Electro-Pneumatics (BEE 417L)

Electro-Pneumatics (BEE 417L)

• Electro-pneumatic is a combination of electrical and pressurized air systems
• Used in various industrial applications (production, assembly, pharmaceuticals, chemicals, packaging)
• Often used in low-cost industrial automation
• Controls pneumatic components using electrical impulses
• Integrates electrical and mechanical components with a compressed air source

Advantages

• Greater reliability
• Reduced installation complexity
• Easily modifiable and adaptable control system
• Easy handling
• Secure mounting
• Environmentally-friendly coupling system

Steps in Electro-Pneumatic Controls

• Signal Input Devices: Signal generation using switches, contactors, and proximity sensors
• Signal Processing: Combination of contactors, relays, or programmable logic controllers
• Signal Outputs: Processing results activate solenoids, indicators, or audible alarms

Signal Flow in Electro-Pneumatic System

• Command execution: Initiate the process
• Signal output: Final control elements (directional control valves)
• Signal processing: Intermediate elements (processing, shuttle, two-pressure valves, pressure control valves, sequencers)
• Signal Input: Input elements (directional control valves—mechanically/manually operated, air barriers, pneumatic components)

Components of Electro-Pneumatic System

• DC power supply
• Switches (control/push button)
• Relays
• Solenoid valves
• Sensors

Power Supply Diagram

• Transformer
• Rectifier
• Stabilization and power supply unit

Types of Switches

• Control switches
• Push button switches (normally open, normally closed, changeover)

Push Button Switches

• Normally Open (NO): Contact is open in normal condition. Pressing activates the circuit
• Normally Closed (NC): Contact is closed in normal condition. Pressing opens the circuit
• Changeover (CO): Allows switching between two circuits

Limit Switches

• Activated when a machine part or work piece is in a certain position
• Primarily actuated by a cam or cylinder piston
• Used for detecting the positions of mechanical elements

Detent Switches

• Keep the selected operating position unchanged, except when a new position is selected
• The switch is either in a latching or detent condition

Pressure Switches

• Pneumatic-electrical signal converter
• Sense pressure changes and open/close an electrical switch when a pre-determined pressure is reached

Temperature Switches

• Automatically detects changes in temperature, opening/closing an electrical switch when a threshold is reached
• Protect fluid power systems from damage caused by malfunctioning components (pumps, strainers, coolers)

Reed Proximity Switches

• Magnetically actuated proximity switches
• Similar to relays, using a permanent magnet instead of a wire coil

Relays

• Electromagnetically actuated switches
• Used for signal processing
• Resist heavy power surges for harsh environments
• Voltage application attracts the armature to the coil core, changing relay contact states
• Spring return mechanism returns the armature to its original position after voltage is removed

Timers or Time Delay Relays

• Provide time delays in control systems
• Common types are On-Delay (pull-in) and Off-Delay (drop-out)

Electronic Sensors

• Inductive, optical, and capacitive proximity switches
• Three electrical contacts (supply voltage, ground, output signal), without moving parts
• Two types depending on polarity of output voltage (positive switching, negative switching)

Inductive Sensors

• Detect nearby metal objects using induced currents due to magnetic fields
• Sensing distance relies on metal part conductivity and permeability, along with sensor coil diameter

Capacitive Sensors

• Detect materials at distances of a few centimeters, based on capacitance changes, due to changing dielectric constant

Optical Proximity Sensors

• Sophisticated light sensors using an emitter and a detector
• Types include opposed mode and emitter/detector in one unit
• Polarized light is used in some retroreflective sensors

Diffuse Sensors

• Use a broad light beam over a given range; sensitivity adjustment lets the sensor focus on a specific distance; require well-controlled conditions for accurate detection

Electric Counters

• Consist of a coil, associated circuits, contacts, reset coil, release button, and a display window
• Two types: Up Counter and Down Counter

Up Counter

• Counts electrical signals upwards from zero.
• Incremented by one with each electrical pulse input

Down Counter

• Counts electrical signals downwards from a preset value
• Decremented by one with each electrical pulse input

Safety Operation

• Pressurized air lines should be handled with care; switch off pressure immediately if detached
• Connect tubing before switching on the air supply; avoid manual operation of limit switches during fault finding
• Follow operating procedures for single-acting cylinders (direct and indirect control) to ensure safe operation

This quiz focuses on the principles of electro-pneumatics, which merges electrical and pneumatic systems in industrial applications. It covers advantages, control steps, and signal flow in electro-pneumatic controls essential for automation. Sharpen your understanding of this technology and its practical implications in various fields.