| 摘要 |
A current measurement circuit with improved resolving power, a control method thereof, and a digital protection relay using the same are provided to increase the resolving power by amplifying a signal corresponding to difference between signals outputted from two sample and holds in turn. A current measurement circuit with improved resolving power is composed of first and second sample and holds(103,106) sampling and outputting an input analog signal according to a sampling cycle in turn and holding the sampled signal; a subtracter(110) outputting a signal corresponding to difference between the signals output from the first and second sample and holds according to a sampling cycle in turn; a multiplexer(120) selecting one of the signals outputted from the first sample and hold or the subtracter, and outputting the selected signal; a PGA(Programmable Gain Amplifier)(130) setting different gain values according to the signal outputted from the multiplexer, and then amplifying the signal outputted from the multiplexer at the set gain value and outputting the amplified signal; an ADC(Analog-to-Digital Converter)(140) converting the analog signal outputted from the ADC, into a digital signal; and a microprocessor(150) controlling the first and second sample and holds to sample and hold the input analog signal in turn. The microprocessor controls the multiplexer to select and output one of the signals outputted from the first sample and hold or the subtracter. In addition, the microprocessor controls the PGA to set different gain values according to the signal outputted from the multiplexer. |
