# NLS-Glossary

Absolute displacement transducer

An absolute displacement transducer measures the distance to an object and supplies a signal proportional to the displacement. These transducers are based on various physical principles.

Absolute Pressure

is pressure relative to zero pressure in an empty space (i.e. a vacuum). the gauge (relative) pressure prel is the pressure compared with atmospheric pressure pamb (surrounding air pressure).

Absolute value

In a magnetic coded measuring system, each position or measurement section is coded to an absolute analog value or digital signal.

In mathematics, the absolute value or modulus of a real number x, denoted |x|, is the non-negative value of x without regard to its sign. Namely, |x| = x if x is positive, and |x| = −x if x is negative (in which case −x is positive), and |0| = 0. For example, the absolute value of 3 is 3, and the absolute value of −3 is also 3. The absolute value of a number may be thought of as its distance from zero.

Absorbance

**Synonyms : **

Optical density

Absorbance (A) is the flip-side of transmittance and states how much of the light the sample absorbed. It is also referred to as “optical density“ $A={\mathrm{log}}_{10}(1/T)$. for samples which scatter light, absorbance may be defined as the negative logarithm of one minus absorptance, as measured on a uniform sample. The term is used in many technical areas to quantify the results of an experimental measurement.

Absorptance

**Synonyms : **

Absorptivity

quotient of absorbed radiant flux and incident radiant flux, expressed by $\alpha =\frac{{\Phi}_{a}}{{\Phi}_{m}}$ where ${\Phi}_{a}$is absorbed radiant flux and ${\Phi}_{m}$ is incident radiant flux. This quantity is also defined spectrally in terms of wavelength, in which case “spectral” is added before the quantity name.

Due to energy conservation, α + ρ + τ = 1 except when polarized radiation is observed, where ρ is reflectance and τ is transmittance.

Absorptiometer

An instrument that measures absorption of light, esp by a solution.