I am designing a system which turns on at 45 degC. I want to place a device in series with my circuit that ideally has infinite resistance below 45 degC and then 0 resistance above 45 degC.
I guess the closest I can get to this ideal is using an NTC thermistor but I am struggling to get my head around how to select a B number.
As, to my knowledge, my ideal device doesn't exist I have worked out that an NTC thermistor with a resistance above 10K Ohm at room temp at 10 Ohm at 45 degC would work but, if my calculations are correct, this gives me a B number of 37,000 ish which seems ludicrously high.
I plotted a graph of ln(R) vs 1/T, added my two points and then worked out B as the gradient - is this the correct method? (inferred from this wikipedia article)
Does anyone have any suggestions for an alternative method or where I maybe going wrong in my calculations?