Programmable Logic Controllers Flashcards
PLC stuff
Sectors that PLCs are used include (5 items)
1: Chemical/petrochemical
2: Auto manufacturing
3: Metal smelting/mining
4: Lumber/pulp/paper
5: Food/beverage production
Smaller PLCs are hardly more than _____.
Smart relays.
Large PLCs may have over.120 000 IO points. T or F.
True.
Three items that control systems consist of are:
1: Input devices
2: Controller
3: Output devices
Three examples of input devices are:
Switches, limits, thermostats.
A controller can receive input info in what two ways?
Hard wired circuit or software program.
Three examples of output devices are:
1: Relays
2: Contactors
3: Solenoids
Output devices control devices such as: (5 items)
1: Motors
2: Pumps
3: Heaters
4: Fans
5: Valves
PLCs are able to perform their own _____
Internal diagnostics
Four advantages of PLCs over relay control are:
1: Lower cost
2: Programmability
3: Reliability
4: Expandability
Troubleshooting on a PLC system is _____ and reduces _____.
Easier
Down-time
PLCs are physically smaller than _____ with smaller _____ requirements.
Control panels with numerous relays
Energy
Does hard wiring need to be changed to re-program or update PLC software?
No
A program is usually _____.
Ladder logic
A program graphically displays _____ as well as _____.
Status of devices
Power flow in program
Ambient conditions that some PLCs are designed to withstand are:
Excessive heat, humidity, exposure to mechanical damage (vibration).
Static electronic switching means _____.
No moving parts.
Two ways to expand PLC systems are:
1: New modules plug into existing PLC
2: Add another PLC and link/group with communication data highway
Communication data highway is a means of _____.
Connecting multiple PLCs in a system.
Discreet input devices are _____ (3 items) that are either off or on.
1: Switches
2: Relay contacts
3: Sensors
Discreet output devices such as _____ (4 items) respond to either being energized or de-energized.
1: Pilot lights
2: Contactor coils
3: Relay coils
4: Solenoids
Discreet input and output devices require _____.
Power from a separate source.
Optoisolating is how _____ is achieved between the discreet IO circuits and the internal circuitry of the processor module.
Electrical Isolation.
Analogue devices are either on or off. T or F.
F. They operate over a range of voltage or current.
A solid state electronic switch for DC would be a _____.
Transistor
A solid state switch for AC is a _____.
Triac
An interposing relay does what function?
Relay coil that can handle higher current and is operated by the solid state switch.
Some examples.of measured values are:
Temperature, pressure, speed, position.
The most common analog current standard is _____.
4 mA - 20 mA
Minimum signal for 4-20 mA analog is 4 mA because _____.
Allows PLC to tell difference between 0% signal and broken wire connector.
Proportional control is gained using an analog output card for processes such as a _____.
VFD motor speed controller.
A shield in STP cable is also called a _____.
Drain
STP cable means _____.
Shielded twisted pair
The drain is usually grounded at only one end, usually _____.
In the PLC panel.
PLC programming evolved from _____.
Boolean algebra programs
Three graphic based languages used for PLC programming are:
1: Ladder diagrams
2: Function block diagrams
3: Sequential functions/flow chart
Two text based languages for PLC programming are:
1: Structured text
2: Instruction lists
The most common programming language is _____.
Ladder diagram
The numbers used above symbols in a ladder diagram represent _____.
Input/output terminal address
Each function block may have several inputs and _____.
Settable parameters
Function blocks can be thought of as _____.
Small programs within a main program.
Function block diagrams are commonly used in _____.
Europe
Sequential Function Charts are used for large process controls and can involve _____.
Logic or several LD or FBD.
Text based programs were once commonly used with _____.
Hand held programmers
Structured Text is similar to what computer programming language?
Basic
Instructiom Lists are similar to _____.
Assembler language programs
Instruction Lists are more like the machine code used to make a _____ function than a process to be controlled.
Microchip
Four major hardware components of a modular PLC are:
1: Power Supply
2: Backplane
3: Processor (CPU)
4: IO modules (input/output
The power supplied to a PLC is clean, filtered/regulated and provides _____.
Protection to system components
Does a PLC supply any of the field IO devices?
No
Field IO devices are _____ from the backplane, CPU and power supply.
