APPLICATION OF PRESSURE SENSORS TO THE MEASUREMENT OF SMALL LIQUID MASS FLOWS

New Technologies applied to the manufacture of sensors permit us to ob tain more sensitive devices of high linearity that, with suitable cond itioner circuits, can be incorporated into digital control systems by means of a control and acquisition data board, In this paper a method is described based on pressure sensors which can measure small flows ( in the range 0-10 cm(3) min(-1)) such as those generated in transporta tion through membranes. This problem was treated previously by means o f an automated flowmeter, using a programmable logic controller (Forte J et al 1990 Rev. Sci. Instrum. 61 1123-6). The main problem that we attempt to solve is that of on-line flow measurement, to know the flow at each moment and to take corresponding action in the experimental s ystem. Another method was used before (Molina C et al 1995 Rev. Sci. I nstrum. 65 2726-30) but, if we wanted to make measurements at differen t temperatures, we had to obtain another calibration curve.