Cylinder sensors for extreme environments

For standard industrial applications, standard cylinder sensors are sufficient. Extreme, challenging environments often demand more from a sensor. And that means: special versions and special properties.

For example for:

  • Environments where extreme temperatures prevail (high / low)
  • Explosive environments
  • Environments where aggressive substances such as chemicals and cleaning agents are used
  • Environments with extra demands for machine safety
  • Humid environments
  • Outdoor applications
  • Welding applications

Extreme temperatures

The Festo range includes cylinder sensors suitable for extremely high or low temperatures. With regard to high temperatures, the choice includes the SMT-8M-A and CRSMT-8M solid state sensors. These can be used at temperatures up to 85 °C. The reed cylinder sensors go one step further and can withstand temperatures up to 120 °C.

For high temperatures, the choice is between the SMT-8M-A and CRSMT-8M solid state sensors.

Cylinder sensors for lower temperatures are also available in both versions. Both the reed and solid state versions are suitable for applications up to temperatures of -40 °C.

Machine safety

In special cases, the cylinder sensors must comply with a certain safety level. Typically expressed as SIL (Safety Integrity Level) or PL (Performance Level). When it comes to PLd or PLe, the following steps have to be taken.

Holder with seal

First of all, start with a suitable holder for placing the cylinder sensors. The SAMH-S-N8-S-MK or SAMH-S-N8-L-MK holders with seal comply with the EC Machinery Directive. This ensures that the sensors are inseparably connected to the machine and resistant to rough or improper use.

Standard sensor

To achieve the safety level, the standard sensors SMT-8M can be used because of a MTTF of 4077 years. However, they must be used in parallel in order to provide redundant position feedback.

Safety relay

Finally, it is important to carry out a safety analysis in which the two-cylinder signals are analysed by means of a safety relay. Terms such as redundancy, self-monitoring and self-testing are important here. Safety relays are available from Pilz, among others.

Hazardous environments

In hazardous areas, machines must comply with the ATEX directive. This is a comprehensive directive that focuses primarily on preventing explosions. If this is not possible, the damage must be limited. The ATEX Directive distinguishes between gas and dust explosions and divides the relevant environment into zones. Depending on the chance of a certain dangerous situation occurring and the consequences of this, a zone sets heavier or lighter requirements for the components to be used.


When using cylinder sensors in ATEX environments, Festo shall be solely responsible for the product characteristics of the sensors. The system integrator or machine builder as manufacturer of the assembly is responsible for the use of the sensor in the application.

Ignition source

Cylinder sensors represent a hazard in explosive atmospheres if they can act as an ignition source. This is the case if, for example, they spark during switching or if they give off too much heat. In both cases, this may lead to the ignition of an explosive atmosphere.

Therefore, only cylinder sensors with an intrinsically safe switching output (Namur) are permitted for categories 1GD and 2GD. A suitable type from the Festo range is the SDBT-MS-...-EX6

This output requires the sensor to be connected to an isolated switching amplifier such as the Festo IO module CPX-P-8DE-N-IS.

Aggressive agents

Environments where aggressive agents are used are mainly found in the food industry (cleaning agents) and the chemical industry (chemicals). But also in environments where metal is worked and cooling lubricants are used, or applications where the cylinder sensors come into prolonged contact with water or where acids are used.

An example of a cylinder sensor suitable for these extreme environments is the CRSMT-8M. This cylinder sensor has a high chemical resistance by, among others, a PP housing and a TPE-O cable.

Welding environments

Finally, welding environments are extreme. On the one hand, because of the welding spatter and, on the other hand, because the current sources for the welding process have such a high frequency that they can interfere with the sensor signals. Sensors for welding environments, as a solution, freeze the output signal as long as a welding field is detected. Suitable sensor types from the Festo range are SMTSO-8E-... and SDBT-BSW-1L-....

July 2022