APPENDIX B
SENSOR TECHNOLOGY GLOSSARY
DEFINITIONS AND EXPLANATIONS OF DESCRIPTORS AND OTHER TERMS
A
accuracy.
See characteristics of sensors—accuracy.
acquisition of data [continuous versus discrete, threshold/peak, integrating].
How information from a sensor is to be processed. The use of computer control requires digitized input, which converts continuous, discrete, threshold/peak, and/or integrating sensor information into digital information. See discussion of this descriptor in Chapter 2.
analyte.
A chemical species targeted for qualitative or quantitative analysis.
attenuation.
A decrease in the amplitude of a signal as it passes through any part of the measurement system.
B
background-limited performance.
A situation in which the signal is weak relative to the background noise.
bandwidth.
The range of frequencies over which the measurement system can operate within a specified error range.
breakdown.
Failure of a material resulting from an electrical overload. The resulting damage may be in the form of thermal damage (melting or burning) or electrical damage (loss of polarization in piezoelectric materials).
C
characteristics of sensors
accuracy.
The degree of correctness with which the measuring system yields the ''true value" of a measured quantity, where the "true value" refers to an accepted standard, such as a standard meter or volt. Typically described in terms of a maximum percentage of deviation expected based on a full-scale reading.
limit of detection.
The smallest measurable input. This differs from resolution, which defines the smallest measurable change in input. For a temperature measurement, this would provide an indication of the lowest temperature a sensor could generate an output in response.
linearity.
The degree to which the calibration curve of a device conforms to a straight line.
range.
The difference between the minimum and maximum values of sensor output in the intended operating range. Defines the overall operating limits of a sensor.
resolution.
The smallest measurable change in input that will produce a small but noticeable change in the output. In the context of chemical separations, defines the completeness of separation.
response time.
The time it takes for the sensor's output to reach its final value. A measure of how quickly the sensor will respond to changes in the environment. In general, this parameter is a measure of the speed of the sensor and must be compared with the speed of the process.
selectivity.
The ability of a sensor to measure only one metric or, in the case of a chemical sensor, to measure only a single chemical species.
sensitivity.
The amount of change in a sensor's output in response to a change at a sensor's input over the sensor's entire range. Provides an indication of a sensor's ability to detect changes. For some sensors, the sensitivity is defined as the input parameter change required to produce a standardized output change.1
conformance.
The closeness of a calibration curve to a specified curve. Equipment that is in conformance is in compliance with specifications, industry standards, or other guidelines.
constraints.
See discussion of this descriptor in Chapter 2.
isolation.
How much a device must be isolated from various disturbances or effects which compromise information integrity or sensor reliability. For example, electromagnetic isolation provides immunity to interference from electromagnetic radiation. This improves the overall quality (and therefore accuracy) of a sensor signal.
packaging.
How the packaging material or design limits the environments in which the sensor can be used.
cross-sensitivity.
The influence of one measurand on the sensitivity of a sensor another measurand.
crosstalk.
Electromagnetic noise transmitted between leads or circuits in close proximity to each other.
D
detectability.
See characteristics of sensors—limit of detection.
distortion.
Inaccuracy in a reproduced or amplified signal, such as shifted frequencies, unequal delays, or unequal change in amplitude ratios of the components of an output signal.
drift.
Gradual departure of the instrument output from the calibrated value. An undesired slow change of the output, which is not a function of the measured quality.
dynamic characteristics.
A description of an instrument's behavior between the time a measured quantity changes value and the time the instrument obtains a steady response.
dynamic error.
The error that occurs when the output does not precisely follow the transient response of the measured quantity.
E
economic factors.
(See discussion of this descriptor in Chapter 2.)
acquisition cost.
The cost to purchase the sensor technology.
development cost.
The investment required to develop the technology.
life-cycle cost.
The cost of acquiring and maintaining the technology over its useful life.
maintenance cost.
The investment in resources to maintain the sensor technology.
manufacturability.
The cost-effectiveness of a sensor technology.
eddy current.
Electrical current induced in a conducting material by a variation of magnetic flux.
electrode.
A conductive element used to emit, collect, or control the movement of electrons or ions in an electric field.
efficiency.
In the context of chemical separations, a measure of the ability to separate.
end points.
The output values at the upper limits of the sensor's range.
error.
The difference between the measured value and true value.
F
ferroelectric material
A dielectric material made from molecules containing dipoles (asymmetric distributions of electrical charge) which spontaneously align.
free impedance.
The impedance at the input of a transducer when the impedance of the load is made zero.
frequency response.
Two relations between sets of inputs and outputs. One relates frequencies to the output-input amplitude ratio; the other relates frequencies to the phase difference between the output and input.
G
gain.
The ratio of the amplitude of an output to input signal.
grounding.
Creating an electrically conductive path to the earth or some other conducting body at zero potential with respect to the earth.
H
hysteresis.
The difference in the output when a specific input value is approached first with an increasing and then with a decreasing input. This phenomenon occurs in ferroelectric materials and results in irreversible loss of energy through heat dissipation.
I
impedance.
The complex ratio of a force-like quantity (force, pressure, voltage, temperature, or
electric field) to a corresponding related velocity-like quantity (velocity, volume velocity, current, heat flow, or magnetic field strength).
implementation
(See discussion of this descriptor in Chapter 2.)
format (integrated signal processing, multichannel, multiplexing).
The manner in which a number of sensor signals over time or space are mixed.
mode (contact vs. noncontact, remote, in situ, invasive vs. noninvasive, nondestructive vs. destructive).
