Near Intersection of I-35 & I-90 Southern Mn. | The speed of the Raven Injection pump utilizes the Pulse Width Modulation concept. The motor is wired "hot' to a 12V source and the ground is Connected/Disconnected to control the speed of the motor and thus ultimately the output of the pump. This ON/OFF switching occurs very rapidly. This allows the motor to go from stopped to full speed or any other speed in between.
This may be something like 100 Hz. This means that within each 1/100 of a second, the circuit could be ON or OFF or some of each. The ratio of the ON time slice compared to the total time slice is called the Duty cycle. So the Duty cycle can range from 0-100%. If the ON time and the OFF time are equal, the Duty cycle would be at 50%. The system adjusts this ratio in an attempt to get the calculated applied rate to closely agree with the target rate.
If the system detects that the output as measured by the "flow meter" connector is producing a rate less than the desired target rate, the circuitry increases the "width" of the time that the system is connected to ground. This in effect raises the average voltage and the motor speeds up.
The analog sensor is called tach feedback by Raven. It consists of a small motor that is driven from the large pump motor by an O-ring belt. The small motor behaves as a generator. I think of this as being somewhat akin to a mechanical governor. Since it takes a fair amount of voltage to get the pump turning, the system "watches" the feedback from this generator as it is a tach of sorts of the rotation speed. As the pump gets up to speed, the tach feedback voltage increases which works with the control circuit to reduce the PWM to the motor so that it doesn't over speed.
At full speed this tach feedback generator should produce 9 Volts. As you have noted when this fails either due to a bad connection, failed generator or broken O-ring, the generator does not produce any output and the motor goes to full speed. To test this sensor, disconnect the connector and start the pump which should go to full speed. Put a voltmeter across the leads and observe the output voltage - it should be 9 volts.
In your above reply you mention that the analog speed sensor went bad and the motor ran full speed. That is what I would expect. The monitor indicated a rate of about 10X the desired rate which I would again expect. You then say that you take this to indicate that even the event of failure of the motor speed signal the flow signal is still valid. This would be true if the pump were operating properly in other respects. I want make sure that your operators don't get the idea that as long as the desired rate is shown that all is necessarily well.
Yes the digital speed sensor takes on the role of a flow signal and is why Raven uses the same connector as a their flow meters. Yes the vacuum sensor circuit is either open or closed. Again its purpose is to warn the operator of an obstruction which can cause the pump to produce less than its desired output.
Edited by tedbear 11/26/2018 07:33
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Ag Leader Direct Inject, injection pump inlet restriction