Isolated electrically
The means for a PLC to communicate with other components and distribute power for internal operations is done through _____.
A backplane
A backplane is a _____
Power and communications bus
What is another name for a complete unit PLC?
Shoebox PLC
Shoebox unit PLCs often replace _____.
Small relay systems.
What does a processor do?
Executes user programs and communicates with other devices.
What does STP stand for?
Shielded twisted pair
What is the sequence of carrying out processor functions called?
Processor scan
What type of memory is used in PLCs?
RAM, ROM, EEPROM.
What happens if volatile memory loses its electrical power source?
Memory cleared of all data
What is required for volatile memory to keep stored data and programs when power is removed?
Battery backup
Non-volatile memory is considered _____.
Permanent.
Is RAM a volatile memory or non volatile?
Most is volatile. Non volatile has self contained battery within package of memory chip.
ROM is volatile or non volatile?
Non volatile
ROM info may be altered or written to by a user, true or false?
False
What does RAM mean?
Random Access Memory
What does ROM mean?
Read Only Memory
What does EEPROM mean?
Electrically erasable programmable memory
EEPROM is integrated circuit memory considered to be (volatile, non volatile?)
Non volatile
An example of EEPROM is _____.
Flash memory cards/USB drive
What are some switches that may be used as a sensing device?
Pressure, temperature, or mechanical limit switches with an on/off signal
Analogue sensing devices would have signals of changing levels of _____ or _____.
Voltage, current.
7 control functions that special IO modules are used for:
1: Position control
2: High speed counters
3. Temperature controls
4: Proportional integral derivative control (PID)
5: Fuzzy logic control
6: Identification sensors cam positoners
7: Analogue IO
How many cables would be between a remote IO and a PLC?
1
What is a data highway?
LAN cabling that connects a number of PLCs (and PCs) to exchange programs/data
What is the most common analogue voltage standard?
0 - 10 V DC
PLCs are actually an _____ _____ with specially designed hardware and software.
Industrial computer
“Hardware” in PLCs refers to _____. (3 items)
Mechanical, electrical, and electronic components.
What are the four basic components of an Automated Control System?
1: PLC
2: Input devices
3: Output devices
4: AC circuits
CPU power supply, input devices and output devices all need their own _____.
Separate AC supply.
Lights, coils, solenoids, magnetic starters and meters are examples of _____.
Output devices
Is the programming device required when the program is running?
No, except to monitor the program.
A desktop computer, laptop or hand held programmer are examples of _____
Programming device.
Desktop computers, laptops and handheld programmers are also called _____.
HMI, Human Machine Interface
The power supply of a CompactLogix controller is located where in the module?
Anywhere in the 2nd to Fourth position.
The power supply of a CompactLogix controller is located where in the module?
Anywhere in the 2nd to Fourth position.
What is the maximum position for the IO modules in a CompactLogix?
12
In a single bank CompactLogix system, you cannot place more than _____ between the power supply and end cap, making a maximum of _____ modules.
8 I/O modules, 11
Data is _____ (received) by a processor and _____ (sent) to other PLC components
Read, write
A processor module has _____ ports and _____ for a _____.
Two communication, one slot, memory card.
The power supply will be sized to accomodate the load of _____.
All of the cards in the assembly.
Input/Output modules provide an _____ between the processor and the _____.
Interface, discreet field device
Analogue modules provide an _____ between the processor and the _____.
Analogue IO field devices.
Endplates complete the assembly, with the leftmost housing _____ and the rightmost housing _____.
Battery for the EEprom
Terminal assembly to terminate backplane.
Can a programming device both read and write to a PLC processor?
Yes
What provides housing for the modules?
A chassis or separate enclosure.
What does a power supply do?
Converts AC or DC voltage to specified value with required VA capacity to operate electronic equipment
The power supply is considered the first line of _____.
System reliability and integrity.
PLC power supplies are designed to operate under constant frequency and voltage only. T or F.
False. Designed for wide range of fluctuations that may occur in a large system.
If the supply frequency fluctuates more than the specified values, what will the PLC do?
Shut down the processor.
What is EMI?
Electromagnetic interference
Where would a power supply need to be shielded?
Areas where EMI is generated
Power supplies are selected according to _____.
The current requirements of the modules
What are two ways to provide power to the field IO devices?
