Amplifier IC suggestion for Sub Milivolt negative voltage

Thread Starter

hgreene624

Joined Jun 5, 2017
3
Hello all,

I am working on a project with a flame rod sensor that outputs a very small voltage in the presence of a flame. The sensor outputs a -0.05mv according to my multimeter. I plan to hook this up to an arduino and want to amplify and maybe run through an op amp comparator circuit to send a clean binary signal to the arduino. Since the flame is either present or no I dont really need a analog signal.

I plan to use an LM324 op amp IC. and am experimenting with an AD623 instrument amplifier but I think the voltage differential is too small at -0.05mv.

Does anyone have any suggestions about how to make this circuit function or other components i should use?

Thanks
 

MrChips

Joined Oct 2, 2009
22,902
You don't need any fancy circuitry.
Use an n-channel FET in depletion mode to amplify your signal.
An FET in depletion mode is normally ON and takes a negative gate voltage to turn it OFF.
Hence it should respond to a small negative signal on the gate.
 

Thread Starter

hgreene624

Joined Jun 5, 2017
3
You don't need any fancy circuitry.
Use an n-channel FET in depletion mode to amplify your signal.
An FET in depletion mode is normally ON and takes a negative gate voltage to turn it OFF.
Hence it should respond to a small negative signal on the gate.
could you recommend a MOSFET with adequate sensitivity -0.05mv ish. I wouldnt think that all MOSFETS are that sensitive ya?
 

DickCappels

Joined Aug 21, 2008
6,971
An OP-07, which is inexpensive and readily available can do it. It is now made by TI. It would probably need to have its offset adjusted -just add a 20k pot.
 

crutschow

Joined Mar 14, 2008
26,417
That's a flame rod that generates an ionization current in a flame with an AC voltage applied to it as described here.
So I believe you need more than just an amp.
One of these circuits may work for you.
 
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