There are two main reasons for this.
- Grain compaction.
- Temperature stability.
If the grain has only just been laid, then the compaction is uneven throughout the depth and will become stable after a few days on the floor or in the bin. You’ll see the readings stabilise as the compaction settles down.
If the grain has been down for some time, then most commonly the GrainSpear hasn’t been inserted into the grain far enough, it really needs to go in for approximately half its length to get an accurate reading.
When the GrainSpear is initially turned on, the first reading it displays is temperature. This is deliberate, as the temperature of the sensor needs to stabilise before a moisture reading is taken. The most common error is for the operator to switch the instrument immediately to moisture before inserting the spear and not allowing the temperature to settle.
That depends on how good your sampling regime is, because sampling is often the biggest source of error in moisture measurement. The more samples you do per load the more confident you’ll be about the accuracy. Typically +/- 0.5% would be a sensible margin of error to use.
There are two questions here.
- Is the reading in one year different to a reading in another for the same product?
- Is there great variability within samples from one year but not in another?
If the question is 1), then growing and harvesting conditions will be different year to year and can affect the readings especially with freshly harvested grains. These differences will usually disappear within a week or two once stored.
If the question is 2), then this usually means that something affected the harvesting, such as lodging, sprouting or a high proportion of green grains. Also other things will affect resistance and capacitance readings, such as soil contamination, screenings or other non-grain material. Also ensure that the correct volume of sample is used for testing, the smaller the volume, the greater the error. If you’re not sure what the volume should be, check the instrument user manual or call the Sinar Technology Service Centre.
Don’t be too eager to get the crop in, make sure it’s fully ripe before harvesting as a lot of technical problems are due to unripe seed within the sample, particularly with Oilseed Rape.
The moisture in the samples off the drier will not be distributed evenly and also the temperature will not be stable. Allowing the commodity to settle for a few days will even these differences out and thus provide a more consistant reading. To obtain a more accurate reading directly off the drier, spread the sample on a tin tray and allow it to cool to ambient temperature. Although our meters do have in-built temperature compensation if there is a big differential in temperature the compensation system is not as effective, i.e. hot grain out of the drier and a sample cell at ambient temperature.
The best way is to send it back to the Sinar Technology Service Centre where we have all the correct equipment and calibration standards to check and adjust the instrument across it’s entire range of functionality.
It’s very important to monitor on-floor drying, or in-bin storage, regularly. If you’re using a meter, rather than a Grainspear, samples must be collected and tested using a sampling probe. This will ensure that samples are taken from the commodity at various, pre-determined levels and not just randomly up and down the heap. The horizontal position of each sample should be noted along with the results to ensure that drying is progressing both vertically and horizontally. This process means taking a lot of samples and testing, but it’s essential to ensure correct drying and to detect problems, like blocked ducts or fungus growth, at an early stage. Talk to our sales department for your sampling probe requirements.
Meters that are regularly calibrated by us should give reliable results. Getting an unexpected claim does not always mean that your meter is wrong but is an indication that something may be wrong. A good way of ensuring that your meter is correct is to purchase known calibration standards from us (part No 1900-6352), and check your meter against them regularly throughout the harvest. At the first sign that your meter is incorrect contact the Sinar Technology Service Centre and we will help you solve the problem.
Checking your meter against another meter of different manufacture and unknown accuracy is not recommended as this can give misleading & confusing results.
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