E1BGLOSS 09/14/2010
11:19:49 Page 579
coupled system The combined effect of interconnected
instruments used to form a measurement system.
critical pressure ratio The pressure ratio necessary to
accelerate a fluid to a velocity equal to its speed of sound.
cut-off frequency The 3 dB design point frequency of a
filter.
d’Arsonval movement Device that senses the flow of
current through torque on a current carrying loop; it is
the basis for most analog electrical meters.
D/A converter A device that converts a digital number
into an analog voltage.
damping ratio A measure of system damping-a
measure of a system’s ability to absorb or dissipate
energy.
data acquisition board A device that contains a
minimum of components required for data acquisition;
usually connected to a computer.
data acquisition system A system that quantifies and
stores data.
deflection mode Measuring method that uses signal
energy to cause a deflection in the output indicator. See
loading error.
dependent variable A variable whose value depends on
the value of one or more other variables.
design-stage uncertainty The uncertainty due only to
instrument error and instrument resolution; an
uncertainty value based on the minimum amount of
information that is known at the early stage of test
design.
deterministic signal A signal that is predictable in time
or in space, such as a sine wave or ramp function.
diaphragm meter A type of positive displacement flow
meter that measures gas volume flow rate by
alternately passing isolated but known volumes of the
gas between two chambers.
differential-ended connection Dual-wire connection
scheme that measures the difference between two
signals with no regard to ground.
digital signal Representation of an analog signal that is
quantized in both magnitude and time.
deviation plot Graphical representation of the
difference between a reference and expected value.
direct memory access Transfer protocol that allows a
direct transmission path between a device and
computer memory.
discharge coefficient Coefficient equating the ratio of
actual flow rate across a flow meter to the ideal flow
rate if no losses or flow separation occurred.
discrete random variable Random variable whose
value is not continuous.
distortion Any undesirable change in the shape of a
waveform that occurs during signal conditioning or
measurement.
dispersion The scattering of values of a variable around
a mean value.
disturbance An effect that changes the operating
condition of a control system away from its set-point.
Requires controller action to maintain or re-establish
the set point.
Doppler anemometry Refers to various techniques that
use the Doppler shift to measure velocity.
Doppler flowmeter Flowmeter that uses the Doppler
shift in the frequency of ultrasonic waves passing
through the fluid flow to indicate volume flow rate.
dynamic calibration Process of calibration such that
the input variable is time-varying.
dynamic pressure Difference between the total and
static pressures at any point.
dynamic response Response of a system to a welldefined sine wave input.
dynamometer Device for measuring shaft power.
earth ground A ground path whose voltage level is
zero.
elastic region An operating range of strain versus load
wherein a material returns to its initial length when the
load is removed.
error Difference between a measured value and its true
(actual) value. In controls, it is the difference between
a sensor value and a set-point.
error fraction A measure of the time-dependent error in
the time response of a first-order system.
expanded uncertainty Uncertainty interval with the
combined effects of random and systematic
uncertainties at a stated confidence level (typically
95%) other than one standard deviation.
electromagnetic flow meter Device that bases fluid
flow rate on the magnitude of the current induced in a
magnetic field caused by the velocity of the fluid
passing through that magnetic field.
end standard Length standard described the distance
between two flat square ends of a bar.
expansion factor Coefficient used to account for
compressibility effects in obstruction flow meters.
extraneous variable A variable that is not or cannot be
controlled during a measurement, but that affects the
measured value.
feedback-control stage Stage of a measurement system
that interprets the measured signal and exerts control
over the process.
firewire A serial method for data transmission between
a computer and peripherals using a thin cable and
based on the IEEE 1394 standard.
first-order system A system characterized as having
time-dependent storage or dissipative ability but
having no inertia.
fixed point temperature Temperatures specified
through a reproducible physical behavior, such as a
melting or boiling point.
flip-flop A switching circuit that toggles either on or off
on command. Also called a bistable multivibrator.
