Temperature switches in machine building: Which kind suits?

Temperature switches are used in machine building and 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. Depending on 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 electronic 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 the type can 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 also be provided.
The wide usability of the electronics is reflected in the purchase costs. Cripple sets limits on the operating temperature. Its maximum value is, typically,150 �C, which is sufficient for the majority of applications, however. As a way 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 used for industrial applications. They cover ? based 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 ideal 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 is not possible, however.
When it comes 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 an array of applications. These instruments can also switch with low voltages up to 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 limited temperature range (max. 200 �C), because 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.
Also read our articles
Overview: How does the IO-Link work?
Safety temperature limiter for plants safe to use

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