| 摘要 |
An ultrasonic height control system for an agricultural machine utilizes a transmitter/receiver transducer system (MUS, LL, L, CA, CB, R, RR) with signal processing in a microprocessor (P). The transmit-receive time elapse is used in further signal processing (including averaging of samples (Stage C)) to determine the measured height of the transducer above the soil. If the height is not correct then an error signal Ear can be used through automatic control (Fig 7 and 5 D.) to adjust hydraulics on the machine to reset the desired height. When a field is other than firm and level, a problem exists in monitoring the received relected signal (Rx) and analysing accurately the point in the signal trace which is representative of the true leading edge of the reflected signal because of background noise and varying degres of soil reflectivity. The envelope (A1) of the amplitude of the received signal is monitored and first and second time values (t3 and t6) are recorded respectively when the amplitude envelope exceeds a threshold value and subsequently when the amplitude envelope falls below a threshold value. Computation is made of a reference time value (tref) falling between the recorded time values and this reference time value is used in the microprocessor (P) for providing an error signal (E) for machine adjustment purposes. Preferably, a delay controller (Fig 7) delays a machine adjustment for a time inversely proportional to the magnitude of the detected error and monitors for persistence of the error. |
