How Yield Monitors Work

There are four different measuring techniques used for yield monitors around the world today. Ron C. Johnson, a writer and lecturer on precision agriculture and author of the book, Target Farming, A Practical Guide to Precision Agriculture, outlined for Precision Ag Illustrated a closer look at how yield monitors do their monitoring.

Johnson notes that there are four measurement techniques and several others currently under development. The four main measurement techniques in use are: Impact, or Mass Flow; Weight; Optical; and Nuclear. “The first two types of yield monitors are common in North America whereas the last two are European in origin and not commonly seen here (although the optical type is gaining popularity),” says Johnson. He notes that the nuclear monitor is currently outlawed in North America.

Impact, Or Mass Flow Yield Monitors

Impact yield sensors measure force exerted on a plate, paddle or fork by the grain coming off the top of the clean grain elevator. According to Johnson, John Deere’s sensor uses a potentiometer (which is a variable resistor something like the volume control on a stereo or TV). The potentiometer is mounted to a two-part bracket. Half the bracket is bolted to the combine frame and the other half is connected to the impact plate. The two halves of the bracket are held together by flexible strips which allow some movement as the grain hits a deflection plate. The harder the grain hits this plate the more the resistance of the potentiometer changes. This change is converted to an electronic signal which can be used to calculate yield.

Some impact-type yield monitors use a load cell instead of a potentiometer. A load cell is also a resistive device but it’s made of thin wire bonded to a flexible membrane. The membrane is then bonded to a metal member which receives mechanical stress from the impact plate. As the member flexes slightly, the thin wire is stretched enough to change resistance. Again this change in resistance is converted to an electrical signal which is used to indicate the yield.

Some yield sensors use a paddle (Ag Leader), others a fork (MicroTrak), which extends down into the flow of grain as it comes off the top of the elevator. The paddle or fork is sensed by using the load cell device. Impact yield monitors come up with a yield value by reasoning that the more grain coming off the top of the elevator, the more force exerted against the load cell.

Weigh-Type Yield Monitors

Weigh-type monitors use a load cell connected to a metal arm which supports the weight of either the hopper itself or the grain flowing through the clean grain cross auger. The more grain in the auger, the more force exerted on the load cell. Auger speed, temperature, suspension and inertia are factors which must be taken into account in this type of system.

Ag Tech is one of the companies manufacturing weigh-type yield monitors.

Optical-Type Yield Monitors

These monitors are manufactured by RDS in England and are now being sold by Satloc, Inc. These monitors use an infrared light and detector installed across the clean grain elevator. Empty auger paddles temporarily block the infrared beam shooting across the auger housing. When grain is on the paddles the beam is blocked a high percentage of the time as compared to the reading from an empty auger paddle. Like the impact monitor, calibration is accomplished by combining a certain amount of grain while in calibration mode. The actual weight is logged on a monitor and the monitor correlates the light signal with the yield.

Nuclear Yield Monitors

These monitors use a small radioactive source which transmits a beam of particles across the clean grain elevator and measures how much comes out the other side. The more grain the less radiation that gets through the flow. AGCO currently uses this method on monitors sold in Europe.

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