Truck electrical circuit fundamentals Flashcards
what is a constant power circuit
circuits that are connected to the battery terminal of a starter
type 1 circuit breaker
cycle OFF when breaker rating is exceeded . breakers automatically cycle back ON once overload is removed from the system
Type 2 circuit breaker
equipped with a heat producing resistor and a bimetallic strip that responds to heat by moving away from the heat source
where is a type 1 circuit used
headlights
What is the purpose of daytime running lights
enhance the visibility of the truck during the day and poor weather conditions
what is the purpose of the daytime running light terminal block or module .
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
when mounting or changing clearance /marker and tail light systems
always refer to government regulations
what Is a rheostat
its a heat creating variable resistor .
what is PWM
it is a digital signal that turns the circuit voltage on or off
how is PWM DUTY cycle measured
as a % value of ON time vs OFF time
is it possible to make some electromechanical flashers operate in LED light circuits
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
on some electromechanical flashers have one extra terminal that is labelled as a pilot terminal . what would this terminal be used for
in most cases the output from the pilot terminal illuminates a turn signal indicator light circuit
how are backup lights controlled
a transmission mounted switch or ECM . they will come on when the driver shifts the vehicle into reverse
in order for the cab interior light circuit to be able to turn OFF what must happen
all door switches must be in a closed position
what is a solenoid
an electromechanical device that turns electrical energy into linear movement
what is a discrete solenoid
it only has two positions fully open or closed
a door latch would use what type of solenoid
a discrete solenoid
what is a proportional solenoid
a solenoid that can move in an infinite number of positions
what is a latching solenoid
is a discrete solenoid that remains fixed at the end of its travel when it is deenergized
why is a high value resistor installed in parallel with a solenoid
to prevent self induced arching when a solenoid is de energized
what is a clamping diode
acts as a one way electrical current check valve
DC motors use magnetism and electricity to produce what
rotary mechanical motion
what component in a DC motor rotates
armature
what is the limiting force of rotational speed of a unloaded DC motor
CEMF counter electromotive force
what is CEMF
its the voltage produced by a DC motor when it is turning
what are the two types of DC motors
permanent magnet DC motors and field wound DC motors
how can you change the direction a PM motor rotates
by changing the polarity of the magnetic field
where are parallel wound dc motors used
where uniform speed and low starting torque are desirable, such as fan blower motor
what are some methods to allow variable speed motors to rotate at various speeds
. variable electrical resistance
. multiple shunt windings
. pulse width modulation
what is important to remember when mounting voltage-reducing resisters
never mount them near any easily melted or combustible material
(CMVSA) stipulates that cruise control systems must have .
three methods of engine speed control disengagement
what is the purpose of battery isolation switches
to prevent parasitic drains while the truck is parked
what is important to remember when installing a battery isolation switch
install fuses in both positive and negative leads to prevent damage to wiring harness
how can you reduce or eliminate interference and static noise
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
how do the truck positioning system warn the driver of potential collisions
a forward looking mono pulse radar sensor able to detect fixed and moving objects up to 500ft away
can you turn off the CWS
no . it is always active at vehicle speeds above 24 kph
the tire pressure control system allows the driver to do what
to match appropriate tire pressures to the road conditions and the trucks load and speed
what is a stepper motor
an electronic device that only moves a set amount every time it is pulsed with an electronic current
even though trucks are equipped with air horn systems they must also be equipped with
an electric horn
what are the purpose of park contacts in a windshield wiper circuit
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
what is the purpose of an inverter
to turn 12 v dc power into 110 v ac power . they can be configured to produce 50 to 10000 w of ac power
what is the purpose of audible warning devices
to alert the driver of a potential hazard or problem involving various truck operation
what prevents all the warning lights from illuminating when only one warning light has been triggered
isolating diodes
if the alternator warning indicator light illuminates where would you be able to check to confirm the problem
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
what type of gauge is connected directly into the system they are measuring
direct acting gauges
what are a few examples of direct acting gauges
Air pressure - Oil pressure - engine temperature - Speedometer -
what type of gauge requires a sending units and can receive analog and digital signals
indirect acting gauge
what might cause a indirect gauge to give inaccurate readings
poor or corroded electrical connections
what are the three types of analog gauges
. balancing coil
. stepper motor
. air core
electromagnetic gauge or balancing coil will not be affected by
voltages changes
how does the stepper motor gauge control the direction of movement
a microprocessor to generate a pulse width modulation signal
what type of gauge receives information from the vehicles j1708 and j1939
a digital gauge
what is the simplest type of sending unit
diaphragm sending unit
where would you find an example of variable resistor
a fuel sending unit
what is the purpose of an anti - slosh unit
an electronic filter that minimizes the gauge pointer fluctuation as fuel sloshes around the fuel tank
what is a thermistor
a variable resistor whose resistance changes significantly with increase and decrease in temperature
what are two types of gauges that can determine the condition of the truck electrical system
. voltmeter and ammeter
what would provide the driver with the most accurate information about the condition of the truck electrical system health
ammeter
what are the two different methods trucks use to display amperage on a dash mounted gauge
the ammeter circuit - shunt meter
what is an advantage of a shunt ammeter
the cables up to the dash gauge are small gauge size and can be protected by fuses preventing dash fire
the speed sensor is a
small permanent magnet-style pulse generating sensor
what is the first step in the procedure for calibrating the speedometer
calculate the pulse per mile
how is a tachometer utilized
by measures and displays the speed and revolution of the truck engine in revolutions per minute
what is baud rate
the speed of data transfer over network
how is baud rate measured
in kilo bites per second
what is the back bone of a network
the method of connection such as wires or fiberoptic cables
what is a stub
is a segment of data link that branches off the back bone and connects to each node
what is the maximum length a stub can be
1 meter
what is a node
a computer or other device that has a unique address
what is the vehicle communication data bus
the communication network that connects to all the multiplexed components of a vehicle system
what is protocol
a common language for data communication between control modules
what is topology
the logic structure of the control modules on the data bus
what is multiplexing
the ability to send and receive digital signals over a pair of twisted wires at high speed
what networks run at a 9600 baud rate
J1587 and J1708
what are the two major disadvantages of J1587/J1708
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
what is the message identifier
indicates the source address of the transmitting node
what is the parameter identifier
indicates what data the following message corresponds
what is the checksum
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
what color is the J1587/J1708 twisted pair cables
orange and white
dose the J1587/J1708 require a terminating resistor
no
what is the first step in troubleshooting multiplexing
determine if the system is receiving power
the J1939/CAN is capable of communicating at a rate of
250kb/s
J1939 is a twisted pair of wires that are usually colored
green and yellow
what are the two types of J1939 cables
shielded and unshielded
what is the purpose of the drain wire in a shielded J1939 wires
is to prevent internal signals from radiating out and to block outside electromagnetic interference from corrupting the signal
how many twists per foot is adequate to provide a clear signal
12
both unshielded and shielded J1939 cables must have what at each end
120 ohm resistor
with two 120 ohm terminating resistors connected in parallel, the total resistance of the circuit will be
60 ohms
a total loss of communication in a J1939 system usually indicates
voltage or hardware problem
a partial loss of communication in a J1939 system will usually indicate
data bus device failure
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
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
if a reading of 120 ohms is obtained when measuring J1939
one if the terminating resistors is removed or is open
