Yield Monitor Calibration Advice by:Joe Luck Extension Precision Agricultural Engineer

September 11, 2013

Checks and Adjustments to Ensure Quality Yield Data Collection

Adusting the yield monitorFigure 1. Sensors should be calibrated and yield monitor settings checked and adjusted annually.

Yield monitor data is one of the most important data layers in site-specific crop management. Yield data allows you to evaluate management practices at the end of the season and begin making plans for the upcoming year. With such a significant source of information on the line, it pays to be diligent and minimize data collection errors during harvest. A well-calibrated yield monitor system should estimate the total yield harvested from a field to within 1% to 3% error.

While many people focus on the actual monitor in the combine cab, it’s important to remember that the yield monitoring system consists of several sensors positioned throughout the harvester. As with all sensors, errors can be expected; however, with proper calibration and maintenance, these errors can be managed.

Calibrating the Mass Flow Sensor

UNL Extension Precision Agriculture Engineer Joe Luck discusses yield monitor adjustments on the September 13 Market Journal. 

For most systems, a mass flow sensor (typically located at the top of the clean grain elevator) is used to estimate the flow of grain through the combine. The grain leaving the elevator paddles contacts the impact plate connected to the mass flow sensor. This sensor sends out a voltage signal proportional to the flow of grain. Proper calibration of this sensor will help ensure a more accurate estimate of grain flow. The calibration procedure can vary slightly among manufacturers so it’s important to follow the procedures provided for your system.

Calibrating the mass flow sensor usually involves harvesting two to six loads, weighing each load, and entering these weights into the yield monitor console. When harvesting the calibration loads, generally operators will harvest a full header width at the maximum travel speed for the first load, then either reduce the header cut width or travel speed for subsequent loads. The goal is to vary the grain flow through the clean grain elevator (which impacts the mass flow sensor) to represent ranges expected during harvest. Try to use all the calibration loads allowed your system, spreading out the grain flows from the least to the most expected.

For example, if you’re harvesting with a 12-row header, the first calibration load might be at a constant speed of 5 mph with all 12 rows, then 10 rows, then 8 rows and so on to only 2 rows. This would provide six calibration loads. Another example would be to harvest a constant 12 rows at 6 mph, then 5 mph, 4 mph, and so on to only 1 mph, again providing six calibration loads. In general, as the speed and header cut width vary, so does the flow of grain through the clean grain elevator. For systems requiring only two calibration loads, generally one is at maximum harvester capacity and the second is at a low flow rate, always calibrate using both.

Mass flow sensorFigure 2. It’s important to calibrate the mass flow sensor at the beginning of each harvest season as well as when switching between crops.

Another important point about yield data accuracy is that test weight, moisture content, and crop type can affect the output from the mass flow sensor. Therefore, a separate calibration is essential for each crop and sometimes, when factors change from field to field, for the same crop. For example, you’ll want to recalibrate the sensor when changing from high moisture to low moisture corn or when switching between hybrids with substantially different test weights. While calibration of the mass flow sensor may seem like a waste of time, it’s critical for collecting accurate yield data.

Some good news is that many grain carts now come with load cells to measure weight, making a separate weigh wagon unnecessary. Also, with most systems you don’t necessarily have to calibrate at the beginning of the harvest season; calibrations later in the season can be applied to previously collected data. Calibrating slightly later in the harvest season can also allow operators to focus on setting the harvester properly for minimizing losses and damaged grain or foreign matter entering the grain tank.

Calibrating the Grain Moisture Sensor

Another component of the yield monitoring system that requires calibration is the grain moisture sensor. While it doesn’t directly measure the yield during harvest, measuring the moisture content allows the yield to be adjusted to a “marketable” grain moisture content. This can be important because most people like to know the actual yield value after adjustments at the elevator.

Check for GPS Updates

Thankfully, the GPS system on the combine doesn’t require any major calibration; however, it’s good to do a couple pre-harvest checks of this important component of the yield monitor system. First, check to see if the firmware is up to date for the GPS unit. Many manufacturers will notify owners of updates, but generally, the easiest method is to check online for the latest version. If your version is out of date, usually the update can be downloaded onto a flash drive or thumb drive and uploaded to the GPS receiver. Older systems might require a direct connection to a computer.

Also check the GPS offset distances in the yield monitor. Verify that the distance from the cutter bar or snapping rollers to the GPS antenna is entered correctly.

Checking the Lag Time

It’s also good to verify the lag time that’s been entered into the yield monitor console a couple times when you start harvesting. The lag time is the time from when the crop is cut to when it impacts the mass flow sensor. Typical values range from 10 to 15 seconds. An easy way to check this is with a stopwatch as you begin harvesting a pass. Keep in mind that there is a short time (maybe two seconds or so) from when the grain impacts the mass flow sensor until it reaches the bin. You’ll want to reduce your measurement by that amount.

Importance of Annual Checks

While calibrating the yield monitor may seem time consuming, it’s a very important part of successful precision agriculture machinery and data management. You want to have confidence in the data you’re collecting as it will affect your management strategies and evaluation in the future. Stay tuned for future information on CropWatch.unl.edu about post-processing yield data to further reduce errors.

If you need help with your current yield monitoring system or are trying to collect harvest data for the first time and need assistance, please feel free to email me at jluck2@unl.edu or call 402-472-1488.

Joe Luck
Extension Precision Agricultural Engineer

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