Duty Cycle Apps and Spray Calculators

Normal spray calculators that most of you will be familiar with ask you to input a desired rate per hectare, speed and nozzle spacing.

A set of results will be displayed showing different nozzles at different pressures and you simply choose the nozzle most suitable. Some calculators, like ARAG/ASJ’s allow you to input a duty cycle. The idea is  that you pick a duty cycle that will be suitable for your machines operating frequency (10Hz, 15Hz, 30Hz, 50Hz or 100Hz) and the job at hand.

If you are spot-spraying for instance with lower frequency PWM equipment, it is advisable to operate as close as possible to the maximum duty cycle. You’re not going to be speeding up past your maximum spot spraying speed, you want maximum skip avoidance and have room for slow down as required. A duty cycle of 90% or 95% may work for you.

For general spraying the lower frequency PWM sprayers, a good practice is to optimise you Duty around 80% at your average travelling speed. You’ll be slowing down for headlands and the DC will back off to something more appropriate for turn compensation.

PWFM systems are a bit different. They have duty range between 10% and 90% or a bit less with larger nozzles. They use frequency modulation in addition to duty cycles to manage the rates. The Agrifac Strict Spray Plus nozzle advisor, does not ask for a duty cycle input. It's not necessary due to the broad range of performance and simply comes when the results are displayed.

It is very handy to know though, where on the DC scale your nozzle will be at a certain speed and pressure for perfect turn compensation. Something close to the middle is optimum 50% to 65% or so (slowing for turns) is usually a good fit as shown above.

Our Fantastic Nozzle range of Apps and calculators work a different way to the ASJ's and Agrifac's. With PWM and PWFM systems, we ask you to input only speed and nozzle spacing. Then using default pressure and duty cycles which we customise to your specific sprayer, we display a list of nozzles of various sizes and their rates per hectare. We also show Spray Quality and if the displayed nozzle does not suit, there are various other nozzles you can select from of differing Spray Qualities below the results.

From that point, simply adjust pressure and duty cycle to your liking until you achieve the rate per hectare and Spray Quality that you are looking for with one of the nozzles in the display, at a pressure and duty cycle that is appropriate for your machinery and the job.

You have all the information required to input your spray controller, namely rate, pressure and nozzle specification.

See what's on the menu at App Central.

Dave Young

05 October 2023