Temperature Switches – Always Monitoring the Heat

Controlling, monitoring, and supervising the temperature of hydraulic oil is extremely important for the service life and functionality of a hydraulic system. Oil that is too hot can damage seals, become too thin, or even oxidize. This produces sharp-edged suspended particles that damage the hydraulic system from within. Temperature switches were developed to control the temperature both automatically and for monitoring purposes.

Types of Temperature Switches

Temperature switches and temperature sensors are available in two fundamentally different designs: as cable sensors or socket switches.

Temperature Switches as Cable Sensors

The cable sensor is a temperature sensor that can be installed freely within the hydraulic system. It is completely immersed in the medium and thus provides a particularly valid measurement value. It is designed to be hydrodynamically optimal so that it does not disturb or impede the flow of the medium. The cable sensor can be inserted deep into hydraulic systems and reach points that are barely accessible from the outside. A disadvantage of the cable sensor is that it cannot be securely fixed. Its positioning must therefore be chosen very carefully, as in the worst case it could tear off and block or damage a hydraulic component, such as a valve or pump.

Temperature Switches as Socket Switches

The socket switch is screwed on from the outside at a designated location. It is particularly easy to install and is intended for permanent use. In addition to the signal line to the central control system, it is also suitable for installing a local reading point for the hydraulic temperature directly on site.

Structure of a Temperature Switch

A temperature switch is a combination of a temperature sensor and current regulator. However, the switched currents are usually very low. Typically, these are control currents. In the best case, a temperature switch can serve as a trigger for a relay.

On the sensor or probe side, the resistance thermometer has become established as the standard design. It consists of a bimetal that changes its shape under the influence of heat. In doing so, it changes its electrical resistance. This change in electrical resistance can be interpreted as a measurement value for the temperature change. For this purpose, temperature switches either have their own operators—for example, modules with integrated displays—or the measurement value is converted in a central monitoring station.

Applications of Temperature Switches

Temperature switches and temperature sensors are used in all complex hydraulic systems. Simple hydraulic systems such as lifting platforms or jacks generally do not require this monitoring and protection function.

However, as soon as a hydraulic system is operated continuously and supplied by an electric pump, at least one temperature switch should be installed for monitoring and protection. Temperature switches are typically standard in larger forklifts and construction machinery.

Complex stationary hydraulic systems usually have several temperature switches integrated. Fundamentally, the temperature switch serves to trigger an alarm or a safety device. For example, an integrated cooler for the hydraulic oil is usually coupled with a temperature switch and an electric shut-off valve. In this way, the temperature of the hydraulic oil can be optimally maintained at a constant level.

However, a temperature switch is never installed exclusively to control a protection mechanism. A monitoring function is always one of the temperature switch’s tasks.

Always Work with Redundancies

Temperature switches, unlike any other hydraulic switches, are designed for redundant configuration. Only at least doubled measurement acquisition reliably protects against incorrect switching if one switch fails. To be completely safe, the modules used should come from different manufacturers. This also eliminates the risk of endangering the hydraulic system due to a manufacturing defect in the temperature switches.