Controls and PLC Flashcards
What is a bleed hole on a valve?
A hole in a shut off valve that allows pneumatic air pressure to vent to atmosphere.
When shutting down and LOTO pneumatic systems, should the safety pins holding raised equipment be installed before or after shutting off the local air safety valve?
Before
The raised load should be pinned before shutting off the air.
With electrical controls, ____ devices prevent serious failures in the equipment.
safety
With electrical controls, ____ devices provide signals to the machine logic.
input
With electrical controls, ____ provide control management and regulation.
logic
With electrical controls, ____ devices provide power output control and interface.
power
This component of an electrical system conditions and suppresses voltage spikes and surges in feed power and can boost voltage during a short term slump.
Transient suppression transformer
A.K.A power line conditioners
What component of a PLC system is used to protect the processor and modules from low voltage conditions?
Transient suppression transformer
In regards to PLC’s, what is a power line conditioner?
A transient suppression transformer.
On electrical controls systems, any device that converts a mechanical/physical (pressure, temperature, rotation) characteristic into an electrical signal is called:
An input
What is a discrete switch?
A swtich that is either on or off
A light switch is a good example of a discrete switch.
What are the two common types of electrical pressure switches listed in the module?
- bellows-operated
- diaphragm-operated
What device is used to provide actuation of a temperature switch?
Bimetallic strip
This electrical switch is used where a rapid shutdown of equipment for safety or process reason is required.
Emergency stop (EDS) switches
This type of electrical switch is used to cause an action or prevent an action that would be detremental to the equipment involved or that would be hazardous to personnel.
Interlock switches
These are the sequence valves of electrical.
What function do interlock switches on reversing motor started provide?
They prevent both starters from closing at the same time.
This would result in a short circuit situation.
What type of electrical device is used to prevent an action from occurring if another action is already taking place, where damage could occur if both actions were to happen at once?
Interlock switch
This type of process control and monitoring switch detects objects by sending and receiving sound.
Ultrasonic proximity switches
What types of materials would a capacitive proximity switch be used to detect?
non-metallic materials
What type of materials would an inductive proximity switch be used to detect?
metallic materials
On an electrical control system, would a push button be an input or output?
It would be an input.
This would be an operator input.
True or false: Pushbuttons, selector switches and toggle switches all close one or more set of mechanical contacts to provide a control signal to an output or to a logic device.
True
These are all input devices.
On an electrical system, would a pilot light be an input or output?
It would be an output
Outputs are devices that change a small electrical control signal into usefull work.
On an electrical system, would a solenoid valve/servo valve be an input or output?
It would be an output.
Outputs are devices that change a small electrical control signal into usefull work.
On an electrical system, would a motor starter be an input or output?
It would be an output.
Outputs are devices that change a small electrical control signal into usefull work.
This device uses low voltage to switch a higher voltage.
Relays
What causes an electrical relay to activate or change states?
Magnetism in the coil
This causes the armature to pivot or slide, either making or breaking the contacts.
When it comes to electrical relays, what does the number of poles indicate?
How many separate circuits are controlled by a switch.
These can be both normally close (NC) or normally open (NO).
These are the number of electrical contacts that can be switched by the relay.
True or false: The contacts in a relay are always normally open, which closes (turns on) the circuit when power is applied to the coil.
False
Relay contacts can be both normally open and normally closed.
When it comes to electrical relays, what is a throw?
The number of positions that relay poles can be moved into.
These are both single poles switches, the only difference being the number of throws.
When it comes to electrical relays, what is the contact voltage rating?
The voltage the relay contacts can safely handle.
When it comes to electrical relays, what is the contact current rating?
The allowable current that the contacts can handle.
The relay contacts must be able to interrupt (open), carry, and make (close) this level of current safely.
With electrical relays, a ____ indicates the number of circuits that one switch can control for one operation of the switch.
pole
With electrical relays, a ____ indicates the number of contact points of a pole.
throw
Identify the number of poles and throws of the following electrical relay:
Single pole single throw (SPST) relay
Identify the number of poles and throws of the following electrical relay:
Single pole double throw (SPDT) relay
Identify the number of poles and throws of the following electrical relay:
Double pole single throw (DPST) relay
Identify the number of poles and throws of the following electrical relay:
Double pole double throw (DPDT) relay
This type of electrical relay stays in the on position after a brief application of power to the coil.
A latching relay
This type of relay also has an unlatching coil.
What are the two main types of time delay relays?
- pneumatic
- electronic
This type of time delay relay function results in the timed contacts changing state (from the energized position) after the pre-set time interval when the coil is de-energized.
