Industrial Controls/PLC Flashcards
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 a 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?
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, and programmable logic
What are the three types of relay logic?
The and, or, and 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
What is a master control relay?
It is used as an emergency stop in a ladder system
What are the components of a control system in a Plc?
Input devices, output devices, processor
How is a PLC selected?
Usually selected on the number of input and output points
What are the major hardware components to a PLC system?
Chassis and backplane, power supply, processor, I/O modules
What power supply should be used for the PLC?
Always use the recommended power supply device, or you risk damaging the plc
What concepts do all PLC units run on?
The binary concept
What is the basic principles of a Plc logic circuit?
A signal comes from an input device. It is interpreted by the processor and the set of rules programmed. The processor outputs a signal to the output module, which then sends a signal to the output device.
What is the ROM?
It is the PLC program, and is non volatile memory
What is the difference between the indicator lights on an input and output module?
The indicator light comes on when the input is made (limit switch activated). The output light comes on when the signal is sent, but there is no feedback to say output device is actually operating (cut wire)
What is the examine if closed symbol?
—-] [—-
The XIC is true when the bit is on one
Symbol is backwards from a relay
What is the examine if open symbol?
—-]/[—-
The xio instruction is true when the bit is 0
Opposite of a open relay symbol
What is an output energize symbol look like?
—-( )—–
What is the truth table for the and function?
Input A. Input B. Motor A True. True. True True. False. False False. True. False False. False. False
What is the truth table for the or function?
Input A. Input B. Motor A True. True. True True. False. True False. True. True False. False. False
