MQ8 H2 Sensor circuit

[heavyhank]

Hi,

I'm trying to tackle a 'failsafe' problem with the following circuit http://dlnmh9ip6v2uc.cloudfront.net/dat ... c/MQ-8.pdf
In Fig.2.
The Vout is wired to an ADC chip, which then sends a digital signal to the unit telling it if any H2 has been detected. The unit will detect if the sensor module is not plugged in, so I'm guessing it is a normally closed position on the unit (if the sensor isn't plugged in, the position is open and the unit will not start up. So, in a way, this is a failsafe of sorts. However, I've a number of sensors which do not detect H2 yet will still close the circuit - I assume the heater coil has failed therefore the sensor doesn't reach the required temp for it to pick up H2.

My question is, how can I introduce a circuit that will give a similar Vout signal to the ADC if the heater fails?

I'm not an engineer, so please give me laymans terms if you can.. Thank you!

[pebe]

Have you included the pot, RL ?

[heavyhank]

Yes, as far as I know...

[heavyhank]

Really, I suppose what I need is for the circuit to open in the event of a heater failure.
I'm not sure how this will be possible as A - B will always be connected. As I said, I'm no engineer..But I had thought if the heater fails, perhaps if I introduce a similar voltage to the ADC then I can trigger the same error as thought the sensor had detected H2. I can't see how else I could do it..?

[pebe]

There is nothing in the data sheet that gives details about heater failure.
Could you use a multimeter to measure the resistance A to B with no heater volts applied and let us know the result?