Improved line frequency monitor.

摘要

The input line signal is input to a standard power transformer to reduce its voltage, and a Schmitt trigger is connected to the secondary of the power transformer. The Schmitt trigger detects the zero-crossing of the line signal voltage's AC waveform, producing a square-wave output representative of the input signal. This square-wave output is sampled by a microprocessor, driven at approximately 2.0 MHz, which measures the number of 2.0 MHz timing between the leading edges of each period of the square-wave signal, calculates the average line signal frequency, and notes the time of day as appropriate. Line signal voltage measurements can also be monitored. Keybaord input is provided for instructing the microprocessor with new averaging and measurement parameters. An alarm signals deviations beyond preset limits of frequency.