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In the process of open-pit coal mine production, mining and transport loss of excavator accessories, iron and other large ferromagnetic objects with the coal into the crusher, will result in crusher jammed, broken tooth damage and even motor burn down and other serious production accidents, based on the principle of low frequency eddy current detection can effectively detect ferromagnetic objects, the characteristics of the ferromagnetic objects open-pit mine secondary crushing plant movement monitoring research. Taking SANDVIK's CR610/14—35 double-tooth roller sieve crusher as the experimental object, the mechanism of the detection system was analytically modeled according to the principle of electromagnetic mutual induction. The results of modeling and experiments show that the eddy current generated by ferromagnetic objects is weak due to the existence of strong background noise. The signal to noise ratio(SNR)can be improved by optimizing the parameters of the detector and planning the path of the detector. According to the characteristics of the experimental object, the maximum SNR was obtained when the ratio of the radius of the metal to the detection distance was 0.048, and the ratio of the coil radius to the detection distance was 0.044 5. In the 1~35 kHz segment, the SNR is higher in the low frequency band than the high frequency band. The initial value and response time of the path entering the detection area perpendicular to the detection axis have obvious advantages over the path entering the detection area parallel to the axis.

Under environmental stresses, trees often change their morphological and physiological components to acquire the most limited resources. In northeastern forest region of China, the decomposition and mineralization of litters occur slowly due to low temperature, which often results in forest trees suffering from nutritional stress. With pot culture in greenhouse, this paper studied the effects of nitrogen stress on the physiological and morphological components of Fraxinus mandshurica seedlings. The results showed that under N stress, the net uptake rate of nitrogen and phosphate by the seedlings decreased, while their nitrogen and phosphate use efficiency were higher than those of the seedlings supplied with 8 mmol x L(-1) or 16 mmol x L(-1) of nitrogen during the early growth stage. When suffering from N stress, the leaf mass ratio of the seedlings reduced, with specific leaf area and root mass ratio increased. The relative growth rate increased with the increasing N concentrations supplied to the seedlings during the whole growth period. Under N stress, the net assimilation rate decreased, which resulted in the decrease of total biomass, and the root/shoot ratio was significantly higher than that of the seedlings supplied with 8 mmol x L(-1) or 16 mmol x L(-1) of nitrogen during the early growth stage. There was no significant difference during the late growth stage.