Automatic recognition of different types of liquid level sensors

摘要

A system for indicating the level of a liquid in a container is operable with either an analog type liquid level sensor producing an output signal which varies linearly in magnitude with the level of liquid, or a digital liquid level sensor producing a cyclic pulse width modulated signal which varies in duration according to the liquid level. One or the other type sensor is connected to an analog wire and a microprocessor is programmed to detect positive and negative going edges of pulses on the wire and generate values representing the duration of the pulses. If pulse edges are detected, the microprocessor uses the generated values representing the duration of the pulses to access a conversion table and obtain a multi-bit value for energizing the display. If no pulse edges are detected, the magnitude of the signal on the analog wire is converted to an equivalent digital value which is applied to a second conversion table to derive a multi-bit value for energizing the display. The liquid may be a fuel and the container may be the fuel tank of a vehicle.