Which Temperature probe do I need for my temperature controller?

 6th Feb 2014

Which Temperature probe do I need for my temperature controller?

Most temperature controllers can be set to operate with a number of different temperature probes.

A thermocouple or Pt100 input will achieve the same purpose: it will allow you to wire a temperature probe directly to the terminal of the controller. The controller will then interpret the signal and display the temperature.

Temperature probes: a simple Thermocouple probe (left), a head mounted Temperature probe - can be Thermocouple or PT100 (right)

general purpose probe head mounted probe


You can find on the internet a detailed article on how these two types of probe work.
To summarise, we can say that a Pt100 probe is typically more accurate, slightly more expensive than very standard thermocouple but it is limited to 500 degC.
The thermocouple probes are available in a wider range of types, for ranges of temperature up to 1700 degC. Standard probes are less expensive than PT100 probes. However, fast response thermocouples and high temperature probes can be much more expensive.

A Thermocouple probe has two wires (one +, one -) while PT100 probes have 3 or 4 wires although most controllers will only accept 3 wires.

Voltage or current inputs are used to receive a signal from another instrument / device.

Typical ranges can be 0-5V, 1-5V, 0-10V, 2-10V, 0-20mA, 4-20mA.

On most controllers (and that the case with Fuji Electric controllers as well) the 4-20mA input is actually a Voltage input (1-5V) and you have to wire a 250 Ohm resistor to convert the Current signal to Voltage so that the controller can read it (we supply the resistor free of charge with our controllers)

Examples of devices or instruments that can be used as an input on a controllers:
Pressure transmitters or pressure transducers
- Temperature transmitter (alternative to read the information from the probes mentioned above)
- Humidity transmitters
Level transmitters
Flow transmitters
- Signal generated from a computer
- To read the output of another controller

The Fuji Electric PXR and PUM series of temperature / process controllers come with either a Thermocouple/Pt100 input or Voltage/Current input. This has to be specified at the moment of ordering. You can change a probe type via the front panel and you can change from voltage to current (and current to voltage) but you cannot have a Voltage/current input if your controller is set up for a probe and vice versa.

Fuji Electric PXG and PXH process controllers have a universal input that can be changed from one type to any other by the end user at any time via the front panel.

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