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Circular 1252
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Using SpotOn® Digital Meter for Boom Sprayer Calibration

SpotOn Sprayer Calibrator model SC-1

The SpotOn® Sprayer Calibrator is a digital flow meter produced by Innoquest Inc. as a tool for verifying nozzle output (desired flow rate is measured in gallons per minute; gpm) and calibrating a sprayer quickly and easily. The SpotOn® meter has three electrodes prepositioned inside the tube that sense the rising water level and provide a flow rate by measuring the time it takes to fill the meter’s tube. The meter works only with fluids that conduct electricity, such as water. The procedure outlined here is for using a SpotOn® meter (model SC-1; pictured here) for calibrating a boom sprayer. 

Calibration Procedure:

  1. Determine the following parameters for your intended pesticide application: target application rate or spray volume (gallons per acre; gpa), nozzle spacing (inches), and ground speed (mph).
  2. Using the tables provided in this publication, determine the desired flow rate (in gpm) required to attain the target application rate (in gpa) for the selected nozzle spacing and ground speed. For nozzle spacing (or application rate and speed) other than what is provided here, use the formula provided after the tables (Equation 1) to calculate the desired flow rate.   
  3. With the sprayer in a stationary position, adjust the spray pressure to the same setting that you intend to use during actual field application. This can be achieved by adjusting the throttle setting or engine rpm, or from an in-cab display if the sprayer is equipped with a rate controller.
  4. Turn on the sprayer and perform a quick visual check on all the nozzles, looking for proper functioning and uniform application across the boom. Make sure that the sprayer can maintain the desired pressure when the boom is turned on.
  5. To turn it on, press the START button on the SpotOn® meter. The LCD will flash “000” momentarily indicating it is working properly. Then the meter will show “- - -” on the LCD, indicating that it is ready to take a new measurement.
  6. Place the SpotOn® meter under a nozzle so that all nozzle flow is transferred quickly from the nozzle to the meter. Note that the most accurate measurements are made with the meter held at a slight angle to the vertical. This keeps the water from flowing down the sides of the meter and accidentally triggering the sensors.
  7. As the meter starts filling, the LCD will start flashing “- - -” indicating that a reading is in progress. When the water reaches the top sensor of the meter, a flow rate will be displayed on the LCD. Check the flow rate on multiple nozzles (preferably all) across the sprayer boom.
  8. Compare the meter readings (gpm) to the target flow rate determined from the provided tables for your desired application rate.
  9. If the meter readings differ from the target flow rate by more than ± 5%, check the individual nozzles and/or change the spray pressure to increase or decrease flow rate as needed.
  10. After each adjustment, repeat steps 3 through 9 to verify the nozzle output and determine if actual nozzle output matches the target flow rate.
  11. During measurement, if a reading needs to be restarted for some reason, simply empty the SpotOn® meter and re-press the START button to prepare it for a new reading.



Table 1. Flow rates (gpm) based on mph and gpa with 18-in. nozzle spacing.

 

Target application rate in gallons per acre (gpa)
Speed in mph 5 7.5 10 12.5 15 17.5 20 25 30
4.0 0.06 0.09 0.12 0.15 0.18 0.21 0.24 0.30 0.36
5.0 0.08 0.11 0.15 0.19 0.23 0.27 0.30 0.38 0.45
6.0 0.09 0.14 0.18 0.23 0.27 0.32 0.36 0.45 0.55
7.0 0.11 0.16 0.21 0.27 0.32 0.37 0.42 0.53 0.64
8.0 0.12 0.18 0.24 0.30 0.36 0.42 0.48 0.61 0.73
9.0 0.14 0.20 0.27 0.34 0.41 0.48 0.55 0.68 0.82
10.0 0.15 0.23 0.30 0.38 0.45 0.53 0.61 0.76 0.91
11.0 0.17 0.25 0.33 0.42 0.50 0.58 0.67 0.83 1.00
12.0 0.18 0.27 0.36 0.45 0.55 0.64 0.73 0.91 1.09
13.0 0.20 0.30 0.39 0.49 0.59 0.69 0.79 0.98 1.18
14.0 0.21 0.32 0.42 0.53 0.64 0.74 0.85 1.06 1.27
15.0 0.23 0.34 0.45 0.57 0.68 0.80 0.91 1.14 1.36
16.0 0.24 0.36 0.48 0.61 0.73 0.85 0.97 1.21 1.45
17.0 0.26 0.39 0.52 0.64 0.77 0.90 1.03 1.29 1.55
18.0 0.27 0.41 0.55 0.68 0.82 0.95 1.09 1.36 1.64
19.0 0.29 0.43 0.58 0.72 0.86 1.01 1.15 1.44 1.73
20.0 0.30 0.45 0.61 0.76 0.91 1.06 1.21 1.52 1.82

 

Table 2. Flow rates (gpm) based on mph and gpa with 20-in. nozzle spacing.

 

Target application rate in gallons per acre (gpa)
Speed in mph 5 7.5 10 12.5 15 17.5 20 25 30
4.0 0.07 0.10 0.13 0.17 0.20 0.24 0.27 0.34 0.40
5.0 0.08 0.13 0.17 0.21 0.25 0.29 0.34 0.42 0.51
6.0 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.51 0.61
7.0 0.12 0.18 0.24 0.29 0.35 0.41 0.47 0.59 0.71
8.0 0.13 0.20 0.27 0.34 0.40 0.47 0.54 0.67 0.81
9.0 0.15 0.23 0.30 0.38 0.45 0.53 0.61 0.76 0.91
10.0 0.17 0.25 0.34 0.42 0.51 0.59 0.67 0.84 1.01
11.0 0.19 0.28 0.37 0.46 0.56 0.65 0.74 0.93 1.11
12.0 0.20 0.30 0.40 0.51 0.61 0.71 0.81 1.01 1.21
13.0 0.22 0.33 0.44 0.55 0.66 0.77 0.88 1.09 1.31
14.0 0.24 0.35 0.47 0.59 0.71 0.82 0.94 1.18 1.41
15.0 0.25 0.38 0.51 0.63 0.76 0.88 1.01 1.26 1.52
16.0 0.27 0.40 0.54 0.67 0.81 0.94 1.08 1.35 1.62
17.0 0.29 0.43 0.57 0.72 0.86 1.00 1.14 1.43 1.72
18.0 0.30 0.45 0.61 0.76 0.91 1.06 1.21 1.52 1.82
19.0 0.32 0.48 0.64 0.80 0.96 1.12 1.28 1.60 1.92
20.0 0.34 0.51 0.67 0.84 1.01 1.18 1.35 1.68 2.02

Equation 1. Calculate the desired flow rate for a boom sprayer given any nozzle spacing, application rate, and ground speed.



flow rate (gpm) = application rate (gpa) x ground speed (mph) x nozzle spacing (in.) / 5940

Status and Revision History
Published on Mar 01, 2022

Faculty
Simerjeet Virk Assistant Professor and Extension Precision Ag Specialist, Crop & Soil Sciences Eric P. Prostko Extension Agronomist - Weed Science, Crop & Soil Sciences

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