In this article, Schurter discusses the application of switches and displays in potentially explosive environments.

When operating in a potentially explosive environment, products and equipment must comply with ATEX directives in the EU. ATEX certification means that a product can be used in a potentially explosive atmosphere and will not ignite hazardous air-gas mixtures. ATEX is the European certification, while IECEx is applied worldwide. In order to be able to offer ATEX/IECEx certified products, the manufacturer requires product certification and production site certification.

As an example of application, the pharmaceutical industry involves working in places with potentially explosive atmospheres. Laboratory and production equipment used in these environments must be controlled, requiring a human-machine interface. The simplest option is switches. There are many different switching technologies, the most familiar being mechanical. However, there are also capacitive, piezoelectric and non-contact variants. Not all of them are suitable for a potentially explosive atmosphere, with one exception: piezo.

The piezo effect describes the change in electrical polarization and thus the occurrence of an electrical voltage on solids (primarily crystals) when they are elastically deformed. In short, if a piezo switch is pressed, an electrical signal is generated. Here’s the big difference: the piezo switch doesn’t need an electrical supply for a tactile process. Where there is no electrical supply, there are almost always no dangerous sparks.

Piezoelectric switches are also robust. They are hermetically sealed and have no mechanical switching contacts, so there are no sparks or penetration of explosive substances. Schurter’s PSE EX family of switches have housings made of aluminum or stainless steel. They are designed to offer maximum reliability and long service life. Thanks to their hermetically sealed enclosures (IP69K), they are predestined for use in the harshest environments, overhead explosive installations and areas with flammable air-gas mixtures, mist, vapor and dust.

What about touchscreens? Things get more complicated with more complex input systems. Here, manufacturers must ensure that no gases can enter the system, where sparking of electrical parts could lead to an explosion. In HMI systems for ATEX environments, air cavities where gases can accumulate must be reduced to a certain minimum.

To achieve this, it is necessary to stick with a special glue between the display and the sensor. Also, the display needs to be adjusted in many cases. This means opening up the back of the display and filling air cavities with different materials. The front glass of the HMI system can be specially treated to ensure that it has the necessary impact resistance in the event of an explosion. In many cases, such HMIs are used outdoors and/or in particularly harsh environments. Therefore, water resistance and EMC compliance should also be considered.

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Safety in potentially explosive environments

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