Temperature Alarm for Boiler or Freezer
On the subject of temperature-sensing, what would be an ideal specification for a device intended for a high/low temperature alarm? The output should take the form of a ‘switching’ action, with a definite and rapid change from a very low to a very high resistance. The switching point would have to be programmable, between, say, −10 and +90 °C. The device would have to be sealed, preferably with flying leads sealed in, for measurement of liquids. Other items in the specification would include a hysteresis of around 2°C; switching capacity — let’s say 1 A at 250 V a.c. or d.c., to be on the safe side; and power requirements as small as possible, so as to permit continuous operation from a battery supply.
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