Spread Testing Guide




This guide is intended to help drivers taking vehicles fitted with Transpread ComputerSpread Controllers to properly present their vehicles for Spread testing.

We have produced this guide because we continue to hear horror stories from customers whose vehicles have failed to obtain a satisfactory spread test result even when the vehicle has been pre-tested and is known to be performing correctly.

In most cases the apparent problems are due to the computer not having time to stabilise on the correct rate before measurement commences, or not a long enough run after the boxes to correctly fill the centre.

Why not?

Here's how it works.

When you first enter a 'Start" from the front screen the computer has no reference to establish a starting point for conveyor speed so it starts the conveyor at the 'Conveyor offset' + the 'Jump and adjusts from there.  This is the standard setting, not many operators actually matches this setting to the product, door opening or terrain, so in almost every case, the rate for the first few yards will be changing as the computer works out the correct conveyor speed. This doesn't normally matter. Once the computer has worked it all out and corrected the conveyor speed all is well. After this initial start-up the computer will restart spreading when the spread switch is turned on, at the conveyor speed applicable when the spread switch was turned off. The original setting will not be referenced again until a new job is selected or one of the job parameters (e.g. Spin Speed) is changed.

Unfortunately, if you are undertaking a spread test, this is likely to be every run!

So what is the effect of this?

As the truck passes over the test trays the outside trays are filled first with the material thrown forward and to the outside of the truck. The last trays to be filled are the ones immediately behind the truck, which may not be filled until the truck is 20 metres or more past the trays.

So what does this do?

If the test requires a drive % of say 45% and the manual setting is  20% the conveyor will be going too slow when the spread switch is turned on. To calculate the correct speed the computer needs to get the ground speed and the conveyor speed and start accelerating the conveyor and measuring the effect. Depending on how much adjustment is required this can take several seconds. In the field this is not an issue. It only happens once at the start of the job, however, when spread testing, especially if space is limited, this could be the duration of the test.

Let's assume the desired rate is 450 kg per hectare and corresponds to 45%. Because the changes are smaller at lower drive numbers 20% may equal 100 kg per hectare. If spread is turned on say 10 metres before the test trays the computer may be on drive 30% when the first boxes are filled and drive 40% when the last ones are filled. However when the trays are weighed the rate applied when the outside trays were filled will have been much less than both the programmed rate and the rate applied when the centre boxes were filled.


The converse is also true. If the jump setting is too high the conveyor will be slowing down as the trays are crossed.


How will I know this has happened?

Most likely, the rate as calculated by the spread testing program will not match the rate programmed into the ComputerSpread Controller.

If the calculated rate and the programmed rate vary by more that 10% something is probably wrong. If the truck is known to apply product at the correct rate in the field and the calculated hectares match the actual hectares spread then the problem is likely to be the way the truck is being driven during the test. This does not mean the driver is doing anything wrong. It just means the test environment doesn't match what happens in the field.

Run-up is usually the problem. There seems to be an inherent reluctance to turn spread on before the test boxes are reached. It is essential to have a good run-up prior to going over the test boxes to allow the controller to stabilize on the correct rate. 100 meters across the paddock with spread on is a good start. Also the test should be conducted at the same speed as the run-up. Donít speed up or slow down going over the boxes and donít forget, if the fertiliser is going 15 meters out either side of the truck itís probably going 20 meters out the back, so, donít slow down or turn spread off too soon, and make sure there is enough product in the bin and that itís piled up against the back door.

If you are testing in a yard and can't go spreading fertilizer every where then do a run with nothing in the bin. Let the computer stabilize by watching the conveyor speed until it settles to a constant rate then turn spread off. You can now put fertilizer in the truck and go for a test. Don't forget to allow time for the conveyor to carry the fertilizer to the drop-off point. If the first test result is unsatisfactory and the measured rate doesn't match the programmed rate try another run before changing any settings. It's quite likely that the fertilizer hadn't reached the drop-off point or the speed of the truck was different. An option with model 693 and 793 computers is to note the drive number when the conveyor is running at the correct speed and enter this into the controller as the manual conveyor drive %. This will ensure that as you make changes to other parameters such as spinner speed the computer will start spreading at the correct drive % for the vehicle speed and the selected rate for the product being tested.

What else can cause problems?

The machine must be clean. Build-up of fertiliser around the spinners or on the spinner fins will affect the pattern. If you are trying to spread more than 16 metres and your vehicle was supplied with deflectors and vanes these will need to be fitted and adjusted to suit the spinner speed and the product. Also, have you got the correct spinners and rubber deflectors? These may have been changed for a specific reason which no longer applies or the wrong replacements may have been fitted at some time.

If you have any doubts about the ability of your vehicle to spread test to the required standard contact Transpread. Our Customer Service Representatives will test the vehicle, make any adjustments necessary and provide a report detailing the results. This provides all the information necessary to set up the vehicle for a subsequent spread test. It also means that if problems are encountered during testing we are familiar with the vehicle and able to advise what action is necessary to correct the problem.

Click the button  below to see a recommended spread testing layout and indicates where the product will land in relation to the vehicle.