Fiber Optic Sensing
System
Definitions
(PDF)
ABSOLUTE PRESSURE TRANSDUCER: A pressure transducer or
pressure sensor that has an internal reference chamber sealed at
or close to 0 psia (full vacuum) and normally provides
increasing output voltage for increases in pressure.
ABSOLUTE SIGNAL CONDITIONER: A signal conditioner that has
an internal reference that does not require periodic
calibration.
ACCURACY: The standard deviation of measurement error
between a measured value and the actual (true) value. The
measurement includes combined error of the system for
nonlinearity, repeatability, and hysteresis and is expressed as
a percent of the full-scale output.
ARMORED CABLE: An optical or electrical cable that is
protected by a metallic outer sheath. The sheath protects the
cable from being cut or crushed.
AXIAL LOAD: A load applied along or parallel to and
concentric with the primary axis.
CALIBRATION: The comparison of transducer voltage outputs
against the outputs of a reference standard.
DAMPING: The reduction of response at the resonant
frequency through the use of a damping media such as oil.
Usually specified as the ratio of critical damping.
DEAD VOLUME: The volume inside the pressure port of a
transducer at room temperature and barometric pressure.
DEFLECTION: The change in length along the primary axis or
distance a diaphragm moves at the center between no-load and
rated load conditions.
DIAPHRAGM: The sensing membrane which is deformed when
pressure is applied.
DISTRIBUTED TEMPERATURE SENSOR: A sensor capable of making
temperature measurements over an extended distance. This
terminology usually refers to a signal processing method that
determines temperature profile along the length of an optical
fiber many kilometers long.
DYNAMIC SIGNAL CONDITIONER: A signal conditioner that
measures environmental parameters that may change over short
time periods much less than one second.
ELECTRONIC:
A transducer that converts a measured
environmental parameter (temperature, pressure, etc.) into a millivolt signal and then into a digital or analog signal that
can be transmitted with minimal electrical interference, i.e.
4-20 mA two wire output or RS-485 Modbus.
EXPLOSION-PROOF: Incapable of explosion. This term
usually refers to a burst-proof, heavy-walled enclosure that
contains electronic equipment that may ignite an explosive gas.
FABRY-PEROT:
An
interferometric sensor that consists of two partially reflective
plane parallel surfaces.
FIBER BRAGG GRATING:
A periodic change in the refractive
index of an optical fiber along a specified length.
FIBER OPTIC SENSOR:
A sensor that uses optical fiber as the
primary means of making a measurement.
FLUSH DIAPHRAGM:
Sensing element is located on the very tip
of the transducer (NO pressure port).
FREQUENCY RESPONSE:
The range of frequencies over which the
transducer ouput signal follows changes in the measured
environmental parameter.
FULL SCALE:
The full range of the environmental parameter
that can be measured with a device.
FULL SCALE OUTPUT:
The difference between the minimum
output (normally zero) and the maximum output.
GAGE
(GAUGE) PRESSURE : The pressure above (or below) atmospheric
pressure. Represents positive difference between measured
pressure and existing atmospheric pressure. Can be converted to
absolute by adding actual atmospheric pressure value.
GAGE
(GAUGE) PRESSURE TRANSDUCER: A transducer that measures
pressure relative to the atmospheric pressure.
HYSTERESIS:
The maximum difference between output readings
for the same measured point, one point obtained while increasing
from zero and the other while decreasing from full scale. The
points are taken on the same continuous cycle. The deviation is
expressed as a percent of full scale.
INTRINSICALLY-SAFE:
Equipment that never generates an
ignition source and poses no explosion hazard.
INCHES OF WATER:
A measure of pressure normally used for
measurements of differential pressure.
LINEARITY:
The maximum deviation of the calibration curve
from a straight line between zero and full scale, expressed as a
percent of full scale output.
LINE PRESSURE:
The maximum pressure in the pressure vessel
or pipe for differential pressure measurement.
LOAD:
The weight, torque, or force applied to the
transducer.
MEASURAND:
Environmental parameter to be measured, e.g.
temperature, pressure, strain, vibration.
MOUNTED RESONANT FREQUENCY:
The frequency at which the
internal spring/mass system of an accelerometer resonates,
producing a 90º phase shift in output signal vs. applied
acceleration.
MULTIPOINT CONNECTOR:
Connector with more than one fiber optic connection point or
termini.
OPERATING PRESSURE RANGE: The pressure range over
which the unit provides a calibrated output.
OPERATING TEMPERATURE RANGE:
The temperature range
over which the unit provides a calibrated output.
OPTICAL:
A transducer that converts a measured
environmental parameter (temperature, pressure, etc.) into an
optical signal which is transmitted through an optical fiber to
an electronic converter that transforms the optical signal into
a digital or analog signal, i.e. 4-20 mA two wire output or
RS-485 Modbus.
OUTPUT:
The electrical signal measured at the output
terminals of a fiber optic signal conditioner which is produced
by an applied input to a transducer.
