Nonlinear distortion meter , INI, ( harmonic coefficient meter) - a device for measuring nonlinear distortion coefficient , SOI (harmonic coefficient) of signals in radio engineering and electronic devices.
Content
Application of nonlinear distortion meters
Most often, INIs are used in the low and sound frequency range when monitoring and testing high-quality amplifiers of sound range, sound reproducing and recording devices, for controlling the modulating paths of transmitters and other similar equipment.
Classification
According to the method of processing and presentation of measurement information, the receivers are divided into analog and digital .
In analog devices, the signal under test is processed by analog devices — analog filters, amplifiers, etc. These devices are fundamentally inherent in the error caused by the analog signal processing method, so nonlinearity and other errors in the measurement channel introduce distortions into the signal under study.
In digital devices, the analog signal directly at the INI input is digitized by means of an analog-to-digital converter with a sampling frequency and the number of quantization levels sufficient to measure distortion with a given accuracy. Further processing of the array or stream of digitized samples to obtain the result of the measurement is performed by mathematical methods of some digital computer - a computer or microprocessor . In such an INI, the analog measurement path ends at the ADC.
Both classes of INI have their advantages and disadvantages, for example, analog devices have a larger frequency range of measured signals compared to digital INI and are usually simpler and cheaper. Digital INIs, as a rule, have greater accuracy, but narrower the frequency range of the studied signals. The preferred choice of a particular method and instrument depends on the nature of the signal being studied and the accuracy required. For some applications any method is suitable.
Analogue INIs
By the principle of operation, analog NIIs are divided into selective and spectral.
Selective Analog INIs
In selective PIDs, the first harmonic is either suppressed by a rejection filter and the sum of the upper harmonics is measured, or vice versa, the first harmonic of the signal is selected and its amplitude is measured with a band-pass filter . The result of the measurement after a simple calculation is presented in one of the forms, based on the mathematical definitions of the CED.
Analogue INIs with a rejection filter are the simplest, since it is relatively easy to suppress the 1st harmonic by analog methods. Typically, such an INI consists of a notch filter tuned to a frequency of the 1st harmonic with automatic gain control (AGC) and a rms meter . The AGC standardizes the sensitivity of the instrument when the signal voltage changes when measuring the amplitude of the first harmonic, and the voltmeter measures the root-mean-square value of the voltage of higher harmonics, usually up to the fifth harmonic inclusive. An analog or digital indicator is used as a reading device. Many such NIIs additionally perform the function of a rms wideband voltmeter.
Spectral Analog INIs
In spectral instruments, the amplitudes of the line spectrum of the periodic signal under study are measured. Based on the measured amplitude of the 1st harmonic and the measured amplitudes of higher harmonics, the SOI is calculated.
Simple computations of SOI based on measurements of amplitudes of harmonics are usually performed inside the instrument. The final result of the measurement is displayed on an arrow or digital indicator.
Digital INIs
In devices of this type, mathematical processing of the samples from the ADC signal from the ADC is performed. The type of mathematical processing and processing algorithms can be very different, but usually they are reduced to spectral methods, as in spectral analog NII. For signal samples using the digital Fourier transform (usually the Fast Fourier Transform - FFT algorithm is used), the line spectrum of the signal is reconstructed and the SOI is calculated from the spectrum.
Digital devices are usually complemented by various user-friendly service functions - for example, a visual graphic representation of the measurement result, statistical processing, etc.
Some examples
- C6-5
- C6-11
- C6-12
- SK6-18
- CK6-20
- CK6-20a
- СК6-220
- MEGURO MAK-6571W
- HM8027
- HP 4333A
Main standardized characteristics
- First harmonic operating frequency range
- Permissible measurement error
- Measuring range
- Sensitivity and Dynamic Range
Literature and Documentation
Literature
- Handbook of radio measuring instruments: In 3 tons; Ed. V.S. Nasonov - M .: Owl. radio, 1979
- Shkurin G. P. Reference book on electrical and electronic measuring instruments - M., 1982
Regulatory and Technical Documentation
- GOST 8.331-99 GSI. Harmonic Ratio Meters Methods and means of verification and calibration
- GOST 8.110-97 GSI. State verification schedule for means of measuring harmonic coefficient
- TU 4-DLI2.770.005TU-85 Measuring instrument of nonlinear distortions of SK6-13
- TU 4-LT2.008.002TU-83 Analyzers of distortion of television signals K3-2
Links
See also
- Radio measuring devices
- Nonlinear distortion factor