Variable rate technology

The discovery and use of metals at the end of the Stone Age was one of the most important steps in the development of modem technology. Most base metals are, unfortunately, not stable. In unfavorable environments they can be destroyed at variable rates by corrosion. The study of such corrosion reactions and the methods by which corrosion of metals can be fought is a task of great economic significance. 

Abstract This chapter looks briefly at the history of precision farming techniques and how they have evolved up to the present day. It covers the costs and benefits of the technology and techniques, and then describes the various mapping methods that can take place on-farm these days. It discusses the use of auto-steering and variable rate application in particular. It also discusses the difficulties sometimes encountered when interpreting data. Finally it looks at the possible future of precision farming, with its potential use of robotics and data management. 

Control decisions for variable rate application can be implemented either on-line or off-line. In the on-line, or sensor-based approach, the controlled equipment incorporates onboard sensors and the sensor data are used immediately for automatic control. In the off-line, or map-based approach, data are collected and stored in one operation, and the controlled equipment uses the information in a separate field operation. The map-based approach allows more flexibility in data manipulation and pre-processing but requires multiple field operations. Most systems currently available are map-based, but more on-line systems will likely become available as real-time sensing technologies become more mature. Hybrid systems which rely on a combination of both mapped and real-time data may also come into more widespread use. 

There can be an element of maintenance costs that is fixed and an element which is variable. Fixed maintenance costs cover routine maintenance such as regular maintenance on safety valves which must be carried out irrespective of the rate of production. There also can be an element of maintenance costs which is variable. This arises from the fact that certain items of equipment can need more maintenance as the production rate increases. Also, royalties which cover the cost of purchasing another company s process technology may have different bases. Royalties may be a variable cost, since they can sometimes be paid in proportion to the rate of production. Alternatively, the royalty might be a single-sum payment at the beginning of the project. In this case, the single-sum payment will become part of the project s capital investment. As such, it will be included in the annual capital repayment, and this becomes part of the fixed cost. 

Coupling digital controls with networking technology permits information to be passed from level-to-level within a corporation at high rates of speed. This technology is capable of presenting the measured variable brom a flow transmitter installed in a plant in a remote location anywhere in the world to the company headquarters in less than a second. 

A recent innovation to improve recovery functions is a variable-speed submersible pump. When used with electronic controls, it is possible to select a fluid surface elevation and adjust the pumping rate periodically to maintain that fluid level at that elevation. Another adaptation of existing control technology uses an electrically adjustable valve to throttle the pump output. As the fluid level declines, the throttle restricts flow to prevent a further decline. 

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