Simple (?) Flame Rectification Relay Control

Thread Starter

Jerry Dziuba

Joined Feb 18, 2016
I have searched my fingers raw looking for a relay/switch controlled via a flame rectification sensor that can run off of 12 (preferred) or 24vdc. I have run across quite a few using 115vac but all I have found using DC are wanting to do way more control than I need (ignition, purging, recycle, etc.). I was hoping maybe someone had a circuit that maybe I could build from scratch to do the simpler - if the sensor sees flame, activate the relay, sensor loses flame, deactivate.
Thanks in advance if you can steer me towards a solution.

Thread Starter

Jerry Dziuba

Joined Feb 18, 2016
The AC type flame detection uses the flame as an halfwave rectifier, and passes dc current,came across this circuit using can be modified using a fet op amp like the CA3240.
That circuit looks very doable, but I'm not really circuit level savvy, where would I hook up a relay to actuate upon seeing flame?

Also, if you could humor my ignorance, what benefits and how hard would it be to modify that circuit with the CA3240?

Thanks, I really appreciate your responses and help.


Joined Aug 12, 2014
ultraviolet sensor like the "fire eye" sensor. just looking for light will false on hot glowing parts of burner.
Back in my coffee roasting days I worked with a "fire eye" UV system a lot. I was quite happy with it, aside from the fact that someone installed our whole burner assembly 90° from its intended position, which put the sensor and its tube dead vertical, meaning it periodically filled up with soot/dust/debris and had to be cleaned up in order to "see" the flame again.

So, another vote for UV, but don't be careless with sensor placement!


Joined Jun 22, 2012
The circuit shown has a relay on the output, it uses a jfet transistor on the sense input, which is just biased slightly on, turning the relay on, when the flame is lit it turns the transistor off, this turns the relay off, the input can be fed into a CA3240 op amp comparator doing the same job.


Joined Aug 1, 2013
An infrared photo diode or photo transistor would not have the thermal mass delay of a thermocouple, and would not need a circuit with a 30 megohm (!) input impedance. What is the response time you need in the on and off directions?



Joined Dec 13, 2013
we use fire eyes, flame rods and other type flame detectors here on ovens and heat treat burners. the flame rod is usually one rod, with its tip in the flame, insulated from groundwith a fairly high voltage on it that conducts when the flame is lit through the ionization of the flame. the fireeye is an ultraviolet detector that "sees" the flame. the fire rod usualoly has a specialized transformer connected to it that unballances a bridge when the flame goes out.

Thread Starter

Jerry Dziuba

Joined Feb 18, 2016
I'm back again...

That prefab board was real close to working perfectly but because neither probe is a straight to ground reference I can not seem to get it to work with using the igniter rod and pilot tube as sense points. Close, but no cigar. As such, I'm about to try the DIY method using this circuit:

I'm having trouble locating the listed transistors (TIS34, BC125, BC126) and cross referenced them to the following NTE numbers (NTE-132, NTE-123AP, NTE-129). I was hoping those would be alright since it was stated that "semiconductors not critical" but was worried about the NTE-132 as there was also mentioned "but TIS34 may need selection because of parameter spread". Can anyone shed some light on whether my cross references appear okay and what problems might this "selection because of parameter spread" cause and is there anything I need to look into as a possible pitfall?

Or... if anyone has any suggestions on how to modify the MXA042 board ( ) to be able to deal with using the igniter rod and case ground as probe points I'd welcome those as well!

Thanks again for all the help and suggestions. It has truly helped in keeping this project moving forward.


Joined Sep 17, 2013
You could substitute a
2N3819 or other N-channel jfet for the TIS34,
2N3904 or other NPN low power bjt for the BC125,
2N3906 or other PNP low power bjtfor the BC126.

R5 might need tweaking depending on the jfet chosen, so that the 'window detector' works as intended.