The Pressure Balance Piston Gauge

The Pressure Balance (Piston Gauge).—The pressure balance was originally used as an instrument for the measurement of high pressures. In the past twenty years its performance and the theory underlying its operation have been refined, and it is not only accepted as a primary standard in its original application, but is also taking a place in applications hitherto reserved for the mercury column, i.e. in the measurement of pressures below 130 kPa. The pressure balance is unlikely to supersede the mercury column completely, but for many purposes it is more suitable than the latter because, to give one reason, of its relative portability. 

The effective area of a piston gauge has frequently been obtained by using it to measure the vapour pressure of carbon dioxide at 0 °C or at 0.010 C, the values of which are well established. Carbon dioxide is relatively easily prepared in a state of high purity, and a simple apparatus has been described for the calibration experiment. Its value, however, probably lies not so much in its use for calibration of the balance, since this can be done more easily and economically in a standards laboratory, as in its use in the opposite sense to demonstrate that the technique adopted for 

Piston gauges were originally developed for the measurement of pressures above atmospheric (the pressure measured is the gauge pressure - for the absolute value the atmospheric pressure must be added to the value 

The force F exerted by the total mass my, of the piston and its load (the weights) is given by 

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