Video-camera-based sensor to measure gas/oil interface heights for pressures up to 17 MPa

This paper describes a gas/oil interface height sensor for determining the fluid head corrections when comparing a gas-operated pressure balance with an oil-operated pressure balance. The sensor can also be used to establish the balance point of the comparison from the rate of change of the interfac e height. In the sensor, a video camera views the interface within a transp arent pressure cell. The cell is made from a polished polycarbonate cylinde r, outer diameter 50 mm, inner diameter 10 mm, designed for a working press ure of 17 MPa. A safety shield surrounds the cell. The video camera magnifi es the image of the interface and a reference scale in the cell, allowing t hem to be viewed remotely. The sensor can measure interface heights with a standard uncertainty of 0.05 mm. Results of a comparison of pressure balanc es using the sensor show that over the range 1.6 MPa to 11 MPa, the balance points can be determined with a standard uncertainty of less than 4 Pa.