A phase-measurement error compensation technique suitable for automation

A phasemeter is presented which incorporates zero crossing detectors (ZCD's) with hysteresis. The system performance is good when the ZCD's are fast bipolar comparators, but worse when they are operational amplifiers whose switching times are heavily dependent on both the amplitude and frequency of the input signal. To improve the performance a new error correction technique is introduced, which has been successfully implemented in the laboratory and is suitable for use in automated instruments. The technique is based on measuring the erroneous phase angle, then isolating the error sources and measuring the error angle separately. The difference between the two measured values is the correct phase. Thus in general, using a computer in conjunction with lower quality hardware can give the same results as higher quality hardware; a result which can be useful and cost effective in many computer-based systems.