Fluke Calibration’s differential pressure cell and null indicators are designed to separate two media physically while only contributing five parts per million uncertainty to the measurement process.
The differential pressure cell has two pressure chambers separated by a thin metal diaphragm. A difference in pressure in the two chambers causes a deflection of the diaphragm which is sensed by an LVDT circuit. The output from the LVDT is displayed on the indicator.
The differential pressure cell and indicator is capable of indicating when zero differential pressure exists between two systems to within five parts per million. However, it is not intended to measure the magnitude of a differential pressure.
Approved gas media in either chamber include dry air, nitrogen, CO2, and the noble gases and exclude hydrogen and oxygen. Liquid media in the top chamber may be virtually any nonconducting, noncorrosive liquid. Liquid media in the lower chamber can be virtually any noncorrosive media. For applications where water will be used in the lower chamber, Fluke Calibration offers a differential pressure cell manufactured from monel.
A variety of configurations can be provided, including a differential pressure cell equipped with a constant volume valve for deadweight gauge crossfloat calibrations.
A zero offset correction curve is supplied with all differential pressure cells and indicators, except those equipped with a constant volume valve since the differential pressure cell is re-zeroed at each pressure during a crossfloat calibration. This curve is a one-time process and the differential pressure cell and indicator do not require periodic testing or calibration.
During manufacture, all testing of the differential pressure cell is performed with nitrogen; therefore the instrument is supplied with each chamber dry. Once the user has committed either chamber with a liquid, changing that chamber to a different liquid is not recommended as it requires disassembly, cleaning and replacement of the diaphragm. This procedure should only be performed at the factory, and requires a new zero offset correction curve.