Would you be surprised if I told you that the yield monitor in your combine could actually do your farming operation more harm than good? That's right; grain flow could be holding you back from collecting accurate information with your yield monitor.
Without accurate information what decisions could be skewed on your operation? Some examples that come to mind are variety trials, field averages, splitting bushels with landlords, etc. Not to mention the possible screw ups with crop insurance, if you use it for that.
The two manufacturers of yield monitor systems that hold a majority of the market share in my area are Ag Leader and John Deere. The accuracy of both John Deere's and Ag Leader's systems is directly related to how well they are calibrated in the field.
If you read the section on calibration in either manual, they both talk about grain flow. So what is grain flow? Grain flow is the amount of material, or grain that comes through your combine. It is directly related to three things: swath width, ground speed and yield of the grain.
So to produce an accurate calibration you will need to account for each of these variables.
When you calibrate your yield monitor you are helping the computer build an electronic model that relates the pressure put on the flow sensor, at the top of the clean grain elevator, to pounds of grain. The pressure on the flow sensor is driven by how much grain is flowing past--hence the term grain flow.
During normal operation where you are carrying a full head of grain and your ground speed is constant, the variation in grain flow is due to changes in yield of the crop. This is what we are trying to measure with a yield monitor. It is well understood that during normal operations of a combine the operator is usually speeding up and slowing down based on variations in crop yield to keep the threshing mechanisms working at capacity. The reason the operator does this is because they are trying to keep grain flow somewhat constant to maximize efficiency and minimize loss.
This actually is a good thing for producing accurate data with a John Deere yield monitor.
We will talk more about that next week when we discuss what true accuracy is and the best methods for calibration.