Transcript COMPUTERS AND INPUT SENSORS

COMPUTERS
AND
INPUT SENSORS
MICROCOMPUTER OPERATION
HAPPENS IN STAGES
Memory
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INPUT STAGE
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INPUTS: All
sensors produce
are a voltage
signal of some
type
Some Inputs are
“conditioned”
before going to the
microprocessor.
– Amplification
– A/D Conversion
INPUT CONDITIONING
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Microprocessor
can only process
some types of
signals
Must amplify some
signals
Must convert
analog signals to
digital signals
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A/D converter takes
snapshot of analog
signal
Computers only
understand 1’s and
0’s.
– 1 = On
– 0 = Off
Voltages are classified
into different ranges
Each range is
assigned a numeric
value
Values are translated
into a binary code
BINARY CODE
PROCESSING OPERATION
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Digital signal
compared to
lookup tables
Information is sent
to microprocessor
Microprocessor
decides what to do
Issues a command
to output actuator
TYPES OF MEMORY
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DIFFERENT TYPES
READ ONLY MEMORY (ROM)
 RANDOM ACCESS MEMORY
(RAM)
 KEEP ALIVE MEMORY (KAM)
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READ ONLY MEMORY
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Permanent memory
Microprocessor can only read
information from ROM
Information cannot be erased
Contains info such as: programs,
look up tables to tell how vehicle
should perform. Data and formula’s
used to perform calculations
Vehicle information: # of cylinders,
valve size, transmission type, rear
end
RANDOM ACCESS
MEMORY
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Information stored temporarily
Can be written to or read from
When Ignition is turned off, memory
is erased.
Used to store information from
sensors, results of calculations and
data subject to constant change.
KEEP ALIVE MEMORY
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Information can be read, written and
erased from KAM
KAM is not lost when ignition key is
turned off
Disconnecting Battery will erase
KAM
KAM allows for adaptive strategies
Stores diagnostic codes
PROCESSOR LOCATION
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Usually under dash or inside car
Sometimes under hood.
Susceptible to water, dirt, dust, heat
and vibration
Some are built in to component
Body Computers located many
different places in vehicle.
Some cars centrally locate all
processors
HANDLING THE
PROCESSOR
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TOUCH THE VEHICLE CHASSIS TO
DISCHARGE STATIC ELECTRICITY
TURN POWER OFF BEFORE
DISCONNECTING PROCESSOR
BE SURE DVOM CONNECTIONS ARE
CORRECT
BE SURE TO USE THE CORRECT
TEST INSTRUMENT
OUTPUT STAGE
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Microprocessor
issues commands
in the form of
voltages
Can display
information on a
Scanner or Digital
dash
Can control
hydraulic, vacuum
or electrical
components.
OUTPUT DRIVERS
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Microprocessor
send digital
signals to output
drivers
Drivers usually
do not send
voltage to
actuators
Microprocessor
controls actuator
ground circuit
INPUT SENSORS
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ALL SENSORS PERFORM SAME
BASIC FUNCTION
– DETECT MECHANICAL CONDITION
(MOVEMENT)
– CHEMICAL STATE CHANGE
– TEMPERATURE CONDITION
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ALL SENSORS CHANGE ABOVE
INPUT INTO VOLTAGE SIGNALS
THAT PROCESSOR CAN USE
3 WIRE SENSORS
REFERENCE VOLTAGE SENSOR
OR VOLTAGE MODIFIER
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VOLTAGE REFERENCE
SIGNAL WIRE
SIGNAL RETURN (GROUND)
THROTTLE POSITION
SENSOR
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CHANGES MECHANICAL ACTION INTO
ELECTRICAL SIGNAL
SOME ARE ADJUSTABLE
SOME READ HIGH VOLTS AT IDLE, SOME
LOW VOLTS AT IDLE
TWO WIRE SENSOR
VOLTAGE MODIFIER
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SIGNAL CIRCUIT
GROUND CIRCUIT
TWO TYPES OF
TERMISTORS
– NTC = REDUCES
OHMS WHEN TEMP
INCREASES
– PTC = INCREASES
OHMS WHEN TEMP
INCREASES
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MAF SENSOR
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USES HOT WIRE
PCM MONITORS
COLD WIRE TEMP.
SENDS CURRENT
TO HOT WIRE TO
MAINTAIN 392
DEGREES ABOVE
COLD WIRE
AMOUNT OF
CURRENT
DETERMINES
INTAKE AIR FLOW
CYCLE
DUTY CYCLE
PULSE WIDTH
FREQUENCY
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PULSE WIDTH
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LENGTH OF TIME IN MS, ACTUATOR IS
ON
IE, “DURATION OF ON-TIME”
PULSE WIDTH MODULATION
VANE AIR FLOW METER
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USES THREE
TYPES OF
VOLTAGE
MODIFIERS
– SWITCH
– POTENTIOMETER
– THERMISTOR
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MOVES DOOR TO
DETERMINE AIR
FLOW
WHEATSTONE BRIDGE
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THREE FIXED AND ONE VARIABLE
RESISTOR
PCM ALWAYS TO BALANCE THE BRIDGE
USED TO MEASURE PRESSURE AND
MECHANICAL STRAIN
VOLTAGE GENERATOR
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GENERATES IT OWN VOLTAGE SIGNAL
COMPARES INSIDE AIR TO OUTSIDE AIR
SIGNAL IS .1 TO 1.0 VOLT
LOW VOLTAGE MEANS SENSING LEAN
HIGH VOLTAGE MEANS SENSING RICH
O2 SENSOR SIGNAL
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Signal range is
between 0.0 and
1.0volt
Normal operation
is from 0.2 to 0.8
volts
PCM will always try
to do the opposite
from what 02
sensor is signaling
02 CROSSCOUNTS
Generally, about 2 to 3 crosscounts is normal operation
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ZIRCONIA SENSOR
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TITANIA SENSOR
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DIAGNOSTIC LOGIC TREE
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LOGIC TREE OR
DIAGNOSTIC
CHART
SOME CHARTS
INCLUDE
EXPLANATIONS
MANY
MANUFACTUERS
USE THIS TYPE
DIAGNOSTICS
LOOK UP TABLE USED TO
DETERMINE BLOCK
LEARN/INTERGRATOR
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SCANNER
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SCANNERS READ
CODES AND DATA
STREAMS
TEST ACTUATORS
GRAPHING
LAB SCOPE
DVOM
TECHNICAL INFO
GM PROM
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CONTAINS SPECIFIC PROGRAMS SUCH
AS; SPARK ADVANCE, FUEL INJECTION
SOME ARE ELECTRONICALLY ERASABLE
REPLACEABLE SEPARATE FROM PCM
CODE CHART
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SELF DIAGNOSTICS
(SELF TEST MODE)
“HARD FAULTS”
“SOFT CODES” OR
“MEMORY CODES”
ACCESS TROUBLE
CODES WITH
SCANNER OR BY
MANUAL METHOD
ERASING FAULT
CODES
DATA LINK CONNECTOR’S
(DLC)
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