#WishIknew – What is measurement range?


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 measurement range is!

If you’re following Visaya this week, then you probably already know about measurement range, since we mentioned it in other #WishIknew posts on calibration and instrument range. In case you haven’t read those yet, we’ll break down those terms here.

Measurement or measuring range is the total range that the device can measure in normal conditions. When I say normal, I mean no overpressure limits (OPL) or maximum working pressure (MWP), things like that. You’ll usually see this range when you look up a device on the vendor’s website.

Courtesy of Rosemount – an example from the Rosemount™ DP Level Transmitters and 1199 Diaphragm Seal Systems

You can also calculate the measurement range by finding the difference between the upper range limit (URL) and the lower range limit (LRL) of the device.

Keep in mind the difference between calibration range and measuring range. Measurement range covers the total range of your device. However, in your process, you might not need that whole range. Therefore, you calibrate your device to read a range of values within the measuring range, and we call this your calibration range. Let’s see this in an example.

If you’re looking into the Cerabar PMP75 from Endress+Hauser, the website states that it can measure pressures from -1/0 up to 400 bar (measurement range). But your process only varies from 30 to 100 bar. So you calibrate your device to read between 30 bar, your LRV, and 100 bar, your URV. That gives you your calibration range. And that’s it!

Related tags: #WishIknew Calibration Measurement range Measuring range
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