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 what zero calibration is!

When you started looking into calibration, you probably came across two terms, zero calibration and calibration span. In this #WishIknew post, we’ll tackle zero calibration. If you’d like to know more about calibration span, then we have a #WishIknew explaining it here.

To understand zero and span in calibration, we need to look at the difference between the measuring range and calibration range.

zero calibration
Courtesy of Emerson

Measuring range covers the entire range that the device can measure, from the upper range limit (URL) to the lower range limit (LRL). When you look up a device on a vendor site, you’ll see the LRL and URL of that device.

However, let’s say you have a device that can measure -100 to 100 bar. But your application only goes from -20 to 50 bar. Therefore, you’ll calibrate the device to read only from -20 to 50 bar. In this case, you set your lower range value (LRV) to -20 bar and your upper range value (URV) to 50 bar.

Now, the zero calibration is the value where the device reads zero percent of the process value (PV), which is the LRV. So for this process, you have a PV of -20 bar.

Got it? Any questions, just drop a comment!

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