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Granular application is configured using the product density and a spreader constant to determine the flow rate.
The product density is the weight of product being applied in a specific amount depending on the units it is being applied in.
Density or Meter Cal is measured in:
- Pounds per Cubic Foot for US units applied in Pounds per Acre
- Kilograms per Cubic Meter for Metric units applied in Kilograms per Hectare
Note: | The term "Meter Cal" as used with Raven equipment is "Pulses per 10 units of measure." |
1 lb per cubic foot = 16.02 grams per liter
US to Metric: | Pounds per Cubic Foot x 16.02 |
Metric to US: | Kilograms per Cubic Meter 16.02 |
Example:
The spreader constant is the amount of material discharged per revolution of the encoder on a belt or chain. This is defined in pulses per cubic foot or per cubic centimeter. Most encoders pulse 180 or 360 times per revolution, but there are other types available (a gear tooth sensor is one example). Please ensure the correct values are used for the encoder pulse. If the spreader constant number is too big (>99,999), then the sensor may need to be changed to a sensor with fewer pulses per revolution.
A spreader constant is needed to accurately measure the amount of dry product dispensing out of a machine. Raven controllers and field computers use this number in the calculation to speed up or slow down the bed that is being used. It is critical that this number is calculated properly. Many bed manufacturers provide a spreader constant table with their models of beds. This usually is the best source for finding the spreader constant number. In most cases, contact with the bed manufacturer will be the best way to find the spreader constant. In cases that the manufacturer is unavailable or the information is not available the following formulas may be used. Please use the best formula to suit your needs.
If calculating it manually, the following information will be needed:
| | Measurements (In Inches or Centimeters) |
---|
L | = | Length of belt/chain travel per 1 revolution of the rate sensor/encoder. |
GH | = | Gate Height |
GW | = | Gate Width |
Encoder Count per Revolution * |
* This number will be on the encoder. If the count is unknown, use the steps below:
- Enter 10 in the Meter cal or Density.
- Enter 0 in the Total Volume in the Tally Register.
- Turn the sensor 1 revolution.
- The number in the Total Volume is the counts per 1 revolution.
US Units
- Determine the cubic feet discharged per 1 revolution of the sensor for US units.
L x GH x GW 1728 | = | cu ft/rev |
Note: | 1728 is the Raven constant for calculation in cubic inches per cubic feet. |
- Determine the rate in pounds (Spreader Constant).
Encoder Count cu ft/rev | = | Spreader Constant |
Example:
L | = | 13 inches |
GH | = | 7 inches |
GW | = | 15 inches |
180 Encoder Counts |
The US spreader constant is
228.
Metric Units
- Determine the cubic centimeters discharged per 1 revolution of the sensor for Metric units.
L x GH x GW 100,000 | = | cu m/rev |
Note: | 100,000 is the Raven constant for calculation in cubic centimeters per cubic meters. |
- Determine the rate in kilograms (Spreader Constant).
Encoder Count cu m/rev | = | Spreader Constant |
Example:
L | = | 33.02 cm |
GH | = | 17.78 cm |
GW | = | 38.1 cm |
180 Encoder Counts |
Note: | The Metric examples above (L, GH, GW) are exact conversions from the US measurements in the previous example. |
33.02 x 17.78 x 38.1 100,000 | = | 0.22368 |
The Metric spreader constant is
805.
If the spreader constant provided by the manufacturer is known (for a specific gate height), there is an easy way to adjust the spreader constant for your desired gate height.
The manufacturer spreader constant for 1.5 inch gate height is 1000, but you want your gate height to be 1 inch.
Manufacturer Spreader Constant x 1.5 | = | 1" Spreader Constant |
If you want to figure for a different gate height, it is recommended to figure for the 1 inch gate height (see above), then divide the 1 inch spreader constant by your desired gate height (3 inches, for instance).
- Metering Wheels
- Augers
- Systems that do not allow for measuring the L, GH, and GW.
US Units
- Set spreader constant to 0.
- Enter a meter cal or density of 200.
- Clear, or enter 0 in the Total Volume of the Tally Registers.
- Run the machine and collect a sample large enough to weigh accurately, then perform the calculations below:
Meter Cal x Total Volume from Tally Register Actual Weight | = | New Meter Cal |
(New) Meter Cal x Product Density 10 | = | Spreader Constant |
Example:
Meter Cal | = | 200 |
Total Volume | = | 500 |
Actual Weight | = | 550 |
Product Density | = | 50 |
The US spreader constant is 909.
Metric Units
- Set spreader constant to 0.
- Enter a meter cal or density of 440.
- Clear, or enter 0 in the Total Volume of the Tally Registers.
