Keep a Close Eye on your Moisture Meter!
- 1 day ago
- 6 min read
Updated: 6 hours ago
For a grain producer, a difference of a few tenths of a percentage point in moisture content may seem negligible. However, this small difference can affect drying time, grain storage, and even the sold weight.
The 919/3.5-inch moisture meter, known for its durability, remains widely used on farms and at grain elevators across Canada. However, to be confident in the measurement obtained, it is not enough to simply place a sample in the cell and read the result. You must regularly verify that the device consistently provides a reading comparable to a reference value.
That is precisely the role of reference samples.
919/3.5-inch Moisture Meters in Canada
In Canada, the Canadian Grain Commission (CGC) maintains up-to-date conversion tables used with Model 919/3.5-inch moisture meters or equivalent devices. These tables allow the dial reading to be converted, taking the sample temperature into account, to a percentage of moisture content. Canadian calibrations are monitored and revised to ensure they remain consistent with reference methods.
The Canadian Grain Commission produces conversion tables (Canadian calibrations) for the Model 919 for operating temperatures between 11 and 30 °C. For this reason, it is recommended that samples, whether hot or cold, be allowed to gradually return to room temperature in an airtight container before taking a measurement.
The Commission annually compares the results of its reference moisture meters (919 and AM5200-A) with a reference method using oven drying. Its findings indicate that a properly calibrated and well-maintained 919 moisture meter can produce results comparable to those of other recognized technologies.
What is a Reference Sample?
A reference sample is a quantity of grain whose moisture content has been determined using a reference method or calibrated instruments. This value then becomes a known target.
For example, if a wheat sample has a reference moisture content of 14.2%, a moisture meter in good working order should produce a result very close to this value when the proper procedure is followed. If the meter instead reads 13.8% or 14.6%, this discrepancy warrants investigation.
The reference sample is not used solely to calibrate the instrument. Its primary purpose is to verify the instrument’s accuracy, detect any drift, or confirm the reliability of the measurement method.
What is a Calibration Sample used for?
1. To Verify that the Moisture Meter is Still Providing Accurate readings
The primary benefit of a calibration sample is simple: it lets you know if the moisture meter is measuring correctly.
Over time, several factors can affect the results of a 919 unit: wear and tear on components, a dirty sensor cell, poor electrical contact, an inaccurate scale, improper filling technique, or even variations in grain temperature.
A unit may continue to produce highly repeatable results while still being slightly off. In other words, it may almost always display the same value, but that value may be consistently too high or too low.
The reference sample helps identify this problem. If several consecutive readings deviate from the known value, the user can check the scale, clean the cell, review their procedure, and, if necessary, have the device inspected.
2. To Avoid Costly Decisions During Harvesting and Drying
The second important factor concerns decisions made based on the reading.
A reading that is too low may lead one to believe that grain is ready for storage, when in fact it still contains too much moisture. This increases the risk of mold growth, overheating, or a loss of quality.
Conversely, a reading that is too high may lead the producer to unnecessarily prolong the drying process. This results in additional propane or natural gas consumption. Over-drying also causes a loss of marketable weight. After all, 1% moisture equals 1% revenue.
In this context, a reference sample acts much like a trusted benchmark. It helps ensure that day-to-day decisions are based on a reliable measurement rather than on a mere impression that “the meter seems to be reading correctly.”
3. To Standardize Results Between the Farm and the Grain Center
The third advantage is the ability to compare results across different locations.
It often happens that a producer, for example, measures corn at 14.8% on the farm, while the buyer measures 15.3%. This difference may be due to the instrument, but it can also be caused by sampling, grain temperature, or the distribution of moisture within the kernels.
Reference samples allow you to compare multiple moisture meters using the same grain. This makes it possible to determine whether the devices provide similar results under the same conditions.
This verification is particularly useful before harvest, after a repair, or when recurring discrepancies appear between results from the farm and those from the grain center.
CAUTION!
Temperature, however, remains a critical factor. If there is a temperature difference between the reference sample and your moisture meter, this difference can introduce a calibration error. In fact, a 1 ℃ difference corresponds to a 0.1% discrepancy in the interpretation of your moisture meter’s reading. When aiming for a calibration accuracy of ± 0.1%, it quickly becomes clear that a temperature difference is critical.
