When you have a question about process automation that needs a short answer, let us know with #WishIknew and @Visaya! We’ll reply with a #WishIknew post. It’ll give a quick explanation, then some related articles, videos, or reviews if you want to know more.
I wish I knew how to calibrate a control valve!
This procedure will depend on the positioner you have installed on your control valve. The valve positioner receives data from the controller, then sends pressure to the valve to move it up or down.
If you have a pneumatic positioner receiving a signal between 3 and 15 psi, the procedure is entirely manual. Beyond that, the procedure can differ between vendors. For this discussion, we’ll use a Fisher pneumatic positioner and give you an overview of its calibration.
First, you need to check the operation cam. Do you have the right cam for your positioner? Did you install it correctly? Then, you need to check the feedback arm. You may need to follow certain steps to install the positioner on the valve, such as keeping the valve in 50 percent of the range when mounting the positioner.
You’ll also need to confirm you have the air supply connected for enough working pressure and the positioner output connected to the valve actuator. Yes, lots of steps before the actual control valve calibration, but you must do them all for your procedure to work.
Now we begin the control valve calibration! First, you need to supply 4 milliamps (mA) to set the zero position. Then, you’ll supply 20 mA and adjust the span using the flapper. The video below will explain the supply and output pressure to make sure you provide the right pressure to the actuator.
When you finish the span adjustment, check the zero. You may need to do it again. You’ll go back and forth between zero and span until you have the correct travel. Last but not least, you need to ramp up and down the valve’s travel, using 4, 8, 12, 16 and 20 mA.
That pretty much covers it, the process of control valve calibration. If you have more questions, drop a comment!