PLC Industrial Controls Flashcards
What does PLC stand for?
Programmable logic controller
What is the difference between control power and main electrical feed power?
Main electrical feed power is fed from disconnects and circuit breaker’s they also feed sections of a motor control center(MCC) Control power is the electrical supply that feeds things such as control consoles, solenoid valves, photocells etc.
What are the decision-making devices of electrical control systems?
Logic devices
What are some examples of electrical control inputs?
Mechanical movement, pressure, temperature, speed, light, float level
What is a switch?
It is a device designed to make and break an electrical circuit
What are some different types of switches?
Pressure switches, temperature switches, emergency stop switches, interlock switches
What did temperature switch is frequently contain?
Bimetallic element
What are some process control and monitoring switches?
Limit switches, pressure switches, liquid level switches, photocells, flow switches proximity switches
What is a control output?
The device that changes a small electrical signal current into useful work Some examples are pilot lights ,numeric displays, solenoid valves, servo valves, motor starters
What is a relay?
Uses low-voltage to switch to higher voltage. They have an electromagnetic coil and they make or break contact with the fixed contacts when power supply to the coil
How are released typically specified?
By the number of poles and numbers of throws The number of poles is the number of inputs and the number of throws is the number of possible outputs
What are some different types of relays?
- Latching Relays
- Time Delay relay’s
- Counters
- Solid-State Relays
What is the use of latching relay?
It remains in the switched state, until current is reversed to force another switch. It will not automatically switch back when power is removed
What are the two types of time delay relay’s?
- TDD-time delay de-energize
* TDE-Time delay energize
What is a solid state relay?
Is a relay with no mechanical linkage, no moving parts, so it will not arc when switching under load, can be used for high amps (1200 amps)
How is logic performed in a circuit?
Relays are connected in special ways by creating conditions to be met to get an output
What are the two types of logic available?
Hard Wired Logic
Programmable Logic
What are the three types of relay logic?
- AND Function
- OR Function
- NOT Functions
What is the “AND” function?
One relay controls a foot pedal, and one controls a limit switch. It could be wired that foot pedal “and” limit switch must both be made to activate solenoid
Describe the “or” function used with relays?
A foot pedal relay, “or” a limit switch relay must be made to activate solenoid
What is a sealed in relay?
Once it has been given a momentary on signal, it can be wired to stay on until the circuit is broken by another device.
How are ladders always shown?
In the de-energized state
What does a time delay and a pressure switch look like?
Both look like a single pole on off switch. The time delay will have an arrow up or down for TDD or TDE. The pressure switch will have a semi-circle
What does a normally open relay look like?
- –| |—- normally open
- –||— normally closed
