Design Of Wireless Radar Level Meter Based On FMCW Radar

The traditional way of ranging can’t detect the liquid level accurately within the container due to the impact of dust, moisture and temperature etc, while FMCW radar could work accurately and safely in complex environment. Besides, most level meters use cable transmission to communicate, the installation wiring of which is very complicated, whereas the Zigbee protocol based on the IEEE802.15.4which has the features of low power consumption, high-capacity and easy networking, realizes the wireless communication in industrial field. Therefore, combining the above two technologies, a wireless FMCW radar level meter system based on Zigbee is designed in this paper.Firstly, the principle of the FMCW radar ranging is introduced, the IF signal is analyzed from the frequency&time domain and the formula is deduced. Comparing several high-accurate measurement algorithms, the formula fitting algorithm suitable for this system is selected. Then, an overall design is put forward, which consists of DDS module, FMCW radar, signal acquisition and processing module, the Zigbee transceiver module.The DDS module is composed of microcomputer and AD9833to produce triangle wave for modulating FMCW radar; Signal acquisition and processing module consists of pre-process module and DSP processing module. In hardware development, the design and debugging of hardware high-pass filter and automatic gain control circuit is introduced. In software development, ADC module in DSP and FFT calculation process is described. A modified FFT algorithm library is used to calculate4096point FFT. Based on the results of FFT, the peak search and formula fitting is used to calculate the distance to be measured, then the measurement results can be displayed directly in the field and sent to the Zigbee module through the serial port; measurement results can be received and transmitted by Zigbee transceiver module and displayed on the upper machine.Finally, the system has been proved to process the IF signal and get the measurement results quickly after testing. The result shows that the accuracy reaches the design requirement, meets the demand of stable measurement in complex situations and reduces the difficulty of the communication wiring, which has certain application value.