Messung von Physikalischen Größen

Eine Messgröße ist die physikalische Größe, die bestimmt werden soll (in der Metrologie häufig „Measurand“ genannt). Erst wenn eindeutig feststeht, was gemessen wird – beispielsweise die Länge einer Kante an einem festgelegten Ort, die Temperatur einer Oberfläche bei definiertem Emissionsgrad oder das Profil entlang einer Laserlinie – wird eine Messung reproduzierbar.

Das Messergebnis besteht aus Messwert und Einheit; formal kann man schreiben:

x = {x} · [x]

Transduction describes the conversion of a physical quantity into an evaluable signal (usually electrical).

Optical systems, for example, convert geometric information via light projection and camera imaging into pixel coordinates. Thermal systems detect infrared radiation and derive temperature values from it.

The measurement chain includes the sensor, signal conditioning (amplification/filtering), digitization (ADC), evaluation, and, if necessary, compensation. Each element of the measurement chain contributes to measurement uncertainty.

Physical quantities are defined within the International System of Units (SI). The base quantities include:

• Length in meters (m)
• Time in seconds (s)
• Temperature in kelvin (K)

Derived quantities include:

• Velocity v = s / t
• Acceleration a = Δv / Δt
• Frequency f = 1 / T
• Force F = m · a
• Pressure p = F / A

In geometric inspection, additional characteristic quantities include:

• Angle
• Form deviation
• Roughness

In thermography, relevant quantities include:

• Temperature fields
• Gradients

In practice, this means that every measurand becomes accessible only through an interaction between the measurement object and the measurement system. This interaction is implemented by a measurement principle that converts the quantity into an evaluable signal – the process of transduction.

Optical sensing relies on light–matter interactions (reflection, scattering, imaging), while thermal sensing utilizes electromagnetic radiation in the infrared range.