Monitoring yield monitors
A yield monitor is only as good as the data it collects, warns Kent Shannon at the University of Missouri. “Remember, garbage in equals garbage out,” he says.
The engineer provides the following five steps to ensure monitors are running dead-on accurate.
1. Set the value of the harvest position. A monitor recognizes the start of harvest when the separator is turned on and the header is in harvest position. Because different monitors require different header positions, it's up to you to set the value. Once set, the activated separator and the header in this position will always tell the yield monitor that it's harvesttime.
2. Set the platform or header width. Some combines automate this process. Others require you to enter platform width or the number of header rows.
3. Set your travel speed. Using harvest width and travel speed, the combine calculates the acres harvested per hour. If the combine has GPS, there are no further adjustment steps at this point. But if the harvester is using speed pickup or Doppler-shift systems, you need to calibrate the speed sensor. To do this, drive a known distance and then correct the sensor's output as necessary.
4. Set the amount of grain for the area. At this point, the monitor knows the number of acres harvested but still needs to know the amount of grain for the area. Grain is measured indirectly with a mass-flow sensor. There are two types of sensors used most frequently.
The first measures the force of grain from the clean grain elevator with an impact plate. The force is added up to determine the accumulated weight of the grain. If the clean grain elevator paddles are not functioning properly, however, the weight won't be measured correctly.
If the paddles are damaged or worn, they may produce low readings because the grain can't reach the top of the conveyer where the impact plate is. Fixing this may require new paddles or an adjustment to the paddle height. Note that the sensor output is not proportional to grain weight because of the difference in friction and the way grain falls at high and low mass-flow rates. For example, 1 volt could be 5 pounds of grain; 2 volts could be 12 pounds.
The second, less commonly used mass-flow sensor measures the height of grain as it passes through the clean grain elevator. The sensor uses this to estimate the volume and then the density, or mass of grain per volume. With this, the sensor estimates the weight of the grain. The number used to determine the density is based on the volumes from earlier calibration loads. Because the relationship between weight and volume of grains does not stay constant for too long, a calibration load should be done every two or three weeks.
Calibration load recommendations vary greatly based on the manufacturer. If you haven't already, read your operator's manual and follow the specific instructions for your combine. This may involve harvesting at average rates, at varying rates, or running multiple calibration loads. Most combines allow you to continue harvesting until you have the weight ticket from the calibration load, so the process will not slow down harvest.