External source or auxillary control transformer
What does Line Signal Conditioning do?
Purifies AC sine wave to eliminate voltage surges, current spines, or other incoming electrical noise.
Five duties of the power supply module are:
1: Line Signal Conditioning
2: Step down voltage
3: Rectifier converts AC to DC
4: Filter smooths DC to fairly constant, negligible ripple
5: Voltage Regulator provides steady output to components
Where is the power supply of the CompactLogix mounted in this lab? What are its output current ratings?
Immediate right of the processor.
4A at 5V DC and 2A at 24V DC
What system activities do a processor govern?
Receiving, analyzing, processing and transmitting data.
What are two other terms for processor?
CPU, microprocessor
The CPU is the _____ of the system.
Intelligence
The CPU and memory _____ to execute the _____ (+4 items).
Work together
Operating system, interpret/execute user programs, communicate with devices, perform other housekeeping.
Primary function of PLC processor that is also called Processor Scan:
Read/store status of all input devices, execute user program by solving ladder logic, update status of outputs.
What are the five steps of a processor scan? Which step is the longest?
1: Input scan
2: Program scan
3: Output scan
4: Service communications
5: Housekeeping/overhead
Program scan is the longest time interval.
A Watch Dog timer is part of what area of the system? What does it do?
Internal diagnostic system.
Shuts down processor and creates fault code if time out error occurs.
Is it dangerous to edit online when a controller key switch is on the RUN position?
Yes
Will the controller execute tasks while keyswitch is in PROG position?
No
Can you edit online in run mode of the REM keyswitch position?
Yes
Does battery backup continue running the processor during a power outage?
No. Only keeps programming intact.
Primary function of a processor is:
Read inputs, solve ladder logic, and update outputs
Which modules are used to electrically isolate the processor from the field devices?
I/O modules
Status indication on IO modules helps with _____.
Faster system analysis
Input modules take signals from devices and converts to a _____ _____ usable by the processor.
Voltage level
Sensing devices can be things such as: (5 items)
1: Switches
2: Photo-eyes
3: Proximity switches
4: Limit switches
5: Pressure transducers
What is Opto-isolator?
Small relays/filter circuitry.
What does optoisolating protect the processor from?
Voltage transients and magnetic interference.
Output modules send information to an output field device via _____ _____.
Electrical interface.
Are output modules equipped with surge protection and/or fusing?
No.
What kind of protection is usually used for inductive loads?
Surge suppresion
A loading resistor connected in parallel with a load will have what effect?
Limit the effects of leakage current through solid state outputs.
What size resistor would be used for a loading resistor at 120 VAC? And for 240 VAC?
120: 15 kiloohm, 2 watt
240: 15 kiloohm, 5 watt
What will develop over an unloaded output?
Hazardous condition.
Discreet IO modules are available in _, __, or __ points per module.
8, 16, 32
What are the AC ratings of digital AC input modules?
24, 120, 240
What are the DC ratings of digital AC input modules?
5(TTL), 24, 48
What are the AC and DC ratings of digital AC output modules?
120/240, 24VDC, 5 VDC(TTL)
What is the current rating of digital AC output modules?
0.5 A - 2 A per output point
What can a relay output of a digital DC combination module control?
5-265 VAC, 5-125 VDC, loads up to 2.5 A per point to a max of 20 A per card.
What would the voltage be at 75% of the signal?
7.5 VDC
What would the current be at 25% of the signal?
8 mA
What would the voltage be if the current were 12 mA?
5 VDC
What percentage of signal is 16 mA? What would the voltage be?
75%
7.5 VDC
What would the current be at 0% signal and 0 VDC?
4 mA
Special purpose modules for specialized needs could include applications such as:
Motion Control
Video Recognition module
ASCII module
High speed counter modules
Servo positioning module
Compact IO to PowerFlex drives
Thermocouple (mV) signals
Resistance temperature detector (RTD) input module
What causes voltage transients?
Contact bounce and electrical noise
Only some input modules use input filtering. T or F.
False.
Analogue signals are typically interpreted as _____ _____ by the PLC
Integer value
What are four items represented by analog signals?
Pressure, temperature, flow, weight.
PLCs typically use __-bit signed binary processors.
16
Analog signals use voltage or current with a _____ _____ to the process signal.
