Working principle and development of frequency counter

Digital frequency meter is an indispensable measuring instrument in scientific research and production fields such as computers, communication equipment, audio and video. And it has a very close relationship with many electrical parameter measurement schemes and measurement results. Therefore, the frequency measurement is more important. This article mainly introduces the working principle of the frequency meter.

1.What is a frequency meter

A frequency meter is also called a frequency counter. It is an electronic measuring instrument that specifically measures the frequency of the measured signal. It is a commonly used measuring instrument that digitally displays the frequency of the measured signal. The measured signal of the digital cymometer can be a square wave, a sine wave or other periodically changing signals. It can also be called an intelligent counter, which uses decimal numbers to display the frequency meter of the measured signal.

　　Frequency is the reciprocal of the signal period, that is to say, the number of signal cycles completed per unit time, generally one second is the basic unit time.

　　The frequency meter is mainly composed of four parts: time base (T) circuit, input circuit, count display circuit and control circuit.

　　In the digital circuit, the frequency counter is a sequential circuit, which is mainly composed of a trigger with a memory function. It has been widely used in computers and various digital instruments. Not only requires the circuit to generate a signal with accurate frequency and high stability, but also can easily change the frequency.

　　2. Application of frequency counter

The most commonly used equipment for measuring frequency in the market is oscilloscope, spectrum analyzer and frequency counter. Compared with the other two, the frequency meter is the first choice when measuring frequency, because the frequency meter can not only capture the signal quickly and accurately. The measurement accuracy is also very high when measuring the change of signal frequency.

　　 Although the spectrum analyzer can accurately measure the frequency and display the spectrum of the measured signal, the relative measurement speed is relatively slow. The oscilloscope has lower measurement accuracy and larger error during frequency measurement.

　　 Therefore, frequency counters are widely used in aerospace, aviation, electronic technology, measurement and control and other technical fields.

　　In traditional manufacturing enterprises, the change of vigilant oscillator output frequency can be quickly captured. Users can quickly find faulty crystal oscillator products by using frequency counters to ensure product quality. In the measurement experiment, the frequency counter is used to calibrate the local oscillator of various electronic measuring equipment. In the frequency counter sub-wireless communication test, the frequency counter can be used not only to calibrate the master clock of the wireless communication base station, but also to analyze the frequency hopping signal and frequency modulation signal of the radio station.

　　 Its basic function is to measure sine signals, square wave signals and various other physical quantities that change per unit time. In the process of design, installation, and debugging of analog and digital circuits, digital frequency meters are often used because of the use of decimal number display, rapid measurement, high accuracy, and intuitive display.

　　3, the basic principle of frequency meter

The basic principle of 　　 digital cymometer is to use a frequency source with high frequency stability as the reference clock to compare and measure the frequency of other signals. The measured signal is processed by the amplifying and shaping circuit to output the pulse signal format that the counter can accept, and the frequency is the same as that of the measured signal.

The function of the amplifying and shaping circuit is to use the amplifying circuit to amplify the input periodic signal (sine wave, triangle wave) when the voltage of some input signals is small, making these input signals easier to measure.

In general, the shorter the gate time, the faster the measured frequency value will be refreshed, but the measured frequency accuracy will be affected. On the contrary, when we have higher requirements for the frequency value accuracy, we need to increase the gate time, and the longer the time. The longer the frequency value is, the more accurate it is, but the longer the corresponding frequency interval is. The gate time can be illustrated by an example. For example, the gate time of 1s means to calculate the number of pulses of the signal to be measured per second.

　　 The basic circuit of the digital frequency meter is composed of input channel, time base generation and change unit, main gate, control unit, counting and display unit. The intelligent counter accumulates the number of oscillations of the input signal to be measured within the gate time or the number of standard time signals in the time interval to be measured to measure frequency, period and time interval.

　　 The gate circuit is used to control the counting time and consists of a NAND gate. One end of the NAND gate is input by the second pulse provided by the time base circuit, and the other end is input after shaping by the signal to be measured. The working principle of the circuit is: the second pulse provided by the time base circuit is used as the gate control signal. When the gate control signal is high, the gate opens, and the shaped pulse signal enters the frequency divider circuit through the gate; when the gate control signal is low level , The gate is closed and the pulse signal is prohibited to pass.

　　 The gate circuit is used to control the counting time and consists of a NAND gate. One end of the NAND gate is input by the second pulse provided by the time base circuit, and the other end is input after shaping by the signal to be measured. The working principle of the circuit is: the second pulse provided by the time base circuit is used as the gate control signal. When the gate control signal is high, the gate opens, and the shaped pulse signal enters the frequency divider circuit through the gate; when the gate control signal is low level , The gate is closed and the pulse signal is prohibited to pass.

　　The time base circuit is used to generate a standard time signal. This standard time signal is the counting standard time of the control counter, and its accuracy determines the measurement accuracy of the frequency counter to a large extent. For example: the time base circuit provides the standard time signal T, and its high level duration is 1s. When the 1s signal arrives, the gate opens, and the counter starts counting when the measured pulse signal passes through the gate. When the 1s signal ends, the gate closes and the counter ends counting while keeping the original state unchanged. If the number of pulses recorded by the counter within 1s of the gate time is N, then the frequency of the measured signal = NHz. The role of logic control circuit has two aspects:

　　 (1) Generate a latch pulse to make the digital display on the display stable;

　　 (2) A clear pulse is generated to make the counter start counting from 0 for each measurement.

　　 4. Development of frequency meters

　　 Before the advent of the counter, the frequency meter was used to complete the frequency measurement, and the frequency meter was a coordination device with very low accuracy. The frequency counter is the first batch

　　 One of the first instruments to accurately measure signal parameters by digital means.

With the development of electronic technology, the various functions of frequency counters have become mature and perfect. In addition to frequency measurement, most frequency counters also integrate the following functions: frequency ratio, time interval, period, rise/fall time, phase, duty Ratio, positive/negative pulse width, sum, peak voltage and time interval average, etc. The highest level of extension of the frequency meter function is to integrate the functions of the modulation domain analyzer.

The frequency counter is an instrument for precise measurement of signal parameters in a digital way. It measures frequency, time interval, phase and the characteristics of event counting. Frequency counters and other similar products provide high precision and analysis capabilities for research and development, and provide high Efficiency and provide low cost and portability for maintenance.

　　5, frequency meter recommendation

　　 At present, the measurement range, measurement accuracy, measurement function and stability of the SYN5637 high-precision frequency counter of China's local property have been greatly improved compared with the traditional frequency counter. This frequency counter is equipped with a constant temperature crystal oscillator as the reference as standard. The frequency measurement resolution can reach up to 12 bits per second, and the measurement frequency can reach 24GHz. It has multiple data communication interfaces, intuitive data analysis and graphic display. Contact our staff if you need it.