Explosion protection, functional safety and adverse environmental conditions such as moisture, cold and corrosive media are applications that require very special switching devices. Such switching devices are available in the Steute Extreme range, including the position switches "Ex 99", "Ex 97", the safety switches "Ex AZ 16" and the safety sensors "Ex RC SI M 30".

On offshore installations such as drilling rigs, the requirements of explosion protection must be taken into account. All electrical equipment is exposed to moisture. In many maritime oil fields there are permanently negative temperatures. In addition, there are areas and machines that have to be protected by fencing for reasons of occupational safety and where access to or access from safety switchgear must be monitored.

Looking at the overall market of safety switching devices, this is a real niche application. With the combination of explosion protection and frost and / or moisture one can even speak of the niche in the niche. Nevertheless, there is this need, which requires sophisticated developments of such safety switching devices. In the Extreme program of the manufacturer there are novelties for such applications.

Position switch for the extreme

One of these innovations is the Ex 99 series. The position switches corresponding to the dimensions of DIN EN 50041 were developed from the ground up for extreme areas of application and also for safety-related uses. They have been tested and approved in accordance with Atex and Iecex for use in gas Ex zones 1 and 2 and dust Ex zones 21 and 22. In addition, they are suitable for temperatures down to -60 ° C, which places high demands on the housing design and sealing in particular.

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The housing of the position switches are therefore made of high-quality glass fiber reinforced plastic. This material ensures that even with an 7 Joule shock test at -60 ° C, the high degree of protection of the switching devices (IP 66) is maintained. The designers also paid great attention to the sealing. The seal of the housing cover is fully vulcanised. The sealing of the switch tappet takes place via a redundant sealing system, which consists of an external low-temperature sealing collar and an internal Teflon sealing ring.

As is customary with the manufacturer's position switches, a wide range of actuators is available, such as tappets, roller tappets, roller levers, parallel levers, rotary levers, adjustable rotary levers and feeler springs. As switching inserts, the user can also choose between different variants for functional safety applications. The standard dimensions create the conditions for the new Extreme switch series to be well integrated into the surrounding construction.

Position switches for gas Ex and dust Ex areas

The Ex 97 series, which is also new, has a very similar property profile. Their dimensions correspond to DIN EN 50047, they are suitable for gas Ex and dust Ex areas (zones 1 and 2 as well as 21 and 22) as well as for temperatures down to -60 ° C.

The sealing materials are approved by the manufacturers up to -95 ° C and the lubricants up to -75 ° C. Thus, there is a sufficient "safety distance" to the admission temperature of -60 ° C. This gives the user the certainty that the position switches work reliably under real extreme conditions. Of course, this also applies if they are used for functional safety tasks such as monitoring the position of protective doors and flaps under extreme conditions.

Safety switch in robust design

It is one of the manufacturer's principles to offer the user alternatives whenever possible. Therefore, for the "classic" application of safety switchgear under Ex conditions, in addition to the new Ex 97 and Ex 99 series, a "classic" switch type is also available: The safety switch with separate actuator Ex AZ 16 is now available in new versions.

This series is not suitable for as wide a temperature range as the position switches. But she is also suitable for extreme situations. In order to comply with the requirements of explosion protection, a separate terminal compartment with type of protection "Ex e" is provided for the cable connection. On request, the Ex AZ 16 is also supplied with a pre-fabricated cable. The user has the choice between versions with two and three contacts. New in the program is the switch insert variant with two NC contacts and one NO contact. The available versions also include movable actuators, which are used with narrow opening angles of the protective door.

Non-contact safety sensors

As an alternative to the electromechanical switching devices described so far, there are also Ex safety sensors Ex RC SI M 30 in a cylindrical metal housing. Due to their contactless operating principle, they can also be used in areas in which electromechanical devices reach their limits. They are perfectly sealed and have a very long service life even in very dusty environments. The innovations in the Extreme range also include a sensor in a plastic housing, which, like the new position switches, has a safety function for use in extreme temperatures down to -60 ^oC was developed.

This means that even in these very special niche areas for switchgear, the user can make the fundamental decision between electromechanical switchgear and sensor technology. The author Rainer Lumme is Product Manager Extreme, Steute Schaltgeräte GmbH & Co. KG, Löhne.

Picture above: For safety-related applications in hazardous areas and at low temperatures: the Ex 99 series

The author Rainer Lumme is Product Manager Business Unit Extreme, Steute Schaltgeräte GmbH + Co. KG, Löhne.