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Automation Technologies 4/2016

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Automation Technologies 4/2016

Economical reliability

Economical reliability of electronic pressure switches Hygienic design: the pressure switches are suitable for applications in sterile process technology SENSORS AND MEASUREMENT Joachim Zipp Automated processes increase the process safety of sterile production processes. They eliminate the potential for errors that inevitably exists when all routine control tasks are carried out manually. This also applies for the upstream and downstream cleaning and sterilisation processes. Thus, even simple pressure monitoring tasks are carried out electronically – conveniently with a switch. The control of the replenishment of ultra-pure water or sterile air is a classic example for a straightforward switching task in the supply units. Electronic pressure switches are used in such applications, not only for measurement technology reasons, but also for efficiency ones: Plant control, whether through PLC or relays, is more economical when using such decentralised elements. From these determining factors of reliability and economy, the requirement profile for the pressure switches is derived. They must be robust in order to survive in harsh industrial environments. Commissioning, maintenance and service operations must be uncomplicated and fast, so that plant downtime is avoided, or is, at least, reduced to the shortest possible duration. In such applications, electronic switches with transistor switching output and an integrated digital display have proven particularly useful. There generally a limit value, e. g. for over or under-pressure or level, has to be monitored. For the connection to machine control, a binary, digital input is sufficient for this purpose. The digital display is a Author: Joachim Zipp, Global Market Segment Manager, Food and Pharma, Wika Alexander Wiegand SE & Co. KG, Klingenberg/Germany helpful component during commissioning and maintenance, en abling the measured value to be checked conveniently and directly on site in the system. Single switch model with a wide variance For pressure switches, the typical applications in sterile process technology require numerous measuring ranges up to 25 bar with gauge, vacuum or absolute pressure. Should continuous measurement be required over and above the switching function, the operator will need an instrument with an additional analogue output (up to 20 mA). On the basis of these requirements, one can generate a wide variance with a single switch model. With the PSA-31 from Wika, for example, there are around two million combinations in total (from the possible process connections, measuring ranges and output signals) possible as a standard design. Simple operation and good readability The three-key system and the alpha-numeric display of the PSA-31 ensure fast, intuitive menu navigation without the need for additional assistance. The simple operation of the pressure switch is supported by the large and ergonomic arrangement of the keys, giving the operator a clear, tactile feedback. The pressure switch operates with a 14-segment display. Its high resolution considerably increases the readability of the parameters in the setup and thus minimises the risk of mistakes. The display can always be positioned to face the operator and the M12 connection aligned according to the desired cable routing of the plant. Also a display is available, which can be rotated through 180°. The readability of the display is made even easier by the inclined angle, and it offers a large viewing angle due to the LED technology. Photographs: teaser fotolia, other Wika AUTOMATION TECHNOLOGIES 4/2016

Ultrasonic through-beam sensors – ideally suited for critical applications Melanie Harke Ultrasonic through-beam barrier for contact free detection of objects specially in the most diverse applications e.g. with bottles or plastic foils. They are available in cubical as well as cylindrical housing. Find out more about the advantages, applications and the functional principle of this technology. The through-beam barrier consists of two constructively-identical units that operate as a transmitter and a receiver. Through the control input, the two units are able to recognize whether they are supposed to work as a transmitter or a receiver. If pin 2 +UB is activated, this unit functions as a transmitter. The functional principle: The transmitter emits acoustic pulses on a cyclical basis that are captured by the receiver. If an object interrupts the pulses between the transmitter and the receiver, the switching output of the receiver is set. The small, cuboid ews 15/CD is compatible with many of the light barriers and easily makes the transfer to the ultrasonic through-beam barrier, especially with critical applications. The microsonic through-beam barriers enable switching frequencies of up to 500 Hz. Industrial application examples are: n counting objects or containers on a conveyor belt, n presence-control of objects with an irregular surface, n detection of packaging, n counting of small objects on a conveyor belt, operating at high speeds, n checking for film tears and n presence-control of objects under difficult production conditions. Counting bottles in the bottling plant The quick reaction time of the ultrasonic through-beam barrier is especially useful in the recognition and rapid bottle counting required in a beverage industry filling plant. The ews range from microsonic conquers this challenge with a high switching frequency of up to 500 Hz. The response delay is less than 2 ms. These optimum conditions mean that the system can easily recognize bottles with a fast pace and can address very small gaps between two bottles at high speeds. It’s often challenging to accurately measure glass or plastic bottles. Capacitive and optical sensors just don’t have the same accuracy. Ultrasonic through-beam barriers solve this problem. Filling plants often spray water to clean the bottles. This, as well as other difficult conditions do not affect the ultrasonic through-beam barriers. Monitoring sheet tears in the packaging industry A highly transparent film with a width of only 10 µm is to be monitored for web tears on a packaging machine. The pulsing of the feed can produce a strong wave effect in the film. Utilizing an ultrasonic proximity switch is not possible in this situation, as the strong wave effect in the film reflects the ultrasonic beam. The ews ultrasonic through-beam barrier addresses this problem: The sound emission of the transmitter is to be set so the very thin film interrupts the pulsed sound wave completely. The rapid response of the ews-25/M18/CD of only 2 ms means that the through-beam barrier is activated quickly and reliably to a film tear. Photographs: Microsonic Author: Melanie Harke, Marketing, microsonic GmbH, Dortmund, Germany About Microsonic The company is a globally recognised specialist in ultrasonic sensors for applications in industrial automation technology. Examples are ultrasonic double-sheet control that work with no calibration at all, label sensors and ultrasonic proximity switches. The number of employees is about 80 in total. 17 AUTOMATION TECHNOLOGIES 1/2016 AUTOMATION TECHNOLOGIES 4/2016