Temperature switches are employed 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. Depending on task at hand, 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 may 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 can be fitted with digital communication (IO-Link). The benefits 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 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, normally,150 �C, which is sufficient for the majority of applications, however. To be able to fulfil their tasks, electronic temperature switches need, in addition to a power source, an additional contactor since their transistor only switches very 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 used for industrial applications. They cover ? according to the version ? temperatures around 400�C.
This instrument type also offers the operator the possibility of selecting multiple switch points and setting them independently. It 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 and, furthermore, offer an on-site display. A further processing of the signal is not possible, however.
With regard 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 variety of applications. These instruments can also switch with low voltages around 250 VAC, and with this they can manage without 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), 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 can be found on the WIKA website.
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