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Erratic Actual Rate / Can't Hold Target Rate (Control Valve Tuning)

Article ID: 98
Last updated: 24 Jun, 2019
Revision: 11
Views: 6625


My actual rate is jumping around, why am I not able to hold the target rate?


There may be multiple reasons why an applicator will not hold target rate. First, make sure the controller settings match the quick reference sheet that was provided with the installation kit. Also, make sure that the Rate Display Smoothing option is checked in Configuration Setup > Equipment Settings.

Once those have been verified, we may need to ensure the flow meter or encoder is operating normally, and has not been damaged. This should be investigated if the actual rate is occasionally lost completely; meaning the display is not receiving any rate feedback. 

However, if actual rate is always displayed, but will not lock onto rate, the Control Valve Settings may need to be adjusted. For CAN A Liquid/Dry this can be found under Configuration Setup > Controller Settings. For ISO Liquid this can be found under the gear icon > Control Valve Settings. 

For most cases, only adjusting one setting can smooth out erratic rate control: 

  • For Servo valves, the Response Threshold determines where the control channel switches between using Valve Response 1 and 2 speed settings. The default setting is 3. Making small (1-2 at a time) adjustments to this value is usually all that is required to fine-tune rate control.
    • ​Decreasing this value will have the overall effect of speeding up servo valve response.
    • Increasing this value will have the overall effect of slowing servo valve response.
  • For PWM valves, the Gain determines how aggressively the control valve responds when making rate change adjustments. Default value is 800. Making adjustments to this value is usually all that is required to fine-tune rate control. (Adjustments can be minimal (10 at a time) or large (100 at a time), depending on the overall effect you want the valve to have)
    • ​Increasing this value will cause the system to respond MORE aggressively in order to match target rate.
    • Decreasing this value will cause the system to respond LESS aggressively  in order to match target rate.

If more fine-tuning is required, please refer to your Feature User Guide for instructions and Control Valve Setting definitions.

Content last reviewed on: 06/20/2019
Reviewed by: AMJ