Sensors In Yield Monitoring
Sensors used in grain yield monitoring,
their functions, and how grain yield is calculated instantaneously.
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| Displacement-type grain flow sensor. |
Yield monitoring is one of the most popular precision agricultural applications among farmers across the country. Yield monitoring sensors have enabled farmers to quantify inherent variability that exists in their fields. It has given a sense of realization to farmers what factors (such as weeds, insects, pests, diseases, soil compaction, etc.) can cause significant damage to their crop. Traditionally, farmers had one average number in terms of crop yield for a field. Average crop yield masks the variability in yield that exists across a field. Although farmers know their fields well and are able to estimate the performance of crop in different parts of the field, yield monitoring have transformed those “estimates” into real, quantified crop yield values.
More and more combine manufacturers are providing their customers with combines that are equipped with Global Positioning Systems (GPS), yield monitors and mapping technology. It is fast becoming a standard part of new combines. This article provides information on various sensors and their functions in a grain yield monitoring system. Although some of the sensors may vary from one manufacturer of yield monitoring system to another, most instantaneous yield monitoring system has the following sensors: (i) Grain flow sensor; (ii) Grain moisture sensor; and (iii) Ground speed sensor.
(i) Grain Flow Sensor: There are several grain flow sensor that are commercially available. However, the most common one used for grain crops is the “Impact Plate Sensor”. It is mounted at the top of the clean grain elevator i.e., in the path of the grain. The volume of the grain moving through the clean grain elevator is measured two ways: (a) by the amount of force the grain applies as it hits the impact plate, or (b) by the amount of displacement of the impact plate that occurs when grain hits the impact plate. Either way, the force on the impact plate or displacement of the impact plate is in-directly related to the amount of grain flowing through the clean grain elevator. This measurement is recorded by the computer in the combine every second along with the GPS data, which is used to prepare a yield map.
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(ii) Grain Moisture Sensor: Determining moisture content of the grain is important for various reasons including, time of harvest, estimating costs associated with drying of grain, storage and handling issues to minimize losses, and the farmer’s ability to make comparisons in crop performance. There are several grain moisture sensors that are commercially available. However, the most common one is based on measuring the di-electric properties of the grain. As the grain flows through the clean grain elevator, the grain moisture sensor that is located near the grain flow sensor measures the di-electric constant of the grain. Di-electric property is related to the moisture content in the grain. The higher the di-electric constant of grain, higher the moisture content. (iii) Ground Speed Sensor: There are various ways by which ground speed can be measured, such as radar sensors, GPS unit readings, shaft speed sensors, etc. Speed information is needed by the computer in the combine to estimate the area harvested in certain time period. Speed is converted into distance (multiplying speed by time). Distance covered is then multiplied by the swath width of the combine header to calculate the area harvested. The information from the grain flow sensor along with information from the speed sensor together provide instantaneous data to calculate grain yield harvested every second at a certain moisture content that is ascertained from the moisture sensor. |
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For example: An 8-row header at 30-inch row spacing recorded the following information for the previous second on a corn yield monitoring system. Grain flow sensor recorded: Instantaneous yield for the previous second is calculated as follows. (i) Area harvested during the previous second: 8 row corn x 30 inch spacing = 240 inch or 20 ft header width. Combine speed for the previous second was 4 miles/hour i.e., 4 miles/hour x 5280 ft/mile x 1hr/3600 seconds = 5.9 ft/second (Speed of combine) Area = 20 ft x 5.9 ft = 118 ft2. |
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The combine harvested 30lbs of grain during the previous second from an 118 ft2 area. That translates into
30 lbs/118 ft2 x 1 bushel/56 lbs x 43,560 ft2/acre = 198 bushels/acre grain yield. This would be the wet grain yield at 17.5 % moisture content.
(iii) Corrected grain yield at 15.5 % moisture content:
(198 bushels – [198 x 0.175]) x 1/0.845 = 193 bushels/acre corn grain yield at 15.5 % moisture.
The computer on the combine performs the above calculations instantaneously for all the readings recorded by the yield monitoring sensors and displays the information on the “Display Console” in the combine. Farmers view the yield information every second as they drive their combine across the field.
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The sensor pictures used in this article were reproduced by permission of Deere & Company, John Deere Publishing, Moline, IL. All rights reserved. |
