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4th year HET > Truck electrical circuit fundamentals > Flashcards

Truck electrical circuit fundamentals Flashcards

1
Q

what is a constant power circuit

A

circuits that are connected to the battery terminal of a starter

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2
Q

type 1 circuit breaker

A

cycle OFF when breaker rating is exceeded . breakers automatically cycle back ON once overload is removed from the system

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3
Q

Type 2 circuit breaker

A

equipped with a heat producing resistor and a bimetallic strip that responds to heat by moving away from the heat source

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4
Q

where is a type 1 circuit used

A

headlights

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5
Q

What is the purpose of daytime running lights

A

enhance the visibility of the truck during the day and poor weather conditions

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6
Q

what is the purpose of the daytime running light terminal block or module .

A

lowers system voltage by 2 or 3 v so the daytime running lights are visible but will not blind other drivers . this can also be achieved through a series of terminating resistors

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7
Q

when mounting or changing clearance /marker and tail light systems

A

always refer to government regulations

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8
Q

what Is a rheostat

A

its a heat creating variable resistor .

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9
Q

what is PWM

A

it is a digital signal that turns the circuit voltage on or off

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10
Q

how is PWM DUTY cycle measured

A

as a % value of ON time vs OFF time

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11
Q

is it possible to make some electromechanical flashers operate in LED light circuits

A

yes by adding a terminating resistor . by balancing the resistance in a system by the number of turn signal lights . if you change the number of lights the resistance value must change as well

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12
Q

on some electromechanical flashers have one extra terminal that is labelled as a pilot terminal . what would this terminal be used for

A

in most cases the output from the pilot terminal illuminates a turn signal indicator light circuit

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13
Q

how are backup lights controlled

A

a transmission mounted switch or ECM . they will come on when the driver shifts the vehicle into reverse

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14
Q

in order for the cab interior light circuit to be able to turn OFF what must happen

A

all door switches must be in a closed position

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15
Q

what is a solenoid

A

an electromechanical device that turns electrical energy into linear movement

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16
Q

what is a discrete solenoid

A

it only has two positions fully open or closed

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17
Q

a door latch would use what type of solenoid

A

a discrete solenoid

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18
Q

what is a proportional solenoid

A

a solenoid that can move in an infinite number of positions

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19
Q

what is a latching solenoid

A

is a discrete solenoid that remains fixed at the end of its travel when it is deenergized

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20
Q

why is a high value resistor installed in parallel with a solenoid

A

to prevent self induced arching when a solenoid is de energized

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21
Q

what is a clamping diode

A

acts as a one way electrical current check valve

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22
Q

DC motors use magnetism and electricity to produce what

A

rotary mechanical motion

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23
Q

what component in a DC motor rotates

A

armature

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24
Q

what is the limiting force of rotational speed of a unloaded DC motor

A

CEMF counter electromotive force

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25
Q

what is CEMF

A

its the voltage produced by a DC motor when it is turning

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26
Q

what are the two types of DC motors

A

permanent magnet DC motors and field wound DC motors

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27
Q

how can you change the direction a PM motor rotates

A

by changing the polarity of the magnetic field

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28
Q

where are parallel wound dc motors used

A

where uniform speed and low starting torque are desirable, such as fan blower motor

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29
Q

what are some methods to allow variable speed motors to rotate at various speeds

A

. variable electrical resistance
. multiple shunt windings
. pulse width modulation

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30
Q

what is important to remember when mounting voltage-reducing resisters

A

never mount them near any easily melted or combustible material

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31
Q

(CMVSA) stipulates that cruise control systems must have .

A

three methods of engine speed control disengagement

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32
Q

what is the purpose of battery isolation switches

A

to prevent parasitic drains while the truck is parked

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33
Q

what is important to remember when installing a battery isolation switch

A

install fuses in both positive and negative leads to prevent damage to wiring harness

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34
Q

how can you reduce or eliminate interference and static noise

A

install a series coil (filter choke) or a parallel - connected capacitor to the units power lead - a parallel - connected capacitor can also be used to reduce noise at the source

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35
Q

how do the truck positioning system warn the driver of potential collisions

A

a forward looking mono pulse radar sensor able to detect fixed and moving objects up to 500ft away

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36
Q

can you turn off the CWS

A

no . it is always active at vehicle speeds above 24 kph

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37
Q

the tire pressure control system allows the driver to do what

A

to match appropriate tire pressures to the road conditions and the trucks load and speed

38
Q

what is a stepper motor

A

an electronic device that only moves a set amount every time it is pulsed with an electronic current

39
Q

even though trucks are equipped with air horn systems they must also be equipped with

A

an electric horn

40
Q

what are the purpose of park contacts in a windshield wiper circuit

A

they return the wipers to a per set rest position by supplying current to the motor after it has been turned off allowing the motor to reach the park position

41
Q

what is the purpose of an inverter

A

to turn 12 v dc power into 110 v ac power . they can be configured to produce 50 to 10000 w of ac power

42
Q

what is the purpose of audible warning devices

A

to alert the driver of a potential hazard or problem involving various truck operation

43
Q

what prevents all the warning lights from illuminating when only one warning light has been triggered

