Design of signal amplitude eigenvalue obtaining system based on LABVIEW

introduction

　　LabVIEW has two basic windows, the front panel window and the flowchart window. The front panel window is used to set control objects and display objects, which is equivalent to the display screen or pointer of a conventional instrument; the flowchart window is used to write and display the graphical source code of the program, which is equivalent to the statements in language programming. It is composed of various modules that can perform certain functions connected by connecting lines.

　　The signal characteristic value represents some time domain characteristics of the signal with a numerical value, which is the simplest and most intuitive time domain description of the test signal. In the test system, some analog instrument meters are often used to indicate the characteristic value of the signal. After the test signal is collected into the computer, the signal characteristic value can be processed in the test virtual instrument, and the characteristic value of the signal can be intuitively displayed on its front panel, which can provide users of the virtual instrument with a quick way to understand the changes of the test signal. Now, a system for obtaining the amplitude characteristic value of periodic signals and random signals is designed based on LabVIEW.

　　1 Signal Amplitude Characteristic Value Analysis

　　1.1 Amplitude characteristic value of periodic signal

　　The amplitude characteristic values ​​of periodic signals are often expressed as peak value, peak-to-peak value, mean value, mean square value and effective value.

　　(1) Peak value xp and peak-to-peak value xp-p

　　The peak value xp refers to the maximum absolute instantaneous value that the signal x(t) may appear in one cycle, that is: xp=|x(t)|max.

　　The peak-to-peak value xp-p refers to the absolute value of the difference between the maximum instantaneous value xmax and the minimum instantaneous value xmin of the signal within one cycle, that is, xp-p=|xmax-xmin|.

　　The peak value and peak-to-peak value of the signal give the extreme range of signal change and are the basis for selecting the range and dynamic range of the test equipment.

　　(2) Mean μx

　　Mean of a periodic signal

　　It represents the average power of the signal. 

　　2 LabVIEW realizes the calculation of signal amplitude characteristic value

　　2.1 LabVIEW realizes the calculation of amplitude eigenvalue of periodic signal

　　The most simple and effective way is to use the Amplitude and Level Measurement VI in the Express VI. The path to reach it is Function → Signal Analysis → Amplitude and Level Measurement.

　　As shown in Figure 1.

　　The parameter dialog box is divided into 4 areas, namely the items for amplitude eigenvalue calculation, the results of the current signal amplitude eigenvalue calculation, the input signal preview window, and the windowed signal preview window. Among them, the most important is the item setting for amplitude eigenvalue calculation.

　　Use the Express signal generator to generate a simulation signal, and its parameter settings are shown in Figure 2. This is a triangle wave signal with DC offset and Poisson noise interference. The front and back panels of the test VI that uses amplitude and level measurement to detect all the amplitude feature values ​​that it can detect are shown in Figure 3.

　　2.2 LabVIEW realizes the calculation of random signal amplitude eigenvalue

　　Amplitude and level measurements are mainly used to process periodic signals, so the parameters that can be obtained do not include random signals and standard deviations. However, the configuration statistics in the Express VI can be introduced.

　　It is located on the same template as the signal amplitude and level measurements, as shown in Figure 4.

　　Now use the Express signal generator to generate a simulation signal, and its parameter settings are shown in Figure 2. This is a triangle wave signal with DC offset and Poisson noise interference. The front and back panel diagrams of the test VI that is configured to statistically detect all the amplitude feature values ​​that it can detect are shown in Figure 5.

　　The parameter dialog box is divided into five areas, namely the items for the required amplitude characteristic value statistics, the results of the current signal amplitude characteristic value statistics, the input signal window and the statistical extreme value, and the statistical sampling characteristics. Among them, the most important is the setting of the amplitude characteristic value statistics items. Now to obtain the amplitude characteristic value of the random signal, just select the root mean square, standard deviation, and variance.

　　3 Signal Measurement and Analysis

　　By using a signal generator to generate a simulation signal, you can set certain parameters of the simulation signal, such as the signal type, frequency, amplitude, offset and other parameter values. In addition, you can also change the noise type: binomial distribution noise, Gaussian white noise, Poisson noise, etc. By adjusting and setting the parameters of the simulation signal and observing LabVIEW make corresponding changes to its characteristic values, you can effectively and intuitively verify the analysis results from multiple aspects. For example, given a triangle wave signal with DC bias and Poisson noise interference, you can see the size of some characteristic values ​​of the current signal through the Express VI front panel.

　　4 Conclusion

　　The reliability of the system test and analysis results has been proven through actual measurements. The system can be used to conveniently conduct on-site testing and analysis, improve test efficiency and result accuracy, and get rid of the shortcomings of traditional test and analysis instruments, such as single function, high cost, and inconvenience in carrying.