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