How the installation position can affect the accuracy of pressure sensors

The accuracy of pressure measurement may depend on the mounting position of the pressure sensor. Special attention should be paid to this if the installed sensor is designed for pressures up to 1 bar.

Errors may occur if the position of the pressure sensor significantly differs from the position used during calibration at the manufacturer. At Keller, by default, pressure sensors are calibrated in a vertical position, with the sensitive element facing down (see illustration). If the operating organization installs one of these calibrated sensors in the opposite position (vertically, with the sensitive element facing up), measurement errors may occur during pressure measurement.

The reason is obvious – in the latter position, the actual weight of the oil filling of the pressure sensor will affect its accuracy. The diaphragm, housing, and filling liquid act on the sensor due to Earth's gravitational force. This effect is present in all piezoresistive pressure sensors but can cause significant error only in low-pressure ranges.

The lower the measured pressure, the higher the measurement error. When using a 100 mbar sensor, the measurement error is one percent. The higher the measurement range, the lower the effect. Starting from 1 bar pressure, this error becomes insignificant.

The magnitude of the deviation of the measured pressure depends on the filling oil and the type of diaphragm chosen. It is calculated by the formula for the horizontal position: P = pgh (Pa), where h is the height of the oil column (m), p is the density of the oil (kg/m3), g is the gravitational acceleration (m/s2).

Accordingly, for series 33X transmitters, when changing the position to horizontal, the deviation does not exceed 2 mbar. If it is necessary to mount pressure sensors in a position different from the recommended one, you must inform our specialists of this information when ordering for proper calibration of the devices.