Phase difference measuring apparatus and mass flowmeter thereof

摘要

A phase difference measuring apparatus for accurately measuring the phase difference (fine time difference) of two signals with the same frequency with a reduced number of bits for A/D conversion is disclosed. In addition to output signals of an upstream side pickup and a downstream side pickup of a mass flowmeter, an output signal of the upstream side pickup or the downstream side pickup is supplied to a comparator, a PLL circuit, an antialiase filter, a sample and hold circuit, and an A/D converter. These circuits quantize these signals and send the quantized signals to a band pass filter. The band pass filter extracts a predetermined signal component and outputs it to a DFT. The DFT performs complex Fourier transformation on the input signal. Thus, the phase difference between two signals with the same frequency (such as an upstream side pickup signal and a downstream side pickup signal) can be accurately detected with a reduced number of bits for each of the A/D converters. <IMAGE>