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To overcome the shortcomings of wired natural gas intelligent alarming system, a natural gas intelligent alarming system based on wireless sensor networks was designed. The components of the system and its working principle were described in detail. Its nodes use a density sensor for data collection, wireless transmission chip CC1101 for data short-range wireless transceiver and the wireless network, and MSP430F449 microcontroller for controlling core. Nodes communicate with the background host through serial interfaces. The system can achieve density of natural gas dynamically and comprehensive real-time monitoring. Node has a dual function as terminals and routers, in addition to data processing, but also for other nodes to forward the density data storage, management, and integration, and taking in collaboration with other nodes to complete some specific tasks. The system has some advantages such as low cost, low power consumption and small size, which has a good application prospects.

For solving level alarm of high pressure vessels or corrosive liquid vessels, a new non-contact level alarm device was designed by using ultrasonic wave. The attenuation characteristics of ultrasonic echo wave remained in the wall of vessels is analyzed when the medium in vessels is liquid or gas. A new method for measuring fixed-point liquid level was proposed by using this principle, and the system of level alarm was proposed. In this way, the transducer is only needed to touch to the outside surface of the wall of vessels. The device is very suitable for measuring fixed-point liquid level of high pressure vessels or corrosive liquid vessels, and has the merits of high sensitivity and reliability.

According to the characteristic of short-wave frequency-hopped (FH) communication, an OFDM/FH system based on iterative demodulation and decoding is proposed. By combining the advantage of NSD technique and iterative demodulation and decoding, the method could compensate the SNR loss caused by differential modulation and improve the reliability of short-wave communication and improve the system reliability. Numeric simulation results show that the proposed method could effectively improve the system BER performance and reach good transmission efficiency.