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1. directly detect the voltage element, directly detect the voltmeter, and directly indicate the measured voltage value after detecting the measured voltage. The AC measurement of multimeter belongs to this category. In addition, this instrument is usually used as an indicator instrument in electronic equipment.
2. Amplification detection voltmeter Amplification detection voltmeter. The measured AC voltage is first amplified by a broadband amplifier, and then it is detected that the DC voltage drives the ammeter to deflect. Because of the first stage amplification, the sensitivity of input impedance is improved, and the scale nonlinearity and the drift of DC amplifier caused by the detection circuit working in small signal are avoided. However, the frequency range of the measured voltage is limited by the amplifier frequency band. Generally, the upper limit frequency of this voltmeter is megahertz, and the z small range is millivolts.
3. Detect the amplified voltmeter and detect the amplified VI-242-CX voltmeter. It converts the measured voltage into DC voltage after being detected by the detector, and drives the DC microammeter to deflect after being amplified by the DC amplifier. The frequency characteristic of this voltmeter amplifier does not affect the frequency response of the whole voltmeter, so the frequency range of the measured voltage mainly depends on the frequency response of the detection circuit, and its upper limit frequency can reach 1GHz. This kind of voltmeter is called high frequency millivolt meter.
Because the detection diode has a certain initial voltage when it is turned on, the scale is nonlinear, the input impedance is low, and the common DC amplifier has zero drift, so the sensitivity is not high. For example, the DYC-5 voltmeter falls into this category.
4. Modulated voltmeter. In order to make the micro-ammeter driven by the measured high-frequency voltage produce large deflection even if the value is small, it is required that the DC amplifier has high gain. But in general, the zero drift of high-power DC amplifier is serious, so modulation amplifier is used. Its working principle is to convert the measured high-frequency voltage into DC voltage through the peak detector in the probe and send it to the input end of the instrument; After range conversion and filtering, DC voltage is converted into AC (generally 50Hz) voltage by chopper, and then amplified by AC. Z is demodulated by the detector and becomes an amplified DC voltage corresponding to the input, which drives the micro-ammeter pointer to deflect, thus achieving the purpose of measuring high frequency. DA- 1 high frequency millivoltmeter belongs to this category.
As can be seen from the above discussion, the core of any type of AC voltmeter is the detector. The magnitude of AC voltage can be characterized by its peak value (u,), average value (u) or effective value (u). According to the three characteristics of AC voltage, voltmeter can be divided into peak voltmeter, average voltmeter and rms voltmeter. However, no matter what kind of voltmeter is made of geophone, the scale of its ammeter is generally measured by the effective value of sine wave, except in special circumstances. Therefore, special attention should be paid to this point when using analog AC voltmeter. That is to say, the general analog AC ammeter can only be used to measure sine wave voltage, but when the analog AC voltmeter is used to measure non-sine wave or distorted sine wave, its indicating value is meaningless.
5. Heterodyne Voltmeter For amplifier-detector voltmeter, it is difficult to raise the upper frequency limit due to the contradiction between the gain and bandwidth of broadband amplifier; However, due to nonlinear distortion and other reasons, the sensitivity of the detection amplifier voltmeter is limited. In actual measurement, it is often necessary to measure those voltages with wide frequency range, high frequency and weak signal level. The above two voltmeters are not competent, especially when measuring weak signals, which are limited by noise and interference.
The spectrum of noise is wide, but the measured positive voltage is single frequency. Therefore, in a certain high frequency range, the measuring line must have good frequency selectivity, so as to convert various voltages with different frequencies into video or intermediate frequency voltages with fixed frequencies; At the same time, because the band-pass filter of the intermediate frequency amplifier can be made very narrow, that is, in the case of high gain, the influence of internal noise is greatly weakened. The voltage measuring circuit composed of the above principles is the heterodyne voltmeter (also called measuring receiver).
2022- 12- 12 answer
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What is an average voltmeter?
Ordinary voltmeter first amplifies the measured AC signal, then detects it, and finally indicates the reading through DC meter. This is an amplification-detection voltmeter. Voltmeter is an instrument for measuring voltage, commonly used voltmeter-voltmeter symbol: V. There is a permanent magnet in the sensitive ammeter, and a coil made of wire is connected in series between the two ends of the ammeter. The coil is placed in the magnetic field of the permanent magnet and connected with the pointer of the ammeter through the transmission device.
