In some cases, operational errors are unavoidable, but often combine operators can minimize the impact that errors will have on yield estimates. The following best management practices will help you collect accurate yield data during harvest.
Mass flow sensor calibration: The mass flow sensor is the most critical component of the yield monitoring system. The calibration procedure for the mass flow sensor is time-consuming, but absolutely vital for the accurate yield measurements. Since mass flow sensor readings may be affected by crop type, moisture content, and test weight, operators should consider performing separate calibrations under these differing circumstances. A separate calibration procedure should always be performed – and stored in the in-cab display.
A good rule of thumb is to have a different calibration for corn over and under 20% moisture content.
The mass flow sensor calibration process involves harvesting small loads of grain (around 3000 pounds), depending on manufacture specifications and measuring the scale weight of each load.
One problem associated with mass flow sensors is the response is nonlinear. The nonlinearity becomes an issue when only one or two loads are used during the calibration process. An example of this is shown in the screen shot where sensor output is plotted versus mass flow rate through the clean grain elevator. When a two-point calibration is used (one point for high flow and one for low flow), a discrepancy occurs between the calibration equation and the actual values. In this case, between the two calibration points, mass flow rates – and thus, yield – will be overestimated.
Typically the operator can choose from two methods for varying the flow rates for proper mass flow sensor calibration: 1.Constant speed with vary cut width 2. Varying speed with constant cut width. Both options can achieve the same result of varying flow through the clean grain elevator.
Moisture sensor operations: While most moisture sensors do not require much service and maintenance throughout the harvest season, operators should check, when possible, that the sensors are clean and functioning normally.
In general, moisture sensors provide adequate estimates of grain moisture ranging from 10% to 33%. The harvest moisture content is an important measurement. It helps correct back to the desired yield value set by the market, or the moisture content at which the operator sells grain locally.
Lag time settings: It takes some time for the grain to travel through the combine once it’s cut at the header. As such, mapping programs use a delay or lag time to locate when and where the grain impacting the mass flow sensor was cut. Having an appropriate lag time setting for the in-cab display is necessary to compensate for the grain flow delays through the machine.
For most harvesters, the lag time should be between 10 and 15 seconds, but operators may want to confirm this by double-checking the lag time. This can be accomplished by measuring the amount of time from when the crop is first cut until it enters the bin, keeping in mind one or two seconds should be subtracted from this value since the mass flow sensor is ahead of that point.
Header Position Sensor: The header position sensor should be installed correctly, and the operator should be sure to raise and lower the header only when exiting or entering the uncut crop. This will ensure that yield data points are logged properly, and data are shifted according to the lag time setting.
Header cut width: Header cut width has been one of the toughest problems to solve with regard to accurate yield estimates.
Yield monitors offer automated cut width setting using swath control technologies, which reduce the width entry based on field coverage logged during harvesting. As the header passes over previously harvested areas, the cut width is automatically decreased.
For more information, contact a specialist today.
