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 protect from overheating they either switch the equipment or machine off or switch on a fan for cooling. With regards 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 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 as well.
Furthermore, switches of the type could be fitted with digital communication (IO-Link). The advantages 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, typically,150 �C, which is sufficient in most 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 very low power.
Completely 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. In general, expansion thermometers are used for industrial applications. They cover ? based on the version ? temperatures up to 400�C.
This instrument type also 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). An additional 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.
With regard to price and performance, the switch solution described here’s 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 variety of applications. These instruments can also switch with low voltages around 250 VAC, sufficient reason for this they are able to manage without additional contactor.
Bimetal temperature switches operate with lower accuracy. Working exclusively as Skyrocket , 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 quite 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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