Agriculture Reference
In-Depth Information
temperature within a plant greenhouse or an animal housing facility that was estab-
lished by the farm manager. This value is entered into the automation system by the
user (human) through some type of analog or digital interface. If the human is to suc-
cessfully interact with the automation system, the interface must be designed so that
it has a proper human factors design and appropriate man-machine interfaces. The
system must show proper concerns for human limitations, including human sensing
and actuation limitations and human accuracy and dynamic response. If the human
interaction is to be repeated at frequent intervals, it must be designed to avoid under-
loading or overloading the humans with demands to interact with the system.
Rather than a fixed setpoint or a setpoint that the human changes directly, a rela-
tionship should be entered in some automation systems. For example, this might be
a relationship between milk production and dairy concentrate feed to be fed to an
individual cow. Another example would be the relationship between fruit tree size
and the amount of fertilizer to be applied above the root zone of that particular tree.
These relationships are often input into the agricultural automation system by some
type of computer programming in a high-level language.
Setpoints can also be supplied by other automation systems. For example, a pre-
cision agriculture system may generate setpoints for a pesticide applicator automa-
tion system. Or there may be multiple serial or parallel control systems in which a
supervisory control system supplies the setpoints to individual automation systems.
The sensors used to gather human input can be pushbuttons, dials, and the like.
These often provide voltage levels to the automation system via switches, potentiom-
eters, encoders, etc. Of course, keyboards, touch screens, and keypads can be used to
provide input to computer-controlled systems. Whatever input hardware is used, it is
usually important to provide the human with confirmation that the input has occurred.
This can be accomplished by such methods as sound, deformation, or screen display.
Here we are including human interfaces within the category of sensors. However,
the term “sensors” is most often used to refer to items that measure a physical quantity
without human intervention. For example, temperature-sensitive hardware devices,
such as thermocouples and thermistors, which provide variable voltage outputs, are
called “sensors.” In agricultural automation, the greatest use of sensors is those that
measure agricultural variables. These may be as diverse as those devices that mea-
sure soil organic matter percentage, atmospheric temperature, animal weight, plant
height, and a seemingly endless variety of other parameters.
Such sensors are a critical element, often the most crucial, to the successful per-
formance of the agricultural automation system. They must measure the quantities
accurately. Sensor accuracy can be subdivided into static accuracy and dynamic
accuracy. Static accuracy is the accuracy of the sensor when the quantity being mea-
sured is not changing. The first requirement of agricultural automation systems is
that the sensors give accurate data in such situations.
However, it is sometimes forgotten that sensors must also have dynamic accu-
racy. When the parameter being measured changes, the sensor must follow that
change sufficiently fast so that the agricultural automation system still performs the
approximately correct actions. There often is a trade-off between static accuracy and
speed of response. Sensor design and selection must reflect the appropriate trade-off
depending on the nature of the particular application.
