Circuit for measurement of alcohol concentration in aqueous solution for vehicle antifreeze solutions

摘要

The circuit measures the alcohol concentration in the contents of a tank (1) fitted with a screw cap (2) and a feedthrough (3) for a support (4) carrying a circuit board (5) near the floor (6). The board carries interdigitated parallel electrodes between which the capacitance is measured at regular intervals with AC voltage at low frequency. The capacitance depends strongly on the alcohol content and varies also with temperature, which is monitored by a sensor on the circuit board. A warning is signalled when the concentration falls below a desired lower limit, and when the freezing-point obtained from a look-up table nears the measured temperature.