PURPOSE: To improve resolution, by driving load cells by an AC current, applying the outputs to an adder, synchronously detecting the output of the adder and the signal of a reference voltage, respectively, converting the results into a DC voltage by an LPF, and converting the analog value to the digital value.
CONSTITUTION: Load cells LC1WLC4 are connected to secondary windings N21W N24 of a transformer T which is connected to an oscillator 1. The cells LC1W LC4 are arranged at the four corners of a load cell scale. An adding circuit 2 is connected to the output sides of the cells. The outputs of buffer amplifiers A1WA4 of the circuit 2 are inputted to an adder A7. An amplifier A5 imparts voltaged divided values of a reference voltage generating circuit. An amplifier A6 is provided for adjusting a zero point. The output of the adder A7 is inputted to an A/D converter 5 through a synchronous detecting circuit 3 and an LPF4. In a circuit 6, a special reference voltage winding N2B of the transformer T is provided. The output through amplifiers A8 and A9 is inputted to the converter 5 through a synchronous detecting circuit 7 and an LPF8. Thus low frequency noises are removed and the resolution can be improved.
MOCHIZUKI MASARU
YAMAMOTO SEIICHIROU
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