Proportional magnitude
When might you want to use additional surge suppresion? (4 items)
Inductive loads such as relays, magnetic starters, solenoids and low VA motors
Electrical isolation between processor and IO module is achieved by optical isolation as well as _____.
Small relays in the IO modules
What is peripheral equipment?
Accessory or auxiliary to a central system
What are some methods to input a program to a PLC processor?
1: PC or laptop with software
2: Operator Interface Devices
3: Modems
4: Printers
5: Alphanumeric displays
6: Communication devices
7: Memory device
What is memory in a PLC?
A two dimensional array of storage cell, each cell storing a single bit of information.
What values represent a bit of information?
A 0 or a 1.
Binary data is stored in memory by a process called _____.
Write
Binary data is retrieved from the memory by a process called _____.
Read
Data storage locations, each identified by an address, is called _____.
Memory
What is BIT an acronym for?
BInary digiT
What are the 1s and 0s of binary representative of?
Presence or absence of voltage at that particular location.
If a bit’s status is 1, is it considered ON (set) or OFF (reset)?
ON
If a bit’s status is 0, is it considered ON (set) or OFF (reset)?
OFF
When might you group bits for transferring?
Transferring numbers from a thumbwheel to digital readout or PLC.
What is a byte?
A group of bits (the smallest value that can be handled simultaneously by the processor).
What is a typical byte size?
8 bits
What is a “word”?
Grouping/number of bits in a sequence treated as a unit.
What is the word length of the CompactLogix PLC?
32 bits
What is a memory flash card?
RAM memory module that can insert directly innto PLC processor.
All PLCs must have memory allocated for _____ (4 items).
1: Executive programs
2: Processor work area / Scratch pad
3: Data area
4: User program area
Which two items are not accessible to users and are part of the System Memory?
Executive and Scratch Pad
System Memory could be described as equivalent to _____.
BIOS of a pc
Executive memory is considered to be _____.
Permanent
Scratch pad memory is considered ______ storage.
Temporary
Which two items are accessible to the user?
Data Area and User Program
Data Area and User Program can be described as _____.
Application memory
Max memory size specified by the manufacturer will usually only include the _____.
Application memory
What are the two basic items that memory stores?
State of input/outputs (Data area)
Program that controls the outputs (User program)
A “tag” can refer to a _____ location or a structure location that is _____ in size.
Single bit
Multiple words
What are the three properties assigned to a tag?
Type, Scope and Data Type
What are the four types of tags?
1: Base tags
2: Alias tags
3: Produced tags
4: Consumed tags
All data stored in four byte groupings in 32 bits of consecutive data is called _____ tag.
Base
Alias tags refer to memory that is defined by _____.
Another existing tag
Four ways that Alias tags can be used are:
1: Programming ladder
2: Assigning descriptive name to IO device
3: More simple name to complex tags
4: Descriptive name for element of an array
Produced tags and Consumed tags are used when _____ and are always ______.
Information needs to be shared between controllers
Controller scoped tags
Program Scope tags can be accessed by all routines in the controller. T or F.
False
Controller Scope tags are accessible only by the parent program. T or F.
False
What type of languages are most commonly used with PLCs?
Graphic based
How many words of Data Table memory do counters and timers require? What are they?
Three - Accumulated, Preset, Address
What is the max time that can be programmed in a TON instruction?
- 523 hrs
- 394 min
- 647 s
When an output bit is “1”, it’s corresponding output terminal is “off”. T or F
False
What does the accumulated value in a CTD need to be to turn off the .DN bit?
Below the preset value
Data types may be ______ or ______.
Atomic or structured
Five atomic data types are:
1: Bool (single bit of a 32 bit word)
2: Sint (short integer, 8 bits [1 byte] of a 32 byte word)
3: Int (integer, 16 bit group of 32 bit word)
4: Dint (double integer, 32 bit word)
5: Real (32 bits, includes decimal, used for math/analog process conrol.)
What are the three kinds of strutures?
1: Module Defined Structures
2: Predefined structures
3: User Defined Structures
Data, status and fault information is contained in which structure?
Module Defined Structures.
Control, counter, and timer structures are found in which structure?
Predefined Structures
Name, data type, style and radix are required by which structure?
User Defined Structures
An array lets you group data under a common name as long as what condition is met?
