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 protect from overheating they either switch the equipment 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
Where a higher accuracy is requested, the operator should resort to an electric switch. With this particular instrument, it is possible to change the limit values yourself and set several switch points. Electronic temperature switches can 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 as well.
Furthermore, switches of the type could be fitted with digital communication (IO-Link). The benefits of these are a straight faster parametrisation along with extended diagnostics functions and integration into automated processes. Via an LED display, an on-site indication can even be provided.
The wide usability of the electronics is reflected in the purchase costs. It also 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, and a power source, an additional 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 the version ? temperatures around 400�C.
This instrument type offers the operator the possibility of selecting multiple switch points and setting them independently. Sick And Tired is also 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. An additional processing of the signal is not possible, however.
Regarding 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, sufficient reason for this they can manage without additional contactor.
Bimetal temperature switches operate with lower accuracy. Working exclusively as switches, they neither provide a local display, nor do they enable any processing of the signal. Their compact design also only permits a limited temperature range (max. 200 �C), since the plug connection is very close to the hot area.
Note
More info on the TSD-30 electronic switch, on the SB15 dial thermometer with switch contact and on the TFS35 bimetal temperature switch are available on the WIKA website.
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