Patent ID: 7038473

Claim:
A method for measuring a fluid level by means of a rheostat having a resistor ( 40 ) that is connected in series at first and second end points ( 44 , 50 ) with a stabilized power supply (U o ) and a limiting resistor (R V ) and having a float operated electrical contact that slides over the resistor, the method comprising: (a) connecting the first and second end points and the sliding contact so that voltages (U F ) and (U E ) present between the electrical contact and the first and second end points, respectively, are to be determined; (b) calculating the value of the voltages (U F ) and (U E ), utilizing in each case the resistance value (R U ) existing between the sliding contact and the resistor; and (c) thereafter calculating the resistance value (R X ) of that portion of the resistor located between the first resistor end point ( 44 ) and the sliding contact, using calculations in which the contact resistance value (R U ) is eliminated from the measurement equations expressed by the values of the voltages (U F ) and (U E ).