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 protect from overheating they either switch the gear or machine off or switch on 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, it is possible to 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 as well.
Furthermore, switches of the type can 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. Six-figure , an on-site indication may also be provided.
The wide usability of the electronics is reflected in the purchase costs. It also sets limits on the operating temperature. Its maximum value is, on average,150 �C, which is sufficient for the majority of applications, however. So that you can fulfil their tasks, electronic temperature switches need, and 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. In general, expansion thermometers are used for industrial applications. They cover ? with regards to the version ? temperatures around 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 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 regards 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 have become 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, 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 restricted temperature range (max. 200 �C), because the plug connection is very close 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.
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