Method and circuit arrangement for converting a measured voltage into a digital value

Claim 1

A method for digitizing a measured analog signal, comprising the following steps: (a) producing a compensation signal and adding said compensation signal to said measured analog signal to form a sum signal in such a way that a mean value of said sum signal becomes zero when said measured signal and said compensation signal are balanced, (b) said producing of said compensation signal comprising providing at least two auxiliary compensation values in the form of fixed frequency (f T ) square wave signals each having a keying ratio adjustable independently of the keying ratio of any other auxiliary compensation value, (c) modifying said keying ratios in response to a deviation of said mean value from zero in such a way that said mean value returns to zero to form a null signal, (d) integrating said null signal to form an integrated signal having said fixed frequency (f T ), (e) converting said fixed frequency integrated signal into a digital value, (f) subtracting a fixed value from said digital value to provide a null balancing value having an I-value, (g) supplying said null balancing value to a control circuit, (h) multiplying, in said control circuit, said null balancing value with a given integration factor (I-factor) to form a first product value, (i) adding said first product value to said I-value of said null balancing value, (j) multiplying, in said control circuit, said null balancing value with a given proportionality factor (P-factor) to form a second product value (P-value), (k) adding said I-value and said second product value (P-value) to form a PI-value, (l) wherein said modifying step is performed by adjusting said keying ratios of said auxiliary compensation values in accordance with said PI-value, and (m) using said I-value as a measure of said measured analog value.

Claim 2

A method for digitizing a measured analog signal, comprising the following steps: (a) producing a compensation signal and adding said compensation signal to said measured analog signal to form a sum signal in such a way that a mean value of said sum signal becomes zero when said measured signal and said compensation signal are balanced, (b) said producing of said compensation signal comprising providing at least two auxiliary compensation values in the form of fixed frequency (f T ) square wave signals each having a keying ratio adjustable independently of the keying ratio of any other auxiliary compensation value, (c) modifying said keying ratios in response to a deviation of said mean value from zero in such a way that said mean value returns to zero to form a null signal, (d) integrating said null signal to form an integrated signal having said fixed frequency (f T ), (e) converting said fixed frequency integrated signal into a digital value, (f) subtracting a fixed value from said digital value to provide a null balancing value having an I-value, (g) supplying said null balancing value to a control circuit, (h) multiplying, in said control circuit, said null balancing value with a given integration factor (I-factor) to form a first product value, (i) adding said first product value to said I-value of said null balancing value, (j) multiplying, in said control circuit, said null balancing value with a given proportionality factor (P-factor) to form a second product value (P-value), (k) adding said I-value and said second product value (P-value) to form a PI-value, (l) wherein said modifying step is performed by adjusting said keying ratios of said auxiliary compensation values in accordance with said PI-value, and (m) using said I-value as a measure of said measured analog value.

Claim 7

An apparatus for digitizing a measured analog signal in accordance with the follow-up principle, comprising a summing circuit having an input for said measured analog signal, a further input for a compensating signal and a sum output, first signal integrator means (2.1) having an input connected to said sum output, a comparator connected with one input to an output of said first signal integrator means, means for providing a saw-tooth voltage having a constant amplitude and a constant frequency (f T ) connected to another input of said comparator, an AND-gate having one input connected to an output of said comparator, oscillator (2.24) means providing a signal with a frequency (f t ) connected to another input of said AND-gate, signal counter means having an input connected to an output of said AND-gate, control circuit means for providing said compensating signal, said signal counter means having a digital output connected to a trigger input of said control circuit means, frequency divider means connected to said oscillator means and providing at an output a square wave with the frequency (f T ), said sawtooth voltage providing means comprising second integrator means (2.26) for converting said square wave into said saw-tooth voltage, said second integrator means having an input connected to said frequency divider means, change-over switching means for supplying said compensating signal to said further input of said summing circuit, said change-over switching means having control inputs connected to respective control outputs of said control circuit means for controlling the operation of said change-over switching means in response to control signals provided at said control outputs of said control circuit means (3), said change-over switching means producing auxiliary compensating voltages from reference voltages, and resistor circuit means connecting said change-over switching means to said further input of said summing circuit, said resistor circuit means providing a weighting ratio of N:1 for said auxiliary compensating voltages.

Claim 8

An apparatus for digitizing a measured analog signal in accordance with the follow-up principle, comprising a summing circuit having an input for said measured analog signal, a further input for a compensating signal and a sum output, first signal integrator means (2.1) having an input connected to said sum output, a comparator connected with one input to an output of said first signal integrator means, means for providing a saw-tooth voltage having a constant amplitude and a constant frequency (f T ) connected to another input of said comparator, an AND-gate having one input connected to an output of said comparator, oscillator (2.24) means providing a signal with a frequency (f t ) connected to another input of said AND-gate, signal counter means having an input connected to an output of said AND-gate, control circuit means for providing said compensating signal, said signal counter means having a digital output connected to a trigger input of said control circuit means, frequency divider means connected to said oscillator means and providing at an output a square wave with the frequency (f T ), said sawtooth voltage providing means comprising second integrator means (2.26) for converting said square wave into said saw-tooth voltage, said second integrator means having an input connected to said frequency divider means, change-over switching means for supplying said compensating signal to said further input of said summing circuit, said change-over switching means having control inputs connected to respective control outputs of said control circuit means for controlling the operation of said change-over switching means in response to control signals provided at said control outputs of said control circuit means (3), said change-over switching means producing auxiliary compensating voltages from reference voltages, and resistor circuit means connecting said change-over switching means to said further input of said summing circuit, said resistor circuit means providing a weighting ratio of N:1 for said auxiliary compensating voltages.