Editor’s choice
Valve position sensors: making the right choices
I 10
n almost any process plant, if a valve fails to open or close when required and the control system is not immediately alerted to the problem, the consequences are likely to be costly, disruptive and possibly dangerous. To help minimise these risks, valves are almost invariably fitted with position sensors to check that they have operated correctly before the process is allowed to proceed. It is easy to see that these sensors perform a vital task so, when selecting them, it is worth thinking carefully about which type of sensor is best for the job in hand. This will, of course, depend on the type
of valve being monitored and, to a lesser extent, on its role. For ordinary actuated valves, the usual solution was, for many years, to use cams mounted on the actuator shaft to operate mechanical switches which would signal open and closed status. In more recent times, the switches have been replaced by inductive proximity sensors which offer non- contact operation and are, therefore, completely wear free. Today, an even more convenient solution is to use a dual sensor which combines the sensors for the valve open and closed positions in a single unit. This reduces mounting time and, if a version that supports a fieldbus interface such as AS-i is selected, it also reduces wiring complexity and installation time. These dual sensors are now available in a wide range of types, including hygienic versions for the food industry and NAMUR versions for hazardous area applications.
If you think that valve position sensors are uninteresting devices and that there is little to choose between them, read on, says Andy Walker of ifm electronic. They have a vital role to play in almost every sector of industry and choosing the right valve sensor for the application can make a big difference to plant performance and reliability.
Sensor manufacturers typically supply target pucks – which replace the cams associated with mechanical switches – for use with their dual sensors. These are available in standard versions for valves with a 90º operating angle, and adjustable versions for valves with other operating angles. In addition, leading manufacturers offer mounting kits that allow the dual sensors to be used conveniently with manually operated valves. Dual sensor solutions are an ideal
choice for the majority of everyday valve applications but, in critical applications where a valve seat fault would be particularly problematic or expensive, there is a better choice: smart valve sensors, such as those offered in ifm’s MVQ range. These work with a standard valve actuator, but continuously monitor the shaft position. The positional information can be accessed via an IO- Link interface, so that the control system can check, for example, for valve wear or failure to close fully because of the presence of debris on the valve seat.
April 2022 Instrumentation Monthly
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78
