CABLE SENSORS SHOULD NOT HANG

Even temperature sensors get hung up – and lose the game!

Did you know that temperature sensors in the cable version are not designed to hang from the cable at depth? This use always reminds me of a game of hangman. See below to find out why cable sensors are generally not designed to be hung freely.

A little theory

Temperature sensors can be distinguished between resistive temperature sensors (RTD or often Pt100, Pt1000) and thermocouples (TC or often K-type, T-type, S-type, etc.) and others. Cable sensors are mostly resistive, as the accuracy classes and the corresponding temperature sensitivity of the insulation (insulation jackets of the connecting cable) make them well suited for air and media temperature measurements in the -50 to 400 °C range:

up to 80 °C – PVC cable,

up to 100 °C – rubber cable,

up to 180 °C – silicone cable,

up to 250 °C – Teflon-coated cable,

up to 400 °C – glass fibre cable with metal braid.

The most suitable connection cables for RTD sensors are those with copper conductors (Cu), mostly of thin cross-sections such as 0.22 or 0.50 mm2. The recommended binding is 3 wires.

Why shouldn’t they hang, what is the impact?

• The cable has its own mass,
• the sensor has its own mass,
• the sensor protection has its own mass (tube or other protection),
• the way it is made has “its own weight” as fillers, glues, protections … are added,
• all added elements have a mass, e.g. handles, reinforcements, weights …,
• Often, users themselves even put extra weight on the cable sensor to stop it floating, dancing, swirling, etc.

The sum of all these masses causes stretching of the connecting wires of the cable, stress on the joints and especially stress on the sensor joint, which are mostly ceramic-based and very thin wires. All this leads to an interruption and the sensor fails. Often, it first interrupts, then fails completely.

It follows from the above that cable temperature sensors in conventional designs are not designed to be suspended at depth. If you need such an application, please let us know and we will advise you and design a special implementation accordingly.

Of course, you don’t need to complicate things too much if you hang the sensor from the ceiling or from a fixed place with a short cable and it stays there. In such cases, if the cable is too long, shorten it or make a loop. Just be careful wherever the temperature sensor might be drifting, floating on the surface, etc. In these cases, please call us.

Author Aleksandra Lepenik
August 2022

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Tel: +386 2 62 96 720.

They are always available for opinions and explanations:

• Measurement expert Zoran Lepenik
• Aleksandra Lepenik, expert in temperature measurements

More at: https://www.elpro.si/kategorija-izdelka/temperaturna-tipala-elpro/