Week 4: Mechanical Switches, Electromechanical Switches and Solid State Switches Flashcards
(48 cards)
What is a mechanical switch
It is operated mechanically to turn ON or OFF current in an electrical circuit based in mechanical inputs like button, pressers, levers and or physical contacts
Components required to make a mechanical switch functional
They have one or more sets of movable electrical contacts connected to an external circuit that touch each other to make contact for current flow and separate to interrupt current flow
How does the mechanical switch operate
The load is connected in series with the power supply and mechanical switch. As long as the switch is open, there is no current flowing.
Classifications of switches by contact arrangement
Some contacts are normally open until closed by operation of the switch, while others are normally closed and opened by the switch action.
Switch with both types of contact
A changeover switch
Applications of mechanical switches
Pushbuttons, selector switches, limit switches, Toggle switches, flow switches, float switches, slide switches
How does a flow switch work
These notice when air or liquid starts moving in pipes and react accordingly
How a float switch works
These have a floating device that triggers a switch based on water level changes.
Limitations of mechanical switches
For a large load current, switch contacts have to be made heavy to carry current without overheating. This increases the size of the switch. Sparking during breaking causes wear and tear. High inertia results in low operation speed.
What is an electromechanical switch
It is a mechanical switch operated electrically to turn ON or OFF the current in an electrical circuit.
Common example of electromechanical switch
A relay, an improved form of a mechanical switch
What is a relay
A relay is an electrical switch that controls a high voltage circuit using a low voltage source. It isolates low voltage from high voltage circuits.
Contacts on a relay
NC contact, NO contact, Pole, Relay coil
How a relay works
Current through the coil magnetizes it, creating a magnetic field that moves the pole from NC to NO contact
Applications of electromechanical devices
Automatic changeovers, microprocessor control of heavy load, overload relays for machine protection
Advantages of electromechanical devices
Requires small power, permits smaller switch, remote operation, no sparking risk due to relay coil switching
Limitations of electromechanical devices
Slow operation, moving parts lead to wear and tear
What is a solid state switch
Device that uses electronic components to turn ON/OFF current in a circuit without moving parts
Difference between mechanical and solid state switch
A solid state switch operates by changing internal electronic state with a control signal
Meaning of solid state
No moving parts, uses semiconductor devices
Beneficial characteristics of solid state devices
High speed, absence of sparking
Examples of solid state devices
Transistors (BJT, MOSFET), SCR, SSR, UJT, TRIAC
Four regions of BJT operation
Saturation Region, Cut-off Region, Active region, Breakdown region
BJT regions applicable for switching
Saturation Region, Cut-off Region
