The design and implementation of a fully automated crossfloat system for the comparison of piston gauges in both gauge and absolute measurement modes

摘要

The pressure crossfloat is a well established method for comparing the output of piston gauges with various media. The crossfloat is the most common method for determining the area of a test piston-cylinder relative to a reference piston-cylinder. The traditional crossfloat procedure is a tedious manual process that is highly dependent on operator skill, patience and experience. Due to the need to access the masses to make small mass adjustments, operation is normally gauge mode only. In order to meet a high demand for low pressure, gas operated piston gauge systems, DHI has designed and implemented a fully automated crossfloat system over the range of 9 kPa to 7 MPa. The intent of the system is to be able to perform unattended crossfloats to determine the test piston-cylinder performance characteristics and determine effective area in either absolute or gauge mode. The crossfloat station was put into regular operation in late 2006 and has exceeded the expectations of its designers. The automation is made possible by the use of two automated mass handling systems_[4] and a low differential pressure transmitter used to determine the final equilibrium point between the two piston-cylinders. This paper describes the design of the automated calibration system, the challenges of its implementation and the results of numerous crossfloats performed over six months of automated operation.