Delay on de-energize (TDD)
This is an OFF delay.
This type of time delay relay function results in the timed contacts changing state after the pre-set time internal when the coil is energized.
Delay on energize (TDE)
This is an ON delay.
With this type of relay, electrical power is confined to non-moving components.
Solid state relays
True or false: Relays can be connected in circuits in special ways to create machine logic.
True
This is known as relay or hardwired logic.
Which of the following devices make decisions based on the machine conditions?
A) Power devices
B) Output devices
C) Input devices
D) Logic devices
D) Logic devices
These can be relays in relay logic or CPU’s in PLC logic.
What are the two common types of logic found in electrical systems?
- Relay (hardwired) logic
- Programmable logic
The type of electrical logic that cannot be changed without rewiring of its components is called:
Relay (hardwired) logic
This makes it much less flexible.
The type of logic that is stored on computers or programmable logic contollers (PLC’s) is called:
Programmable logic
What are the three main fuctions found in relay logic?
- AND function
- OR function
- NOT function
Identify the following relay logic that is used to energize the solenoid (AND, OR, NOT):
AND logic
This can be thought of as series logic, because the logic has to go through both contacts to be true.
Identify the following relay logic needed to energize the solenoid (AND, OR, NOT):
OR logic
This can be thought of as parallel logic, becuase the logic can go throught either contacts to be true.
This type of relay logic inverts the logic of an input, where the off state results in an output signal.
NOT logic
In this example, the normally closed relay contact is made when the relay is de-energized, resulting in a signal being sent to an output.
What is a sealed-in relay?
A relay that has been wired to remain energized until the circuit to it is broken by some other device.
This is usually done with a normally open contact wired in parallel with the start/on button.
Identify the following electrical schematic symbol:
NO foot switch (spring returned)
Identify the following electrical schematic symbol:
Time delay on close swtich
This type of relay is used to shut down control power to the controls for a certain machine or area of an operating plant and are usually controlled by a E-stop or a key switch.
Master control relays
The keyed switch allows the circuit to be locked out be removing the key
True or false: Master control relays can be used to control electrical logic and programmable logic controller outputs.
True
This type of relay is a common way of starting electric motors and is like a heavy duty relay.
Full voltage starter
This type of motor starter consists of two identical starter mounted in one enclosure.
A reversing motor starter
These will have both mechanical and electrical interlocks.
How does a reversing motor starter change the direction of the motor?
By swapping the connections of two of the motor’s power supply lines.
To reverse a three-phase motor, any two conntection to the motor leads can be interchanged.
True or false: To reverse a three-phase motor, any two connections to the motor leads can be interchanged.
True
On relay logic ladder diagrams, what do the circled letters to the left of the schematic indicate?
Ladder rung numbers
On relay logic ladder diagrams, what do the numbers to the right of ladder rungs indicate?
Reference numbers indicating where else in the drawing the parts of the component are located.
When it comes to troubleshooting, what is a symptom?
A sign that something is wrong with a piece of equipment.
When it comes to machine maintenace, what is a measureable symptom?
Symptoms that are found during routine measurements or that are done to further investigate symptoms picked up by your senses and observations.
What are two values that need to be accounted for when measuring and evalutation symptoms of a machine?
Dynamic and static values
An example of this is the full load amps of motor without load (static) vs. with load (dynamic) ⟶ the amp draw should be higher when the motor is loaded up.
When it comes to electrical circuits, what are process control and monitoring swtiches used for?
To provide inputs to a logic device.
These can be limit switches, pressure switches, flow switches, etc.
When it comes to electrical circuits, what are operator input control switches used for?
To allow an operator to input signals into a logic device.
When it comes to electrical circuits, what are safety shutdown switches?
Input devices that are used to automatically shut down the process.
These are a type of process and monitoring switch.
These usually include things like pressure swtiches, temeprature switches, etc.
With machine troubleshooting, what is a cause analysis?
A process used to identify the underlying causes or reasons behind a problem, failure, or event in order to prevent it from happening again.
What are the three types of components that make up an electrical control system?
- Input devices
- Processor
- Output devices
In an electrical control system, a(n) ____ device senses specific conditions of a process or system.
input
These includes switches, pushbuttons, pressure sensors, etc.
In an electrical PLC control system, a(n) ____ receives information and decided on a response by a hard-wired circuit arrangment or by a software program.
processor
This is specific to PLC control systems.
In relay logic systems, the logic devices are the relays themselves.
In an electrical control system, a(n) ____ device controls operating devices to bring about an appropraite change in the system being monitored.
output
These could be pilot lights, displays, and coils that control solenoids, relays, or motor starters.
