By Elizabeth Hawkins, Field Specialist, Agronomic Systems, Ohio State University Extension
Across Ohio, combines are busy collecting more than just grain. Yield monitors are also busy collecting data with the hope that this information will lead to more profit in the future.
The yield monitor does not directly measure the number of bushels per acre of grain produced; instead, these estimates are calculated based on a combination of data collected by sensors in the combine and information provided by the grower. Because of this, the accuracy of the yield estimate is dependent on the accuracy of all the information that is being used to calculate it, and care needs to be taken to ensure all of the data being collected is correct.
The grain flow estimate is an important piece of the yield estimate calculation. Many combines today are equipped with an impact sensor that is used to collect this information. We’ve all heard that proper calibration of the impact sensor is essential to obtain accurate yield estimates, but why? In order to understand why proper calibration is so important, we need to understand how the impact sensor collects data and how that data is used to help estimate yield.
Impact sensors do not actually measure yield (in bu/ac) or the amount of grain going through the combine (as in lb/sec); they simply detect and record a voltage. The voltage reading changes as the amount of grain moving past the sensor increases or decreases which makes it possible to use the voltage reading to estimate the grain flow rate (in lb/sec). The yield monitor uses a calibration curve to make the conversion from voltage to flow rate. The flow rate is then combined with other information (moisture, speed, header width) to calculate the yield estimate.
The accuracy of the grain flow estimates (and subsequently, the yield estimates) depends on how good the calibration curve is, or more simply, if the yield monitor knows what to do for every voltage reading it sees. Proper calibration allows us to prepare the yield monitor to recognize the changes in flow rates by teaching it what the differences in voltage signals mean. A good calibration will show the yield monitor an example of the lowest possible grain flow rate, the highest possible grain flow rate, and several levels of grain flow rates in between. Collecting yield data without calibrating is like taking a test you forgot to study for; letting the yield monitor guess what the voltage readings mean can (and most likely will) result in incorrect yield estimates.
For more details on yield monitor calibration, see Tips for Calibrating Grain Yield Monitors—Maximizing Value of Your Yield Data ANR-8 at https://go.osu.edu/yieldmonitor