Automatic Scaling

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?

You could take out a calculator and figure out that 17.42 mA is 83.875% of the 4 to 20 mA scale, and therefore, the equivalent pressure should be 2516.25 psi (83.875% of the 0 to 3000 psi pressure scale). Doing this for each point is a time consuming process that can be avoided by using an ASC-400 with the automatic scaling option.

The ASC-400 has an upper and lower display, which can be set to read whatever parameter you are testing. In our example, the lower window would be set to pressure and the upper window to mA. Once scaling is selected on the upper window, you simply enter the details of the transmitter you are testing into the ASC-400, and it will automatically convert the mA signal to the equivalent pressure reading. The main number on the upper display will be the scaled reading, and the actual mA value will also be included in the upper right corner. This removes all conversion work, allowing you to easily compare the known pressure reading (from the process) with the converted or scaled pressure reading (from the transmitter’s mA signal). This saves time, and more importantly reduces potential calculation errors.