Electrical actuation systems

Intro.. Actuator is a device which is used to actuate a process. Actuate is to operate the process. Switching devices – mechanical switches, eg. relay and solid state switches, eg diodes, thyristors and transistors app – switch on or off electrical devices Solenoid – type devices used to actuate valves of hydraulic and pneumatic systems. (flow control) Drive systems – DC motor, AC motor and stepper motor.

Basic electronics Semi-conductor Diode Transistor Resistor

Mechanical switches Electronics specification and abbreviation Expansion of abbreviation British mains wiring name Description Symbol SPST Single pole, single throw One-way A simple on-off switch: The two terminals are either connected together or disconnected from each other. An example is a light switch. SPDT Single pole, double throw Two-way A simple changeover switch: C (COM, Common) is connected to L1 or to L2. SPCO Single pole, centre off    switches with a stable off position in the centre DPST Double pole, single throw Double pole Equivalent to two SPST switches controlled by a single mechanism DPDT Double pole, double throw Equivalent to two SPDT switches controlled by a single mechanism. DPCO Double pole changeover or Double pole, centre off Equivalent to DPDT. Some suppliers use DPCO for switches with a stable off position in the centre Mechanical switches

Mechanical switches Relay - A relay is an electrically operated switch.

Relay Electrically operated switches in which changing the current in one circuit switches a current on or off in another circuit. NO – normally open , NC – normally closed Output from controller is small so it is often used with transistor. Relays are inductances Free – wheeling or fly back diode. Importance To operate a device which needs larger current.