Liquid level detecting and indicating system with coil type measuring device

Claim 1

A level detecting and indicating system for detecting a level of a measured object on the basis of a resistance changed in accordance with variation of the position of said measured object and indicating the level in response to a magnetic field produced to correspond to the resistance, comprising: power supply means with switching means for supplying an electric power and stopping the power supply; gauging circuit means coupled through said switching means to said power supply means and including a bridge circuit comprising at least variable resistor means and coil means, said variable resistor means being arranged such that its resistance is changed in accordance with the variation of the position of said measured object; potential followup circuit means for detecting the voltage at one end of said variable resistor of said gauging circuit means, said potential followup circuit means including a capacitor which is coupled through said switching means to said power supply means and charged with first and second time constants so that its voltage becomes equal to the detected voltage at the one end of said variable resistor means, said first and second time constants being switched from each other in response to first and second charging signals; timer circuit means including time measuring means for measuring a time period elapsed from a turning-on of said switching means, said timer circuit means generating said first charging signal to said potential followup circuit means before elapse of a predetermined time period from the turning-on of said switching means so that said capacitor is charged rapidly with said first time constant and generating said second charging signal thereto after the elapse of said predetermined time period so that it is charged slowly with second time constant; disturbance detecting circuit means coupled to one end of said capacitor of said potential followup circuit means and the one end of said variable resistor means of said gauging circuit means for comparing the voltages thereof with each other to detect a abrupt variation of the voltage at the one end of said variable resistor means and generating a control signal in accordance with the result of the detection; and potential control circuit means coupled to said disturbance detecting circuit means for controlling magnitude of the voltage at the end of said variable resistor means in response to said control signal from said disturbance detecting circuit to remove the abrupt variation of the voltage thereat.