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Pepperl+Fuchs Blog

Using AS-Interface to Monitor Valve Position

Posted by David Fink on Thu, Apr 30, 2015

An automated valve assembly typically consists of a rotary travel process valve, a pneumatic actuator, a solenoid valve and in some cases, a bracket to mount the valve to the actuator.  The operation of the valve assembly is accomplished by energizing and de-energizing the solenoid. But how can the operator in the control room tell if the valve is open or closed?

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By adding a valve position sensor to the assembly, you now have a feedback device that advises valve position electronically. Our valve position sensors mount directly to the top of standard pneumatic actuators, which normally are compliant to ISO 5211 / DIN 3337 Standards.

The valve position sensor is a dual inductive proximity sensor in that it has 2 individual sensing zones, one for detecting the valve when it is in the open position, the other for the closed position.  As all inductive proximity sensors require a metal target, the targets for the valve position sensors are pre-mounted to a rotary puck.  The puck contains 2 targets offset by 90 degrees and rotates with the valve.  The threaded holes in the top plate of the actuator conform to the standard in terms of location and size.  Our sensor mounts directly to these holes and an assured non contact sensing distance is maintained by the puck, which is mounted to the actuator’s output shaft.

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AS-Interface is a simple yet versatile bus network system which was designed for Actuators (A) and Sensors (S).  To operate a valve position sensor mounted to a valve assembly on an AS-Interface is really no different than operating any proximity sensor via AS-Interface.

There are 2 types of valve position sensors, one that is an AS-Interface intelligent sensor and one that is a standard sensor.  The intelligent version connects directly to the network without the need for an additional AS-Interface enabled I/O module.  It also provides a solenoid driver output, which means that if the solenoid you are using is rated at 2.5 watts or lower, it can be directly powered by the AS-Interface power.  It also provides for lead breakage and short-circuit monitoring via data bit D1.

Alternatively, you can use a standard valve position sensor and an AS-Interface I/O module to connect the sensor to the network.  If a solenoid consuming more than 2.5 watts is required, the solenoid can be run from aux power. This is typical in the case of a larger size valve in a high pressure application.

In lieu of a solenoid, you can control the compressed air flow to the actuator by using a pneumatic I/O AS- Interface module.  This is also a perfect application if instead of a standard actuator you are using a pneumatic cylinder to operate your valve.

AS-Interface can also alert you if your valve has encountered a mechanical problem such as an impingement of the valve’s closing element caused by foreign material in the flow stream or if the valve is somehow damaged. If the valve is neither open nor closed within the process’s normal cycle period, then the polling status data collected by AS-Interface will indicate the abnormal situation so corrective action can be taken.

If you have a valve that travels either less than 90 degrees or more than 90 degrees, we have developed adjustable range pucks to accommodate that situation.

When you need to detect the position of a manually operated valve via AS-Interface, an accessory bracket provides a pad to mount both the sensor and the puck.  The rotation of the valve is picked up by a mechanically linked shaft between the valve stem and the puck.  When the valve is opened or closed by a worker, the sensor detects the position and advises the position of the valve via AS-Interface.

If you are unsure as to which valve position sensor or puck to select or whether your pneumatic actuator can accommodate our sensor and puck, it's easy to connect with our technical experts to help you make the correct choice.

Questions about AS-Interface? Ask an Expert!

Topics: AS-Interface

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