Overload protection circuit for liq. flow meter - has potentiometer across measuring cell to reduce voltage fluctuations caused by tube being empty or affected by foam

摘要

The liquid flow meter has a transfer tube (13) through which a liquid is passed. Mounted in diametrically opposite positions on the wall of the tube are two electrodes (11, 12). These electrodes receive voltages dependent on the flow of liquid through the tube and pass them to the inputs of a sensitive two-channel amplifier (16). The conductivity sensed by the electrodes is subject to substantial fluctuations caused either by the tube being empty or by the passage of foam within the liquid. To reduce the effect of these fluctuations, a potentiometer (17) is connected across the electrodes. Its resistance value is of the order of the inverse of the expected liquid conductivity at the electrodes. A further fixed resistor (18) may be connected across the electrodes.