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Mastering PLCs
6 Advantages of PLC - correct answer 1. Less space
- Lower cost
- Resistant to Environment
- Direct Interface
- Easy Programming
- Flexible 6 Basic Components of PLC - correct answer 1. Input Modules
- Output Modules
- Processor Module (Controller)
- Power Supply
- Programming Device
- I/O Chassis 3 methods of entering a PLC project - correct answer
- Personal CPU
- Secure Data (SD) Card
- Handheld terminal RSLinx - correct answer collection of drivers to connect programming software in the PC to Allen Bradley controllers Driver - correct answer program that connect software to hardware Serial Communication - correct answer exchange data electronically usually via Ethernet or USB
USB groups binary data into __________, which are organized into packets. - correct answer Fields 5 types of packets - correct answer 1. Token (identify type of data to follow
- Data (fields of binary data)
- Handshake (ask & receive acknowledgement)
- Start of Frame (synchronize the host)
- Status (check for errors) ControlLogix users can employ both personal computers and __________________ to program PLCs. - correct answer memory modules Who Active - correct answer a network search utility that shows layout of every network that has a driver configured in RSLinx Firmware - correct answer read-only program Most PLCs use ____________________ to back up memory during power-down conditions. - correct answer lithium batteries AB 1756-L7x PLCs use onboard _________________ to back up program during power loss. - correct answer nonvolatile memory Energy Storage Module (ESM) - correct answer provides back up power to transfer the program/status data from working memory to the nonvolatile memory on power loss Image - correct answer -entire PLC memory (includes firmware, ladder routines, data tables, configuration data) -SD card used to back up image
I/O Diagrams - correct answer used to show physical components between I/O devices and PLC I/O terminals Shape of an input terminal in I/O diagram - correct answer rectangle Shape of an output terminal in I/O diagram - correct answer diamond Basic Operation of PLC Ladder Logic (3 parts) - correct answer
- Logic continuity
- Six Logic Elements
- Parallel rung operation Controller may contain _____________ tasks. Each task contains ____________ programs. - correct answer 1- 1- Routine - correct answer logic instruction that provides operating instructions for PLC controller Hierarchy of tasks, programs, routines - correct answer Tasks contain programs Programs contain routines Controller's physical memory is _________________. - correct answer 32-bit DINTs How many bits?
- BOOL
- SINT
- INT
4. DINT
- REAL - correct answer 1. 1-bit
- 8-bit
- 16-bit
- 32-bit
- 32-bit Tasks - correct answer contain & schedules all user logic files Project - correct answer software file that stores all programming instructions, hardware configurations, and tag data for a processor Studio 5000 project file extension - correct answer .ACD 2 ways to check firmware revision - correct answer 1. controller properties in Studio 5000
- controller's LED display at power up Purpose of I/O configuration - correct answer 1. instructs controller to consume data packets produced by I/O module
- contains instructions sent to module for operation Electronic keying - correct answer compares module defined in project to installed module on controller 3 communication parameters - correct answer 1. Requested Packet Interval (RPI)
- Inhibit Module
- Major Fault on Controller if Connection Fails while in Run Mode
3 applications where input tags match output tags - correct answer
- sequencing operations
- simultaneous operation of more than one output
- motor control programs 2 applications of internal output instructions - correct answer
- memory logic
- interlocks 3 types of data tags - correct answer 1. module- defined
- pre-defined
- user-defined 4 tag types - correct answer 1. base (references memory location)
- alias (references an existing tag)
- produced (references memory location to send that info to another PLC)
- consumed (references memory location to receive that info from another PLC) Array - correct answer collection of numerically indexed tags with related data Arrays can be used for _________ type instructions that address blocks of data tags - correct answer file Element - correct answer each tag in an array First index in an Array is? - correct answer Zero
Interlocking - correct answer output turns on/off only if certain inputs/outputs are in a certain state 2 applications of interlocking - correct answer 1. sequencing
- safety 4 factors of discrete input modules - correct answer 1. type of current (AC or DC)
- level of voltage
- number of inputs (points)
- active high or active low 5 factors of output modules - correct answer 1. type of current (AC or DC)
- level of voltage
- number of outputs (points)
- load capability
- solid state or relay contact switching Main difference between solid state and relay contact switching? - correct answer Solid state is faster Relay can handle higher current Solid State Switching - correct answer -in DC, uses transistors as switches -in AC, uses semiconductors called triac -can be active high or active low Inductive loads can lead to arcing across hard contacts, to prevent this use a ______________________. - correct answer Surge suppressor (voltage snubber)