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What kinds of analog AC voltmeters are there? What structural types do they belong to? What are their characteristics?
According to the different sequence of AC /DC conversion (detection) circuits, analog AC voltmeter can be roughly divided into the following categories. 1. directly detect the voltage element, directly detect the voltmeter, and directly indicate the measured voltage value after detecting the measured voltage. The AC measurement of multimeter belongs to this category. In addition, this instrument is usually used as an indicator instrument in electronic equipment. 2. Amplification detection voltmeter Amplification detection voltmeter. The measured AC voltage is first amplified by a broadband amplifier, and then it is detected that the DC voltage drives the ammeter to deflect. Because of the first stage amplification, the sensitivity of input impedance is improved, and the scale nonlinearity and the drift of DC amplifier caused by the detection circuit working in small signal are avoided. However, the frequency range of the measured voltage is limited by the amplifier frequency band. Generally speaking, the upper limit frequency of this voltmeter is megahertz, and the minimum range is millivolts. 3. Detect the amplified voltmeter and detect the amplified VI-242-CX voltmeter. It converts the measured voltage into DC voltage after being detected by the detector, and drives the DC microammeter to deflect after being amplified by the DC amplifier. The frequency characteristic of this voltmeter amplifier does not affect the frequency response of the whole voltmeter, so the frequency range of the measured voltage mainly depends on the frequency response of the detection circuit, and its upper limit frequency can reach 1GHz. This kind of voltmeter is called high frequency millivolt meter. Because the detection diode has a certain initial voltage when it is turned on, the scale is nonlinear, the input impedance is low, and the common DC amplifier has zero drift, so the sensitivity is not high. For example, the DYC-5 voltmeter falls into this category. 4. Modulated voltmeter. In order to make the micro-ammeter driven by the measured high-frequency voltage produce large deflection even if the value is small, it is required that the DC amplifier has high gain. But in general, the zero drift of high-power DC amplifier is serious, so modulation amplifier is used. Its working principle is to convert the measured high-frequency voltage into DC voltage through the peak detector in the probe and send it to the input end of the instrument; After range conversion and filtering, DC voltage is converted into AC (generally 50Hz) voltage by chopper, and then amplified by AC. Finally, it is demodulated by the detector and becomes an amplified DC voltage corresponding to the input, which drives the micro-ammeter pointer to deflect, thus achieving the purpose of measuring high frequency. DA- 1 high frequency millivoltmeter belongs to this category. As can be seen from the above discussion, the core of any type of AC voltmeter is the detector. The magnitude of AC voltage can be characterized by its peak value (u,), average value (u) or effective value (u). According to the three characteristics of AC voltage, voltmeter can be divided into peak voltmeter, average voltmeter and rms voltmeter. However, no matter what kind of voltmeter is made of geophone, the scale of its ammeter is generally measured by the effective value of sine wave, except in special circumstances. Therefore, special attention should be paid to this point when using analog AC voltmeter. That is to say, the general analog AC ammeter can only be used to measure sine wave voltage, but when the analog AC voltmeter is used to measure non-sine wave or distorted sine wave, its indicating value is meaningless. 5. Heterodyne Voltmeter For amplifier-detector voltmeter, it is difficult to raise the upper frequency limit due to the contradiction between the gain and bandwidth of broadband amplifier; However, due to nonlinear distortion and other reasons, the sensitivity of the detection amplifier voltmeter is limited. In actual measurement, it is often necessary to measure those voltages with wide frequency range, high frequency and weak signal level. The above two voltmeters are not competent, especially when measuring weak signals, which are limited by noise and interference. The spectrum of noise is wide, but the measured positive voltage is single frequency. Therefore, in a certain high frequency range, the measuring line must have good frequency selectivity, so as to convert various voltages with different frequencies into video or intermediate frequency voltages with fixed frequencies; At the same time, because the band-pass filter of the intermediate frequency amplifier can be made very narrow, that is, in the case of high gain, the influence of internal noise is greatly weakened. The voltage measuring circuit composed of the above principles is the heterodyne voltmeter (also called measuring receiver).