Glossary 579
11:19:49 Page 579
coupled system The combined effect of interconnected
instruments used to form a measurement system.
critical pressure ratio The pressure ratio necessary to
accelerate a fluid to a velocity equal to its speed of sound.
cut-off frequency The 3 dB design point frequency of a
filter.
d’Arsonval movement Device that senses the flow of
current through torque on a current carrying loop; it is
the basis for most analog electrical meters.
D/A converter A device that converts a digital number
into an analog voltage.
damping ratio A measure of system damping-a
measure of a system’s ability to absorb or dissipate
energy.
data acquisition board A device that contains a
minimum of components required for data acquisition;
usually connected to a computer.
data acquisition system A system that quantifies and
stores data.
deflection mode Measuring method that uses signal
energy to cause a deflection in the output indicator. See
loading error.
dependent variable A variable whose value depends on
the value of one or more other variables.
design-stage uncertainty The uncertainty due only to
instrument error and instrument resolution; an
uncertainty value based on the minimum amount of
information that is known at the early stage of test
design.
deterministic signal A signal that is predictable in time
or in space, such as a sine wave or ramp function.
diaphragm meter A type of positive displacement flow
meter that measures gas volume flow rate by
alternately passing isolated but known volumes of the
gas between two chambers.
differential-ended connection Dual-wire connection
scheme that measures the difference between two
signals with no regard to ground.
digital signal Representation of an analog signal that is
quantized in both magnitude and time.
deviation plot Graphical representation of the
difference between a reference and expected value.
direct memory access Transfer protocol that allows a
direct transmission path between a device and
computer memory.
discharge coefficient Coefficient equating the ratio of
actual flow rate across a flow meter to the ideal flow
rate if no losses or flow separation occurred.
discrete random variable Random variable whose
value is not continuous.
distortion Any undesirable change in the shape of a
waveform that occurs during signal conditioning or
measurement.
dispersion The scattering of values of a variable around
a mean value.
disturbance An effect that changes the operating
condition of a control system away from its set-point.
Requires controller action to maintain or re-establish
the set point.
Doppler anemometry Refers to various techniques that
use the Doppler shift to measure velocity.
Doppler flowmeter Flowmeter that uses the Doppler
shift in the frequency of ultrasonic waves passing
through the fluid flow to indicate volume flow rate.
dynamic calibration Process of calibration such that
the input variable is time-varying.
dynamic pressure Difference between the total and
static pressures at any point.
dynamic response Response of a system to a welldefined sine wave input.
dynamometer Device for measuring shaft power.
earth ground A ground path whose voltage level is
zero.
elastic region An operating range of strain versus load
wherein a material returns to its initial length when the
load is removed.
error Difference between a measured value and its true
(actual) value. In controls, it is the difference between
a sensor value and a set-point.
error fraction A measure of the time-dependent error in
the time response of a first-order system.
expanded uncertainty Uncertainty interval with the
combined effects of random and systematic
uncertainties at a stated confidence level (typically
95%) other than one standard deviation.
electromagnetic flow meter Device that bases fluid
flow rate on the magnitude of the current induced in a
magnetic field caused by the velocity of the fluid
passing through that magnetic field.
end standard Length standard described the distance
between two flat square ends of a bar.
expansion factor Coefficient used to account for
compressibility effects in obstruction flow meters.
extraneous variable A variable that is not or cannot be
controlled during a measurement, but that affects the
measured value.
feedback-control stage Stage of a measurement system
that interprets the measured signal and exerts control
over the process.
firewire A serial method for data transmission between
a computer and peripherals using a thin cable and
based on the IEEE 1394 standard.
first-order system A system characterized as having
time-dependent storage or dissipative ability but
having no inertia.
fixed point temperature Temperatures specified
through a reproducible physical behavior, such as a
melting or boiling point.
flip-flop A switching circuit that toggles either on or off
on command. Also called a bistable multivibrator.
Glossary 579