Quartz crystal frequency calibration method circuit

Everyone knows that the frequency stability of an oscillator made of quartz crystal is very high. However, how to determine the frequency of the crystal, judge whether the crystal is qualified, or select a crystal from many crystals to see whether the known frequency meets the nominal value, etc. is indeed a problem. problem. Here is a method of calibrating the frequency of quartz crystals. The frequency calibration circuit is simple and applicable. It can be used whether it is used to select crystals, check the quality of crystals, or calibrate frequencies. The frequency correction circuit is composed of integrated block CD4069, as shown in the figure below. When using it, first calibrate the test circuit. First connect the frequency meter to pin 4, and connect a standard crystal between points A and B. Then adjust and fine-tune C1 and C2 until the frequency meter reads the frequency value of the standard crystal. At this time, test The circuit calibration is completed. Then remove the standard crystal from points A and B and connect it to the crystal to be tested. At this time, the number displayed by the frequency meter is the standard frequency value of the crystal to be tested. If the frequency meter shows zero, it means the crystal is bad; if the frequency meter shows instability, it means the crystal to be tested is defective. This method has been used by manufacturers to detect crystals.