Ratio meter for capacitive-type displacement converter

Claim 1

A ratio meter to determine the ratio of a first input signal representing the difference between two variables and a second input signal representing the sum of these variables, said meter comprising: A a span adjustment circuit responsive to the difference between the two variables to produce said first input signal; B a bias circuit having an adder to one input of which is applied the product of the first input signal and a first constant and to another input of which is applied the product of the second input signal and a second constant to produce a biased output which is the sum of these products; C a duty converter constituted by a comparator having a non-inverting input and an inverting input, and a switching circuit controlled by the duty pulse output of said comparator, the biased output of the bias circuit being applied to said non-inverting input, the second input signal being applied to said inverting input through said switching circuit in accordance with the duty pulse output of said comparator; and D a filter coupled to the output of said comparator to smooth the duty pulses to yield the desired output.