Intro to PLC's Flashcards
T/F: Programmers can force an output action to operate after a worker has pushed in the E-stop button.
True
What are the 4 sizes of PLC’s?
- ) Nano (Up to 32 I/O)
- ) Micro (32 to 128 I/O)
- ) Medium (128 to 960 I/O)
- ) Large (960 to thousands of I/O)
How many Inputs/Outputs can a nano-sized PLC have?
Up to 32
How many Inputs/Outputs can a micro-sized PLC have?
32 to 128
How many Inputs/Outputs can a medium-sized PLC have?
128 to 960
How many Inputs/Outputs can a large-sized PLC have?
960+
T/F: PLC’s were first used in large industrial processes and machines.
True
T/F: PLC’s are not used in commercial or residential applications.
False
A ____ occurs when any body part becomes part of an electrical circuit.
Electric Shock
T/F: All facilities have the same color code for different types of conductors/cables.
False, facilities will have their own code, which is important to know.
T/F: PLC’s can control DC, AC, or both.
True
____ grounding is the connection of an electrical system to the earth, and provides protection for the structure from lightning strikes.
Building Grounding
____ grounding is the grounding of all machinery electrical systems and all non-current carrying exposed metal to earth.
Equipment Grounding
____ grounding is establishing a quality ground to protect sensitive electronic equipment from electrical noise and fault currents.
Electronic Grounding
The NEC states that the GEC (Grounding Electrode Conductor) should have less than __ Ohms to ground.
25
T/F: The NEC states that the Electronic Grounding Conductor should have less than 5 Ohms to ground.
False, there is no code for grounding electronics, but it will usually be specified by the owner/engineer/manufacturer.
T/F: Electronic Shield drains are always grounded on both sides.
False
____ is an electrical charge at rest.
Static Electricity
Usually, it takes no more than __ Volts to destroy a circuit board, which makes PLC’s so vulnerable to ESD.
5V
The electronic ground (Shield Drain) is usually grounded at which end?
The end in the panel
A snubber circuit utilizes a ____ to suppress voltage spikes by absorbing excess voltage, and dying.
MOV (Metal Oxide Varistor)
All input devices can be put into two basic categories, ____ and ____.
Manual and Automatic
What is the most common voltage for PLC Input terminals?
24V
The ____ terminals of a PLC deliver voltage to any device or actuator controlled by the PLC.
Output
T/F: Input devices can be wired in any configuration.
True
T/F: Output devices can be wired in any configuration.
False, they cannot be wired in series.
How many Output devices can be displayed on each rung of a ladder diagram?
1
Can combination circuits be used for Input devices?
Yes, such as a 250 Ohm resistor between a 4-20mA system and a 1-5Vdc device.
Why is polarity important for both inputs and outputs?
Because reversed polarity can give you a negative reading, which creates issues for the PLC’s logic and for actuation of outputs.
PNP, switched on the positive or negative side?
Sinking or Sourcing?
Positive, Sourcing
NPN, switched on the positive or negative side?
Sinking or Sourcing?
Negative, Sinking
T/F: PLC control voltages are based on what devices are to be connected to the PLC.
True
It is important that the ____ is installed in dual-voltage rated PLC’s. (Or that the selection switch is in the correct position)
Jumper Link
A(n) ____ relay is a smaller relay (with a smaller control current) switching a larger load, such as power to a motor starter.
Interposing Relay
Why are common input voltage ratings on 12 or 24 volts?
Because they’re safer to work on, and require less power.
T/F: Most larger PLC’s have a variety of different cards.
True
What are some common Output voltage ratings?
- 12v
- 24v
- 50v
- 120
A ____ is the negative power supply terminal of a DC-powered PLC.
Sink
A ____ is the positive power supply teminal of a DC-powered PLC.
Source
____(s) are graphic representations of a device on a diagram.
Symbols or Glyph
____ symbols are drawn as very generic symbols, but with text describing the component.
PLC
“____” = Shelf State
Normally
A ____ drawing is literally a rendered picture of what the cabinet/device looks like.
Pictoral
A ____ shows the connection of all devices and components of a PLC.
Wiring Diagram
A ____ diagram has a series of single lines (rungs) that indicate the simplest representation of the control circuit logic.
Ladder
What is AND logic?
Two NO contacts in series, both must be closed to energize the load.
What is OR logic?
Two NO contacts in parallel, one must be closed to energize the load.
