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Glossary of Common Terms
Here is a list of terms particular to stress and strain measurement with their definitions.

Glossary

  • Abscissa

    In a system of rectangular Cartesian coordinates, the distance of a point along the horizontal X-axis from the vertical Y-axis. Usually the independent variable.
  • Absolute Strain

    Change in the length of a line segment in a deformed body.
  • AC coupling

    Use of a special circuit to remove the static (DC) components from the input signal to the amplifier in an instrument, leaving only the components of the signal that vary with time
  • Active arm (Wheatstone bridge)

    An arm of a Wheatstone bridge incorporating a variable resistor as a sensor for strain, temperature, or other measurand.
  • Adhesive, strain gage

    A specially formulated and qualified material of finite thickness, applied between the surface of the test specimen and gage backing during gage installation that mechanically bonds the strain gage backing to the test specimen and provides for transmission of strain from the specimen surface to the gage backing and grid.
  • Adjacent arms (Wheatstone bridge)

    Any two arms of a Wheatstone bridge circuit joined at a common corner.
  • Adjacent corners (Wheatstone bridge)

    Any two corners (P+, P-, S+, S-) in a Wheatstone bridge separated by a single bridge arm.
  • Algebraic maximum

    The most positive number in a set.
  • Ambient temperature

    Temperature of the environment in which a strain measurement is being made.
  • Amplifier

    1. Portion of a strain gage instrument that increases the magnitude of an electrical signal, usually the output from the Wheatstone bridge. 2. A strain measurement instrument without a built-in readout, such as a signal conditioning amplifier.
  • Amplifier balance

    Feature of strain gage instrumentation that enables the amplifier to be adjusted so that no output signal is produced when no input signal is present.
  • Analog signal

    A voltage, current, or other signal of infinitesimal resolution that is continuously variable with time.
  • Analog-to-Digital conversion (ADC)

    The process of subdividing an analog signal into discrete time segments, comparing the signal over those time segments to discrete voltage levels, and reporting the results of the comparisons in the form of digital outputs of binary numbers having a resolution of n bits.
  • Anisotropic material

    Material having mechanical properties that are not the same in all directions at a point in a body of it. There are no planes of material symmetry. That is, the properties are a function of the orientation at a point.
  • Anisotropy

    A characteristic of a material with materials properties that differ in value along axes in different directions.
  • Apparent strain( Thermal output)

    1. Portion of the measurement signal caused by a temperature-induced change in resistance of a strain gage that is independent of, and unrelated to, the mechanical strain in the test part. 2. The reversible part of the temperature-induced strain of a strain gage installed on an unrestrained test specimen when exposed to a change in temperature. References Vishay Measurements Group Tech Note TN-504, Strain Gage Thermal Output and Gage Factor Variation with Temperature. 1. OIML International Recommendation No. 62
  • Arm (Wheatstone bridge)

    All the resistive components, including strain gages, leadwires, and bridge completion resistors, between adjacent corners of a Wheatstone bridge.
  • Auto-Balance

    Feature of a strain gage instrument containing special circuitry to automatically zero-balance the instrument before strain measurements are made.
  • Axial gage factors

    Gage factors of a strain gage subjected to a uniaxial strain in the transverse and longitudinal directions, the ratio of which is the transverse sensitivity coefficient of the strain gage.
  • Axial loads

    Loads and load components applied along an axis in such a way that no bending or torsion moments are produced.
  • Backing (carrier) , strain gage

    A thin layer of insulating material on which the grid of a strain gage is affixed to one side during manufacturing and an adhesive is applied to the other during installation for bonding the gage to the test surface, and through which strain is transmitted from the cured adhesive to the grid.
  • Balance (Zero Balance)

    State of a strain gage instrument which has been adjusted to yield no output. The instrument may be zero-balanced even if the Wheatstone bridge is resistively unbalanced.
  • balanced bridge (Wheatstone bridge)

    A Wheatstone bridge for which the arm resistances have been adjusted in such a way that no output is present between the signal corners when a voltage is applied between the power corners.
  • Balco Alloy

    High resistance alloy of 30% iron in nickel and used for making temperature-sensitive compensation resistors for application in transducer circuits.
  • Band-Pass

