Pepperl+Fuchs Blog

Using AS-Interface to Control Pneumatically Operated Process Valve Assemblies

Posted by David Fink on Thu, Mar 05, 2015

15 common questions answered about AS-Interface and valve assemblies

1. What is the process valve assembly comprised of?

A typical assembly is a rotary travel valve such as a ball valve or butterfly valve mounted to a pneumatic actuator equipped with a dual position inductive sensor such as our model F31, a target which we call a puck, and a solenoid valve.


2. What does the inductive sensor detect?

The sensor detects if the valve is in the open position or closed position and operates like every other inductive proximity sensor.

3. How does the valve assembly operate?

The actuator is operated by compressed air which is supplied from a solenoid valve.  When the operator wants to open or close the valve, he has the control device such as a PLC or other supervisory system energize or de-energize the solenoid. When the electric coil on the solenoid valve is energized, compressed air is supplied to the actuator, which then moves a piston inside the actuator. This piston turns the process valve 90 degrees — opening or closing it.  When the coil is de-energized, the valve returns to its former position.

4. Where do you mount the sensor and target?

The sensor is easily mounted on top of the actuator using the threaded holes located in a NAMUR-compliant pattern. The target (puck) mounts onto the actuator accessory shaft, which turns with the valve and actuator.  The sensor has 2 detecting zones and the puck has 2 targets offset by 90 degrees. The appropriate sensor (#1 or #2) changes state when it detects either of the 2 positions of the valve, on or off.

5. Can you operate a valve assembly using an actuator sensor interface?

Yes, we have intelligent position sensors that offer both position sensing and AS-Interface direct connectivity. They also provide a solenoid driver output. There is even a data bit assigned for solenoid valve status.

6. So, in addition to detecting valve position, the device powers the solenoid as well?

Yes, as long as the electrical current rating of the solenoid does not exceed 2.5 watts @ 24 VDC.

7. What if I need to use a higher current solenoid?

We also have valve position sensors that are identical in size and mounting but operate as standard inductive sensors.  You use the sensor with an actuator sensor interface module to connect to the network.  You would then operate your solenoid from AUX power.

8. What advantages are there in using an AS-Interface intelligent sensor?

These sensors simplify your wiring, provide lead breakage monitoring, solenoid status, and fault condition monitoring.

9. If I look at a valve assembly equipped with a valve position sensor, can I tell the position of the valve?

Yes, in addition to the LEDs which indicate power and solenoid power status, there are also 2 LEDs which alternately illuminate when the valve is in the open or closed position. Also, the puck has high visibility flow direction indicators.

10. What if you have a valve that travels less than 90 degrees as a requirement of the flow conditions?

We have pucks that are adjustable to accommodate valve travel that is less than or more than 90 degrees. Additionally, regardless of whether the actuator is considered as small, medium, or large size, our sensor mounts the same way.  We have 2 puck sizes which direct mount to most standard actuators.


11. I have heard of situations where there is some kind of mechanical intrusion or a foreign object in the pipeline which prevents the valve from fully closing. Can a sensor detect that?

Yes, the sensor will advise if the valve is fully open or fully closed and will change state when either position is active. The LED for open position will illuminate when the valve is open and the LED for the valve closed position will illuminate when the valve is closed.  When neither LED is illuminated, then the valve is either in the process of rotating to its desired position or it may be stuck. The PLC will energize and de-energize the solenoid as the flow system requires, and the PLC will detect that the proper output has not been detected by the AS-Interface gateway. When the valve functions normally, the output of the sensor will again advise valve open or valve closed.

12. Is there a way to operate a pneumatic actuator on an AS-Interface network without using a solenoid?

Yes, we have a pneumatic I/O module VBA-4E2A-G1-ZE-P-S (AS-Interface powered) and also the VBA-4E2A-G1-ZE-PEXT-S (Aux powered). They can provide AS-Interface controlled pneumatic pressure to a standard pneumatic actuator or to 1 or 2 single cylinders and also feature extended addressing as do all of our valve position sensors.

13. How do I know if the valve and actuator I have will accept your valve position sensor and puck?

Our technical support team can help you with that — you can connect with them right from this blog!

14. What are the model numbers for the AS-Interface valve position sensors and pucks?

The sensors begin with: NCN3-F31...  The Pucks are either BT65A or BT115A. For the adjustable versions just replace the A with a B.

15. If I have a manually operated valve, can it be equipped with a valve position sensor and also be on the AS-Interface network?

We can supply a bracket to mount our sensors and pucks to most process valves and yes, the AS-Interface network can detect the valve position even though an operator has to manually cycle the valve using the valve’s hand-operated lever.

Questions about AS-Interface? Ask an Expert!

Bonus podcast!

Listen to a podcast from David Fink and Helge Hornis about how to use AS-Interface to monitor valve position.

Topics: Inductive Sensors, AS-Interface

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