The choice of temperature sensor

One of the most frequently asked questions by our customers is the type of temperature sensor to use in their process.

We can state that the first thing that distinguishes the two types of probes is obviously the temperature range; which sees the RTD excel on ranges ranging from -50 °C to 250 °C, and thermocouples used above all on high and very high temperatures.

Analyzing the best type of probe, however, we need to make a reflection on the basis of numerous characteristics that separate the former from the latter.

In general we tend to emphasize the degree of precision that the PT100 can offer, both in the immediate and after quite long periods of time, a remarkable stability and a linear output signal and practically free of external disturbances. All these features make it indispensable in those areas where reading accuracy is of fundamental importance as well as reliability over time. This is why we find it commonly used in the sectors related to the pharmaceutical industry or in the food industry processes.

On the other hand, this type of probe has a low mechanical resistance which could jeopardize its correct functioning in case of vibrations or as regards processes with moving parts with considerable stress.

As far as thermocouples are concerned, they find their main use on the measurement of temperatures up to 1800 °C but without neglecting the field of cryogenics, where the “T” type thermocouples are the first ones to excel.

This type of sensor has as main characteristic that of reading speed, also due to its physical structure that allows us to have probes with diameters in the order of a few tenths of a millimeter. Also their mechanical resistance is quite high and guarantees a use also in those sectors where there is a considerable dynamic stress of the process.

Their fundamental limit is that of a lower precision compared to PT100 and a lesser reliability over time. Moreover, as regards the thermocouples, being their output value in mV, it is susceptible to electromagnetic interference especially if the wiring is not carried out with suitably shielded cable.

Finally, we can do a cost analysis that sees yes, the price of RTD higher than that of thermocouples, but, on the whole system, we should also consider the cost of wiring, which, while in the former can be done with normal wire in copper, in thermocouples it must necessarily be carried out with a compensated cable of the same type as the probe.

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