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Variable Rate Fertilizer Spreader Contolled with FMX (pics)
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tedbear
Posted 1/8/2018 10:57 (#6488837 - in reply to #6488793)
Subject: RE: Variable Rate Fertilizer Spreader Contolled with FMX (pics)


Southern Minnesota Between Freeborn & Wells
You may be unhappy with the performance of the Raven Fast Close valve in this application. The valve must close when application should stop but then open partially to start applying at the correct rate. This involves "hunting" as the valve must be opened to get the action started, then closed slightly to get on the target rate. The system has no way of knowing how far open the valve should be. The system purposely opens the valve until the calculated applies rate is high and takes a stab at turning it back down a little. This hunting may result in poor application until the system "settles" down on the correct position.

Many controllers can work with PWM hydraulic valves instead. Here the system sends out short shots of 12V to hold the valve partially open. When the power is removed, the valve closes and application stops. The advantage of this arrangement is that the control is done digitally (such as numbers between 0-127) and the system can "remember" what position was used last. It can quickly resume that position when application is started again. This generally results in better application since the system can jump to the correct position and doesn't need to hunt around. If the calculated applied rate doesn't match the target rate quite closely, the system changes the ratio of the ON time versus the OFF time of the signal to the valve. This means that the valve will hover at a different position in an attempt to get the applied rate to match the target rate.

Edited by tedbear 1/8/2018 11:00
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