Near Intersection of I-35 & I-90 Southern Mn. | The Ag Leader 4000451 cable is used with Ag Leader's Liquid Product Control module. It has a branch to connect to a Raven Flow Meter and a two pin control branch.. The two pin control branch can control Raven control valves such as a Raven butterfly type valve or ball valve for inline or by-pass control. This branch can be used to produce a PWM type of control which can be used with a PWM hydraulic valve, small DC motor or a larger DC motor by using an external Motor Driver. The behavior of the control circuitry is determined by choosing the appropriate control type when creating the configuration.
The Liquid Product Control module is often mounted on the implement or within the cab in Self-Propelled rigs, The system also needs another module in the cab itself, One choice would be the Auxiliary Input Module with an external switch or the Ag Leader SC 110 CAN switch box.
I happen to use such a system on my Hagie STS-12 sprayer. It is quite similar to what you propose. In my case the oil flow changes the speed of a centrifugal spray pump and I have 7 section valves.
I have a box on the floor which contains both an Ag Leader Auxiliary Input Module and an Ag Leader Liquid Product Control Module. A wiring harness connects the original Hagie section switches and Master switch to the Auxiliary Input Module. This is how the operator conveys their boom intentions to the system.
The Liquid Product Control module is connected to a flow meter and the PWM hydraulic valve that controls the hydraulic spray pump. This cable is equivalent to the one you asked about. My Liquid Module is also connected to a wiring harness that controls the 7 ON/OFF valves on the booms.
As you are likely aware, PWM (Pulse Width Modulation) uses the concept of completing a circuit for a brief period of time and then breaking it for a brief period of time. If the output were observed on an oscilloscope, you would see 12V pulses of a certain width each followed by a gap of 0V. This happens very rapidly like 100 times/second. This is called the Frequency. The ratio of the "ON" time to the time period is referred to as the Duty Cycle. The Duty Cycle can vary from 0% (completely OFF) to 100% (completely ON). In normal operation the Duty Cycle is somewhere in between. It is possible to view the current PWM output while applying which can be helpful for troubleshooting.
The PWM control valve is fairly simple in operation. A magnetic field is created during the "ON" portion of time which causes a spring loaded valve to open. If the Duty Cycle is 0%, the valve remains closed and no oil flows. If the Duty Cycle is 100%, this is equivalent to a constant 12V and the valve opens completely. When the Duty Cycle is somewhere between, the valve cannot go from completely closed to completely open instantly and ends up "hovering" somewhere in between. To increase the flow, the system increases the Duty Cycle (longer ON time) and the valve opens slightly more.
When setting up the PWM configuration you are presented with some choices. This allows you to tailor how the PWM system behaves for your situation. One of the questions deals with Zero Flow Offset. In your case, that would be the Duty Cycle value where your piston pump just starts to turn. This value creates an absolute lower limit for the PWM Duty Cycle. You set it by trial & error by observing the pump behavior with different Zero Flow Offset values. It the Zero Flow Offset is too high, the pump would never stop. If the Duty Cycle were set quite low or at zero, the system would stop but might take an unacceptable amount of time when application is again called for.
Another question deals with "what to do when all sections are shut off". The choices amount to 1) Stop the action by reverting to the Zero Flow Offset or 2) Go to some other Duty cycle.
In your case you would only have one section and you would want the Duty Cycle to revert to the Zero Flow Offset value so your positive displacement pump stops.
In my case with the sprayer, I want my spray pump to continue to pump while turning around on the Headlands to provide agitation and good flow when application begins again. Originally I didn't understand the ramifications of this setting and inadvertently had it set to revert to stop. The result was that when starting a new pass, the initial flow rate was too low resulting in underapplication until the system "caught up". Changing the setting and adjusting the Standby Duty Cycle solved that problem.
To set my Standby Duty Cycle. I observe the Duty Cycle needed under normal conditions of ground speed and rate. I can then set my Standby Duty Cycle with that value as a reference.
If I set the Standby Duty Cycle rather low then the system will be slow to get back up to rate when application resumes.
If I set the Standby Duty Cycle quite high, the application rate might start out high and then ramp down. My spray tips prevent extreme overapplication. A bit of trial & error helps determine a good Standby Duty Cycle value.
This brings up your other question of do you even need boom valves. In general I would say no. Your pump would go to an "OFF" status based on auto swath, an implement switch or operator intervention on the switch box.
However if you wish to be able to split the implement up in sections you might want to use section valves. It would also be advised to provide some type of pressure relief valve in the output from your positive displacement pump. This would be set somewhat higher than is necessary for normal application. Normally that pressure relief would be closed but could pop off to allow excessive flow to return to the tank under unusual situations. Another thought is agitation. If agitation is necessary with your product an arrangement would be necessary to handle it.
Edited by tedbear 12/12/2024 10:17
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Running a piston pump with integra, cable clarification
