Temperature switches in machine building: Which type suits?

Restricted are employed in machine building along with 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 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 particular 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 therefore 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 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. In order 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 is the wide temperature range. In general, expansion thermometers are employed for industrial applications. They cover ? according to 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). 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.
With regard to price and performance, the switch solution described here is 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 wide range of applications. These instruments may also switch with low voltages up to 250 VAC, and with 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 restricted temperature range (max. 200 �C), since 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 can be found on the WIKA website.
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