Electricity + Control May 2019

SENSORS, SWITCHES + TRANSDUCERS

New pressure switch for process industry WIKA has released a new pressure switch with high switch differential adjustability for the process indus- try. The PSM-700 mechanical pres- sure switch is designed for control and monitoring applications. The measuring element is a fully weld- ed bellow made of stainless steel 316L. The corrosion-resistant pres- sure switch is suitable for use in a wide range of media in the process industry. The case is made of a high-grade aluminium alloy which enables the pressure switch to withstand harsh operating conditions. The PSM-700 is equipped with UL listed micro switches to ensure durable opera- tion and long service life. It has a high switch point repeat- ability of ≤ 0.5%, which enables reliable switching. The adjustable switch differential to a wide range of up to 60% of the setting range provides for flexible on/off controls. Such a wide setting range is often needed for the on/off control mode of cyclic applications. The switch point can be speci- fied on site. With tamper proofing as an available option, unauthorised adjustment of the switch point can be prevented. Enquiries:WIKA Instruments. T +27 (0)11 621 0000 or email: sales.za@wika.com

Electronic instruments in hazardous areas A Hazardous Area or EX area is an area that contains, or may contain, combustible sub- stances such as gas, vapour or dust. Typical industries with hazardous areas include coal mines, grain storage, chemical and petroleum industries, offshore and onshore oil and gas, oil refining, the pharmaceutical industry and paint shops. In the coal mining process, two hazardous by-products are produced: coal dust and methane. The build-up of either of these substances can be extremely dangerous. Even a tiny spark can set off an explosion. Similarly, grain silo dust, ignited by a spark, can lead to a tragic explosion. Hazardous area zones The level of risk of an explosion is based on the frequency and duration of the presence of an explosive atmosphere. This level of risk is represented by classifying the hazardous area as Zone 0, 1 or 2. - Zone 0 is where an explosive atmosphere is present continuously for long periods of time. - Zone 1 is where an explosive atmosphere occurs occasionally in normal operation. - Zone 2 is where an explosive atmosphere is unlikely to occur in normal operation and, if it does occur, will persist for a short period. These areas are only declared hazardous in case of an abnormal event like an accident or leakage. Safety measures in hazardous areas For ignition to occur, two things are needed: the explosive or combustible atmosphere as described above, and a trigger – that is – a spark or flame. Remove one or both of these conditions and the explosion will not occur. Ventilation equipment can dilute or remove dangerous substances from an enclosed area and, as a direct result, reduce the risk of explosion. This method is used extensively to support safety in the mining and chemical industries. Apart from ‘No Open Flames’ signs, precaution must be taken to prevent electrical equipment from being a source of ignition. A simple electrical switch in the home, for example, generates a tiny electrical spark each time the switch is thrown. This spark, al- though harmless in the home environment, is enough to act as a trigger for an explosion in a hazardous area. In a similar way, sparks can be created by portable electronic devices. In order for devices to be safe for use in hazardous areas, safety precautions have to be built into the design. Intrinsically safe instruments There are several aspects that should be incorporated in the design of intrinsically safe electronics devices. Reducing or eliminating switch sparking is just one. Other consider- ations are the inclusion of fast fuses, controlling component temperatures, eliminating too-tight component spacing that could lead to a short circuit, and reducing circuit current and energy storage. R&C Instrumentation supplies a range of intrinsically safe instruments. These include the Raytek MT4-IS handheld non-contact thermometer which covers the temperature range -18°C to 400°C, the Raytek Mi3-IS 4-wire system fixed pyrometer and the Raytek TX-IS 2-wire loop powered system fixed pyrometer. As part of its recently launched range of vibration sensors, the company offers a selec- tion of ATEX IEC and EX certified vibration sensors. In addition, responding to a special request from a mining client, R&C Instrumentation now also stocks the UT390B+IS laser distance meter. Enquiries: R&C Instrumentation, Tel: +27 (0)11 608 1551, or email: info@randci.co.za

The PSM 700 pressure switch is avail- able with a fixed or adjustable switch differential.

Only intrinsically safe electronics instru- ments should be used in hazardous areas.

Electricity + Control

MAY 2019

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