What is a pressure sensor calibration?
Which methods of calibrating pressure sensors are available?
The usual methods of calibrating pressure sensors are based on exerting pressure on a volume of fluid or gas enclosed in a rigidly test chamber. This pressure is measured precisely and is compared to the output signal from the test object.
The pressure p is defined as a normal stress acting in all spatial directions. It is the resultant of a force F that acts vertically on an area A with uniform distribution.
p = F /A
By using this definition, the pressure (Pa = kg/(m*s2) can be backtraced via the force and area to the basic SI units of kilograms, meters and seconds. Pressure can be measured directly by converting it into a force with the help of a diaphragm or a cylinder with a defined area.
Static pressure sensor calibration using a deadweight tester
A deadweight tester uses traceable weights to exert pressure on a volume of fluid, with precise readout on a pressure measuring instrument. Pressure sensor calibration with a deadweight tester is one of the usual methods of calibrating pressure sensors: a counterweight is placed on a piston cylinder to compensate the pressure present under the piston. Deadweight testers are primary standards: the pressure generated by the deadweight tester is backtraced to the units of mass, time and length. Deadweight testers are used in calibration laboratories to calibrate transfer standards such as electronic pressure measuring instruments.
A deadweight tester can be used to build up the static pressure gradually and keep it constant. The pressure stages are defined by the mass of the weights. To determine the sensitivity of a piezoelectric sensor, the pressures of the individual stages are applied to the sensor, and the output signal from the sensor is compared with the reference pressure. (Illustration: stages of calibration)
This type of calibration is based on continuous loading of the pressure sensor. The pressure generator consists of a spindle that exerts pressure on a piston. This piston generates a pressure in the volume of oil which, in turn, acts on two sensors – one unit under test (UUT), and a backtraced reference sensor. The pressure is built up constantly and relatively slowly within 10 to 30 seconds. This is why this measurement method is called 'quasistatic'. It is a suitable method for calibrating piezoelectric pressure sensors. It is not suitable for pressure sensors with a short time constant, such as sensors with integrated electronics (IEPE).