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 gear or machine off or activate a fan for cooling. According to the task accessible, 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
Where a higher accuracy is requested, the operator should resort to an electric switch. With this instrument, you can change the limit values yourself and set several switch points. Electronic temperature switches can 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 along with extended diagnostics functions and integration into automated processes. Via an LED display, an on-site indication can also 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, typically,150 �C, which is sufficient for the majority of applications, however. To be able 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. In general, expansion thermometers are employed for industrial applications. They cover ? based on the version ? temperatures around 400�C.
This instrument type offers the operator the possibility of selecting multiple switch points and setting them independently. It is also suitable for switching in the low-voltage range (250 VAC). An additional contactor isn’t needed. Dial thermometers with switch contacts function without additional power and, furthermore, offer an on-site display. A further processing of the signal isn’t possible, however.
In terms of price and performance, the switch solution described here’s situated 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 an array of applications. Wounded may also switch with low voltages around 250 VAC, sufficient reason for 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 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 are available 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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