Near Intersection of I-35 & I-90 Southern Mn. | Well, that's positive progress. Your next task is the calibration. I quite certain that 100HZ should be fine.
Here's more info on PWM. The PWM system puts out pulses that affect how far the plunger opens in the hydraulic valve which in turn controls the flow rate of the hydraulic oil going to the orbit motor which in turn runs the metering device.
If you choose 100 HZ. that means that each second is split up into 100 parts each 1/100 of a second in length. During each 1/100 of a second, the circuit could be complete all the time, it could be complete part of the time or complete none of the time.
If the circuit was complete all the time, the Duty Cycle would be 100% and the metering device would be running at full speed determined by the drive, wheels, auger whatever. If the circuit was complete none of the time, the Duty Cycle would be 0% and the metering device would not run at all. Normally the circuit is complete part of that 1/100 of a second and not complete the rest of the 1/100 of a second. This would mean that the plunger in the hydraulic valve would try to go fully open but then fully closed. Because this happens so fast, the plunger doesn't get fully open or fully closed and hovers somewhere in between.
The system compares the applied rate determined by the shaft sensor, meter cal, ground speed, implement width, product density etc. to the target rate that you have entered. It then makes adjustments to the Duty Cycle in an attempt to get the applied rate to closely match the chosen target rate.
These PWM choices for the Duty Cycle fall into a range of values. Commonly this is 0-255. Some systems actually allow you to view which number they are currently outputting to the control valve. Most systems remember the PWM value that they were sending when application stops for some reason (operator shut off Master etc.). When application resumes, the system will jump to that value and then make adjustments as necessary from that point.
This is where PWM shines compares to a servo valve. With a Servo Valve, the system does not "know" the position of the valve. When application resumes, the system cannot command the hydraulic valve to the previous setting. It must open the valve and watch the applied rate and when the applied rate exceeds the target rate, it then reverses and closes down a bit. This often results in oscillation and the system may be slow to "lock on" to the desired rate.
Zero Flow Offset is used with a PWM system. As mentioned above the values often range from 0-255. With many hydraulic systems, the smaller numbers produce flow but it is so low that the orbit motor does not turn at all. In other words it would be senseless for the system to even try to use those smaller PWM values. The Zero Flow offset is the number where the metering device is just on the verge of starting to turn. That means that no matter what, the system will never output PWM values below that point which again should help the system attain the desired rate more quickly.
Each product (fertilizer, granular chemical, etc.) has its own characteristics such as density, flowability etc. The Ag Leader system has you choose the product you are are using and consults its information about that product in order to convert the pulses in usable units such as pounds.
This means that you must do a catch test with each product that you plan on applying. Many times this is the actual product such as fertilizer. Sometimes in the case of certain granular products, the manufacturer will provide "dummy" products for the calibration process. These dummy products have the same density, flow characteristics etc. as the real product but are safer to handle. Ag Leader provides a Wizard to aid the operator in the product calibration process. The system will then retain the values it determines to be appropriate. If you use the same product again, you just choose the product from the product list and the attributes from the prior catch test are used.
Calibrating a granular system is more confusing than calibrating a liquid system. With a liquid system, a flow meter can be used to compute the volume. With a granular system that just counts the number of revolutions of the metering device, the amount delivered depends greatly on several factors.
The output from a flow meter is quite linear within a wide range. In other words, if the flow meter turns twice as fast, it indicates twice the flow.
With a shaft sensor and a granular product this is not nearly such a wide range. If the metering device speeds up past a certain point, the amount of material may actually decrease because there is not enough time for the product to fill in the metering wheel.
Edited by tedbear 6/7/2023 12:40
|
Strip till module on JD cart