They are of the same type
Which part of C5[0] is the subscript?
0
How many dimensions can an array have? What is the benefit of this?
As many as three. Flexibility for 1-3 subscripts.
Three dimensional arrays are generally only used with ______ ______ programs
Motion control
What is a reason for using arrays?
When upgrading from a different model.
The data area of the CompactLogix PLC data area contains what?
Tags
A basic unit of logic is called a _____.
Routine
What types of logic can be used in a routine?
Ladder, function block, sequential function chart, structured text.
What language would you use for machine interlocking and operations that may need to have maintenance personnel troubleshoot?
Ladder logic
What language would you use for continuous process, drive control, and loop control?
Function block diagram
High level management of multiple operations would be coded using which language?
Sequential function chart
Complex mathematical operations, ASCII string handling, and specialized arrays would be coded using which language?
Structured text.
A program contains every _____.
Routine
JSR instruction means:
Jump to Subroutine
If you do not want a program to run, where in the controller organizer should it be stored?
Unscheduled programs folder.
Does a task define when a program will execute?
Yes
Up to __ tasks can be configured in the controller.
6
A watchdog will trigger a _____ if the task runs too long.
Fault
Can you use 5 continuous tasks in a project?
No. Can only use 1.
What is the max periodic tasks that are able to be used in a project?
6
The time period of a periodic task can be configured from 1 ms to ____ s.
2000
The default time period in a periodic task is __ ms.
10
What are the position numbers of a PLC assembly?
1-5
What are the slot numbers of a PL assembly? Which module goes in slot 0?
0-7. CPU/Processor
If the location of the IO module is on the main DIN rail, what is the location part of the address?
LOCAL
Describe the address LOCAL:2:I.DATA.0
LOCAL: location is on main DIN rail. “Adapter type and name” would be used if IO module is remote.
2: Slot number of the module being referenced.
I: Module type. I=Input O=Output
DATA: Discreet IO. Use “Channel #” for analog
0: Bit number from 0-15
What does XIC mean?
Examine if closed
What does XIO mean?
Examine if opened
When an instruction becomes true, that means that it has been _____.
Energized
When an input terminal is energized, it’s corresponding bit is __.
1
When an input terminal is de-energized, it’s corresponding bit is __.
0
What does the input module do before storing the result in the input tag data area?
Filters, isolates the incoming signal and changes it to 5 VDC
Is electrical isolation required between the internal 5 VDC of the output module to the actual operating voltage of the lamp?
Yes
Each word in the IO tags corresponds to what?
A specific slot within a certain chassis.
Are timers input or output instructions?
Output
Is there additional hardware needed for timers?
No. It is in the software.
The minimum timer setting of a PLC timer an be as low as __ ms.
1
All timers require how many words of memory in the timer area of the data table?
Three
What does Mnemonic refer to?
The ‘label’ given to a specific bit.
The three different types of timers are:
1: Timer On Delay
2: Timer Off Delay
3: Retentive Timer On (RTO)
An integral part of most control systems are _____.
Timers
What are five uses of timers?
1: Delay starting cycles
2: Control intervals
3: Repeat cycles
4: Flashers
5: Provide automatic resets
A TON instruction begins accumulating time when the run goes _____.
True
A TON instruction will be true until what happens?
The rung goes false or,
The accumulated value = preset value or,
A reset (RES) instrution, if added, is energized
DINT refers to “double integer”, meaning what?
An actual number
TIMER is a _____ structure.
Predefined
TIME BASE is __ seconds.
0.001
PRESET is the value which the timer must reach for the processor to do what?
Set the done bit (.DN)
The ACCUMULATED VALUE is the number of _____ the instruction has counted.
Time increments
How many status bits do timers have?
3
Status bits are entered in _____.
Mnemonics
(BOOL), or ‘Boolean’ means only ‘high’ and ‘set’. T or F
False.
High or low, set or reset, etc.
In a TON, the TT bit is set when the rung goes _____ and remains set until _____.
True
Until ACCUMULATED = PRESET
In a TON, the DN bit is set until:
The rung goes false
A reset instruction resets the timer.
If a power failure or other circumstance interrupts the TON before the PRESET value is reached, what happens?
Timer enable remains set, TT remains set, ACCU remains the same.
The timer is in the __ area of the tag base?
