Soil moisture meter is a professional instrument for measuring soil moisture. By emitting a certain frequency of electromagnetic waves, electromagnetic waves propagate along the probe, return to the bottom, and measure the output voltage of the probe. The change of soil dielectric constant depends on the moisture content of the soil. From the relationship between output voltage and moisture, the soil moisture content can be calculated. In the same way, the soil moisture detector is also capable of measuring soil moisture, but the soil moisture detector is more focused on measuring soil moisture and soil drought, and has GPS positioning function. So how does the soil moisture meter do digital filtering at design time?
In order to reduce the influence of random interference on soil moisture meter measurement results and improve measurement accuracy, commonly used anti-jamming measures include hardware-based analog filter technology and software-based digital filter technology. Digital filter technology is due to its fast operation speed. Features such as easy modification of filter characteristics, low cost, etc. In the solution of low-frequency interference, random signal filtering and other aspects of the effect is significantly better than analog filter technology.
Different filtering methods are suitable for different use environments. The limiting filter method is mainly used to process slowly changing data, and the key is to select an appropriate threshold value.
The median filter method is suitable for removing the pulse interference caused by the accidental factor fluctuation and the sampler instability. It is not suitable for the rapidly changing data.
The arithmetic average filter method is suitable for filtering signals with random interference. The smoothness of the signal depends entirely on the value of N. When the value of N is large, the smoothness is high but the sensitivity is low.
The weighted average filtering method can adjust the contradiction between smoothness and sensitivity in the arithmetic mean filtering method by weighting coefficient; the moving average filter method can guarantee the real-time performance of the system when the sampling speed is slow;
The low-pass filtering method is a very effective filtering method when the target parameter is a very slowly changing physical quantity, but it cannot filter out interference signals higher than 1/2 sampling frequency;
The composite filtering method is compatible with the merits of the median filter method and the recursive average filter, and can obtain better filtering effects for both the slowly changing signal and the rapidly changing signal.
When the soil moisture measuring instrument is used, its measurement speed or sensitivity is not high, and its measurement accuracy is mainly required, that is, the stability is better at the fixed point measurement. For this purpose, the arithmetic mean filter method and the moving average filter are selected as the measurement. Instrument filter algorithm.
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