final exam 213
In most applications, the braking torque of friction brakes should be
Equal or greater than full-load motor torque
A PLC changes the state of each coil output as it scans each rung of the program. This is done to save processing time. true or false
False
Which transmission medium has the highest data rate?
Fiber optic
Some PLC ladder logic programs use the letters ____ and ____ to indicate input/output contacts & coils.
I, Q I, O X, Y
How are the resistors connected?
In series with the motor terminals and power lines.
What is the most widely used input device in the industry today? It is used to control movement.
Limit switch
The acronym LAN stands for
Local Area Network
Device that can keep track of multiple counts or an ordered series of events.
Shift register
When can a time relay be useful in plugging applications?
When the motor stop time is known and stable
are used to show internal or external outputs on a ladder logic "rung".
coils
Typical PLC modules may include
communication counters input CPU
are used to show external or internal inputs to a ladder logic "rung".
contacts
An encoder uses ASCII code to feedback information to a PLC on a rotating shaft. true or false
false
It is always a good practice to place several relay coils in series for a motor control circuit. true or false
false
Ladder logic programming uses a series of input coils and output contacts for each rung of the ladder program sequence true or false
false
How do remote and local expansion differ? The _________ of the I/O points to be added.
location
Flash memory is a newer type nonvolatile memory used with many PLCs. true or false
true
Small PLC units that do not have expansion slots are sometimes referred to as lunch box or brick type. true or false
true
What devices usually control the action of the magnetic brakes?
Solenoids.
In plugging circuits with time relay, what happens if the time delay is set too long?
The motor stops and turns in reverse direction
A PLCs may be set up as a master or slave depending upon its required functions in a SCADA control system. true or false
True
The biggest problem associated with a control system is
dirt and dust
What type of functional diagram should be included in the (PLC) documentation package?
ladder diagram
Name the three main applications for LANs. Distributed control, distributed _______, and data acquisition.
processing
An encoder is used to measure rotational angles, distance and speed
true
The first and most important step in troubleshooting is _________.
understanding how the system works
PLC operating systems are considered:
Firmware
Choose the BCD equivalent of the decimal number 15
0001 0101
How many different line sequences exist for a three-phase system?
2
The Eaton 512 PLC used in the lab had ______ outputs that could be used to control a small system.
4
When are resistors of a primary resistor starter bypassed?
As the motor approaches its nominal operating speed
The Data file designation "O5:4" refers to
Output module in slot 5 & screw terminal 4
What adjustment potentiometers can usually be found on a soft starter?
Starting voltage, ramp-up time and ramp-down time
The acronym SCADA refers to what?
Supervisory Control and Data Acquisition
How do fail-safe friction brakes normally react in case of a power failure?
The brake is applied automaticaly
A PLC may be programmed using a hand-held device, PC or input module located on the PLC. true or false
True
A PLC program may use timers and/or counters to keep track of a process sequence. true or false
True
What type of switch is used primarily for fluid level in a reservoir?
Float
Which device is best suited to reduce stopping time during jogging?
Friction brake
What causes fast acceleration and damage to the driven machinery?
High starting torque.
Small relay used with a PLC control circuit is often referred to as a(n)
ice cube
PLC programming devices or program loaders include:
Desktop computers Laptop computers hand-held programmers
The two PLC controllers used with lab activities are the DL 105 &
Eaton 512
What happens when primary resistors are used to start a motor?
Energy is lost through heat produced by the resistors
If you're using twisted pair (STP or UTP), coax, or fiber optic (FO) cable, what format is the data being transmitted in?
High-speed serial digital format
In three-wire control circuits, what path does the control current take when the momentary contact is released.
Holding contact
A spare parts list should always include what two items?
I/O module spare processor
Which of the following designations is not an alternate name for fail-safe brakes?
Power-on brakes
What variable do soft starters modify to start motors smoothly?
Motor input voltage
The code most often used to represent alphanumeric information for a keyboard is
ASCII
Logical operations for a PLC program may include
NOT OR AND
What happens if two contactors are energized at the same time in a reversing circuit without interlocking?
Short-circuit
Which of the following starters does not provide reduced voltage upon starting?
Across-the-line starter
What happens when the Cam Switch, Model 3140, is set to the STOP position?
All three power contacts open
Where are transmitted data, preamble and postamble, and source and destination addresses included for transmission on a LAN?
Data packet
The acronym BSR stands for what processor instruction?
Bit Shift Right
Why are starting resistors bypassed?
Both of the answers above are correct
How do plugging circuits create the counter torque necessary to stop a motor?
By reversing two power lines
What is the purpose of a time relay in a primary resistor circuit?
Bypass the starting resistors after starting
If ramp-up time of a soft starter is necessary, what is the effect on starting time?
Increased starting time
In push button interlocking, what happens if the motor is running in the forward direction and you push both forward and reverse push buttons?
No coil is energized
What are three basic considerations in sizing any PLC application?
Number of inputs and outputs amount of memory required maximum scan time
The acronym "PLC" stands for
Programmable Logic Controller
Which of the following statements is a characteristic of a control transformer?
Provides control voltage compatible with relay coils
Which of the following control devices can be used for three-wire control?
Push button
Why are friction brakes used on electric motors?
Quicker stops. More precise stops. Holding a motor position.
What is the effect of reversing the power line sequence of a three-phase squirrel-cage motor?
Reverses motor rotation direction
What can friction brakes be used for?
Secure crane loads or yaw drives Control machine tools. Brake a motor in both directions.
With the following motor power rating equation, what does the constant "SF" represent? P =(T * N)/(K * SF)
Service Factor
If a mechanical interlock is implemented in a reversing starter, what happens if the forward coil is energized, as you try to energize the reverse coil as well?
The forward coil remains the only coil energized
Which control device sees its NO and NC contacts states change following preset time delays?
Time relay
An HMI may be used to visualize the status of a PLC process or manually over-ride inputs or outputs as needed by an operator. true or false
True
What is the first consideration in any retrofit project?
documentation
What is the most important tool a maintenance technician can possess?
documentation
3/3 The Binary system is based on the number 4 true or false
false
The acronym "RTD" refers to remote terminal diner true or false
false
The two PLC controllers used with lab activities were both capable of 120V AC input signals. true or false
false
A controller information product sheet, for example, will give basic information about I/O, memory, scan time, and the basic configuration of the
hardware
The hardware documentation package should consist of
hardware manuals Bill of Materials (BOM) spare parts list
The _______ file is designed specifically to hold "whole" numbers as needed in a PLC program.
integer
What are the two most important parts of the documentation package? Hardware drawings and
program listings
0/3.1 In an RTD, what changes in proportion to the temperature?
resistance
The system ________ diagram is very possibly the most important part of the hardware documentation package
schematic
The process used to diagnose a problem and find a failed component is referred to as _________.
troubleshooting
A backup copy of data is important if a computer is used for maintenance logging. true or false
true
Before any control system development work can begin, it is essential to come to a complete understanding of the requirements of the system to be controlled. true or false
true
By using the system's output forcing option, you can verify all output devices have been wired correctly. true or false
true
The major advantage of a relay lies in its ability to control a load circuit that is electrically isolated from the control circuit. true or false
true
Typical control system issues are caused by loose connections true or false
true
Understanding how the system works is the first step and most important part of all troubleshooting. true or false
true
When the relay coil is energized, the armature moves due to an induced magnetic force created in the core. true or false
true
