremely low current measurements like this.
It is possible to make a Faraday cage, and I also expect to lay out a PCB with traces very far apart to eliminate leakage by the board or anything else.
Has anyone here done anything with picoamp quantification? Any pointers or ideas?
Thanks!
I have an engineering challenge of measuring a very small current produced by microbes... it may be about 10 or 100 pA of current that I need to measure.
The measurement doesn't have to be super-accurate, but accuracy is desirable. Basically, I have to be able to discern between no current and some current, and the ability to quantify the current to the nearest 10 pA would be excellent.
I have found this TI part OPA129, which is a DiFET input for 100 femtoAmp input bias current! The offset error is 2 mV max, but I think that will be okay because my scheme to charge up an extremely low leakage capacitor and read the voltage from it, buffered by this femtoAmp op amp.
I was just reading a Bob Pease essay on capacitor leakage... he is showing that polypropylene capacitors have extremely low leakage, such that they will drop a few mV per year.
The microbes that I want to gain electricity from can probably produce 0.4V or so, and at least 0.1V, so if I can see that capacitors are charging up to 0.1V when connected to the microbes, and do not charge up when everything is the same but there are no microbes, then perhaps this is good enough proof in the pudding.
What I am wondering here are people's input about doing extremely low current measurements like this.
It is possible to make a Faraday cage, and I also expect to lay out a PCB with traces very far apart to eliminate leakage by the board or anything else.
Has anyone here done anything with picoamp quantification? Any pointers or ideas?
Thanks!