The soil moisture rapid measuring instrument is a professional instrument for measuring soil moisture. The instrument transmits electromagnetic waves of a certain frequency, and electromagnetic waves are transmitted along the probes, returning to the bottom and returning, detecting the voltage outputted by the probe, because the change of the dielectric constant of the soil depends on The water content of the soil can be calculated from the relationship between the output voltage and the water. In this way, the measured soil moisture can meet a large part of the requirements, but for some standards in scientific research, the accuracy of the soil moisture measured by the probe needs to be improved. But we can do some work on the basis of the soil moisture meter to make the results achieve higher precision.
When using the probe to measure soil moisture, it will be affected by the environment of the soil. The error measured in the saline-alkali area is the largest. In order to minimize the occurrence of this error, digital filtering is added in the soil moisture meter. Technology to reduce the interference of environmental factors on soil moisture determination, commonly used digital filtering algorithm finite amplitude filtering method, median filtering method, arithmetic average filtering method, weighted average filtering method, moving average filtering method, low-pass filtering method and composite Filtering, etc., one of the many ways is most suitable for the measurement of soil moisture:
1) The limiting filtering method is to obtain data by comparing the difference between the two sets of data and the maximum allowable error value. Mainly used to process data with slower changes.
2) Median filtering method by measuring N sets of data. N is the base number, and the average value is taken as a result of the measurement of the soil moisture temperature meter. Only accidental factors can be ruled out, and those that change rapidly will have no effect.
3) Arithmetic average filtering method, the arithmetic average filtering method is to take N consecutive sampling values ​​for arithmetic average, and is suitable for filtering signals with random interference, which is affected by the data group.
4) Weighted average filtering method, the difficulty of this conversion comparison, the advanced measurement N group data is multiplied by the weighting coefficient, and the cumulative sum is performed.
5) Moving average filtering method, the sliding average filtering method is to sample only once, compare this value with the value of the past sampling, and average the value. The real-time performance of the system can be guaranteed when the sampling speed is slow.
6) Low-pass filtering method, low-pass filtering method is to use the differential equation of the analog low-pass filter to represent the difference equation, so that the software algorithm can be used to simulate the function of hardware filtering, which has a certain effect on those slow changes.
7) Composite filtering method, the composite filtering method combines two kinds of digital filters with different filtering functions to form a composite filter, which has a good buffering effect for fast or slow signals.
By using the above method, and then comparing with the results measured by the soil temperature monitoring recorder or the soil moisture monitoring system, it is found that the arithmetic average filtering method and the moving average filtering are used as the filtering algorithm of the measuring instrument, which can be used in the environment. The interference of each parameter is directly reduced to the lowest, and the accuracy of the value measured by the soil moisture meter is the highest.
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