Temperature switches in machine building: Which type suits?

Temperature switches are used in machine building along with other industrial applications for limiting temperature. They monitor the temperature and react at a predefined point. To safeguard from overheating they either switch the gear or machine off or activate a fan for cooling. According to the task at hand, temperature switches operate as either normally-closed or normally-open switches. Three switch types are considered for industrial applications:
Electronic switches
Example: Electrical WIKA temperature switch TSD-30
In which a higher accuracy is requested, the operator should resort to an electronic switch. With Natural , it is possible to change the limit values yourself and set several switch points. Electronic temperature switches may be used beyond their actual function ? an additional analogue output (e.g. 4 ? 20 mA) enables further processing of the signal and thus continuous temperature monitoring aswell.
Furthermore, switches of the type could be fitted with digital communication (IO-Link). The advantages of these are an even faster parametrisation alongside extended diagnostics functions and integration into automated processes. Via an LED display, an on-site indication may also be provided.
The wide usability of the electronics is reflected in the purchase costs. In addition, it sets limits on the operating temperature. Its maximum value is, typically,150 �C, which is sufficient for the majority of applications, however. So that you can fulfil their tasks, electronic temperature switches need, in addition to a power source, an additional contactor since their transistor only switches very low power.
Dial thermometers with switch contact
Example: WIKA expansion thermometer with switch contact SB15
The outstanding feature of dial thermometers with switch contacts is the wide temperature range. In general, expansion thermometers are employed for industrial applications. They cover ? depending on the version ? temperatures up to 400�C.
This instrument type offers the operator the possibility of selecting multiple switch points and setting them independently. Additionally it is suitable for switching in the low-voltage range (250 VAC). Yet another contactor is not needed. Dial thermometers with switch contacts function without additional power and, furthermore, offer an on-site display. An additional processing of the signal isn’t possible, however.
With regards to price and performance, the switch solution described here is positioned in the mid range.
Bimetal temperature switch
Example: WIKA bimetal temperature switch model TFS35
Bimetal temperature switches are very compact, cost-effective and have been designed for a wide range of applications. These instruments may also switch with low voltages around 250 VAC, and with this they are able to manage without additional contactor.
Bimetal temperature switches operate with lower accuracy. Working exclusively as switches, they neither offer a local display, nor do they enable any processing of the signal. Their compact design also only permits a restricted temperature range (max. 200 �C), because the plug connection is very near to the hot area.
Note
Further information on the TSD-30 electronic switch, on the SB15 dial thermometer with switch contact and on the TFS35 bimetal temperature switch can be found on the WIKA website.
Also read our articles
Overview: How does the IO-Link work?
Safety temperature limiter for plants safe to operate

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