In this paper, the DDS function signal source, digital oscilloscope and ordinary computer are used as the hardware platform. The LabVIEW 8.6 program is configured on the computer to control the function signal source to generate the sweep signal required for the test. The digital oscilloscope collects the sweep signal and the response signal of the test network. Finally, the computer frequency analysis and display, the amplitude frequency characteristics measurement is better achieved.
0 Preface
Frequency characteristics are an important characteristic of circuit networks. In the past, manual measurement methods were used to excite the circuit network by outputting sinusoidal signals at different frequency points, and then measuring the response of the circuit network. A test often takes a long time to complete. It takes only a few minutes to realize the frequency characteristic measurement of the circuit network by using a dedicated frequency sweeper, network analyzer, etc., but the general teaching laboratory is less equipped because of the high price of the equipment. The method of using microprocessor to control direct digital synthesis (DDS) sweep source can better test the frequency characteristics, but the design and fabrication of the sweep signal source, amplitude and phase detection circuits are difficult, and the implemented devices often exist. Shortcomings such as simplicity and unstable performance.
Direct digital synthesis (DDS) function generators with digital interfaces and digital oscilloscopes are widely used in the laboratory. The former can achieve high-precision amplitude and frequency switching, while the latter integrates functions such as data acquisition and software programming. It can provide users with various analysis functions and even save and process waveforms. In particular, most digital oscilloscopes offer built-in waveform amplitude measurements and waveform delay measurements. These instruments, combined with a virtual instrument design platform, make it easy to build automated test systems at low cost. In this paper, LabVIEW8.6 is used as the design platform to realize the frequency characteristic test of the circuit network by using the laboratory computer, the Shengpu F40 digital synthesis function signal source with digital control interface and the Tektronix TDS1012C digital storage oscilloscope. The realization of the system combines the advantages of the point frequency method and the frequency sweep method. The computer uses the RS 232 serial port control function signal source to generate a signal with constant amplitude and continuous frequency change with time as the sweep signal of the measured network acts on the network to be tested. The digital oscilloscope samples and processes the output signal and input signal of the network under test. The computer obtains the amplitude of the signal measured by the digital oscilloscope through the USB interface, and analyzes the amplitude-frequency characteristics of the circuit network through the user-friendly interface of LabVIEW 8.6 software. And show it.
1 system composition
Using the frequency sweep signal to dynamically measure the network under test, the frequency response characteristics of the network under test can be obtained. The ratio of the amplitude of the signal at the input and output of the measured network is the gain of the circuit. The overall block diagram of the system is shown in Figure 1. The computer controls the Shengpu F40 digital composite signal source to generate the sweep signal to the circuit under test through the serial port. The computer reads the RMS value collected by the digital oscilloscope through the USB interface, and uses LabVIEW 8.6 software to process the data and display the amplitude-frequency characteristic curve.
The TDS1000C-SC Series Digital Storage Oscilloscopes come standard with USB connectivity, 16 automatic measurements, limit testing, data logging and context-sensitive help, with bandwidths up to 100 MHz and a maximum sample rate of 1 GS/s, which is fully compliant with the design requirements of this document. When using a digital oscilloscope, in order to avoid aliasing, the sweep speed is preferably placed at a faster sweep speed. This article uses the AUTO SET method to adjust the sampling rate of the digital oscilloscope in time to match the current function generator. Output frequency to complete accurate sampling.
Ningbo Autrends International Trade Co.,Ltd. , https://www.ecigarettevapepods.com