Tips for Calibrating Grain Yield Monitors—Maximizing Value of Your Yield Data

Agriculture and Natural Resources
Originally published by Nathan Watermeier
Elizabeth Hawkins, John Fulton and Kaylee Port

Calibrating grain yield monitors at harvest can be discouraging and time consuming for a combine operator. However, improperly calibrated yield monitors can generate erroneous data that becomes useless or difficult to interpret. Taking the time to calibrate a yield monitor properly pays off when it comes time to using yield map data for post-harvest analyses or supporting decisions based on your yield data.

The first step is to become familiar with your yield monitor and its components. Information provided by your dealer or manufacturer through on-site support, training sessions, user manuals, and online information are all ways to learn about your yield monitor and its components. Today, there is a substantial amount of information online including quick start guides and tips for calibrating grain yield monitors. Each yield monitor has a specific calibration method which is outlined in the manufacturer's calibration procedures manual. In order to maximize the benefits of your yield monitor, this publication outlines several tips to collect quality yield map data and relevant information around setup and calibration before you head to the field.

Prior to Field Operation

  • Backup data from the previous season, if you have not done so already.
    • Best Practices:
      • Place each season under a new folder labeled as yield data and the year.
      • Keep several backup copies of the display/raw data in different locations in case it is lost, stolen, damaged or modified.
      • Delete old files from the memory card.
      • Delete old files from display memory if close to full.
  • Check any data cards or thumb drives to be sure they work properly with your display.
  • Contact your local dealer or manufacturer to make sure that you have the most recent software and firmware upgrades for your yield monitoring and mapping system, the display, DGPS receiver and other components. You can obtain information about these upgrades through your manufacturer's website or by contacting technical support.
  • Check all cables, connections and sensors for wear or damage. Ensure that wiring and harness connections are tight.
  • For clean grain elevator-mounted moisture sensor units:
    • Make sure the sensor is clean and not damaged.
    • Clear the clean grain elevator of old grain and debris.
    • Check to be sure the manual clean-out motor works on the moisture sensor.
  • Inspect the yield sensor.
    • For combines with a mass flow sensor (normally located at the top of the clean grain elevator):
      • Look for wear on the flow sensor’s impact or deflector plate and replace the plate if worn or damaged.
      • Look for any excessive wear on the grain elevator and missing or worn paddles. In some cases, there may even be a hole in the plate, increasing risk of inaccurate yield readings.
      • Check to make sure that the spacing between the paddles and the top of the elevator meets the manufacturer’s requirements.
      • Ensure the clean grain elevator chain is tightened to manufacturer specifications.
    • For combines with an optical sensor (mounted on the side of the clean grain elevator):
      • Make sure the sensors are clean and not damaged.
      • Ensure the clean grain elevator paddles are not rubbing against sensors.
  • If you purchase a new or used combine with an existing yield monitor installed, double check to make sure it is installed properly. Especially check that the mass flow sensor is mounted securely.
  • If a grain cart with scales or a weigh wagon is used to collect data, double check that they are producing accurate weight data. This can be done by simply standing on the hitch to make sure the reading is close or comparing load weights to certified scales.
  • Avoid running electrical wires next to the GPS antenna which may cause interference with the receiver signal. Running wires perpendicular to each other decreases the chance for electrical noise that may occur from other electronics.

During Operation, Prior To Calibration

  • Start-up combine and turn on display to check that the:
    • Display indicates everything is functioning correctly or is properly connected.
    • Memory card or thumb drive is installed properly.
      • Make sure there is proper communication between the data card and the in-cab display. Usually an error message will appear on the display indicating there is no communication with the card.
    • DGPS receiver is providing a position and has differential correction (WAAS, SF1, SF2, RTX or RTK).
      • Note: If purchasing a differential correction service, make sure your subscription runs through harvest.
  • Raise and lower the header to make sure the stop height switch operates properly.
    • Some yield monitors are equipped with a manual button that turns data collection on and off through the in-cab display. You may have to adjust the header height switch to accommodate the preferences of different operators during harvest.
  • Set row width according to number of rows for a row crop header or the appropriate width of a cutting platform header.
    • Some yield monitors have the option to use automatic swath width detection to adjust the swath width when overlap is detected. This feature can be helpful when harvesting point rows or near field edges; however, be aware it may not function properly if your DGPS source has a potential for large positional error (e.g., WAAS) or if there is signal interference or loss.
  • Engage the separator and observe the elevator speed on the in-cab display.
  • Put the combine in drive and make sure the in-cab display is providing a ground speed measurement.
  • Before calibrating, make sure the scale you will be using to weigh the grain is accurate. Certified scales or calibrated weigh wagons are recommended.
    • If you are using weigh wagons, it is recommended to leave the wagon in one location in the field. Moving the weigh wagon through a field causes it to shake and bounce which can throw off the calibration of the weigh wagon.
    • Make sure you are also using the same scales throughout calibration.


The yield estimate produced by a yield monitor is calculated from measurements taken by multiple sensors. Each of these sensors need to be calibrated in order for the yield estimate to be accurate. Consult with your user manual to determine the order in which these calibrations should take place. 

