Crystal oscillator is a high-precision and high-stability oscillator. It is widely used in various types of oscillation circuits such as color TVs, computers, remote controls, and communication systems for frequency generators and clock signals for data processing equipment. And provide a reference signal for a specific system. 　　Quartz crystal oscillator is a kind of resonant device made by using the piezoelectric effect of quartz crystal (crystal of silicon dioxide). Its basic structure is roughly as follows: a slice (referred to as a wafer for short) is cut from a piece of quartz crystal at a certain azimuth angle. It can be square, rectangular or round, etc.), silver layers are coated on its two corresponding surfaces as electrodes, each electrode is welded with a lead wire to the pin, and a package shell is added. Quartz crystal resonator, referred to as quartz crystal or crystal, crystal oscillator for short. Its products are generally packaged in metal shells, but also in glass, ceramic or plastic packages

Aging refers to the change in the frequency of the crystal. It can change in both positive and negative directions. The aging process is caused by the change in the frequency of the oscillator used by the crystal.Aging will be mainly affected by two factors, namely pollution and pressure. Experiments have shown that contamination of crystal wafers will bring about negative changes, while excessive pressure will usually bring about positive changes. 　　When the crystal chip is mounted on the chassis, it is likely to be squeezed or twisted due to the support structure, which will bring pressure to the crystal chip, which will release or relax over time, leading to a positive frequency shift. When assembling the crystal, the proper equipment method and proper chassis help to reduce and reduce unnecessary stress. The installed crystal can be heat treated to accelerate the movement and alleviation of this pressure

We must first understand its operating frequency and adjust the frequency difference under the specified conditions, the reference temperature (25 ± 2 ℃) of the allowable deviation of the operating frequency from the nominal frequency, for a high-reliability system design, the quartz crystal oscillator The choice is very important, especially the design of a system with wake-up from sleep. If the selection is incorrect, it is easy to cause the crystal oscillator to start to oscillate very slowly or not at all. Perhaps it is because the excitation power of the supply voltage to the quartz crystal is reduced. This phenomenon is not particularly obvious at power-on reset, because the circuit is powered on. With enough disturbance, it is easy to establish oscillations. In the wake of sleep, the disturbance of the circuit is much smaller than when the power is turned on, and it becomes a little difficult to start the vibration. In the oscillation circuit, the quartz crystal can neither be over-excited nor under-excited. The choice of crystal must at least consider: nominal frequency, resonance frequency, load capacitance, excitation power, temperature characteristics, and long-term stability

Choose the standard quartz crystal from a manufacturer with proven quality, high reliability, promising development, and good reputation through practice. Obsolete or inferior quartz crystals cannot be used.The technical functions, quality levels, and operating conditions of the quartz crystal oscillator should meet the requirements of the planning circuit.In the case of satisfactory functional parameters, a quartz crystal with low power consumption, low thermal resistance, low loss angle, high power gain, and high efficiency should be selected.The best choice of domestic quartz crystal oscillator. The first choice is the quartz crystal that has passed the certification and conforms to the national standard; the quartz crystal that can be supplied stably through the test and meets the requirements; Youcheng advises to use other quartz crystals that meet the requirements

1. Turn on the multimeter first, turn the arrow of the multimeter knob to the 20 position of DC voltage, insert the red test lead into the voltage hole, and insert the black test lead into the ground hole.How to measure the quality of a crystal oscillator_how to use a multimeter to judge the quality of a crystal oscillator.2. Then prepare the board to be tested, find the position of the crystal oscillator, and find the two pins used by the crystal oscillator, which I marked with black lines.Test point 1: Ground the black test lead and connect the red test lead to a pin of the crystal oscillator. The measured voltage is 2.02 volts.Test point 2: Connect the black test lead to the ground and the red test lead to the other pin of the crystal oscillator. The measured voltage is 2.18 volts.