Temperature switches in machine building: Which type suits?

Temperature switches are employed in machine building and 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. Depending on the task at hand, temperature switches operate as either normally-closed or normally-open switches. Three switch types are believed 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 this instrument, it is possible to change the limit values yourself and set several switch points. Electronic temperature switches may be used beyond their actual function ? yet another analogue output (e.g. 4 ? 20 mA) enables further processing of the signal and thus continuous temperature monitoring aswell.
Furthermore, switches of this type can be fitted with digital communication (IO-Link). The benefits of these are an even faster parametrisation alongside extended diagnostics functions and integration into automated processes. Via an LED display, an on-site indication can 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, on average,150 �C, which is sufficient for the majority of applications, however. So as to fulfil their tasks, electronic temperature switches need, in addition to a power source, yet another contactor since their transistor only switches suprisingly low power.
Dial thermometers with switch contact
Example: WIKA expansion thermometer with switch contact SB15
The outstanding feature of dial thermometers with switch contacts may be the wide temperature range. Generally, expansion thermometers are employed for industrial applications. They cover ? depending on Force-fed ? temperatures around 400�C.
This instrument type offers the operator the chance of selecting multiple switch points and setting them independently. Additionally it is ideal for switching in the low-voltage range (250 VAC). An additional contactor is not needed. Dial thermometers with switch contacts function without additional power supply and, furthermore, offer an on-site display. A further processing of the signal isn’t possible, however.
With regard to price and performance, the switch solution described here is situated in the mid range.
Bimetal temperature switch
Example: WIKA bimetal temperature switch model TFS35
Bimetal temperature switches have become compact, cost-effective and have been designed for a wide range of applications. These instruments may also switch with low voltages up to 250 VAC, and with this they are able to manage with no 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 close to the hot area.
Note
Useful 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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