Control Technologies
Microprocessors and microcontrollers are part of a wide range of technologies used in control systems. These include:
• Electromechanical relays
• Programmable logic controllers
• Microcontroller-based boards
• Dedicated microprocessor designs
• PC-based controllers
• Networked control systems.
To complete an overview of controllers, and to allow comparison with PIC microcontroller- based systems, the essential features of these are outlined below.
Electromechanical Control
A familiar example of an electromechanical sequence controller is found in traditional domestic washing machines (non-digital types). A motorized rotary switch slowly operates multiple contacts in the required sequence to open valves (filling), and switch on motors (washing, spinning and pumping) and heaters. Switched sensors (level, temperature) and safety interlocks (door switch) are connected to the same rotor. In this way, purely electromechanical components can be used to make a robust sequence controller, where the environment is hostile to delicate electronics. However, switches and relays are inherently unreliable because of the moving parts and wear on the contacts due to arcing and mechanical forces.