To calibrate a yield monitor correctly you are required to consider all the parts that make up the yield monitor system: mass flow sensor, moisture sensor and clean grain elevator. Of these the most important is the mass flow sensor.
Located at the top of the clean grain elevator is an impact sensor that measures the impact of the grain that is thrown off the clean grain elevator chain. The impact is converted into a voltage and the yield monitor reads the voltage and converts this into a flow rate of kg/sec.
It is recommended to use a multi-point calibration to generate as accurate yield data as possible.
Image from Precision Ag Basics, courtesy of University of Nebraska.
As seen in diagram A, if the system is only calibrated for one or two flow rates the response is a linear calibration resulting in a potential under or overestimating of yield. In diagram B the system has been calibrated for four flow rates resulting in a non-linear calibration. This will result in a reduced error and data that is a better representation of actual yield.
Other sources of error
Other sources of error in yield data can be caused by incorrect yield monitor setup. These are lag time, header front measurement, header front section control and set up of sensors.
Lag time is the time that is taken for the grain to flow through the header from the cutter bar to the mass flow impact sensor. This needs to be determined correctly to ensure accurate location of the yield readings in the paddock.
Errors in yield data will also occur if the header front measurement is not recorded correctly. If it has been measured correctly, there may still be an error if the system is not fitted with section control or if inappropriate section widths have been set. The system generates an applied map of harvested area and automatically adjusts the yield calculations based on the width of the front that is in un harvested crop. If the header is not fitted correctly, it will assume that it is harvesting a full front and generate erroneous yield data.
Other sensors that can prevent erroneous yield data are a front height sensor and a thresher engagement sensor. The front height sensor logs the height of the front and will tell the system not to log yield data when the front is not at working height, resulting in reduction of erroneous yield data when turning or traversing parts of the paddock
The thresher sensor will only let the system log yield data when the drum or rotor on the header is engaged and working. This results in yield data only being generated when the header is harvesting and not transporting if the yield monitor system is left on.
If you are planning on using your yield data for any agronomic or economic purpose it is important that you collect reliable data by calibrating your yield monitor correctly.
Article written by Adrian Roles, reviewed by Matt Notley and Helen McMillan.