Around the country as farmers are beginning their planting and fertilizing for spring the question sometimes comes up regarding fluctuations in the application rates as they go across the field. This could be the result of a few things. This blog will walk you through the steps to identify the cause of the bounces in rates and how to correct things to ensure you’re applying uniform product across the field.
First, some bouncing in rates occurs all the time. Many controllers don’t show this on the screen because of a feature commonly known as Rate Smoothing. When Rate Smoothing is turned on, if the actual Applied Rate is within the Rate Smoothing % bounds, the controller shows the Applied Rate as being locked on to the Target Rate.If the rate fluctuations are outside the Rate Smoothing bounds or if they seem excessive we need to determine why the fluctuations are happening. We need to determine if the fluctuations are caused by the controller sending fluctuating signals to the valve or if some other factor is the culprit.
First, inspect and clean the pump inlet strainer. Plugged or partially plugged strainers that restrict the flow to the pump may cause irregular pump output. Also, inspect the plumbing from the tank to the pump. Be sure that all clamps are tight and that there are no restrictions in the plumbing. Loose fittings here may not always leak, but they may allow air into the system which can create problems with getting a stable flowmeter reading.
Second, we want to see if we can get a stable flow reading when running the pump in Manual mode.
Run the system in Manual mode. This process varies from controller to controller. On a JD system, this could be Section Test or Calibrate PWM Limits test. On the JDRC 2000, it could be entering a Test Speed and running the pump manually from the Run page.
With the system running manually, watch the flow in GPM (gal/min).
The flow should be steady within a small range. For example, a fluctuation from 12.3 to 12.6 GPM is normal, but a fluctuation from 10-14 GPM is not. If there is only a small fluctuation here, skip to the Application Rate Fluctuates in the Field section below.
If there is a large fluctuation here in Manual mode, observe the system flow. Is the discharge a steady stream or is it pulsing? Are the flow indicator balls floating steady?
If visually the flow is steady, but display reports a fluctuation in GPM, inspect the flowmeter.
If visually the flow is unsteady, the flowmeter is correctly reporting a flow problem.
Look at the pump (Pump RPM sensor on JDRC 2000 is handy here). Is the pump turning steady or is it surging? If the pump is turning steady, then the hydraulic circuit is working correctly. If the pump is surging, there could be a hydraulic problem.
If you notice your application rate fluctuates in field, but in Manual Test mode is stable, this indicates the valve calibration needs changed. The system is surging because the Rate Controller is moving the hydraulic valve too much. You may be able to see this by running a test in AUTO mode with a Test Speed and a Target Rate. On the John Deere controller this would be a Nozzle Flow Check.
It is good to check the PWM Duty Cycle (DC%) here or while going across the field so we can see if the Duty Cycle is fairly stable or if it is jumping around. If the rate jumps around or if the PWM Duty Cycle jumps around, the basic fix is to lower the Valve Calibration number. This could be a Gain (integral or Proportional) or a Valve Response Rate. The example below is for the JDRC 2000. Other displays will vary.
Go to the Setup – System Settings – Control Valve Setup.
Lower the Valve Response rate by 5 or 10. You can do this on the go and see how this change affects the rate.
In extreme cases, it may be necessary to go to Advanced Tuning and adjust other parameters.
Sometimes fluctuation can be caused by having the Control Deadband or Allowable Error set too low. 2-3% is a typical setting for this. Try changing this to 4 or 5% if other steps have not settled down the rate.
Refer to the Tower John Deere Rate Controller Manual, Section G for additional troubleshooting tips and information. Use the PumpRight John Deer Rate Controller Manual, Section G for information regarding this product. For complete product information and set-up, please refer to the product manual for your system. Manuals for each SurePoint Ag product can be found on the Support Page. If further issues persist, please do not hesitate to contact us, we’re here to help and happy to do so!