The definition of measuring range

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 on the vendor’s website.

See an example of a pressure device:

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

You can also calculate the measuring 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. Measuring or measurement range covers the total range of your device. However, you might not need that whole range for the measurement you are doing. Therefore, you should 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!

This measured range usually needs to be sent to a PLC, DCS, etc. In this case, we need a communication protocol to send it and ensure that our system will be able to understand it. For example for an analog output that works with 4/20 mA. We need to configure the device to match the values 4 and 20 to the measuring range of the devices and ensure that the PLC matches the same values. In the other hand, for digital protocols the only thing that matters is that the device and the system can “speak and understand” the same language, which means work in the same protocol. For example, Ethernet IP, Profinet, or HART.

Have some questions about measuring range? Contact our experts!

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