APPARATUS AND METHOD OF MEASURING VARIABLE QUANTITY Russian patent published in 2011 - IPC G01D21/00 

FIELD: physics.

SUBSTANCE: apparatus for measuring a variable quantity by converting the derivative of the quantity has a differentiating measuring transducer for said quantity, which is connected by its output to first and second input terminals of an active electric filter which is based on three-terminal device and an operational amplifier, capacitors of equal capacitance and resistors with equal resistance. Said apparatus also includes electronic switches with a control unit, a comparator, a time relay and a command device, as well as additional resistors. The method of measuring the variable quantity involves converting its derivative using a filter with a transfer function for which the numerator is of the first order and the denominator is of the second order. The output signal of that filter is measured, where all roots of the transfer function of such a filter are real and negative. Poles of said transfer function are multiples and the modulus of its zero is twice greater than the modulus of the poles. The variable quantity is measured with regular repetition of the beginning of the measurement process at zero initial values of the filter variables generated at the instant the output signal of the filter passes through the zero value. Each subsequent repetition of the beginning of the measurement process, except the first, is carried out at the moment when the number of passages of the output signal of the filter through the zero value, after the previous such passage, is equal to a given odd number.

EFFECT: low maximum error when measuring a variable quantity, shorter time for which the measurement error enters the acceptable interval after the beginning of the measurement process at a non-zero value of the measured quantity.

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