| 摘要 |
A threshold transition detector for detecting a transition of an analogue signal across a threshold comprises an analogue to digital convertor (ADC) 404, a digital filter 406 and a comparator 408 arranged to receive the filtered data and switch an output of the comparator to a first state in response to a value of the data exceeding a first threshold (504, figure 5) and switch the output of the comparator to a second state in response to a value of the data being below a second threshold (502, figure 5). The transition detector may be used to sense zero crossings of the waveform from an electrical generator e.g. to measure frequency. Having two thresholds improves the response of the detector to signals with noise or distortion (figure 3). Also disclosed are methods for filtering digital data for display to reduce updating when consecutive values change by less than a predetermined amount and account for large jumps in value more quickly. |
