Deck 3: SCRS, Triacs, Other Thryristors, Discrete Automation Sensors and Devices

Question 1

Thyristors are regenerative and cannot operate in the linear mode.

Answer 1

True

Question 2

Once a thyristor has been triggered, the trigger current can be removed.

Answer 2

True

Question 3

To protect the SCR from dv/dt false triggering, an LC snubber circuit is used.

Answer 3

False

Question 4

The conduction angle is the angle in degrees when the SCR turns on.

Question 5

The firing delay angle is equal to 180 degrees minus the firing angle.

Question 6

Both the SCR holding current and the gate trigger current parameters decrease with increasing junction temperature.

Question 7

Like the SCR, the Shockley diode remains in the on -state until the forward current drops below the holding current.

Question 8

The structure of the diac is PNP material with a slice on N -material at both ends.

Question 9

R2 and R3 set the intrinsic standoff ratio in the circuit below.
?

Question 10

The PUT is a four -layer device similar to the SCR.

Question 11

The PUT gate reference is device dependent, not circuit dependent.

Question 12

The PUT anode leakage current is the current that flows from the gate to the anode with the cathode shorted.

Question 13

Before the triac, designers used two SCRs in series to accomplish the triac function.

Question 14

The peak repetitive off -state voltage of the triac is the maximum allowed value of repetitive voltage that may be applied and not turn the triac off.

Question 15

The triac firing angle is equal to 180 degrees minus the conduction angle.

Question 16

The triac offers the designer an economical and versatile means of accurately controlling AC power.

Question 17

Low frequency operation is the most reliable for a triac.

Question 18

The GCS is like an SCR except it can be turned off by applying a negative potential to its gate.

Question 19

The SCS is like an SCR except the SCS has an added cathode gate.

Question 20

The SCS switches on with positive pulse on cathode gate or a negative pulse on the anode gate.

Question 21

The SBS has two anodes and two gates.

Question 22

The breakover point of an SBS can be altered with an external zener connected to the SBS.

Question 23

Which of the following method is an accepted method of turning off an SCR?

A) Increasing the leakage current
B) Exceeding the breakdown voltage
C) Removing the gate current
D) Exceeding the dv/dt rating
E) None of the above

Question 24

The valley point on the characteristic curve of the UJT is where the ___________.

A) internal resistance of B1 increases
B) internal resistance of B2 decreases
C) internal resistance of B2 increases
D) internal resistance of B1 decreases

Question 25

Triacs operate mostly in quadrant(s)

A) 1.
B) 4.
C) 3.
D) 2.
E) A and C

Question 26

Thyristor(s) with an cathode gate is (are)

A) SCR.
B) Triac.
C) PUT.
D) Diac.
E) A and B

Question 27

Thyristor(s) with an anode gate is (are)

A) SCR.
B) Triac.
C) PUT.
D) Diac.
E) A and B

Question 28

?

-This transistor model represents the_________.

A) Bidirectional triode thyristor
B) Gate controlled switch
C) Silicon bilateral switch
D) Silicon controlled switch
E) None of the above

Question 29

?

-The thryistor that does not have two anodes is the________.

A) silicon controlled switch
B) silicon bilateral switch
C) diac
D) triac
E) none of the above

Question 30

With the anode connected to the positive lead of an ohmmeter and the cathode to the negative lead, a good SCR will conduct when __________

A) the gate is connected to the anode
B) the gate is connected to the cathode
C) the gate is grounded
D) the gate open

Question 31

Which of the following is not a characteristic of a triac?

A) Either a positive or negative gate signal will turn it on
B) It can conduct current in either direction
C) It has an internal intrinsic standoff ratio
D) It is a three terminal device

Question 32

Match the device with its function.

-SCR

A) Breakover thyristor
B) Reverse blocking thyristor
C) Bidirectional thyristo

Question 33

Match the device with its function.

-Triac

A) Breakover thyristor
B) Reverse blocking thyristor
C) Bidirectional thyristo

Question 34

Match the device with its function.

-Diac

A) Breakover thyristor
B) Reverse blocking thyristor
C) Bidirectional thyristo

Question 35

Match the device with its function.

-Unijunction transistor

A) Breakover thyristor
B) Reverse blocking thyristor
C) Bidirectional thyristo

Question 36

Match the device with its function.

-Shockley diode

A) Breakover thyristor
B) Reverse blocking thyristor
C) Bidirectional thyristo

Question 37

Match the device t o the schematic symbol.

-PUT

A)
B) ?

Question 38

Match the device t o the schematic symbol.

-Shockley diode

A)
B)
C)

Question 39

Match the device t o the schematic symbol.

-Diac

A)
B)
C)

Question 40

Match the device t o the schematic symbol.

-UJT

A)
B)
C)

Question 41

The six reasons sensors are used could be sumarized as: protect humans and machines from harm, for part identification and quality, for problem analysis, and to produce the fastest possible production.

Question 42

Sensors are non -contact type devices, have electronics cirucits to generate the measurement, have numerous output circuit options, are always faster than switches , and require an external source of power.

Question 43

Inductive type sensors use an electromagnetic field to sense the presence of a part.

Question 44

Inductive sensors can only detect parts that have some magnetic material present.

Question 45

A part entering the electric field of a capacitive proximity sensor causes the sensor output to change.

Question 46

Two of the five types of proximity sensors offered by vendors are wand and rectangular.

Question 47

In general unshielded sensors have a larger sensing distance and a wider sensing area.

Question 48

The most popular type of proximity sensor style is the cylindrical threaded barrel type.

Question 49

Capacitive proximity sensors generate eddy currents in the parts entering their electric field.

