In order to real-time and accurate access to environmental multi-dimensional information for greenhouse, design of greenhouse environment remote monitoring system based on wireless sensor network was constructed in this paper, which describes the overall structure of the system and the design of software and hardware, The construction of ZigBee network and the process of multi-dimensional information transmission were described. Through the seamless connection of the ZigBee coordinator, the wireless mobile network WIFI and the Internet, the remote real-time interaction and monitoring of the greenhouses' environmental data are realized. which provides an effective solution for remote monitoring of the greenhouse environment information.
The signal of the inductive type time-grating angular displacement sensor is essentially a triangular wave which is similar to a sine wave and contains various harmonic components. How to suppress the harmonic components of each frequency and improve the sinusoidal properties of the sensor signal is an important way to improve the measurement accuracy of the sensor. This paper proposes a modulation method for the sine regular change of the air-gap permeance of the sensor, and the basic model of the sensor is established. Two sensor models with different structural parameters are proposed, and the corresponding simulation and error analysis are carried out. The results show that the measurement error of the f2(θ) type sensor is ±25" in the range of 0°-6°. The sensor designed based on the method presented in this paper has an excellent effect on the sinusoidal enhancement of the signal and the suppression of the error component. It has an important significance for the design of the time-grating angular displacement sensor.
In order to remove the subdivide error and zero error to improve the measurement precision of time-grating displacement sensor angle measuring system, this paper proposed an error compensation method based on sparse sampling. Firstly, harmonic analysis and the error compensation model of the induction signal for time-grating sensor displacement angle measuring system is performed. Then, laser interferometer and time-grating sensor are used to synchronous sample positions at the poles and interior single-pole. Finally, the subdivide error and zero error of measurement are corrected by the compensation model. A time-grating sensor system with 72 poles are taken as subject to test, the result shows that:the peak to the peak value of the measurement error reduces from 138" to 2.69", this is to say, the accurate degree raised 51 times than before. Besides, this method provides full-circle error compensation with fully cancel the subdivide error and zero error based on sparse sampling which greatly improves the correction efficiency and measurement accuracy.
Angular displacement sensor plays an indispensable role in high-precision angular measurement and position feedback. With the development of sensing technology, some traditional incremental measurement methods have been unable to meet the requirements such as anti-interference ability, lossless of power-off data information and other factors that are susceptible to environment and mechanical system changes. Therefore, this paper has proposed a method based on combined measurement for absolute measurement of time-grating angular displacement sensor, which is mainly assembling two time-grating sensors that use different pole pair in a co-prime relationship on the axis. By this method, it can build high-precision and high-resolution sensor that meets vernier-subdivision principle in the form of a combination of "fine sensor and fine sensor". The sensor model and simulation experiment results are introduced by Inventor 2016 and ANSYS Maxwell 16.0, respectively. Then, the absolute position measurement method is validated by analyzing the initial phase of the induced electromotive force of the simulation experiment results with the mathematical method. Experiment results show the absolute measurement method is feasible.
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