Mass-Flow Sensor Vibration Calibration
  • This calibration is used to remove the effect of vibration when the combine is running. Follow the directions in your user manual to complete the vibration calibration. Be sure that:
    • the proper header is attached and in operating position (not resting on ground).
    • the combine is empty of grain.
    • the separator and header are engaged.
    • the combine is running at full RPM.
Temperature Calibration (Moisture Sensor)
  • Take the air temperature using an accurate thermometer when:
    • the combine has been sitting for several hours, possibly in a shaded area.
    • the combine and moisture sensors are empty of grain.
  • Adjust the temperature value according to the user manual.
    • Some displays require you to simply enter the temperature reading from the thermometer, others require you to enter an offset value (usually the difference between the thermometer reading and the sensor reading).
Moisture Sensor
  • Reset the moisture offset in the display to zero.
  • Randomly collect grain from throughout each calibration load to obtain a representative sample.
  • Measure the moisture of the grain sample with an accurate moisture meter.
  • Enter the moisture offset into the display according to your user manual.
  • You might double check calibration after several 100 acres of harvest for a crop or when changing fields.
  • Repeat this calibration for each type of grain harvested.
  • Portable moisture meters vary widely in terms of quality. Some best practices to ensure your readings are accurate include:
    • Taking your moisture meter to your local elevator prior to the start of harvest to test it on grain samples with a known moisture.
    • Taking and averaging multiple moisture readings to reduce the risk of using an erroneous measurement.
Ground Speed
  • Many yield monitors today use GPS to determine ground speed and do not need to be calibrated.
  • If a mechanical speed sensor is being used as a backup, it should be calibrated.
    • These calibrations are conducted by travelling a known distance through the field and timing how long it takes.
      • When calibrating the ground speed sensor, use typical field conditions rather than a road or waterway. Tire slippage can create inaccuracy with calibration.
Mass Flow Sensor
  • Proper calibration of the mass flow sensor is crucial to the accuracy of the yield estimate. There are two common approaches used for calibration: a near-linear calibration and a non-linear calibration.
    • Near-linear calibrations require one or two calibration loads to generate a calibration line.
      • Many older yield monitors use near-linear calibrations.
      • For these systems, you can have different calibration numbers for low, medium and high flows through the combine. Match the calibration number to the crop conditions (e.g., low, medium and high yield).
    • Non-linear calibrations require three or more calibration loads to generate a calibration curve.
      • Use the number of calibration loads recommended by the manufacturer (commonly four to six calibration loads).
      • These loads should be captured over varying grain flows (low to high) by either changing ground speed or cut width as outlined in the operator manual.
  • Regardless of the calibration method, the quality of the calibration loads is important. The following best practices can help ensure the calibration is accurate.
    • Calibration loads should be representative of the different flow rates that will be encountered. It is important to take the time to calibrate the mass flow or volumetric sensors over the full range of expected loads.
      • Harvest calibration loads at different flow rates (low to high). The goal is to have each load harvested at a constant and consistent flow rate. Target flow rates can be achieved by
        • Harvesting each load with a full header at different speeds.
        • Harvesting each load at a constant speed with different harvested swath widths.
    • When harvesting calibration loads, it is recommended to use loads between 3,000 to 8,000 pounds. This helps reduce the overall sensor error while calibrating.
    • Although calibration—in particular at low flow rates—can take time, it is a must to collect quality yield data. The ability of the yield monitor to collect accurate yield data from low- to high-flow conditions will dictate the quality of resulting maps or yield data.
    • Avoid starting calibration loads on turn rows, weed patches or areas of major topography changes in the field.
      • Hillsides and rolling ground can impact calibration load data because of changes in how grain impacts the flow sensor. 
      • If you are unable to avoid topographical changes make sure you get a good representation of loads going up- and downhill and side-to-side of a hill.
    • It is necessary to calibrate for each type of grain for each year.
      • Flow rates tend to be much higher when harvesting corn compared to soybeans or wheat.
      • Other grain characteristics that, between different grain types, can alter the reading produced by the mass flow sensor.
      • The dynamics of grain flow through a combine changes with wear and tear.
    • When conducting on-farm research trials or harvesting fields with multiple varieties, consider creating a calibration load for each treatment or variety. 
    • For example, calibrate for regular corn and high oil corn separately due to the differences in test weight and moisture characteristics of the grain.
    • Calibrate for different moisture levels per type of grain. For example, calibrate differently for corn below 20 percent moisture versus corn above 20 percent moisture.

During Harvest

  • Take good notes on field and operating conditions during harvest. This information will be helpful when reviewing yield maps post-harvest.
  • Correct any malfunctions or errors indicated by the yield monitor. This step can include moisture and flow sensors not working properly and loss of DGPS signal. Make sure the display is actually collecting data. Sometimes one can manually switch off data collection on the display and forget to turn it back on.
  • It is recommended to take your memory card or thumb drive out of the monitor and back-up data onto your computer and data storage devices frequently throughout the harvest season. A simple electrical shock from improper wiring or lightning can destroy data.
  • If you have a long harvest season, it would be wise to perform periodic calibration loads throughout the season to check or improve accuracy. It is suggested to recalibrate if you see:
    • more than a 5 percent difference in error,
    • 5 pound per bushel differences in test weight, or 
    • temperature changes greater than 10 degrees.
  • Be sure to recalibrate after replacing yield monitor components or if changes are made to the elevator chain, paddles or flow sensor during harvest.
    • Tightening the elevator chain, replacing old paddles or changing the distance between the flow sensor and paddles changes the accuracy of the previous calibration.
  • If you run into problems with the monitoring equipment during harvest, check the troubleshooting information in the operator’s manual. Contact technical support if you are unable to solve the issue.
Table 1. List of Various Yield Monitors by Company.
Company Product Name Website
Ag Leader Yield Monitor
AGCO FieldStar II / See FUSE technology or 
Case IH AFS 
CLAAS Quantimeter 
John Deere GreenStar 
New Holland See Precision Land Management (PLM)
Precision Planting YieldSense
Topcon YieldTrakk or

Visit the Ohio State University’s Precision Agriculture Web Site for additional Precision Ag information.