- Run the machine and collect a sample large enough to weigh accurately, then perform the calculations below:
Meter Cal x Total Volume from Tally Register Actual Weight | = | New Meter Cal |
(New) Meter Cal x Product Density 100 | = | Spreader Constant |
Example:
Meter Cal | = | 440 |
Total Volume | = | 226.8 |
Actual Weight | = | 249.48 |
Product Density | = | 801 |
Note: | The Metric examples above are exact conversions from the US measurements in the previous example. |
The Metric spreader constant is 3204.
This procedure is used to correct a spreader constant when doing a catch test. It can also be done in the field after applying a known amount of product.
Current Spreader Constant x Total Volume from Tally Register Actual Weight | = | New Spreader Constant |
Example:
Current Spreader Constant | = | 800 |
Total Volume from Tally Register | = | 9,550 |
Actual Weight | = | 10,400 |
800 x 9,550 10,400 | = | 734.61 |
The new spreader constant is 735.
Most spreader constants provided by manufacturers are for a standard 1 inch gate height. Some manufacturers provide a chart for all gate heights. If there is only one spreader constant number provided, then a calculation of the other spreader constants will be needed to increase or decrease product output.
If the 1 inch gate height is known, the spreader constants for other gate heights can be found using the following formula:
Spreader Constant for 1 Inch Gate Height New Gate Height | = | New Spreader Constant |
Example:
2 Inch Gate Height
5 Inch Gate Height
How to Convert Spreader Constant between US and Metric
US to Metric
US Spreader Constant x 3.53 | = | Metric Spreader Constant |
Example:
The Metric spreader constant is
805.
Metric to US
Metric Spreader Constant 3.53 | = | US Spreader Constant |
Example:
The US spreader constant is
228.
Single product liquid SCS consoles including 440, 450 and 460 can be used to control granular product. Most do not have the "Spreader Constant" for entering the spreader constant value. Instead, the spreader constant value can be converted to a meter cal value for use with the console. The following formulas will give you a meter cal derived from a spreader constant or calculation of product being weighed.
Note: | Although the above SCS consoles can be used to control granular product, Raven does not recommend doing so. Raven will not support the installation and setup of such a configuration nor any issues resulting from controlling granular product with a liquid console. |
Note: | The term "Meter Cal" as used with Raven equipment is "Pulses per 10 units of measure." |
Using a Known Spreader Constant on a Non-Granular Console
US Units
Spreader Constant x 10 Product Density | = | Meter Cal |
Example:
Spreader Constant | = | 1325 |
Product Density | = | 50 |
Enter the meter cal of 265 into the console.
Metric Units
Spreader Constant x 100 Product Density | = | Meter Cal |
Example:
Spreader Constant | = | 4677 |
Product Density | = | 801 |
Enter the meter cal of 584 into the console.
Catch Test Method Using a Spreader Constant on a Non-Granular Console
- Verify there is no decimal in the Meter Cal (decimal shift).
- Enter 200 in Meter Cal.
- Enter 0 in Total Volume.
- Dump a weighable amount on a scale.
- Weigh the sample.
- Calculate in the following formula:
Current Meter Cal x Total Volume from Tally Register Actual Weight | = | New Meter Cal |
Example:
Current Meter Cal | = | 265 |
Total Volume from Tally Register | = | 9,550 |
Actual Weight | = | 10,400 |
265 x 9,550 10,400 | = | 243.34 |
The new meter cal is 243.
Note: | If this spreader constant is used as the regular product, consider using a sensor or encoder that produces fewer pulses per revolution. An encoder that processes fewer pulses per revolution will result in a lower spreader constant value. |
In some rare circumstances, the spreader constant value will exceed the digit capability of the Raven console or field computer (>99,999). If this is the case, use the meter cal formulas above to convert the large spreader constant number to a meter cal value usable with the console or field computer.
Important: | When using the above meter cal formulas, the calculation result is to be entered into the "Meter Cal," and no number is entered into the "Spreader Constant." The spreader constant must remain at zero. |
Another option is to use the decimal shift method to lower the spreader constant value.
Decimal Shift Method
Note: | This method divides the current spreader constant and density by 10. When doing this, a decimal shift must be entered into the console to account for the difference in the spreader constant and density. |
- Use the decimal shift function on the console or field computer.
- Divide the Spreader constant by 10.
- Divide the Density by 10.
- Enter the results above in the Spreader Constant and Density fields.
Example:
Original Density | = | 65 |
Original Spreader Constant | = | 127,819 |
- Shift the decimal in the console or field computer.
- Enter Density of 6.5.
- Enter Spreader Constant of 12,782.