EC (Intro To Progrannable Control) Ch 15 Flashcards
(17 cards)
What are the three basic logic control functions?
- AND: All input conditions must be true
- OR: Any input condition being true will activate the output
- NOT: Reverses the state of an input
Examples include switches for AND, sensors for OR, and normally closed buttons for NOT.
Name five electrical control devices that provide input information.
- Push Buttons (NO/NC)
- Limit Switches
- Proximity Sensors
- Photoelectric Sensors
- Pressure/Temperature Switches
These devices are crucial for detecting conditions or states in a control system.
What types of electrical devices handle logic/decision making?
- Relays
- Timers
- Counters
- PLC Logic
These devices execute control and decision-making functions in a system.
List four electrical devices that provide output/work.
- Contactors
- Solenoids
- Indicator Lights
- Motor Starters
These devices perform actions based on the control logic.
What programming language do PLCs typically use?
Ladder Logic
Ladder Logic mimics relay diagrams and consists of rungs representing logic sequences.
What are three advantages of PLCs over hardwired logic?
- Easier to modify logic without rewiring
- Faster troubleshooting and diagnostics
- More compact
PLCs also offer programmability for complex operations and scalability.
Describe the relationship between the PLC processor and I/O.
The CPU scans Input Table, executes logic, and updates Output Table.
Inputs are read from sensors and outputs are sent to actuators.
Identify three PLC ladder logic symbols.
- | | = Normally open input
- |/| = Normally closed input
- ( ) = Output coil
These symbols represent the basic components in Ladder Logic diagrams.
What does a simple PLC ladder logic for a motor starter look like?
Start PB | Stop PB | OL Relay | Motor Coil
–[ ]——[/]——–[ ]———–( )
This represents the control sequence for starting and stopping a motor.
Name four devices that condition input signals to a PLC.
- Signal conditioners
- Opto-isolators
- Debounce circuits
- Analog-to-digital converters (ADC)
These devices ensure that the signals sent to the PLC are clean and usable.
What is stored in PLC memory?
- Input and output states
- Program
- Timers
- Counters
- Internal variables
This information is essential for the PLC to function correctly.
What are the types of PLC memory?
- RAM – Temporary storage (volatile)
- ROM – Permanent storage (non-volatile)
- EEPROM/Flash – Holds user programs even during power loss
Different types of memory serve various purposes within the PLC.
Outline the logical path of an input in a PLC.
- Sensor sends signal to PLC input
- Input is stored in the Input Table
- CPU reads table, executes logic
- Output table updated
- Actuator is energized
This sequence illustrates how inputs are processed to produce outputs.
Give an example of a simple PLC control circuit.
I0.0 (Start) | I0.1 (Stop NC) | Q0.0 (Motor)
–[ ]————-[/]—————–( )
This circuit represents a basic start-stop control for a motor.
How do you convert relay logic to PLC?
- Replace push buttons with PLC input addresses (e.g., I0.0)
- Replace contactors with PLC output coils (e.g., Q0.0)
- Replace timers/counters with internal PLC instructions
This conversion process allows for easier implementation of control logic.
What is the role of the data communication highway in a PLC system?
- Allows PLCs to communicate with:
- Other PLCs
- HMIs (Human Machine Interfaces)
- SCADA systems
- Remote I/O or networks (Ethernet/IP, Modbus, etc.)
This communication is essential for integrated industrial automation.
What functions does a complete PLC system perform in industrial use?
- Inputs collect data from machines
- CPU processes logic
- Outputs control motors, valves, etc.
PLCs are widely used in packaging, automation, manufacturing, and material handling.
