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 safeguard 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 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 electronic switch. With this particular instrument, you can 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 this type could be fitted with digital communication (IO-Link). The advantages 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. In addition, it sets limits on the operating temperature. Its maximum value is, on average,150 �C, which is sufficient in most of applications, however. To be able 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 is the wide temperature range. Generally, expansion thermometers are used for industrial applications. They cover ? depending on version ? temperatures up to 400�C.
This instrument type offers the operator the chance of selecting multiple switch points and setting them independently. It is also suitable for switching in the low-voltage range (250 VAC). Yet another contactor isn’t 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.
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 are very compact, cost-effective and have been designed for a wide range of applications. pressure gauge 10 bar can also switch with low voltages around 250 VAC, sufficient reason for this they can manage with no 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 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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