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 calibration span is!

To understand calibration span, let’s go back to all the ranges an instrument can have.

When you buy a pressure transmitter, for example, you have the instrument range, which is the pressure range the device can support. This range covers the overpressure that might occur in the device.

The measuring range covers the values where the transmitter works properly, omitting the overpressure zone. The lower range limit (LRL) and upper range limit (URL) define this range.

calibration span

Now, inside the measuring range, you’ll find the calibration span, the range in which your device will be working, depending on your application. The calibration span covers the difference between your upper range value (URV), the maximum value your transmitter can read, and lower range value (LRV), the minimum value the device can read. So there you go!

You should also know that each instrument has a minimum and maximum calibration span it can support. If you go below or over these limits, you’ll lose accuracy in your readings.

Make sense? Let me give you an example, just to make it clearer.

Let’s say you want a pressure transmitter with a measurement range of -100 to 200 kilopascals (kPa). This device can measure pressures as low as -100 and as high as 200 kPa. If your application just requires pressure between -20 to 50 kPa, then this will be your calibration range. Your calibration span is the URV-LRV. By the numbers: 50 – (-20) = 70 kPa. Therefore, you get a calibration span of 70 kPa, which falls inside the span range (10 to 200 kPa).

Now does it make sense? If not, then drop me a line and we’ll post again!

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