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Old 12-19-2015, 06:24 PM   #26
R_p_ryan
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Quote:
Originally Posted by BigJim View Post
You need to specify a sensor wire type. Some PLC use twisted pair some use shielded wire. Cannot be run along or near HV AC >24VAC. etc etc.

In the perfect (industrial) world 4-20 MA sensors are used. As long as you have 20 MA in your circuit you can have a two mile long sensing circuit.
BigJim,
Thanks for the info. I know very little about RTDs. Currently I have a low-cost, stainless steel encased Type-K thermocouple for the exhaust. Do you think I should use an RTD instead? I am planning on having the Ardiuno on a bulkhead in the engine room so the wire lengths would not exceed 8 feet.

For sensors that are never exposed to 250F I was planning on using the electronic "one-wire" protocol with digital ds18b20 sensors

This raises a good discussion on temperature sensors:
Thermocouple vs RTD vs ds18b20

I am no expert on this and these are thoughts about the different temp sensors
  • I don't know enough about RTDs to comment
  • Thermocouples tolerate extreme heat and require a break out board
  • DS18B20 is very accurate and low cost. A single pin can be used to query many sensors

Please let me know if I've gotten any this wrong, and please let me know if the RTD should be included.

Thank,
Robert
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