I have a Rosemount differential pressure transmitter in my plant which needs to be calibrated. Could you explain the calibration procedure for Rosemount DP transmitters?
Rosemount pressure transmitter calibration procedure? Sure can. Before we dig in, I want to differentiate calibration from an adjustment. If you have mounting, positioning, or line pressure effects only, then you can go with an offset trim adjustment to correct. However, if you actually need to calibrate your device, then you definitely need a reference device. Don’t worry, I’ll explain both.
If you have bad readings all over the place, then you probably need to calibrate. To do so, you’ll need a reference pressure device to compare the cranky device to. You’ll also need a pressure source to apply the desired pressure to both devices.
Connect the source to both high legs of the devices and leave the lower legs open to the atmosphere. All set? Good. Time to set your calibration points. Usually, you’ll set 5 points between 0 and 100 percent of the desired value, in steps of 25 percent.
Okay, you start at zero. Make a note of the output from both the reference device and your device. If you have an analogue device, you should also write down the signal. After getting both readings and the error for the zero value, then apply 25 percent of your total pressure range and compare both again. Repeat this process for 50, 75, and 100 percent of your range.
Now that you’ve gone all the way from bottom to top, it’s time to go back. After getting the data from the last point on the rising curve, go down to 75 percent again and repeat the process backwards.
And now that you have the increasing and decreasing curves and all your data recorded – you have taken notes on it all, right? – compare the curve from the reference device to the one for your device and see if the error falls inside the tolerance. If it does, your wonky little device passed! If it failed, don’t worry. We can help it improve its score.
If your device failed the calibration procedure, then you’ll have to do some adjustment so it can get the proper readings in your process. Depending on your device, you might do this locally through the zero-span adjustment, directly on your device. But some devices don’t have this option, so you’ll need a handheld for an assist. Regardless of the method you choose, you can follow these four simple steps, straight from the Emerson documentation itself, on how the Rosemount pressure transmitter calibration procedure is supposed to look like:
- Using a reference pressure device, apply the desired offset trim value (low-pressure value).
- Once the applied pressure has stabilized, use the transmitter’s offset trim command. The offset trim point is typically done at a zero point with no pressure value applied.
- Using a reference pressure device, apply the desired slope trim value (high-pressure value).
- Once the applied pressure has stabilized, use the transmitter’s slope trim command.
And there you go! Now you have your device calibrated. If you want to learn more about calibration principles, we have a video and an article on those.