Temperature switches in machine building: Which type suits?

Temperature switches are used 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 gear or machine off or activate a fan for cooling. With regards to 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
In which a higher accuracy is requested, the operator should resort to an electronic switch. With this particular instrument, it is possible to change the limit values yourself and set several switch points. Electronic temperature switches can be utilized beyond their actual function ? yet another analogue output (e.g. 4 ? 20 mA) enables further processing of the signal and therefore continuous temperature monitoring aswell.
Furthermore, switches of this type could be fitted with digital communication (IO-Link). The benefits of these are a straight 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, on average,150 �C, that is sufficient for the majority of applications, however. So that you can 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 employed for industrial applications. They cover ? with respect 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 suitable for switching in the low-voltage range (250 VAC). An additional contactor is not 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.
In terms of 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 have become compact, cost-effective and also have been designed for a variety of applications. These instruments may also switch with low voltages up to 250 VAC, and with this they can manage without 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. Success permits a limited temperature range (max. 200 �C), since the plug connection is very near 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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