OVERPRESSURE LIMITS:
The maximum pressure or load which may be
applied to the transducer without causing a permanent change in
the performance specifications.
PRECISION:
The ability to repeat
output readings when a system is brought to the same
conditions
and measured at different times. Precision is expressed as the
standard deviation of output readings as a percent of full scale.
PRIMARY AXIS:
The axis along which the transducer is
designed to be loaded; normally its geometric centerline.
PROOF PRESSURE LIMITS:
The pressure at which the unit
no permanent damage occurs but recalibration is required.
PSI:
A unit of pressure measured in pounds per square inch.
PSIA: Pounds per square inch absolute.
PSID:
Pounds per square inch differential normally
expressed in inches of water.
PSIG:
Pounds per square inch gage (normally relative to
atmospheric pressure).
RANGE:
The measured values, over which a transducer is
intended to measure, specified by their upper and lower limits.
RATED CAPACITY:
The maximum value that a transducer is
designed to measure within its specification.
REPEATABILITY:
The ability to repeat
output readings when a system is brought to the same
conditions
from the same
direction and measured at different times. Repeatability is expressed as the
standard deviation of output readings as a percent of full scale.
RESOLUTION:
The smallest change in mechanical input which
produces a measurable change in the output signal.
SAMPLE RATE:
The number of measurements reported per measurement
interval, e.g. 10Hz is a sample rate of ten measurements per
second.
SENSOR:
A device that converts changes in a physical parameter into
a signal which may be optical, electrical, chemical, mechanical,
etc.
SENSITIVITY:
The ratio of change in transducer output to a
change in the value of the measured parameter.
SIGNAL CONDITIONER:
A device that converts one signal type to
another, e.g. optical to electrical, digital to analog. A
signal conditioner usually includes signal processing. The
term is synonymous with the terms signal processor, instrument,
interrogator, and surface unit.
SPAN:
The algebraic difference between the limits of the
range from zero to full scale.
SPECIFICATIONS:
The group of error limits within which each
device is to operate.
STATIC SIGNAL CONDITIONER:
A signal conditioner that
measures environmental parameters that do not change over time
periods less than one second.
STABILITY: The ability to repeat
output readings when a system is maintained at constant
conditions
and measured at different times. Stability is expressed as the
standard deviation of output readings as a percent of full scale.
STRAIN
SENSOR OR STRAIN GAGE: A measuring element for converting force,
pressure, tension, etc., into an signal.
TORR:
A measure of vacuum equal to one millimeter of
mercury.
TEMPERATURE COMPENSATION:
The utilization of supplementary
devices, materials, or components within the bridge to minimize
sources of error caused by changing temperature.
TEMPERATURE CORRECTION:
The correction of a measured output
based on algebraic correction factors applied that are based on
a known temperature.
TEMPERATURE, OPERATING:
The range of temperature over which
a transducer may be safely operated up to full scale without
causing failure, but specifications may not be met.
TEMPERATURE EFFECT ON SPAN:
The change in rated output due
to a change in ambient temperature. Usually expressed as ± a
percentage change in rated output per degree F change in ambient
temperature, over the compensated temperature range.
TEMPERATURE EFFECT ON ZERO:
The change in zero balance due
to a change in ambient temperature. Usually expressed as ± a
percentage change in rated output per degree F change in ambient
temperature over the compensated temperature range.
TOOL:
A term used in the oil and gas industry for devices that are
used downhole. For measurement applications, a "tool"
typically is a device that is packaged for use downhole that
includes one or more transducers.
TRANSDUCER:
A device (or medium) that converts energy from
one form to another. The term is generally applied to devices
that take physical phenomenon (environmental parameters such as
pressure, temperature, humidity, flow, etc.) and converts it to an
electrical or optical signal. The transducer typically
includes one or more sensors in a package that isolates the
optical or electronic device from the environment. This
term is synonymous with the terms gauge and probe.
TRANSVERSE SENSITIVITY:
Signal output as a result of
acceleration perpendicular to the sensitive axis. Specified as a
percentage of sensitive axis output for equivalent right angle
acceleration or as a decimal fraction.
UPDATE RATE:
The time interval between measurements, e.g. 0.1 second when
the sample rate is 10Hz.
VIBRATION ERROR:
The maximum change in output of a
transducer when a specific amplitude and range of frequencies
are applied to a specific axis at room temperature.
WETTED PARTS:
The diaphragm and pressure port material that
comes in direct contact with the medium (gas, liquid).
ZERO ADJUSTMENTS:
Used when 'setting up' a transducer to
adjust the output signal to zero when zero load/pressure is
applied.
ZERO BALANCE:
The output signal of the transducer with
rated excitation and with no-load or pressure applied, usually
expressed as a percent of rated output.
ZERO RETURN:
The difference in zero balance measured
immediately before application of rated load or pressure for
specified duration and measured after removal of the load, and
when the output has stabilized. |