In electrical systems, devices that change a small electrical control signal into useful work are called:
Outputs
These include things such as lights, displays, and coils.
This type of electrical control system was developed to replace costly and inflexible control relay systems.
PLCs
How are PLC’s usually selected?
Based off the number of I/O points required.
I/O point = input/output points
What are the four main advantages of PLC’s over relay control?
- lower cost
- programmability
- reliability
- expandability
Which type of electrical logic system has overall lower costs: relay logic or PLCs?
PLC
PLC’s have no mechanical moving parts to wear out, troubleshooting is quicker, and they require less floor space.
On which type of electrical logic system is component wear a concern?
Relay logic systems
These have moving mechanical (armature) parts that can wear out.
Which type of electrical logic system can more easily be changed: relay logic or PLC?
PLC
Relay logic systems require hard wire changes to change the program.
Which type of electrical logic system is considered more reliable: a relay logic system or a PLC?
PLC
This is due to the PLC having no moving components.
Which type of electrical logic system is more easily expanded: a relay logic system or a PLC?
PLC
Most PLC’s come in a modular format which allows additional I/O cards to be added to the chassis.
How are two PLC’s remotely linked together?
With a communication data highway
This is essentially an ethernet cable connecting the two prcessing units on the PLC’s.
What are the four major components of a PLC?
- chassis (and backplane)
- power supply
- processor (CPU)
- I/O modules
This component of a PLC is the housing in which the controllers, I/O modules and power supplies are inserted.
The chassis
This component of a PLC consists of the address, data and control busses, which allows the controller to communicate with the I/O modules as well as provide power to the I/O modules.
The backplane
When it comes to PLC’s, what is a local rack?
I/O devices that are physically located within the same chassis as the CPU.
These are known as local I/O’s.
When it comes to PLC’s, what is a remote I/O?
An I/O module that isn’t located in the same chassis as the main controller.
These are usually connected with some sort of data cabling.
What is the standard power supplied to a PLC?
120V AC
This is then converted internally to 12V or 24V DC.
What is the primary function of the PLC processor (3 things)?
- read and store the status of all inputs
- execute program depending on inputs and logic
- update the status of the ouputs
This is known as the processor scan.
How is PLC processor memory classified?
By its ability to retain stored data after the electrical source has been removed.
ROM vs. RAM
This type of PLC processor memeory retains data and programs after the electrical power source has been removed.
Non-volatile memory
ROM is non-volatile memory.
This type of PLC processor memory is designed so that information is easily stored and retrieved, but requires a battery backup to retain stored data if the power is removed.
Random access memory (RAM)
Is RAM volatile or non-volatile memory?
Volatile
RAM will loose all information if power is removed wihtout a battery backup.
This type of PLC processor memory is designed to permanently store data and programs if the electrical power source is removed.
Read only memory (ROM)
This is non-volatile memory.
Is ROM volatile or non-volatile memory?
Non-volatile
ROM will not loose its memory if power is removed.
What type of PLC processor memory would be used to store the basic input/output and source code information?
ROM
ROM is non-volitale memory.
What is a discreet input?
An input that is either on (1 or true) or off (0 or false).
This PLC module reads the status of the input devices and writes data to the processor.
The input modules
This PLC module reads data from the processor and writes data to the output modules.
The output modules.
In a ladder logic program, what is required for that rung to output?
Enough of the bits in the rung must be true to make a continuous path from the left to right side.
This type of PLC bit instruction is true when the memory bit is 1 (on).
XIC
Examine if closed/on.
This type of PLC bit instruction is true when the memory bit is 0 (off).
XIO
Examine if open/off.
This type of PLC bit instruction is set to true (1) when the rung logic proceeding it is also true (1).
OTE
Output energize instruction.
Idenitfy the following PLC bit instruction:
XIC
Examine if closed/on.
Identify the following PLC bit instruction:
XIO
Examine if open/off.
Identify the following PLC bit instruction:
OTE
Output energize instruction.
A logical AND function is performed by placing instructions in ____ (series/parallel) with one another.
series
This AND this will make the instruction true.
A logical OR function is performed by placing instructions in ____ (series/parallel) with one another.
parallel
This OR this will make the instruction true.
Identify the following Boolean logic symbol:
AND symbol
Identify the following Boolean logic symbol:
OR symbol
What does a flashing light on a PLC I/O board indicate?
An issue with the I/O module
On a PLC rack, what does a “Force” light indicate?
That one of the I/O points has been forced on or off by the software
Identify which logic function would create the following truth table:
AND function
Identify which logic function would create the following truth table:
OR function