The measurement of a property involves selecting the best combinations of alternatives depending on material, process, and/or product constraints.
scale (single point, integrating, array).
The size of a sample area or volume used to determine the desired property. Sensor measurement of a property or state of the material may be at a point or aggregated over a large area.
inductance.
That property of an electric circuit which tends to oppose change in current in the circuit.
industrial noise.
Electrical disturbances created by an industrial environment, such as 60-Hz noise from AC power lines or sporadic noise from changes in power consumption.
instability.
The tendency to behave in an unpredictable, changeable, or erratic manner.
interchangeability error.
The error observed when a sensor is replaced by another sensor when the quantity being measured is identical.
isolation.
See constraints—isolation.
L
lag.
The time delay required for a system to completely respond to a change in the input signal.
leakage.
The loss of all or part of a useful agent, as of the electric current that flows through an insulator of the magnetic flux that passes outside useful flux circuits.
life (lifetime).
The length of time the sensor can be used before its performance changes.
linearity.
See characteristics of sensors—linearity.
M
magnetometer.
An instrument used for measuring the intensity and/or direction of a magnetic field.
magnetostrictive material.
A material that changes dimension in the presence of a magnetic field or generates a magnetic field when mechanically deformed.
measurand.
A physical quantity, condition, or property that is to be measured.
measurement scale (macro, milli, micro, or nano).
The amount of sample or measure being sampled. Sensor measurement of a property or state of the material may be at a nano (or atomic) level or at various increasing levels of granularity for which the macro (bulk or global) level is the highest. See discussion of this descriptor in Chapter 2.
microsensors.
Sensors having dimensions in the range of 10-7 to 10 -3 meters, as is typical of solid-state sensors employing silicon microtechnology.
minimum detectable signal.
See characteristics of sensors—limit of detection.
N
noise.
Meaningless stray signals and electrical disturbances in a measurement signal that decrease accuracy of the measurement.
nonlinearity.
Lack of constant proportionality between two parameters over a range of measurement.
O
offset.
The output signal of the sensor when the measurand is zero.
operating temperature range.
The range of temperatures over which a sensor can be used with a specified maximum error. See characteristics of sensors—range.
output impedance.
The ratio of output voltage to the short circuit current of an instrument.
overall performance.
The performance of the entire system, which takes into account the contributions from all of the components of that system.
overshoot.
The amount an indicator or system goes beyond its steady-state value before returning to the steady-state value.
P
phase angle.
The difference in the phase relationship of the current and voltage expressed as the angle between the vectors representing the two.
phase shift.
A time difference between the input and output signals.
piezoelectric material.
A ferroelectric material in which an electrical potential difference is created due to mechanical deformation, or conversely, in which the application of a voltage causes dimensional changes in the material.
precision.
The degree of reproducibility among several independent measurements of the same true value under specified conditions.
Q
Q factor.
A rating, applied to coils, capacitors, and resonant circuits, equal to the reactance divided by the resistance. The ratio of energy stored to energy dissipated per cycle in an electrical or mechanical system.
R
range.
See characteristics of sensors—range.
reactance.
The component of the impedance of an electric circuit, not due to the resistance, which opposes the flow of an alternating current.
reliability. (life, multiuse vs. single, calibration vs. accuracy drift).
How well a sensor maintains both precision and accuracy over its expected lifetime. Also includes the robustness of the sensor. See discussion of this descriptor in Chapter 2.
repeatability.
The exactness with which a measuring instrument repeats indications when it measures the same property under the same conditions.
resistivity.
The resistance of a material expressed in ohms per unit length and unit cross section.
resolution.
See characteristics of sensors—resolution.
resonant frequency.
The frequency at which the sensor has maximum output.
response time.
See characteristics of sensors—response time.
S
selectivity.
See characteristics of sensors—selectivity.
sensing element.
The part of a transducer that is in contact with the medium being measured and that responds to changes in the medium.
sensitivity.
See characteristics of sensors—sensitivity.
signal-to-noise-ratio.
The ratio of the output signal with an input signal to the output signal with no input signal.
smart sensor.
A sensor in which the electronics that process the output from the sensor, and forms the modifier, are partially or fully integrated on a single chip.
span.
The difference between the highest and lowest scale values of an instrument.
specificity.
See characteristics of sensors—selectivity.
step response.
The response of a system to an instantaneous jump in the input signal.
strain gauge.
An element (wire or foil) that measures a strain based on electrical resistance changes of the gauge that result from a change in length or dimension strain of the wire or foil.
T
thermistor.
A temperature-measuring device, which contains a resistor or semiconductor whose resistance varies with temperature.
thermocouple.
A temperature-measuring device, which contains a pair of end-joined dissimilar conductors in which an electromotive force is developed by thermoelectric effects when the joined ends and the free ends of the conductors are a different temperatures.
threshold.
The smallest input signal that will cause a readable change in the output signal.
time constant.
The time it takes for the output change to reach 63 percent of its final value.
transduction (self-generating or modulating).
The conversion of the signal to be measured into another, more easily accessible form. Source of energy for transmission of the sensor signal. (See discussion of this descriptor in Chapter 2).
transduction mode (direct or indirect).
How the sensor acquires the desired information from the material. In general, this parameter is an indication of the ability of the sensor signal to provide information regarding a material property or state of interest. See discussion of this descriptor in Chapter 2.
transient response.
The response of the sensor to a step change in the measurand.