How to Use a Reference Sample Properly?
To ensure a valid comparison, the sample must be stored in an airtight container to prevent moisture exchange with the air. A sample left in an open container may therefore gradually change in moisture content and lose its value as a reference.
CAUTION! What to Do Before You Begin
Here are a few guidelines to follow before you begin:
Clean your moisture meter thoroughly.
Turn on your moisture meter at least 1 hour in advance.
Allow your moisture meter to acclimate to a temperature between 15–20 ℃.
Allow your reference sample to acclimate to the same temperature as your moisture meter.
Make sure your charts are up to date (see the CGC website).
Next, follow the instructions for your 919 moisture meter exactly:
use the sample weight required for the type of grain;
check the device’s settings;
fill the cell correctly;
measure the grain’s temperature;
record the dial reading accurately;
consult the Canadian conversion table corresponding to the grain being analyzed.
Conversion tables are not interchangeable across grain varieties. The same reading on the 919 moisture meter may correspond to different moisture contents depending on whether the grain is soft, red, hard, winter, or spring wheat. Note that the varieties grown in Western and Eastern Canada are not exactly the same. It is therefore essential to use the correct conversion chart for the grain being analyzed.
CAUTION!
A single reading is not enough. It is best to take several measurements with the standard sample, ideally more than five. The average value will be more representative of reality and will also eliminate errors caused by the natural variability of the tests.
Highly scattered results may also indicate a problem with sample handling, cleanliness, or stability. They may also indicate that your moisture meter needs to be inspected. A malfunction in one of its components may be the cause.
A Good Practice Before Each Season
The three most important reasons to keep in mind when using reference samples are:
The calibration sample helps confirm the accuracy of your moisture meter.
It reduces the risk of making poor decisions regarding drying or storage.
It makes it easier to compare the instruments at your grain center with those used by buyers.
Ideally, every company should calibrate its moisture meters before the harvest begins and then repeat the process periodically throughout the year. Recalibration is also recommended after a repair, relocation of the meter, or the occurrence of an unusual deviation.
Conclusion
The 919 moisture meter remains an essential measuring tool, but its reliability depends as much on its condition as on the method used by the operator.
Although reference samples can turn a simple reading into a much more reliable measurement, the fact remains that your sampling method must be rigorous. Only a representative sample will give you an accurate picture of what’s in your shipment.
Also, make sure your scale and thermometer are calibrated, and don't forget to update your conversion charts.
Taking all these precautions will help ensure that the entire process is functioning properly. During harvest season, when decisions must be made quickly, this verification can prevent many unpleasant surprises. Spending a few hours checking your measuring instruments can help prevent over-drying, weight loss, storage issues, and disputes at the time of delivery.
Useful Links and Sources
Canadian Grain Commission, Grain Research Laboratory. The Evolution of Rapid Moisture Analysis at the Canadian Grain Commission. https://www.grainscanada.gc.ca/en/grain-research/grl/annual-program-report/2023/evolution-rapid-moisture-testing.html
Canadian Grain Commission. Moisture Content of Canadian Grains. https://www.grainscanada.gc.ca/en/grain-quality/grain-grading/grading-factors/moisture-content/
Canadian Grain Commission. Conversion Tables for Model 919/3.5-inch Moisture Meters or Equivalents. https://www.grainscanada.gc.ca/en/grain-quality/grain-grading/grading-factors/moisture-content/moisture-meter-conversion-tables.html
Canadian Grain Commission. Moisture Meter Comparison. https://www.grainscanada.gc.ca/en/grain-quality/grain-grading/grading-factors/moisture-content/moisture-meter-comparisons.html
Purdue University Extension. Grain Quality Fact Sheet No. 14: Moisture Testing of Grain. https://www.extension.purdue.edu/extmedia/gq/gq-14.html
North Dakota State University Extension. Get Accurate Moisture Content Measurements. https://www.ag.ndsu.edu/news/newsreleases/2009/nov-2-2009/get-accurate-moisture-content-measurements