    A range expressing the limiting frequencies for which a suitable fraction of the maximum output of an instrument is obtained, which for strain gage instrumentation is usually zero Hz (dc) to the frequency at which the output is attenuated to either -3dB (half power, reflecting 70.7% of the input signal) or -0.5dB (about 90% power, reflecting about 95% of the input signal).
  • Bandwidth

    The difference between the frequency limits (bandpass) of a band containing the useful frequency components of a signal.
  • Batch

    The designation for a group of strain gages of the same type and lot, manufactured as a set (made at the same time and under the same conditions).
  • Beam

    A relatively straight, three-dimensional object for which two dimensions are small compared to the third. Usually loaded perpendicular to the largest dimension
  • Bending Loads

    Loads or load components applied normal to an axis through a body, in parallel but separate lines, that produce bending moments.
  • Biaxial Rosette (Tee-rosette)

    Two-element strain-gage rosette in which the grids are oriented perpendicular to one another. Synonym: 90-degree rosette, biaxial rosette
  • Biaxial State

    State of stress or strain about a point in which only two of the three principal stresses or strain are non-zero.
  • Bits

    Units of resolution in the analog-to-digital (A/D) conversion process, for which the most significant bit (msb) equals half the full-scale value of the converter, the least significant bit (lsb) equals 2-n of full scale, and the sum of all n bits equals the maximum measurable signal (full scale less 1 lsb).
  • Body forces

    Forces, such as gravity or magnetic forces, which act on all portions of a body. They, along with surface forces, are of the two kinds that can act on a body.
  • Bondable strain gage

    Strain gage designed to be attached to a test structure or component with an adhesive.
  • Bondable Terminals

    (terminal strip) - A set of copper-coated soldering terminals for connecting small leadwires from the strain gage tabs to larger instrument leadwires. The strips, with insulating backings, are bonded directly to the test specimen to provide stress relief to the gage installation from inadvertant tugs on the instrumentation leadwires.
  • Branch (Wheatstone bridge)

    Two adjacent arms of a Wheatstone bridge between the power corners.
  • Bridge Completion Resistors (Wheatstone bridge)

    Stable precision resistors used in the inactive arms of a Wheatstone bridge to complete the circuit.
  • Bridge excitation (Wheatstone bridge)

    The constant voltage or current supplied to the power corners of the Wheatstone bridge.
  • Bridge output (Wheatstone bridge)

    Electrical output across the signal corners (S+, S-) of the Wheatstone bridge. Sometimes represented as the ratio of the output to the input, i.e., mV/V.
  • Bridge power supply (Wheatstone bridge)

    A source of constant current or constant voltage for providing excitation to a Wheatstone bridge.
  • Bridge voltage (Wheatstone bridge)

    Voltage impressed across the power corners of a Wheatstone bridge by the constant-voltage power supply.
  • Brittle Materials

    Materials that experience little, if any, plastic deformation before the onset of fracture.
  • Calibrate

    To scale the readout of an instrument according to a signal produced by a known value of the measurand.
  • Calibration resistor

    Shunt resistor temporarily installed in parallel with resistive components in a Wheatstone bridge arm to simulate a specific decrease in resistance of those components.
  • Cantilevered Beam

    Beam fixed at one end such that no rotation occurs at the fixed end when the beam is loaded in bending. This idealized condition of determinate end fixity is approached, but never fully achieved, in practice.
  • CLTS matching network

    Small passive resistive network connected between CLTS Temperature Sensors and strain gage instrumentation that (a) linearize the gage resistance versus temperature, (b) attenuate the resistance change slope to the equivalent of 10 microstrain per degree Fahrenheit or Celsius, and (c) present a balanced 350-ohm half-bridge circuit to the strain indicator at the reference temperature of 0 deg F or 0 deg C.
  • CLTS temperature sensor

    Cryogenic Linear Temperature Sensor recommended for use over the range of -452 deg to +100 deg F (-269 deg to +40 deg C). Requires the use of a CLTS Matching Network.
  • Coefficient of thermal expansion (CTE)

    The ratio of (a) the change in length of a line segment in a body per unit of temperature change to (b) its length at a reference temperature.
  • Combined Stress

    A multiaxial state of stress produced by a combination of two or more axial, bending, and/or torsional loads.
  • Common-Mode Voltage

    A voltage (usually unwanted) appearing in common at both inputs of an instrument with respect to the output reference (usually ground).

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