| 摘要 |
An agricultural machine having a machine element supported by and movable relatively to a wheel-supported main frame with power means for moving it up and down relatively in small incremental steps, to vary the distance to ground level. The distance to ground is determined and electrical signals corresponding to the distance generated. A control circuit receives the signals and provides "up" and "down" pulses. A monitor-controller circuit receives the "up" and "down" pulses and transmits them to the power means for actuating an incremental step up or down for each pulse. The monitor-controller determines whether a preselected member of consecutive "down" pulses occur without an "up" pulse between them and within a short predetermined time period and actuates circuit disabling and override means only when the preselected number of "down" pulses occur within the predetermined time period; if so, further "down" pulses are prevented from passing to the power means, and both "up" and "down" pulses are nullified for a set time period, during which the machine element is moved toward or to its initial position.
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