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Scan Tool A device that interfaces with and communicates information on a data link.
Sample A reading taken from an electrical signal. A
wave
f
orm is
crea
t
ed from a successive
number of samples.
Sampling Rate The number of readings taken from an electrical signal every second.
Saturated Driver Fuel injection circuit that maintains the same voltage level throughout its on-time.
Secondary Pickup An accessory that
can be clamped on the high voltage
coil wire used to
measure
secondary ignition patterns.
Shielded Test Lead A test lead that is surrounded by a conductive screen to protect the measurement signal
against environmental influences, such as electrical noise or radiation.
Shift Solenoid A device that controls shifting in an automatic transmission.
Single Shot
A signal measured by an oscilloscope tha
t
only occurs once (also called a
t
ransient
event).
Spark Advance The relationship between the ignition timing and top dead center (DTC).
Spike A (high) voltage pulse during a short period of time (sharp pulse).
Throttle A valve for regulating the supply of a fluid, usually air or a fuel/air mixture, to an engine.
Time Base The time defined per horizontal division on the display.
Trace The displayed waveform that shows the variations of the input signal as a function of
time.
Trigger Determines the beginning point of a waveform.
Trigger Level The voltage level that a waveform must reach to start display.
Trigger Slope The voltage direc
t
ion that a waveform
must have to
start
display.
A positive Slope
requires the voltage to be increasing as it crosses the Trigger Level, a negative Slope
requires the voltage to be decreasing.
Trigger Source The instrument input that supplies the signal to provide the trigger.
Transducer A device that receives energy from one system and retransmits (transfers) it, often in a
different form, to another system.
For example, the cruise control
t
ransducer converts a vehicle speed s ignal to a
modulated vacuum output to control a servo.
Turbocharger A centrifugal device driven by exhaust gases tha
t
pressurize the intake air, thereby
increasing the density of charge air
and
t
he consequent power ou
t
put from a given
engine displacement.
USB Universal Serial Bus (visit www.usb.org for details.)
User’s Last Display The last display having been displayed just before the instrument was turned off.
Vertical Scale The scale used for vertical display (ver
t
ical sensitivi
t
y) expressed
in
certain units per
division.
G-5
NTC
A
resistor that has a Negative Temperature Coefficient; resistance decreases as
temperature increases.
O
2
Sensor Oxygen sensor
Off-time The part of an electrical signal during which an electrical device is de-energized.
On-time The part of an electrical signal during which an electrical device is energized.
OBD II On-Board Diagnostics Second Generation (or Generation Two)
OBD II Systems Provide comprehensive diagnostics and monitoring of emission controlling systems.
Open Loop An operating condition or mode based on programmed instructions and not modified by
a feedback system.
Peak Value The highest or lowest value of a waveform.
Peak-and-Hold A method
for
regulating the current flow through electronic fuel injectors. Supplies
higher current necessary to energize the
injector,
then
drops to a lower level just
enough to keep the injector energized.
Pixel The smallest graphic detail possible for the liquid crystal display (LCD)
Powertrain The elements of a vehicle by which motive power is generated and transmitted to the
driven axles.
Pressure (Absolute) The Pressure referenced to a perfect vacuum.
Pressure (Differential) The pressure difference between two regions, such as between the intake manifold and
the atmospheric pressures.
PTC A resistor that has
a Positive Temperature Coefficient; resis
t
ance increases as
temperature increases.
Pulse A voltage signal that increases or decreases from a constant value, then returns to the
original value.
Pulse Modulated A circuit that maintains average voltage levels by pulsing the voltage on and off.
Rail A manifold for fuel injection fuel.
Range Specified limits in which measurements are done.
Reference Voltage
A
n unal
t
ered voltage applied to a
circui
t
. Battery plus (B+) and ground (GND) are
examples of reference voltages.
Regulator (Voltage) A device that automatically controls the functional output of another device by adjusting
the voltage to meet a specified value.
Relay A generally electromechanical device in which connections in one circuit are opened or
closed by changes in another circuit.
Root Mean Square Conversion of AC voltages to the effective DC value.
(RMS)
RPM Engine speed expressed in Rotations Per Minute of the crankshaft.
G-4
Terminology Description Terminology Description