Question 50

If you are required to select a sensor to detect a plastic part and you need the maximum distance possible, then you would choose an unshielded capacitive sensor.

Question 51

If you are required to select a sensor to detect an aluminum part and you need the a very narrow sensing field, then you would choose an unshielded inductive sensor.

Question 52

A thin flat plate and large solid block of the same metal are sensed by an inductive proximity sensor, the large solid block would be sensed at a greater distance than the thin flat plate since it would have large eddy current values.

Question 53

Mutual interference is only a problem when proximity sensors from different vendors are used too close together.

Question 54

An inductive proximity sensor's output turns on when the internal oscilator starts oscillating but the capacitive proximity sensor operation is just the opposite.

Question 55

Both inductive and capacitive proximity sensors can sense package contents through the packaging material.

Question 56

New setting distances for proximity sensors require experiment data for the actual sensing distance to make the calculations.

Question 57

The two major components present in all photoelectric sensors are a source of light and a receiver to detect the light.

Question 58

Photoelectric sensors have five components that include a light source, light detector, logic circuit, lens, and output switching device.

Question 59

Photoelectric sensors have a much greater range than proximity type sensors.

Question 60

The photoelectric margin parameter is also called gain multiplier.

Question 61

If a photoelectric sensor has a margin of 20, then the light received by the sensor is 20 larger than the light necessary to turn on the sensor.

Question 62

Electronic sensors can be wired in AND type of circuits but the output electronics does not permit OR type of logic to be used.

Question 63

Vision systems can be use to count the number of holes or features on a part, but are not capable of measuring the size the features.

Question 64

Vision systems used in range finding require the use of two or more cameras.

Question 65

Vision systems come in two basic configurations: imaging arrays and linear arrays.

Question 66

The __________type of capacitive proximity sensors is one of two types available.

A) conductive
B) shielded
C) dielectric
D) unshielded
E) All of the above

Question 67

Inductive type sensors could detect a part that had __ material present

A) Water
B) Wood
C) Copper
D) Plastic
E) None of the above
Material present.

Question 68

If metal switch boxes are passing the sensor location at 30 mm then the best choice for a sensor would be

A) Through beam photoelectric.
B) Diffused beam photoelectric.
C) Capacitive proximity.
D) Inductive proximity.
E) None of the above

Question 69

If bottles of shampoo are passing the sensor location at a 100 mm distance and the sensor could be mounted on either side of the conveyor, then the best choice for a sensor would be

A) Capacitive proximity.
B) Transmitted -beam photoelectric.
C) Retroreflective photoelectric.
D) Inductive proximity.
E) None of the above

Question 70

If pill boxes are passing the sensor location at a 40 mm distance and the sensor can only be mounted on one side of the conveyor, then the best choice for a sensor would be

A) Inductive proximity.
B) Capacitive proximity.
C) Transmitted -beam photoelectric.
D) Diffused -beam photoelectric.
E) None of the above

Question 71

The diffused mode sensor used when high background light is present is

A) Fixed focus diffused mode sensor.
B) Wide angle diffuse mode sensor.
C) Distance measurement diffused mode sensor.
D) Background suppression diffused mode sonsor.
E) None of the above

Question 72

A current sinking output

A) has current flowing into the output.
B) is associated with an NPN output transistor.
C) has current flowing out of the output.
D) Both A and B
E) Both A and C

Question 73

The sensor output that has 100 percent isolation between the sensor power and the power of the interfaced device.

A) SCR recitifier output
B) Single pin current sinking output
C) NPN and PNP with switchable outputs
D) Field effect transistor output
E) None of the above

Question 74

When you match a sensor output to a controller input you should

A) have the opposite for the input that you used for the output.
B) have a current sourcing at both the input and output.
C) have a current sinking at both the input and output.
D) not worry about the type it does not make any difference.

Question 75

Analog distance sensors are available in photoelectric and ultrasonic configurations. Select the true statement.

A) The ultrasonic are less sensitive to environmental conditions.
B) The photoelectric are the most accurate.
C) Ultrasonic sensor have been developed quite recently.
D) The photoelectric models have the greatest distance sensing capability.

Question 76

You need a sensor with high margins to count very reflective objects 100 mm from the sensor in a dirty enviroment. What is the best sensor to use?

A) Capacitive proximity
B) Diffuse photoelectric
C) Transmitted beam photoelectric
D) Retroreflective photoelectric
E) None of the above

Question 77

You need a device to sense boxes passing on a conveyor, a sensing distance of 5 feet, that will have all sensor units that require power on one side of conveyor. What is the best sensor to use?

A) Retroreflective photoelectric
B) Transmitted beam photoelectric
C) Diffuse photoelectric
D) Capacitive proximity
E) None of the above

Question 78

The application calls for a sensor to detect metal parts at a fixed distance greater than 60 mm from the sensor location. Access from one side only is permitted.What is the best sensor to use?

A) Retroreflective photoelectric
B) Diffuse photoelectric
C) Transmitted beam photoelectric
D) Inductive proximity
E) None of the above

Question 79

The application calls for a sensor to detect the leading edge of plastic parts at a fixed distance about than 20 mm from the sensor location. Access from one side only is permitted. What is the best sensor to use?

A) Diffused beam shart cutoff photoelectric
B) Diffused beam fixed focus photoelectric
C) Capacitive proximity
D) Diffused beam background suppression photoelectric
E) None of the above

Question 80

The application calls for a sensor to detect small parts passing within a few mm of the sensor location. Access from one side only is permitted. What is the best sensor to use?

A) Diffused beam shart cutoff photoelectric
B) Diffused beam background suppression photoelectric
C) Diffused beam fixed focus photoelectric
D) Diffused beam wide angle photoelectric
E) None of the above