| 摘要 |
A seed counter for counting seeds flowing through a duct includes a light transmitter on one side of the duct and light receiver on the opposed side of the duct together with an electronic circuit effecting analysis of the signals received by the receiver to generate a seed count value which represents accurately as possible the number of seeds passing through the duct. The transmitter and receiver each comprise a channel-shaped body with diodes at a base of the channel with the channel filled with a translucent potting material facing into the duct. The circuit receives the signals which include for each passage of a seed or a clump of seeds a temporary reduction in light intensity which is converted to a reduction in voltage. Prior to start up the steady state voltage is measured and the current to the transmitter varied to provide a predetermined level of signal at the receiver. The circuit includes a DC compression circuit and a AC compression circuit at an amplifier so as to provide an output signal in a required amplitude range. An auto-biasing section maintains a steady state signal at a required level. The amplitude of the signal is compared to a threshold by generating a first signal which is offset by the threshold and a second signal which is delayed by a predetermined time period, the comparison generating a square wave output when one of the signals crosses the other signal. The seed counter is used in a monitoring system having a central monitor which can be operated to vary the parameters of the comparison circuit including the time delay. The use of the comparison circuit assists in determining the difference between a single seed and a clump of seeds passing the transmitter/receiver simultaneously.
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