1. Introduction to mechanical and electromechanical switches
2. Fundamentals of Operational Amplifiers and Comparators
3. Thermal Transducers
4. Optoelectronics Devices
5. Pulse and Timing Control Circuits
6. Thyristors Control Circuits
7. Industrial applications of digital devices
8. Automated Machine Technology and Robotics
9. Industrial Robotics
Actuators
Mechatronic Systems
Mechatronic Systems-Control Architectures and Case Studies
LECTURE OUTLINE
Unit 1: Introduction to Mechanical and Electromechanical Switches
General Principles and Operation
Switches are crucial components in electrical and electronic circuits, used to make or break the path for current from a power source.
They energize or de-energize a load through actuation.
There are various pole and throw combinations to facilitate different switching schemes.
Relevant concepts include:
Bipolar junction transistor switching actions
Hall voltage and magnetic flux cutting across semiconductor materials.
SWITCHES
Definition and Characteristics
Switches serve as input devices (transducers) equipped with metal contacts that allow current to flow when touching.
They are employed to open or close connections within a circuit and are characterized by:
Number of poles (P)
Number of throws (T)
Normally Open (NO) or Normally Closed (NC) connections.
Terminology
Pole: A moving element within a switch that makes or breaks a connection.
Throw: A contact point associated with a pole.
Make or Break Effect
Closing a switch makes a circuit (current flows), while opening a switch breaks the circuit (current ceases).
The idiom "make or break situation" signifies that the outcome will definitely lean towards one of two extreme results.
TYPES OF SWITCHES
Standard Control Switches
Standard Control Switches are commonly used to control electrical circuits, devices, or equipment. Examples include:
Toggle Switch
Push Button Switch
Rocker Switch
Slide Switch
Rotary Switch
Dip Switch
Process Operated Switches
Process operated switches are designed for industrial applications to manage different operational aspects. Types include:
Limit Switch: Activated by physical interaction with an object, used to control machinery movement.
Proximity Switch: Utilizes sensors to detect objects within a specified range, important in automated manufacturing.
Pressure Switch: Reacts to pressure changes, controlling fluid or gas flow.
Level Switch: Detects levels of liquids or materials, pivotal in process control.
Temperature Switch: Activates based on temperature thresholds, utilized in HVAC systems.
Flow Switch: Monitors fluid flow within a system.
Photoelectric Switch: Senses the presence of objects through light detection, eliminating physical contact.
Humidity Switch: Responds to moisture variations, essential in climate control.
Vibration Switch: Detects excessive vibrations in machinery to prevent damage.
Switch Contacts Form
Different forms of switch configurations include:
Form A: SPST-NO (Single Pole Single Throw - Normally Open)
Form B: SPST-NC (Single Pole Single Throw - Normally Closed)
Form C: SPDT (Single Pole Double Throw)
Form AA: DPST-NO (Double Pole Single Throw - Normally Open)
Form BB: DPST-NC (Double Pole Single Throw - Normally Closed)
Form CC: DPDT (Double Pole Double Throw)
And variants with additional configurations such as SPST-DB and DPST-DB (with double break contacts).
NORMALLY CLOSED (NC) vs NORMALLY OPEN (NO)
Normally Closed (NC): Contacts remain engaged until switched, creating an open circuit when actuated.
Normally Open (NO): Contacts stay disengaged until actuated, closing the circuit when engaged.
CLASS EXERCISES
Scenario One: Bedroom Light
Situation: Mr. Holness wishes to have the light turn on automatically when he opens his bedroom door.
Advice: Recommend using a Normally Open switch since it allows the circuit to close (light on) when the door is opened.
Scenario Two: Network Operations Center
Situation: Jane requires a visual cue on the NOCC screen when someone opens the cell site door.
Advice: If Jane wants the visual cue when the door opens, use a Normally Open SPST switch; if when the door is closed, use a Normally Closed SPST switch.
CLASS DISCUSSION ITEM 9.1
Household Three-Way Switch
Definition: A household three-way switch permits controlling lights from multiple locations, utilizing SPDT switches.
Schematic Task: Create a wiring schematic to illustrate AC power connection from two switches to a light fixture for operation from two locations.
Electromechanical Actuating Devices
Relays
Definition: An electromechanical relay consists of a solenoid to establish or break mechanical contacts between electrical leads. Its benefits include controlling several high-power AC loads via low-power DC circuits.
Applications: Relay switches in power controls, various electromechanical elements.
Solenoids
Definition: A solenoid comprises a coil acting as an electromagnet, used to move an armature to facilitate actuation. When powered, it draws a core into the coil, enhancing magnetic linkage.
Applications: Utilized primarily for on-off applications like locking mechanisms or valve operations. They are typically spring-loaded for automatic retraction when de-energized.
Solenoid States
Unenergized: The plunger is extended due to spring force.
Energized: The coil induces magnetism causing the plunger to retract under magnetic attraction, closing the air gap. The spring force returns the plunger to its initial state when power is removed.
RELAY DIAGRAMS
Relay States
Unenergized State: Contact continuity between terminals indicates Normally Closed (NC) contact closed and Normally Open (NO) contact open.
Energized State: Activation leads to a magnetic field effect, altering contact states; NC opens, and NO closes to complete a circuit.
BIPOLAR JUNCTION TRANSISTORS (BJTS)
Definition
A bipolar junction transistor (BJT) is formed from three regions of doped silicon displaying two types: npn and pnp, with npn being the more prevalent variant.
Structure: Comprised of an emitter, base, and collector configured to function effectively in switching applications.
BJTS as a Switch
Configuration: The commonly used configuration is the Common Emitter which provides effective gain and well-defined switching behavior.
Operating Regions:
Saturation Region: Acts as a closed switch (Vce ideally approaches 0).
Cutoff Region: Acts as an open switch (high Vce close to Vcc).
CUT OFF vs SATURATION REGIONS
Saturation: A positive input drives the transistor into saturation where both junctions are forward-biased.
Cutoff: No input leads to both junctions being reverse-biased, effectively switching off the transistor.
Kirchhoff's Voltage Law (KVL)
KVL states that the total voltage around any closed loop in a circuit equals the algebraic sum of individual voltage drops within that loop. KVL is integral for analyzing circuits involving BJTs and switching operations.
THE HALL EFFECT
Definition
The Hall effect describes the creation of a voltage across a conductor when charge carriers are deflected in a magnetic field. The voltage produced is known as Hall voltage (VH).
Hall Effect Sensors
Types of mechanical and electronic sensing devices like microswitches and mercury switches are compared with Hall Effect sensors, which are preferable for non-contact level sensing applications.
Applications: Utilized extensively in automotive and industrial applications, particularly for measuring RPMs of rotating shafts, due to their solid-state reliability and speed compatibility.