sensor
I am troubleshooting a gas heater and all test results point to the flame sensor but I would like to bench test the flame sensor. Any ideas on how I might set up a test environment with on-hand materials like maybe a burner (camp stove, bunsen) and power source, then stick the flame sensor in the flame and compare the uA current to spec?
To figure out what is going on you are just going to have to break down and measure the signals at the + and - input of the comparator to see what is happening there in terms of voltages. Only then can you deduce what is wrong. Make sure to use a volt meter that has a high input impedance and not some cleap 20K ohms input impedance meter.
Some things that can be learned by that are:
If you can get through all of these steps and understand how the circuit performs you should be able to achieve success or conclude that some component is bad.
This looks like the IR photo-transistor used in the common Arduino flame detector modules. Explained here and here.
Here is how it works. The photo-transistor starts conducting when it gets IR light from a flame or any source strong enough. A comparator can be used to convert it to a digital output. The second link above has a schematic that the Arduino modules use.
That being said, this could also be a photo diode since I couldn't find any official specification on this component. The working principle would be similar but the wiring would be different. Basically you could wire this like any other photo diode or transistor. I would wire it in different ways and measure the changes in current/voltage when pointing to a flame. You could start with the schematic below and use a multi-meter to measure the output voltage.
simulate this circuit – Schematic created using CircuitLab
Best Answer
The 'sensor' itself is just a wire. If it is positioned correctly in the flame, connected properly and not shorted to ground it will work, period. The circuitry should (with very, very high reliability) cause a shutdown if the sensor is open or shorted.
Testing the circuitry is much more involved, particularly if you need to verify the fail-safe and redundancy characteristics that are required for safety. If it is faulty it should be replaced in accordance with the manufacturer's recommendations and local codes .
For those unfamiliar with the 'flame rectification' method of flame detection, the 'sensor' looks like this:
The 'flame rod' is a metal wire that extends into the flame The mounting bracket has a ceramic insulator and the flame rod has a spade connector for a wire running back to the electronics. Such an electrode extending into an open flame has diode-like characteristics. The asymmetric conduction (between the rod and the burner, which is grounded) is used to distinguish between shorted, open and resistive conduction (as might be caused by faults or condensation or contamination).
It is extremely important in gas combustion systems to avoid a false positive flame detection output, since that would allow the gas valve to remain open in the absence of a flame. The gas would then continue to flow, mixing with air, until it finds a spark or flame to ignite it, and 'kaboom', as happened recently here (Photo from the National Post):