Calibrating a frequency meter using a radio and a stopwatch

Latest update time：2017-02-07

Reads：

Tools: A radio, a stopwatch, auxiliary circuits

Take the signal from the speaker, a switch, output to the above circuit, the circuit output end is connected to the start/stop button of the stopwatch, first use the frequency meter to measure the stopwatch crystal frequency, then clear the stopwatch, wait until the radio beeps for the quick time, close the switch, after the beep, the stopwatch starts timing, wait for the next hour on the same radio station to do the same operation, and let the stopwatch stop timing. Because the additional delay caused by the circuit parameters offset each other, the stopwatch reading error represents the error of the stopwatch crystal, the radio station timing accuracy is 10mS, and the minimum resolution of the stopwatch is also 10mS. If the stopwatch reading is 0.05S less per hour, it means that the crystal is 12.89ppm faster, and the frequency meter can be adjusted according to this value. If you pursue accuracy, you can wait for 24 hours, and the limit accuracy can be adjusted to 0.58ppm. Some means can be used to ensure the calibration accuracy, such as placing the stopwatch in a constant temperature box or even in an ice-water mixture.

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