Understanding the process of performing a calibration can be intimidating even after you have all of the correct equipment to perform the calibration. The process can vary depending on calibration environment, device under test accuracy and the guideline followed to perform the calibration.
The calibration process consists of comparing the DUT reading to a standard's reading and recording the error. Depending on specific pressure calibration requirements of the quality standards, one or more calibration points must be evaluated and an upscale and downscale process may be required. The test points can be at the zero and span or any combination of points in between. The standard must be more accurate than the DUT. The rule of thumb is that it should be four times more accurate but individual requirements may vary from this.
Depending on the choice of the pressure standard the process will involve the manual, semi-automatic or fully automatic recording of pressure readings. The pressure is cycled upscale and/or downscale to the desired pressure point in the range, and the readings from both the pressure standard and the DUT are recorded. These recordings are then reported in a calibration certificate to note the deviation of the DUT from the standard.
As mentioned, different guidelines detail the process of calibration differently. Below are some of the standards that highlight such differences when calibrating pressure transducers or gauges:
IEC 61298-2 defines the process for “Process measurement and control devices.” The section on "Test procedures and precautions" defines the number of exercise cycles, the number of measurement cycles and test points required.
DKD-R 6-1 “Calibration of Pressure Gauges” defines different process for different accuracy classes of devices. It also defines exercise cycles, number of cycles and points and also minimum times on how long to hold the pressure before taking a measurement.
EURAMET Calibration Guide No. 17 has basic, standard and comprehensive calibration procedures depending on the uncertainty of the device being calibrated. It requires additional information like the standard deviation of the device’s output at each pressure point.
Keep in mind specific industries may require their own calibration processes.