T4
How many timer structures can each timer tag base contain?
Limited only by memory
The time PRESET has a range of 0 - _____.
2,147,483,647
A TOF instruction begins accumulating time when the rung goes _____.
False
A TOF instruction will continue timing until what occurs?
The ACCU=PRESET
The rung goes true
Can you use a RES with a TOF?
No
If the rung goes true before the timer of a TOF has not timed out, will the accumulated value reset?
Yes
In a TOF, the EN bit is set when the rung goes _____.
True
In a TOF, the TT bit is set when the rung goes _____ and the ACCU value is _____.
False
Less than the PRESET value
The TT bit of a TOF is reset when:
The rung goes true
The DN bit is reset
ACCU=PRESET
The DN bit of a TOF is set when the rung goes _____.
True
The DN bit of a TOF is reset when the ACCU is ______ the PRESET.
Equal to
What needs to happen for the ACCU value of an RTO to reset?
Rung goes false, program mode, or power loss to the processor.
When the processor resumes operation or the rung goes true, what value will an RTO that was de-energized with an ACCU value of 10s resume timing from?
10s
How do you reset an RTO accumulated value?
A RES with the same addres in another rung.
An RTO’s .EN bit is set when _____.
The rung goes true
An RTO timing bit will be set when _____.
The rung goes true
The .DN bit of an RTO timer is set when _____.
The ACCU=PRESET
Can you use a RES instruction with a TOF?
No
Why must you not use a RES instruction with a TOF?
May cause unpredictable operation that may result in injuries of personel.
RTOs are in the __ area of the tag base.
T4
Is a counter an output or input instruction?
Output
Counters in PLCs provide the same functions as mechanical counters. T or F
True
Counters only activate a device after reaching the preset value. T or F
False. Activates or deactivates
Counter instructions are _____ outputs.
Internal
Is additional hardware needed for PLC counters?
No
What three words do counters require?
Control word
Preset register word
Accumulator register
What are the three types of counters and their mnemonics?
Count Up = CTU
Count down = CTD
High Speed Counter = HSC
What are five industrial applications for counters?
1: Packaging
2: Product tracking
3: Measuring lengths/speed
4: Keeping track of inventory
5: Reporting
What is the range of a counter in ms?
-2,147,483,648 to +2,147,483,647
The ACCU value of a counter will reset if the instruction is de-energized and then re-energized. T or F
False. Must have a reset.
The PRESET value of a counter is a ___-bit integer value
32
The accumulated value of a counter stops incrementing once the .DN bit is set. T or F
False
A counter with an OV bit wil do what once the limit has been reached?
Wrap around and begin counting from the lower limit.
What is the upper programmable limit in ms?
2,147,483,647 ms
What is the programmable limit in minutes?
35,791.394
What is the programmable limit in hours?
596.523
CTUs and CTDs are in the _____ area of the tag base
C5
Overflow bits are set when ______.
ACCU exceeds PRESET
Should you use a negative preset value in a counter if also using a RES instruction?
No
If a negative preset is used and a RES instruction is executed, what will happen?
Resets the .DN bit, and prevents the counter instruction from operating.
What are the most common ways of transmitting analog signals?
Proportional voltage or current signals
What are 4 common DC voltages?
0-5 Vdc
0-10 Vdc
2-10 Vdc
±10 Vdc
Transmittors and sensors are not analog devices. T or F
False.
Temperature, speed, flow, weight and pressure are all analog devices. T or F
True
How many input and output channels do the CompactLogix analog IO modules have?
4 input, 2 output.
4-20 mA is an analog signal that can be converted by the CompactLogix analog input module. T or F.
True
Two methods of wiring analog IO modules are _____ and _____.
Single ended
Differential
Are all inputs tied to a common ground using the single ended wiring method?
Yes
Which wiring method isolates the channels from one another?
Differential
What 5 things may cause errors in a measurement process?
1: Electrostatic fields
2: Inductive pickup
3: Radio frequency interference
4: Power line noise
5: Ground loop current
What causes ground loop current?
Poor ground connection
Differing common mode voltages in the system
Smaller systems are more likely to have ground loop issues. T or F
False. Large systems would.
What are two ways to prevent ground loop current?
Proper grounding
Equipment with floating measurement
Same ground reference