A

isolating diodes

44
Q

if the alternator warning indicator light illuminates where would you be able to check to confirm the problem

A

the R terminal of the alternator will not show a voltage when checked with the unit operating causing the relay to not energize allowing the warning light circuit to stay energized

45
Q

what type of gauge is connected directly into the system they are measuring

A

direct acting gauges

46
Q

what are a few examples of direct acting gauges

A

Air pressure - Oil pressure - engine temperature - Speedometer -

47
Q

what type of gauge requires a sending units and can receive analog and digital signals

A

indirect acting gauge

48
Q

what might cause a indirect gauge to give inaccurate readings

A

poor or corroded electrical connections

49
Q

what are the three types of analog gauges

A

. balancing coil
. stepper motor
. air core

50
Q

electromagnetic gauge or balancing coil will not be affected by

A

voltages changes

51
Q

how does the stepper motor gauge control the direction of movement

A

a microprocessor to generate a pulse width modulation signal

52
Q

what type of gauge receives information from the vehicles j1708 and j1939

A

a digital gauge

53
Q

what is the simplest type of sending unit

A

diaphragm sending unit

54
Q

where would you find an example of variable resistor

A

a fuel sending unit

55
Q

what is the purpose of an anti - slosh unit

A

an electronic filter that minimizes the gauge pointer fluctuation as fuel sloshes around the fuel tank

56
Q

what is a thermistor

A

a variable resistor whose resistance changes significantly with increase and decrease in temperature

57
Q

what are two types of gauges that can determine the condition of the truck electrical system

A

. voltmeter and ammeter

58
Q

what would provide the driver with the most accurate information about the condition of the truck electrical system health

A

ammeter

59
Q

what are the two different methods trucks use to display amperage on a dash mounted gauge

A

the ammeter circuit - shunt meter

60
Q

what is an advantage of a shunt ammeter

A

the cables up to the dash gauge are small gauge size and can be protected by fuses preventing dash fire

61
Q

the speed sensor is a

A

small permanent magnet-style pulse generating sensor

62
Q

what is the first step in the procedure for calibrating the speedometer

A

calculate the pulse per mile

63
Q

how is a tachometer utilized

A

by measures and displays the speed and revolution of the truck engine in revolutions per minute

64
Q

what is baud rate

A

the speed of data transfer over network

65
Q

how is baud rate measured

A

in kilo bites per second

66
Q

what is the back bone of a network

A

the method of connection such as wires or fiberoptic cables

67
Q

what is a stub

A

is a segment of data link that branches off the back bone and connects to each node

68
Q

what is the maximum length a stub can be

A

1 meter

69
Q

what is a node

A

a computer or other device that has a unique address

70
Q

what is the vehicle communication data bus

A

the communication network that connects to all the multiplexed components of a vehicle system

71
Q

what is protocol

A

a common language for data communication between control modules

72
Q

what is topology

A

the logic structure of the control modules on the data bus

73
Q

what is multiplexing

A

the ability to send and receive digital signals over a pair of twisted wires at high speed

74
Q

what networks run at a 9600 baud rate

A

J1587 and J1708

75
Q

what are the two major disadvantages of J1587/J1708

A

if one part of the network fails the whole network will fail, the slow communication speed limits the amount of nodes that it can support to 20

76
Q

what is the message identifier

A

indicates the source address of the transmitting node

77
Q

what is the parameter identifier

A

indicates what data the following message corresponds

78
Q

what is the checksum

A

follows the final byte of data it is one byte long and completes the message . if the checksum is zero then the message is valid

79
Q

what color is the J1587/J1708 twisted pair cables

A

orange and white

80
Q

dose the J1587/J1708 require a terminating resistor

A

no

81
Q

what is the first step in troubleshooting multiplexing

A

determine if the system is receiving power

82
Q

the J1939/CAN is capable of communicating at a rate of

A

250kb/s

83
Q

J1939 is a twisted pair of wires that are usually colored

A

green and yellow

84
Q

what are the two types of J1939 cables

A

shielded and unshielded

85
Q

what is the purpose of the drain wire in a shielded J1939 wires

A

is to prevent internal signals from radiating out and to block outside electromagnetic interference from corrupting the signal

86
Q

how many twists per foot is adequate to provide a clear signal

A

12

87
Q

both unshielded and shielded J1939 cables must have what at each end

A

120 ohm resistor

88
Q

with two 120 ohm terminating resistors connected in parallel, the total resistance of the circuit will be

A

60 ohms

89
Q

a total loss of communication in a J1939 system usually indicates

A

voltage or hardware problem

90
Q

a partial loss of communication in a J1939 system will usually indicate

A

data bus device failure

91
Q

when measuring the voltage between the CAN high/low and the ground if you were to obtain a voltage reading lower than 2.0 v or higher than 4.0 v what might this indicate

A

it is possible that one or more nodes or the bus is faulty

less than 2.0 v check connectors for continuity . for a voltage higher than 4 v check for excessive system voltage

92
Q

if a reading of 120 ohms is obtained when measuring J1939

A

one if the terminating resistors is removed or is open

4th year HET (31 decks)

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