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

 

Do you have any info on the flame sensor?
Is it similar to the ones used in a gas furnace?

 

You might need to re-think your project: https://en.wikipedia.org/wiki/Flame_rectification

 

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.

 

Do you have any info on the flame sensor?
Is it similar to the ones used in a gas furnace?

this is the flame sensor.
Q3400A Igniter-Flame Rod Assembly

 

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?

 

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.

 

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.