Improved recording vacuum balance

Abstract

This paper describes the construction of a recording electromagnetic vacuum balance with an improved form of control circuit. It was originally designed for the gravimetric determination of adsorption isotherms and measurements of the rate of adsorption on porous solids, but it has proved equally suitable for other applications where rapid changes of sample weight have to be recorded against time. The control system is entirely electronic, and the entire beam assembly and suspension is housed in a vacuum jacket of total capacity of less than one litre. The variation of load corresponding to full-scale deflection of the pen recorder can be varied between 10 and 600 mg with a reproducibility to better than 1%. An electrical zero shift allows the starting point of the scale range to be adjusted by about 50% of the full-scale deflection to allow for variations in the initial weights of samples. The zero setting and the sensitivity of the balance have negligible long-term drift.