The Control of Processes and Machines
All but the very simplest machines and processes require some form of control. In earlier times, ingenious mechanical devices such as gears and cams (A cam is an eccentric or thicker-on-one-side lobe on a shaft that exerts varying pressure at predetermined angles, often used to control valves in internal combustion engines) were used to automate repetitive tasks. These mechanical systems were expensive to produce as they required high tolerance mechanical components, they were maintenance-intensive and were inflexible. Gradually these systems have been replaced by electromechanical systems which have also used cams for sequencing and motor-driven cam and gear systems for timing (Cam Timers are often used in domestic automatic washing machines). The electromechanical systems use a variety of switches and relays to perform logical and control functions and are more reliable and allow more complex equipment to be controlled. Evolution The gradual evolution of control systems from mechanics to electronics has resulted in highly sophisticated units which often employ embedded computers and may even be connected or "networked" to other controllers and computer systems to provide overall control of an entire process rather than a single machine or function.	Bi-axial Rotational Moulding Machine Controller
Networked Dual Fluid Flow Controller designed by Develec Dedicated Controllers Today, many machines are supplied with in-built controllers. The controllers are usually dedicated microprocessor-based boards, specifically designed by the manufacturer to suit the machine. Very often, however, a special machine is needed to perform a specific task. The Fluid Controller depicted on the left is able to control two valves and flow meters to dispense precise quantities of fluids such as oils and fuels. Multiple units may be networked together and controlled from a PC. A problem with dedicated controllers is that older machines may no longer be supported by their manufacturers and changing processes may demand process alterations that are difficult to implement using old-technology controllers.
PLCs A PLC being used by Develec to develop a control system for a rotational moulding machine in Auckland These requirements have led to the introduction of the Programmable Logic Controller or PLC. A PLC is a generic computer-based controller that can be applied in many diverse applications in industry. They are especially useful when custom machines or processes are designed or when existing machines or processes need to be adapted to perform new functions that were not envisaged by the manufacturer. PLCs are traditionally programmed using ladder-logic but lately, procedural languages such as C are in the ascendancy. PLCs can be used in conjunction with and can be controlled by PCs. Database systems such as SQL Server can be designed to store acquired data and to log production events. Internet access can be used to allow remote monitoring of your processes.
One of a pair of custom control panels used to control a rotational moulding machine in Auckland Which Technology is Best? Engineering can often be thought of as a science of compromises. It is impossible to say that one technology is better than another in a generic sense. Technologies are applied to real situations and the situation needs to be intelligently assessed from a technical perspective to determine feasibility. However, one should never neglect consideration of surrounding circumstances (e.g. budget, time constraints, etc) before deciding on an appropriate technology. Contact Develec Develec can use PLCs or can design custom controllers to solve your process control problems.
Where necessary, we design custom systems incorporating both off-the-shelf products such as PLCs and motor speed controllers and custom designed controllers, such as the Fluid Controller above. We can supply mimic panels or use PCs with Touch Screen Control to provide you with a control solution that suits your technical requirements and budget. We do not represent any specific manufacturer of control equipment or PLCs and therefore can evaluate and combine many products from a variety of sources to provide you with the best possible solution.