Electricity and Control May 2020

SENSORS + SWITCHES: PRODUCTS + SERVICES

Intrinsically safe electronic instruments In many industries, there are certain areas that are classified as Hazardous Areas or EX areas. These are areas that contain, or may contain combustible substances such as gas, vapour or dust. Industries that typically have hazardous areas include coal mines, grain silos, chemical and petroleum industries, offshore and onshore oil and gas, oil refining, the pharmaceutical industry and paint shops. In the coal mining process, for example, two by-products – coal dust and methane – can be extremely dangerous if either or both of these substances are allowed to build up. Even a tiny spark can set off a disastrous explosion. Similarly, grain silo dust ignited by a spark can lead to explosions. Hazardous areas 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 in the classification of hazardous areas as Zones 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 order 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 directly reduce the risk of explosion. This method is used extensively in the mining and chemical industries. Precaution must be taken to prevent electrical equipment from being a source of ignition. A simple electrical switch in one’s home, for example, generates a tiny electrical spark every time the switch is thrown. This spark, although harmless in the home environment, is enough to act as trigger for an explosion in a hazardous area. In a similar fashion, sparks can be created by portable electronic devices. For devices to be safe for use in hazardous areas, safety measures are built into the design. In the design of intrinsically safe electronics devices there are several aspects to be considered, of which reducing or eliminating switch sparking is only one. Other considerations could encompass: 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. The Raytek MT4-IS handheld non-contact thermometer for 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 are examples of instruments suitable for use in hazardous areas. All these instruments are available from R&C Instrumentation. As part of its range of vibration sensors, R&C Instrumentation also supplies a wide range of ATEX IEC and EX certified vibration sensors. Additionally, due to a special request from a mining client, the company now also has in stock the UT390B+IS laser distance meter.

Three switch points in one sensor The KQ10 from ifm electronic enables continuous level monitoring from outside the process. It is designed to ‘see’ through all non-metallic walls, to detect granulates or liquids, without contact. Non-contact detection has the added benefit of minimising maintenance requirements. Process values of 0...100% can be transferred continuously via IO- Link over the entire length of 250 mm without dead band. 20 LEDs display the real level inside the vessel directly at the sensor. If several KQ10 units are combined, the detection zone can be increased accordingly. Up to three point levels can be monitored with just one sensor, where normally three sensors would be needed, and this is achieved at the same time as continuous range monitoring. As well as the switch points, other functions such as NC/ NO, hysteresis, or the orientation and detection zone of the sensor can be set. Where the typical conventional solution includes two point level sensors each at the lower (empty) and upper (overflow) ends of the tank, a single KQ10 includes three switch points to indicate empty, full and overflow conditions. This reduces the number of sensors required and installation complexity. Moreover, the KQ10 continuously measures levels in ranges of 250 mm and provides these, in addition to the switching states, as a percentage value, via IO-Link. Slight deposits on the inner walls of a tank do not impair the level detection and they can be signalled via the switching output or IO-Link if the threshold is exceeded. This permanent condition monitoring helps to prevent unplanned production downtime.

For more information contact ifm South Africa.

Tel: +27 (0)12 450 0400, email: info.za@ifm.com

For more information contact R&C Instrumentation. Mobile: +27 (0)71 471 2056, or email: info@randci.co.za R&C Instrumentation supplies a range of intrinsically safe electronic instruments and sensors suitable for use in hazardous areas.

The KQ10 sensor provides for

non-contact monitoring of point levels in non- metallic tanks or vessels.

20 Electricity + Control MAY 2020