With the rapid development of the times, there are more […]
With the rapid development of the times, there are more and more measurement methods for quartz crystals. It is no longer possible to judge only by appearance. The following are some methods for quartz measurement:
The general method is to make an oscillating circuit and connect the crystal to be tested to see if it starts to vibrate. If it starts to vibrate, the crystal is good, otherwise it is bad. A commonly used circuit is shown in the figure: the measured crystal and the field effect tube VT form an oscillator. If the crystal oscillator is good and the oscillator starts to oscillate, the signal is coupled to VD1 through C1, VD2 is rectified, and C2 is filtered. It is amplified by a compound amplifier circuit to drive the LED to emit light. If the transistor is damaged, the oscillator cannot start and the LED cannot emit light. The inductance L is used to prevent the oscillating signal from passing, and can only pass DC. LL represents the crystal to be measured.
In appearance, it is clean and tidy, without cracks, the pins are firm and reliable, and the resistance value is infinite. If the resistance measured with a multimeter is very small and close to zero, it means that the crystal under test has leakage or breakdown and has been damaged. If the measured resistance is infinite, it cannot be determined whether the crystal is damaged. The inspection method at this time: use a test pencil, insert the tip of the test pen into the line hole of the mains, hold one foot of the transistor with your finger, and touch the top of the test pen with the other foot. If the neon bubble is red, it generally means that the crystal is good. If the neon tube is not bright, it means that the crystal is broken.