What is NOT logic?
One NC contact in series, powering the load, if the contact is opened, the load loses power.
What is NOR logic?
Two NC contacts in series, if either is opened, the load loses power.
What is NAND logic?
Two NC contacts in parallel, unless both are opened, the load will remain energized.
____ is when a device is wired point to point, with no use of terminals.
Direct Wiring
____ is when wires are brought to a terminal block, and from that block to its destination.
Terminal Wiring, this method makes it easier to trouble shoot or modify.
What are the 5 sections of a PLC?
- ) Inputs (Terminal Screws receiving inputs)
- ) Outputs (From CPU out to the devices instructed)
- ) CPU (Makes decisions)
- ) Power Supply
- ) Programming Device
The CPU of a PLC makes decisions based on what two things?
Input from sensors/devices, and Programmed logic/parameters.
What is the common voltage of a PLC CPU?
5V
How long can a PLC power supply last on its own when power is shut off? (Hold Up Time)
10ms to 3 seconds
What are the 4 ways to program a PLC?
- ) Integrated Buttons
- ) HMI
- ) Handheld Unit
- ) PC (best)
What is the difference between volatile memory and nonvolatile memory?
Volatile is erased when power is lost.
What does RAM stand for?
Random Access Memory (Volatile)
T/F: The program being ran on a PLC is on its RAM.
True
What does EEPROM stand for?
Electrically Erasable Programmable Read-Only Memory
What is a bit?
The smallest unit of memory.
What is a Nibble?
4 Bits
What is a Byte?
8 Bits
What is a Word?
16 Bit
What is the 5 step operating-cycle of a PLC?
- ) Input Scan
- ) Program Scan
- ) Output Scan
- ) Service Communications
- ) Housekeeping and Overhead
What are the two general types of files in PLC programming?
- ) Program Files
2. ) Data Table Files
What are the 3 Program files we are concerned with?
File 0 - System File
File 1 - Reserved by the Processor
File 2 - Main Program File
(Files 3-255 are subroutines)
T/F: The first 9 Data Table files (0-8) are default files.
True
Which Data Table file cannot be added to, deleted, or changed in any way?
Status files (File 2) or “S” type files.
T/F: Nested branches cannot overlap.
True
What does XIC stand for?
Examine if Closed
What does XIO stand for?
Examine if Open
What does OTE stand for?
Output Energize
What do OTL and OTU stand for?
OTL = Output Latch OTU = Output Unlatch
How do CPU’s scan the program within a PLC?
From Top to Bottom, Left to Right
T/F: If you have parallel inputs, putting the path that is true most frequently on the bottom is fastest.
False, putting it on the top is fastest because the CPU reads from the top down.
What two ways are addresses labeled in the book?
- ) Slot/Bit
2. ) Slot/Word/Bit
Can outputs be placed in series?
Can they be placed in parallel?
Series - No (Only one per rung)
Parallel - Yes
T/F: When timers are moved in the realm of programming, they are logic functions happening in the CPU, not actual devices.
True
What are the 3 types of timer functions?
- ) TON (Timer On-Delay)
- ) TOF (Timer Off-Delay)
- ) RTO (Retentive)
Timer Instruction Words: What do they stand for? EN TT DN RES CTU CTD
- ) Enable
- ) Timer Timing
- ) Done
- ) Reset
- ) Count Up
- ) Count Down
The Count Up (CTU) and Count Down (CTD) Instructions are located in data table __.
5
What Timer instruction is missing?
- Timer Address
- Time Base
- Timer Preset
- _____
Time Accumulated
Timers are located in Data Table __.
4
T/F: If a timer is non-retentive, it will maintain its accumulated time if it loses power.
False
____ system of a building Transmits and Controls the movement of SOME form of energy.
Primary
What are the 4 building system types in the book?
Besides Informational
- ) Electrical
- ) Electronic
- ) Fluid Power
- ) Mechanical
A ____ device is required any time a device is not directly compatible with a PLC.
Interface
A ____ system allows primary systems to work with and communicate with other building systems.
Interface
____’s are different from electromechanical relays in that they don’t have coils or moving parts, and they use much less power.
SSR’s
Electromechanical Relays have Coils and Contacts,
SSR’s have ____ and ____.
Inputs and Outputs
A ____ is a heavy-duty relay for switching high-power loads.
Contactor
A ____ is basically a contactor with overload protection.