Combining CTU and CTD instructions creates a _________________. - correct answer Up/down counter BCD thumbwheel switch - correct answer input device (series of rotary switches) that allows operator to adjust the PRESET value for a timer/counter FRD (from BCD) - correct answer converts BCD to decimal TOD (to BCD) - correct answer converts decimal to BCD Trace (in an I/O chassis) - correct answer path for module communication 3 major faults in processor programs - correct answer
- I/O module connection failure
- Jump to label that does not exist
- stack overflow 3 minor faults in processor programs - correct answer
- arithmetic overflow
- low battery
- output string larger than destination 2 reasons why Power Supply indicator would turn off? - correct answer
- no incoming AC power supply
- no outgoing DC power to modules Grounded Power Distribution System - correct answer -provides power to PLC and I/O devices (step down transformer) -one leg grounded
Ungrounded Power Distribution System - correct answer -used in industrial delta configurations -ground fault indicators determine when circuit is grounded MCR Circuit (Master Control Relay) - correct answer provides control power to output devices 2 Power Distribution Failure Symptoms - correct answer
- all PLC indicators are off
- no output devices energize 2 Steps to Troubleshoot All PLC Indicators are Off - correct answer
- check main power disconnect
- measure VAC across PLC power supply's input terminals (L1 and N) 2 Steps to Troubleshoot No Output Devices Energize - correct answer
- verify power is being supplied to PLC output module
- check output module supply terminals (voltage) First step to troubleshoot chassis power supply? - correct answer Verify power supply is on 3 steps to test PLC discrete input devices - correct answer
- observe operation (toggle switch while watching input module indicator)
- check the voltage (across input terminals)
- test the wiring (continuity test out-of-circuit) Test Mode - correct answer -test program without energizing outputs -helpful for new programs/troubleshooting
AB 1756-L7x Controller Status Display Fault Format - correct answer TXX:CXX 6 Major Fault Types in an AB 1756-L7x - correct answer Type 1 - communication fault/memory backup Type 3 - communication fault between controller and a module or failed chassis Type 4 - programming error Type 6 - user task timer out (increase task watchdog time) Type 7 - anomalies in nonvolatile memory Type 8 - user attempted to put controller in Run mode with keyswitch while downloading a project Where to clear major/minor faults? - correct answer Controller Properties Dialog 5 PLC Troubleshooting Methods - correct answer 1. Symptom and Cause
- Output-Back
- Half-Split
- Shotgun
- Flowchart 4 types of PLC component tests - correct answer 1. your 5 senses
- measurements
- substitution
- component/circuit elimination First step to troubleshoot PLC? - correct answer identify the symptom
3 types of project descriptions - correct answer 1. routine descriptions
- rung comments
- main operand descriptions Event Sequencing - correct answer machines perform actions (events) in an order (sequence) to accomplish a task Power Diagram - correct answer shows how machine action affects PLC inputs and how PLC outputs affect machine action I/O Diagram - correct answer shows how machines devices are wired to PLCs inputs/outputs Truth Table - correct answer detailed sequence that shows the on/off status of every input and output device/address for each step in the sequence The normal operating mode of most machines is ____________ mode. - correct answer automatic Logic Nesting - correct answer placing one branch circuit inside another 3 common stop functions - correct answer 1. cycle stop
- halt
- E-stop What stop function stops a machine after the last step in a cycle? - correct answer cycle stop What stop function stops a machine after the current step and starts the next step in the operation upon start up? - correct answer halt
Program Control Instruction - correct answer instructions used to alter the program scan of a PLC from its normal sequence 3 examples of program control instructions - correct answer
- MCR
- JSR
- JMP/LBL MCR (Master Control Reset) - correct answer -controls a zone of PLC program rungs -can be used as an interlock -MCR and S:FS can initialize a PLC Difference between hardwired MCR and MCR instruction? - correct answer Hardwired MCR is a safety device (E-stop) Where are the two MCR coils located? - correct answer
- MCR rung
- MCR end rung Purpose of Subroutine - correct answer to organize/simplify programs by breaking logic into specialized functions or operations Advantage of JMP/LBL - correct answer speeds up scan time (by jumping over noncritical logic) LBL is always ___________ and always the ______________ on a rung. - correct answer true first instruction JMP/LBL must be in the same ______________. - correct answer Routine
All tag types use _____ bits of memory (no matter how much they actually use). - correct answer 32 bits Allen Bradley uses a _________ formatted output instruction for add, subtract, multiply, and divide instructions. - correct answer block MUL and DIV destination tags are usually ______________ since the outcomes can be very large or fractional. - correct answer REAL Data Transfer Instructions - correct answer transfer (copy) the contents of one tag to another (example: MOV) Programmable Message Display - correct answer displays info to operators/maintenance about status of machine or process Data Terminals on the PMD define the _____________. - correct answer message number Control Terminals on the PMD control _____________________. - correct answer display presentation 4 PMD Control Terminals (from least to most significant bits) - correct answer
- Strobe
- Variable Data
- Reset
- Initialize Strobe Terminal - correct answer displays the message
