RTD vs Thermocouple

For our purposes, which do you prefer?

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Comments

  • edited January 24

    Without a doubt Rtd. 0.1 degree v 1.0 degree or more Having said that I have a controller with about 14 rtd on it. 3 wire and 4 wire and the temp variation is frustrating. Tried calibration using sous vide and boiling water but still annoying variations over the range in the logs I print out. I also have multiple thermocouple transducers on the same controller - k type and C type up to 1800 C and they good for high temp stuff but not accuracy over a small range.

    If anyone has suggestions on good accuracy over the 70 to 100 C range with repeatability across multiple sensors I can’t wait to hear as I have spent a lot of dollars playing with this problem

  • The biggest part is to confirm what class RTD sensors you have …. A, B or C.

    B is or seems to be standard with +-0.3 to 1 deg C accuracy. Class A which obviously is pricier has an approx. accuracy of +- 0.15 to 0.3 deg C.

  • @GD50 said: Without a doubt Rtd. 0.1 degree v 1.0 degree or more Having said that I have a controller with about 14 rtd on it. 3 wire and 4 wire and the temp variation is frustrating. Tried calibration using sous vide and boiling water but still annoying variations over the range in the logs I print out. I also have multiple thermocouple transducers on the same controller - k type and C type up to 1800 C and they good for high temp stuff but not accuracy over a small range.

    If anyone has suggestions on good accuracy over the 70 to 100 C range with repeatability across multiple sensors I can’t wait to hear as I have spent a lot of dollars playing with this problem

    1. try using some high precision 100 Ohm resistors as dummy probes... order 20 or so of the resistors and then grab 4 or whatever of the ones that read the same with a meter and hook them up... does the controller show the same temp on all the ports with the dummy RTD?
    2. buy a name brand, $$$ probe and compare...

    I think one of the two above solutions should ID the issue...

  • SQD
    edited January 25

    For my HMI and control system temp monitoring I use a combination of digital DS18B20 sensors(3 wire) and RTD's. My 2 RTD's are tied to 2 PID controllers for proportional temperature control of the condensers and the DS18B20 sensors are for SCADA temperature display, safety system, historical trending, etc. I find the DS18B20 to be good for about 0.5 degree accuracy. DS18B20's transmit a digital signal which goes to a ModbusIP gateway which sends it to the HMI and PLC. I've attached a pic to show a bit of what I created(this pic was taken right after I shutdown a run). Been using it for about 3 years now and the system works very well for me. But what works for me might not work for others. :)

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  • I have similar with RTD and 1-wire(DS1820B) the RTD are great if you really want the 0.1 degree, such as vapor temp or even fermentation temp for controlling a chiller... for cooling water and such, the 1-wire probes are great... here is a display of 4 of each being monitored by a $5 ESP32 WiFi Dev board (with a $30 RTD amp board and 4x $5 RTD Amps... (displayed in BruControl, with no fluff at the moment)

    you can see the smoother line of the RTD(Blue), this is overnight ambient temps

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  • Your PID controllers need " Clean " power and that PSU has to be grounded correctly. RTDs are very connection sensitive. Its for sure correct that a good quality brand goes a long way. When they are set up correctly they are less problem than Thermocouples, far less. Wiring terminations have to be rock solid. If you have long runs you may need transmitters. Also you may need to used shielded wire and connect only at one end. They are supposed to be wired up with the correct type of extension wire. Conections have to be flawless.

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