I have the attached design for determining if there is continuity through an igniter. The good news is the circuit only uses ~ 5 - 10 mA to test the igniter, so there is no danger of the igniter igniting. The bad news is it does not detect when/if the igniter breaks when it is being ignited - ~2-4A.

The order of operations:
1. Shut off 12V (switch etc. not shown).
2. Connect igniter to terminal (~4 foot wires)
3. Turn on 12V and set Energize Igniter to ~ 3V
4. See green LED is on and test continuity with buzzer switch. Controller reads Continuity OK as ~3V. If no continuity through the igniter ( i.e. bad connection, bad igniter, etc.) then the green LED is not on and the Controller reads Continuity OK ~ 0V. The Continuity buzzer does not sound when the Continuity Check button is pressed.
5. Walk away.
6. Switch Relay Enable to 3.3V and watch the igniter burn with ~2-4 A flowing through the igniter for ~ 1-5 sec

In step 6, the Q13 is off, so there are no continuity indicators (green LED or Continuity OK). I would like to modify the circuit so
1. the continuity LED stays on until/if the igniter actually breaks
2. Continuity OK stays at 3V until/if the igniter actually breaks - most important so the Controller can reset the igniter circuit before the 5 sec time out concludes.
3. The continuity buzzer is irrelevant at this point as the "smart" user is too far away to push the Continuity Check button.

 

I suggest an addition, not a modification: That would be an instrument type amplifier connected across the Energise igniterPOWER MOSFET, to monitor the voltage present. For each step of the process the voltage across the transistor is within some range if it is OK, and zero if there is an "open" fault. The IA output would feed the base of an NPN transistor with it's collector tied to the emitter of Q13 with a resistor, and the NPN emitter tied to system common. So when the current went to zero, the voltage will also go to zero, and the green LED will switch off.

 

I would like to modify the circuit so the continuity LED stays on until/if the igniter actually breaks

Suggest adding the PC817 circuit and BS170 to monitor the state of K4 relay contacts.
The PC817 is activated by the voltage drop across R60 a 1 ohm resistor when the igniter is full on. Output pulls R49 through R61 to ground to maintain Q13 ON.
If K4 contacts are shorted to 12 volts ( stuck or welded) the igniter will fire when "Energize Igniter" is activated as currently configured.
With the BS170 circuit if K4 is shorted D28 will light up when first powered ON indicating a fault
D28 will also light up when "Relay Enable" is activated confirming 12 volt power to the igniter circuit.
What's the reason for the buzzer if D24 is illuminated?

 

Now, a month later, QUESTIONS: FIRST, WHAT IS THE ACTUAL PURPOSE OF THE CIRCUIT, and then second, what hazards involved with the described sequence of activities?? In fact, just what is the activity?? All I see is watching an igniter burn. Is this done from a distance because of a possible explosion hazard??Certainly a different circuit could provide a continuity indication and a safety interlock and be less complex.