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I am designing a control system that runs a fan and electric heater based on the temperature measured inside of a hybrid electrical/solar dryer (for fruits and vegetables).

Temperatures inside could vary between 0 and 200 degrees (very, very roughly).

What kind of sensor would you suggest using for this kind of application?

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  • \$\begingroup\$ Assuming control accuracy is not overly tight (and you need to state that as part of your spec) then many sensors would work. Thermistor, RTD, thermocouple. Of these thermistor is arguably easiest. \$\endgroup\$
    – Russell McMahon
    Commented Nov 20, 2019 at 9:39
  • \$\begingroup\$ These look OK - 1 degree C accuracy 0-100C with 300C max rating $US1.19/1 Digikey. Or these $1.54/1 +/- 0.5C 0-100C and 300C max rated. \$\endgroup\$
    – Russell McMahon
    Commented Nov 20, 2019 at 10:14
  • \$\begingroup\$ Yes, when I was reading that thermocouples need mathematical linearization I was wondering if they could be possibly the easiest. I am quite new to electronics and still need to learn a lot. How about semiconductor sensors like AD590 and LM35? Would they make sense in this application? \$\endgroup\$
    – Anna Sarah
    Commented Nov 20, 2019 at 10:20
  • \$\begingroup\$ Your upper temperature limit of 200C makes most electronic sensors unsuitable. Remote IR sesnors (thermopile) work but probably don't suit. Then you are back to RTD / thermistor / thermocouple ... || IF you have a processor available (an Arduino for a few $ is fine) then linearisation is no real problem. \$\endgroup\$
    – Russell McMahon
    Commented Nov 20, 2019 at 10:39

1 Answer 1

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try this; if the diodes are even close to working as diodes, the hot diode voltage will drop by 200 * 0.002 = 0.4 volts when heated to 200 degree C. Simply measure both voltages, subtract, divide y 0.002 (or 0.0022?) and you'll have a somewhat accurate and cheap temperature estimate.

Is this cheap enough? Calibration is up to you.

schematic

simulate this circuit – Schematic created using CircuitLab

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