PRODUCTIVITY is always front of mind for farmers and the rise of big self-propelled boomsprayers helps you get more hectares sprayed per hour.
Without accurate nozzle control, however, speed variations can cause patches of over or under-dosage which will impact crop yield.
Two of the most advanced nozzle control technologies available are Pulse Width Modulation (PWM) and HARDI H-SELECT.
"It's a fairly common misunderstanding that H-SELECT is just HARDI's PWM offering," said HARDI Australia's product manager Steve Lancaster.
"But the two systems are actually very different.
"Pulse Width Modulation works by switching nozzles on and off several times per second.
"This reduces the amount of fluid leaving the nozzle, which maintains the target set rate where the boom is moving slowly.
"H-SELECT takes another approach entirely.
"It automatically switches between nozzles to deliver the right rate with constant fluid flow.
"Because it uses an array of nozzles, it is called Multi-Step technology."
PWM systems are defined by two factors - pulsing frequency and duty cycle.
The pulses are driven by an electric solenoid with a fixed frequency.
If the controller opens the nozzle for 80 per cent of those pulses to meet the set rate, that's a duty cycle of 80pc.
Mr Lancaster said best practice was to set up the sprayer for an 80pc duty cycle at your normal forward speed.
"In a turn, the speed at different points across a large boom will double between the inner and outer tips," he said.
"So you need capacity for the duty cycle to increase at one end and slow down at the other.
"But it can't get too low or it might leave gaps in the coverage."
On a 15Hz system an 80pc duty cycle equates to 12 opens per second (15 x 0.8 = 12).
At 20 kilometres an hour, that means the nozzle will spray for 300 millimetres and shut off for the other 70mm.
One way to reduce the gap and extend the speed range is a blended system.
This is basically two PWM installations with offset nozzles.
The two cycles then overlap, blending the nozzle outputs for more complete coverage.
Multi-Step systems such as H-SELECT combine up to four nozzles per nozzle body to maintain a set rate as the boom speed changes.
"The nozzles are selected in whatever order and combination best suits the forward speed of the boom at that point," Mr Lancaster said.
"This selection is continually updated against the speed of the boom and switches instantaneously with micro-second blending to avoid coverage gaps.
"Having up to 16 possible combinations makes four nozzles accurate over a very wide speed range.
"You could think of it as 'tiered spraying on steroids', with up 16 tiers instead of the usual three.
"In fact, H-SELECT will work for virtually any speed and boom width and we've got customers using it on 54 metre booms with great results."
While high frequency solenoids and blending have made PWM installations more flexible, the constant on-off switching means they are unsuitable for air induction nozzles and not ideal for producing very coarse droplets.
The continual flow of a Multi-Step system avoids both of those issues.
However, the number of nozzle configurations means a Multi-Step system needs careful planning.
"Whether you prefer PWM or a Multi-Step system like H-SELECT can depend on your sprayer setup, boom width and spraying speeds," Mr Lancaster said.
"But just knowing they're not the same thing, is a good place to start."
