By:  Erdal Ozkan

Whenever I give a presentation about the need to calibrate a sprayer and how to do it, there is always someone asking me this same question: “I have a rate controller in the cab that regulates the flow rate of the sprayer regardless of the changes in sprayer ground speed. I just enter the gallons per acre application rate, and the controller does the rest, just like cruise control in a car. So, should I still calibrate the sprayer? The answer is, Yes, a calibration should be done. Although the rate controllers do an excellent job of regulating the flow rate of nozzles to keep the application rate constant regardless of the changes in travel speed, a manual calibration at least once a year is needed for two reasons: 1) to ensure the rate controller is functioning properly, 2) the rate controller is not forced to operate outside the pressure operating range for the nozzles on the sprayer boom. Let me elaborate on both points I made and share with you the reasons why a manual calibration of a sprayer is a good idea.

1. If you are stopped by a police officer for speeding, telling the police officer that the car was in cruise control set to the speed limit will not get you out of getting a ticket. Cruise controls go bad, and so will the rate controllers. That is why it is best to manually check the flow rate of nozzles to make sure the gallons per acre application rate you enter on the controller matches the gallons per acre rate provided by the nozzles.
2. Your controller may be in good shape, but if the ground speed sensor is giving inaccurate data to the controller, it will not work accurately. For example, if the speed sensor works based on revolutions of the tractor wheels, the ground speed determined may not be accurate, because of the slippage that may occur under some ground conditions. Even the tire pressure being off just a few psi may change the tire revolutions per minute leading to erroneous travel speed readings. Continue reading →