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A frequency meter, also known as a frequency counter, is an electronic measuring instrument specially designed to measure the frequency of the signal being measured. The frequency meter is mainly composed of four parts: time base (T) circuit, input circuit, counting display circuit and control circuit.
Frequency is the reciprocal of the signal period, that is to say, the number of cycles completed by the signal per unit time, generally taking one second as the basic unit time. There are many ways to measure frequency, according to its working principle, it is divided into passive frequency measurement method, comparison method, oscilloscope method and counting method. The counting method is essentially a comparative method, and the most commonly used method is the electronic counter method. Electronic counter is one of the most common and basic digital measuring instruments. Passive frequency measurement
Passive frequency measurement methods mainly include resonance method, bridge method and frequency-transformed voltage method.
1). Resonance method
2). Bridge method
Any bridge whose balance condition is related to frequency can be used for frequency measurement, but the frequency characteristic of the bridge is required to be as sharp as possible.
There are many types of frequency-measuring bridges. Commonly used ones are Wien bridge, resonant bridge and double T bridge. For some contents, please refer to relevant books. [1]
3). Frequency-voltage conversion method
Frequency-voltage conversion method frequency measurement is to first convert the frequency into voltage or current, and then use a frequency scale voltmeter or ammeter to indicate the measured frequency. Mainly divided into Lissajous figure method and periodic method.
Frequency measurement is performed on the oscilloscope according to the number of cycles of the Lissajous figure or signal waveform. This method can measure frequencies ranging from audio to high frequency signals. [2]
counting method
Directly count the number of pulses of the measured signal per unit time, and then display the frequency value in digital form. This method has high measurement accuracy and rapidity, and is suitable for the needs of different frequencies and different precisions. There are two ways to measure the frequency of the electronic counter: one is the direct frequency measurement method, that is, the number of pulses of the measured signal is measured within a certain gate time; the other is the indirect frequency measurement method, such as the periodic frequency measurement method.
Due to the rapid development of digital circuits and the popularization of integrated circuits, counters are widely used. The use of electronic technology to measure frequency has a series of outstanding advantages such as high precision, eye-catching and intuitive display, rapid measurement, and easy to automate the measurement process, so this method is currently the best.