Expert’s answer :How to calibrate an instrument using an external standard
I’d like to answer your question in detail, but I’d need to know what type of product you have. However, I can give you an overview of calibration and how to use an external standard for it.
First off, to find out if the device under test still works properly, you need an external standard (or reference), a highly accurate device with known errors. You may also use other references, depending on where you’re calibrating.
For instance, you can calibrate a Coriolis mass flow meter in a calibration rig. A highly accurate scale compares the mass with the measurements from the meter under test. You might also use a prover, very common in refineries, or a portable calibration rig like those used by service companies.
Take a pressure transmitter, for example. When you need to calibrate, you must check the range at zero, 25, 75, and 100 percent, and then 100, 75, 25, and zero percent. Your external standard will measure the same pressure in parallel.
Once you have these values, you can find the hystereses. If necessary, you can do the offset trim and slope trim too. You can read more about those in this Visaya article.
If the instrument presents values between the limits, you’re good! Just print or save the calibration certificate with the values from the reference and the device under test. Hope that helps!