Calibration Definitions

Absorption

This is understood to mean the penetration of gases or gas mixtures into liquids or solid substances. NO2, for instance, is absorbed/fixed by rubber or silicone hoses.

Adsorption

Adsortpion takes place if gases are held solely by the surface forces when they come into contact with a solid substance, e.g. the inside wall of a hose. These "captured gases are then given off again uncrolledly (e.g. the presence of NO2 ls indicated even though no more NO2 gas is applied).

Calibration Adjustment or Span

To adjust the measured reading to the smallest possible deviation according to the known standard value or reference (i.e. for analyzer calibration gas). Therefore, adjustment requires a change of the instrument settings.

Calibration Check

Comparison of an analyzer's output signal (measured reading) to a known standard.

Cross-Sensitivity

The characteristic of sensors to react not only to the target gas to be verified, but also to other gases.

Error or Measurement (Accuracy)

Indicated measurement minus the true value of the measured variable. This can be represented in a variety of ways:

  • Relative deviation from the measured value
  • Deviation relative to the limit value of the measuring range
  • Absolute indication, for instance as vol.% or ppm

Linearity

Deviation from the correct values of the measured values displayed across a measuring range.

Measuring Range

This is the concentration range in which the target gas can be measured by the sensor/unit with the specified accuracy.

Oxidation

The combination of elements with oxygen. In gases, for instance, the oxidation of NO produces NO2.

Reproducibility (Repeat Accuracy)

Standard deviation of a series of measured values from measurements performed at short intervals of time and carried out according to a defined measurement procedure by the same operator on the same parts, using the same equipment and at the same place.

Response Time

Period of time the sensor/unit needs in order to react to the introduced concentration with a stable signal/indication. In practice, txy times are given, e.g. T90 time. This is the length of time until 90% of the introduced concentration is displayed.

Zero Point

What the sensor signal unit displays in the absence of the gas to be verified (="target gas").