Ensuring the Most Accurate Moisture Readings
4 Aug 2017
When collecting moisture readings with a HarvestMaster plot harvest data system, it is important that you follow these few fine-tuning procedures to ensure the greatest accuracy possible. If you need more general information on grain moisture reading, please refer to the Creating Moisture Sensor Curve section of your Harvest Data Owner’s Manual.
In some cases, we have found harvest systems to be similar enough that the same moisture curve can be used on several harvest systems that have the same hardware configuration (e.g. moisture blade length and test chamber size), and that are measuring the same type of grain. This has been proven most reliably when using the latest models of the High Capacity GrainGage and HM-1000b GrainGage and all models of the H2 series weigh systems.
The following steps will explain some techniques that have been proven to reduce the error in the moisture calibration process. These steps will also help you to produce moisture measurement accuracy levels similar to or better than what can be achieved on a standard bench-top moisture tester.
Selecting a Pre-Calibrated Moisture Curve
Several recommended pre-calibrated moisture curves can be viewed in the spreadsheets at:
- HM400 Capacitance Moisture Sensor Curves (xls)
- HM800 Electro-Magnetic (EM) Moisture Sensor Curves (xls)
- H2 Electro-Magnetic (EM2) Moisture Sensor Curves (xls)
Your harvest systems test chamber volume, size of the moisture blade, and grain type are the factors needed to determine which moisture curve to select. Each factor is referred to in the worksheet tab name. Because the GrainGages have standard moisture blade lengths, the GrainGages are referred to directly in the heading of each moisture curve, in place of the blade length.
If a pre-calibrated moisture curve does not exist for your bucket system or grain type, you will need to create a moisture curve from scratch by following the instructions given in the Creating Moisture Sensor Curve section of your HarvestData Owner’s Manual.
There is no guarantee that these curves will be immediately accurate when first entered into a harvest system, especially on the various configurations of bucket systems made by different manufacturers. However, these pre-calibrated moisture curves provide a good starting point in achieving more accurate moisture readings and reducing the effort required in achieving this level of accuracy.
Entering Pre-Calibrated Curve into HarvestData System
Entering a pre-calibrated moisture curve into a HarvestData system may require copying an existing default curve and then manually entering each individual moisture point. Once all moisture points have been entered, you will need to set the Calibration Temperature (such as to 24 degrees Celsius). Leave the Moisture Correction Multiplier at 0.092 for Corn and change it to 0.045 for smaller grains such as canola, wheat, and barley etc.
Note- If you are using a twin system (two bucket systems on one combine), you can use the same pre-calibrated moisture curve on both sides of the harvest system. To save time and energy, you can enter the moisture curve into one side, and then copy it to the other side.
The pre-calibrated moisture curve has now been entered into the harvest system. Please continue to the next step for instructions on how to test the accuracy of the curve.
Testing Moisture Curve Accuracy
After entering a moisture curve into the system, you can verify the accuracy of that curve by running several previously collected grain samples with various moisture content through the system. The easiest way to obtain calibration samples of varying moistures is to harvest high moisture grain and dry down sub-samples to the desired moisture content. Sealing the samples in a plastic bag and storing them in a refrigerator is a good way to extend the life of the samples. However, always allow the sample to warm to ambient temperature before using them to calibrate or check calibrations.
NOTE: Do not use “re-wet” or “water-added” samples for the calibration process. The physical characteristics of “re-wet” grain are significantly different than freshly harvested or naturally drying field grain and can adversely affect readings from the EM sensor. Storage of grain samples (at room temperature) should be in unsealed containers to prevent the collection of surface moistures. The grain samples should be kept out of direct sunlight as it only takes a few minutes for the grain to start “sweating,” which can also affect readings. It is also important to note that when you are dumping samples through the system, you cycle the grain through the system as it would during normal harvest conditions. For example, if there are holding hoppers present, use the holding hoppers to dump the grain into the system.
When testing moisture curve accuracy, HarvestMaster recommends using samples that are of the same weight as an average plot. We also recommend checking at least 4-5 sub-samples (from each sample) using a high-quality desktop moisture analyzer (i.e. Perten or Gac) no later than 1hr before cycling them through the system. When samples are used to calibrate with, it is good practice to check the moistures both before and after the calibration process. Sometimes the moisture changes and it is better to use an average of the actual moisture of the samples both before and after.
Note: Before proceeding, ensure that the desktop moisture analyzer is properly calibrated.
For even better accuracy, harvest through several test plots (usually field borders), and then compare the results to measurements of the same grain in a desktop analyzer. Record the results, such as the percent moisture difference between the harvest system and the desktop analyzer, onto a sheet of paper or into a spreadsheet.
Use samples that confirm the curves accuracy at the lowest, average, and highest percent moisture content that you will be harvesting. Averaging readings of several grain samples with similar moisture content can also increase the accuracy of tests. This will also verify the exact percent that the harvest system may be off from the desktop analyzer readings. The moisture curve can be manually tuned if needed (see “Manually Tuning the Moisture” section below).
Testing of the moisture curve can be performed in the calibration screen within Mirus, in Harvest mode using a test map (refer to the Generating a Field Map section of your Harvest Data Owner’s Manual for more information), or can be tested in Diagnostics under the Moisture section. If testing in Diagnostics when using FRS, you will need to enter Harvest only to the point of selecting the new moisture curve, press Enter on the curve to enable it, and then you can press Escape until you are back out of harvest. With Mirus, you can simply select the appropriate moisture curve for use.
Note- It is recommended to Retare the empty buckets before performing these tests. A Retare can be performed either in Harvest mode or in the Load Cell section of the Diagnostics menu.
Record all test results for reference while performing the next step of adjusting the moisture curves calibration temperature.
Manually Tuning the Moisture
To adjust the moisture manually in Mirus, go to “Setup, (Select your GrainGage), Moisture Curves”. Highlight the curve you want to edit, and click the “Pencil” icon down below. This will open a screen that lists your moisture curve % and the corresponding moisture voltages. If using FRS, go to the EDIT moisture curve option for the curve you want to tune.
To adjust the curve, we want to move the moisture % either up or down.
Example: This is what you will see in the edit moisture curve screen. If the system is reading 4% Higher than the desktop unit, you would lower each point by 4% starting at 10%. So 10% becomes 6%, 13% becomes 9%, etc…
Always leave 0 at 0.00.
After doing this, rerun your samples and see if the systems match up now.
If the system is reading lower, you would add 4% to each point on the curve starting at 10%, so 10% becomes 14% etc…
Give this a try, if the systems isn't reading correctly still you will have to run a new calibration for the moisture. To do this, we will need 4-8 samples of varying moisture to set a good curve.
Note: Additional information can be found Creating Moisture Curves in Mirus.
Syncing Moisture Calibration Across Combine Fleet
The best time to sync moisture calibrations is right before harvest. The most important step before syncing each combine is to make sure all machines have an accurate moisture calibration (see “Test Moisture Curve Accuracy” above).
Now that all machines have a unique or pecalibrated moisture curve. Take all machines out to the field (preferably all in the same day) and harvest some border plots capturing the samples for each machine. Follow the steps outlined under “Manually Tuning the Moisture” section for each machine.