Calibration drift

Quality control elements required by the instrumental analyzer method include analyzer calibration error ( 2 percent of instrument span allowed) verifying the absence of bias introduced by the sampling system (less than 5 percent of span for zero and upscale cah-bration gases) and verification of zero and calibration drift over the test period (less than 3 percent of span of the period of each rim). 

One problem encountered with the NH probe was that its calibration drifted with time, thus requiring frequent recalibration of the probe. For this reason the probe was abandoned when the measurements with sodium acetate were made. 

Off-gas analysis is routinely carried out either by mass spectrometry or by gas chromatography (GC), in contrast with traditional infrared and paramagnetic off-gas analyzers which are maintenance intensive and have slow response times and significant calibration drifts. 12 ... 

Bennet, A., Gartelmann, D., Mason, J.l. and Owen, J.A. (1970) Calibration, calibration drift and specimen interaction in autoanalyser systems. Clinica Chimica Acta 29, 161-180. 

W.I. Martin and S.S. Grossman, Calibration Drift with Thermometers Repeatedly... 

Aspirate standards, then samples and note absorbance readings. Recheck standards to ensure that calibration drift has not occurred. Prepare a calibration graph and read the sample concentration from this. 

In the following sections we first consider the case where the outlet mole fractions or partial pressures are measured directly, for example by a gas chromatograph, but due to noise or measurement error need to be adjusted in order to achieve the atomic balance required by equation 7.3. Next we consider the case of a mass spectrometer, where calibration is required to derive the partial pressures from mass spectrometer peak readings. In that case it turns out that the procedure used to achieve mass balance also provides a useful way to improve the calibration and to monitor possible changes (calibration drifts) in the mass spectrometer. Finally we consider the case where some components in the feed and/or product are not measured, due either to ignorance or to neglect. It turns out that even in this case it is possible to calculate good approximations to the outlet molar composition to be expected in order to maintain mass and atomic balance. 

A further useful feature is the automatic control and sequencing of multiple functions of the instrument by the built-in electronics, which are effectively a dedicated microcomputer. In some cases a closed loop is involved, so that certain functions are truly automated. For example, an instrument involved in enzyme determinations will monitor the temperature of the reaction cuvette and correct the assayed activity for deviations from the nominal temperature. Also, after initial calibration, an instrument may compare subsequent standards or control samples with the initial value and automatically correct for calibration drift, as well as alerting the operator to excessive drift. 

Calibration, linearity, and hysteresis Calibration drift time, temperature, pressure, etc. 

Calibration drift—the change peak area of a midrange calibration standard over a 6-h period must not exceed 2.0%. 

The system may need to periodically self-calibrate to compensate for any thermally induced calibration drift. 

An often neglected source of fixed pattern noise is that caused by instrument alignment and calibration errors. Unwanted information about the performance of the Raman instrument is added to the Raman spectrum. Calibration drift errors should therefore also be considered. 

The AAS rate monitoring technique has the advantage that it is non-intrusive and can be used in small volumes, in closely spaced regions, and close to a sixrface. Problems with using the atomic absorption techniques concern calibration drift, changing transmission of the optical... 

The accuracy of plume gas ratios reported from multi-gas systems depends on a number of factors influencing the sensor measurement error. These include sensor calibration, linearity and possible calibration drift, the sensor baseUne and possible temperature, humidity and pressure dependences of the sensor output, as outlined below. 

---