Testing a pressure or temperature transmitter requires a calibrator capable of measuring two different inputs. It needs to read the electrical signal from the transmitter (typically in either mA or V), and either a pressure or temperature from the process the transmitter is connected to. Reading both inputs is one thing, but understanding how they relate to each other is something altogether different.

For a closer look, let’s use a 0 to 100 psi, 4 to 20 mA pressure transmitter as an example. The pressure transmitter is set to output 4 mA when 0 psi is read, and 20 mA when 100 psi is read. Any number in the middle will output the appropriate mA signal based on the percentage of the 0 to 100 psi range. For example, at 50 psi (50% of the 0 to 100 psi pressure scale), the transmitter should output 12 mA (50% of the 4 to 20 mA scale). In this scenario, your calibrator will read 12 mA and 50 psi, assuming that the transmitter is working correctly. Doing the math to convert 12 mA to 50 psi is easy, but what if the calibrator is reading 17.42 mA and you’re testing a 0 to 3000 psi pressure transmitter? What pressure does that convert to?