Motor Starter
T/F: According to the book, Interface devices can change one voltage level to another.
True
When you receive your components for a PLC system from the supply house, and you are cross referencing to make sure you receive every part (and correct parts), what piece of documentation should you use?
The Purchase Order
T/F: It is not important to pay attention to spacing and temperature limitations when installing a PLC.
False
What are the 3 ways to terminate a PLC?
- ) Direct Hardwire
- ) Terminal Block
- ) Interface Devices
T/F: Solid wire is used for wiring PLC’s , in most installations.
False
____ and ____ connections should always be used with stranded wire.
Pin and Fork
What is the very first thing to do when performing a Visual inspection on a PLC?
Lock out the disconnect. For Safety
Maintaining a PLC is at its most basic level keeping the ____ and ____ issue free.
Hardware and Software
How often should PLC software be backed up?
And generally inspected?
Annually
T/F: Anyone can work on any given PLC, because they are so simple.
False, certified and competent technicians only.
What are the two types of PLC maintenance inspections?
- ) Visual Inspection (De-energized)
2. ) Energized Maintenance
What is the purpose of Energized Maintenance?
To verify that the Master Control Relay (MCR) is functioning correctly
T/F: The PLC will give a notification light when the battery voltage level falls below the threshold.
True
If the battery is located in the ____ card, you have to shut the PLC off to remove and replace it.
Processor
If the battery is located ____, you can change it while the PLC is running.
Behind the hinged door or cover of the PLC
When vacuuming any debris off of PLC components or anywhere near the PLC enclosure, it is important to use a(n) ____ safe vacuum.
ESD
What are the three TYPES of PLC status lights?
- ) Input
- ) Output
- ) Operational
What are the 5 different Operational Status lights, located on the power supply/processor of a PLC?
- ) Power
- ) Run Mode
- ) Forces
- ) CPU Faults
- ) Battery
What are the four IEC 1010 standard classifications of Electrical Test Instruments?
CAT I
CAT II
CAT IIII
CAT IV
When the CPU hits the ____ it will go back to the beginning of the program and keep only scanning to the ____ until it is removed.
TND
A voltage drop of more than _____ on the PLC output supply terminals indicates that they are overloaded.
5%
PLC power supply voltage should be within ____ of the rated voltage.
10%
A very short unwanted voltage.
Transient
A sustained increase in voltage by at least 10% for a more than 1 minute.
Overvoltage
A sustained decrease in voltage by at least 10% for a more than 1 minute.
Undervoltage
A sustained decrease in voltage by at least 10% for a less than 1 minute.
Sag
A sustained increase in voltage by at least 10% for a less than 1 minute.
Swell
Any Vacuum used on a PLC component must be ___
ESD safe vacuum
What steps must be taken to safely remove a battery mounted to the processor card of a PLC?
LOTO
Remove card
Change battery
When can a battery be changed on a running plc?
Only if the battery is located on the back of the door.
How do you know to change the PLC battery?
PLC will notify you if the battery charge drops below its threshold.
What are the 8 steps of energized maintenance?
- ) Remove LOTO
- ) Turn disconnect on
- ) Open door
- ) Verify that the machine or process won’t be started.
- ) Test the MCR
- ) Test and record incoming 3-phase voltage, and DC power supply voltage.
- ) Verify cooling fans/units are working correctly
- ) Check the PLC power supply and CPU indicator lights.
Energized maintenance is done for what reason?
To verify correct operation of MCR or safeties
What is the first step of visual inspection?
Look for damage. Just Damage. Damage.
What are the 8 steps of visual inspections?
- 1.) LOTO
0. ) Verify that power is off
1. ) Look for damage, physical or from heat
2. ) Air intakes and outlets for dirt, dust, and obstructions.
3. ) Cooling fans
4. ) PLC and its components for dirt and contaminants
5. ) Verify that the environment surrounding the enclosure hasn’t changed
6. ) Inspect Input and Output devices.
7. ) Inspect the enclosure for damage or uncapped holes.
8. ) Tighten all connections
Who can perform inspections or maintenance on PLCs?
Certified Technicians Only
How often is maintenance performed on PLCs?
Annually. (remember this one)
Why is preventative maintenance necessary for PLCs?
To keep Hardware and Software issue free.
What are the two types of components you will have to maintain in a PLC?
Hardware and Software
Backups of _____ is necessary to keep for PLCs.
Program
