Looking to improve spray coverage? Try pulse width modulation

Pulse width modulation maintains spray pressure and droplet size at different travel speeds

Nozzle guy’ Tom Wolf is often asked about ways to improve spray coverage. But as he says — borrowing a turn of phrase from Paul Simon — “there must be 50 ways to improve your coverage.”

And one of them is through pulse width modulation — a relatively new technology that’s “on the move.”

“I believe it’s going to continue to gain market share,” said Wolf of AgriMetrix Research and Training. “It’s a way of controlling flow rate through a hydraulic system. It basically intermittently shuts that flow to the nozzle off and allows you to vary the proportion of time that flow is off.

“But it happens very quickly. It’s almost an indistinguishable pulse.”

The system is designed to override pressure-based flow control.

“That basically means if you want to go faster, you have to have more flow to get higher pressure and finer sprays,” Wolf said at the All-Crops Breakfast earlier this month.

“This eliminates that need by giving you a constant pressure and a constant droplet size. Then you can vary your flow over a much wider range than you could ever do with plain pressure.”

Producers can set the pulse width at varying “duty cycles” ranging between 10 and 100 per cent, depending on travel speed.

“This results in your ability to control the flow,” said Wolf. “If you want to cut your flow in half, you would go to about a 50 per cent duty cycle. At a 75 per cent duty cycle — which is what most sprayers will be operating at — it will be on 75 per cent of the time. When you’re at the full load, it’s on all the time. There’s no pulsing whatsoever.”

All of the systems available on the marketplace, three currently, most of which are after-market retrofits, use an alternating pulse with every second nozzle at 180-degree offset.

“When one is on, the other is off. You never have everything off or everything on.”

But despite the benefits, not everybody needs it, he added.

“It depends on your travel speed and your travel speed fluctuations. If you’re driving 16 or 18 miles per hour and you also would like to drive 10 miles an hour sometimes, you can’t do it with a hydraulic pressure system. The only way you can do that is with this.

“But you don’t need pulse width modulation when it’s square, flat, and straight.”

More information about pulse width modulation can be found at sprayers101.com.

About the author

Reporter

Jennifer Blair

Jennifer Blair is a Red Deer-based reporter with a post-secondary education in professional writing and nearly 10 years of experience in corporate communications, policy development, and journalism. She's spent half of her career telling stories about an industry she loves for an audience she admires--the farmers who work every day to build a better agriculture industry in Alberta.

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