PLC MINANGO VERSION

Question 1

typically involve the handling of circuitry operating at several different voltage and current levels.

Answer 1

PLC SYSTEMS

Question 2

devices may require 24 VDC.

Answer 2

Photoelectric and proximity

Question 2

Power to the PLC and other devices may require the connection of

Answer 2

120 VAC

Question 3

is generally generated as three phase (3N) voltage.

Answer 3

Utility power

Question 4

is a device consisting of a light producing element such as an LED and a light sensing element such as a phototransistor.

Answer 4

Opto-isolator

Question 5

are mechanical contacts and solid-state outputs may take the form of transistor or TTL logic (DC) and triac (AC).

Answer 5

Relay outputs

Question 6

are open collector common emitter or emitter follower.

Answer 6

Transistor outputs

Question 7

are normally used to control moderate loads (up to about 2 amps) or when a very low on resistance is required

Answer 7

Relay outputs

Question 8

are described as three main arrangements or forms.

Answer 8

Relay contacts

Question 9

relay contact is a single pole normally open contact. This is analogous to a single contact normally open switch.

Answer 9

FORM A

Question 10

relay contact is a single pole normally closed contact which is similar to a single normally closed switch.

Answer 10

FORM B

Question 11

relay contact is a single pole double throw contact.

Answer 11

FORM C

Question 12

are referred to as sinking and the PNP units as sourcing.

Answer 12

NPN units

Question 13

will have current flow out of the terminal

Answer 13

sourcing type output

Question 14

is brought to a marshalling panel, where the power is split, feeding multiple fused circuits.

Answer 14

main power feed

Question 15

is the main disconnect fuse, while the remaining fuses are distribution fuses.

Answer 15

Fuse 03FU

Question 16

is passed to the field junction box (FJB) as one wire in a multi-conductor cable. This cable, sometimes called a

Answer 16

-Hot (electrically live) wire 06A
-homerun or main cable

Question 17

exhibit excellent noise immunity, which is particularly useful when connecting to high-impedance loads, such as those found on PLC/DCS I/O modules.

Answer 17

Twisted-pair cables

Question 18

can be particularly sensitive to noise since the attendant current is so low, and the amount of actual work being done is minimal.

Answer 18

high-impedance load

Question 19

are used to describe the way a particular component in the circuit relates to power flow.

Answer 19

sinking and sourcing

Question 20

DC (+) is _____, DCC is ______

Answer 20

DC Positive Terminal
DC common

Question 21

continually scan their input points for the presence or absence of voltage.

Answer 21

Digital input (DI) modules

Question 22

are considered output devices because they force other devices to react when they change state.

Answer 22

Relay contacts

Question 23

can be thought of as relay contacts

Answer 23

PLC digital outputs

Question 24

switch voltage on and off to cause an external device to change state. These modules are either “isolated” or “non-isolated.” If a module is non-isolated, then it is either sinking or sourcing.

Answer 24

DO modules

Question 25

is one in which the power source can be isolated between I/O points. The source is not internally bussed. The cost is two terminals per point, so it is expensive.

Answer 25

Isolated DO Circuits

Question 26

As with the DI PLC module, point density is an important feature of DO modules. As can be seen in the isolated module in Figure, isolation comes with a price. A 16-terminal module has a point density of only eight since two terminals are needed per point. By internally bussing a common, the point density can be improved dramatically.

Answer 26

Non-isolated DO Circuits

Question 27

is twisted pair and shielded.

Answer 27

Cabling

Question 28

is numbered with the transmitter number, and the wires inside are numbered to provide power source information.

Answer 28

signal cable

Question 29

ground should be used to ground all the shields at one point.

Answer 29

quiet

Question 30

is one that is either tied to a dedicated ground triad, or one that is tied to the center-tap of an isolation transformer.

Answer 30

Quiet ground

Question 31

would be one that is physically located far from the transformer, and one that services motors, lights, or other noisy items. That is the basic two-wire analog input circuit.

Answer 31

Noisy ground

Question 32

are always low voltage, usually 24 VDC. As a result, fusing individual analog circuits is not required for personnel safety. Also, most analog I/O modules have current-limiting circuits onboard.

Answer 32

Circuit Protection (Fusing) Analog circuits

Question 33

are susceptible to electronic noise. If, for example, an analog cable lies adjacent to a motor’s high-voltage cable, then the analog signal cable will act as an antenna, picking up the magnetically coupled noise generated by the motor.

Answer 33

Noise Immunity Analog circuits

Question 34

Electronic noise may be greatly reduced by the use of twisted-pair cabling. Most instruments use two wires to transmit their signals. Current flows out to the device in one wire and back from the device in the other.

Answer 34

Twisted-Pair Cables

Question 35

A further refinement in noise rejection is _____ i.e., the use of a grounded braid or foil shield around the conductors. As previously mentioned, the shield should never be grounded in more than one place to avoid ground loops.

Answer 35

Shielding

Question 36

A final refinement in noise rejection is grounded metallic conduit. This is rarely required, except for data communications cables and for particularly critical circuits.

Answer 36

Conduit

Question 37

is made of a special piece of wire whose electrical resistance changes in a predictable way when the wire is exposed to varying temperatures.

Answer 37

Resistance Temperature Detector (RTD) An RTD

Question 38

exploits the electromotive force (EMF) that arises from changes in temperature affecting two dissimilar metals that have been laminated together. This EMF manifests itself as a millivolt (DC) signal.

Answer 38

Thermocouple

Question 39

is thus a two-wire device. It is susceptible to radiated and induced noise and so is usually housed in a shielded cable if extended for a very long distance. The thermocouple signal is also susceptible to degradation due to line loss, so minimizing the cable length is desirable.

Answer 39

Thermocouple

Question 40

K thermocouple spans a useful temperature range of -

Answer 40

200 to 1250ºC.

Question 41

always have power connections in addition to the signal connections. Yet not all such powered transmitters are four-wire.

Answer 41

Four-wire devices

Question 42

is said to be loop powered. This means the device functions by absorbing the energy it needs to generate the signal from the current loop. This is also referred to as “current sinking.”

Answer 42

two-wire device