Quality instrumentation

J. W. Scales, Air Quality Instrumentation, Vols. I and II, Instrument Society of America, 1974. 

Use high-quality instrument air (oil, dust and moisture free)... 

It also follows that investigating the same system by two or more of these techniques provides at best an illusory impression of confirmation. It is therefore worthier, as far as instrumentation is concerned, to focus on a single technique so as to produce a high-quality instrument in terms of accuracy and time window rather than a mediocre multitechnique setup. 

A slightly less accurate determination is possible using a colorimeter with a wide bandpass filter, e.g. a simple (non-interference type) purple-red filter but an interference filter in a quality instrument gives results comparable to a spectrophotometer. 

Maas J.L., Schipper C.A., Knoben R.A.E., van den Heuvel-Greve M.J., den Besten P.J. and de Maagd G-J. (2008). Diagnostic water quality instruments for use in European Water Framework Directive. Published in The Water Framework Directive Ecological and Chemical Status Monitoring. Editors Quevauviller, Borchers, Thompson, Simonart. ISBN 978-0-470-51836-6, Wiley. 

Vendor s reliability. The vendor that supplies the instrument should have a track record of providing high-quality instruments and after-sale support. A vendor audit should be conducted for a new instrument supplier to evaluate the company s ability to build high-quality products. Purchasing an instrument from a financially unstable vendor is risky. 

Figure 18-6 Errors in spectrophotomefric measurements due to dark current noise and cell positioning imprecision in a research-quality instrument. [Data from L D. Rothman. S. R. Crouch, and J. D. Ingle. Jr.."theoretical and Experimental Investigation of Factors Affecting Precision in Molecular Absorption Spectrophotometry." Anal. Chem. 1975,47, 1226.]...

Research-quality instruments provide <0.1 % stray light, and sometimes much less. 

Hydrological data including temperature, dissolved oxygen, pH, and conductivity were collected by using a water-quality instrument package (Hydrolab Surveyor II, Hydrolab Corp., Austin, Texas) on 11 occasions in 1988. Three sites were sampled Stations 60, 100, and 120 are shown on the map in Figure 1. These stations correspond, respectively, to the power pool just behind the dam, the upstream end of the power pool, and a location further upstream at the head of the principal basin. 

Many factors influence the quality of electrophoretic separations, including gel preparation, reagent quality, instrument assembly, electrophoresis conditions, and the nature and quantity of the sample. 

Outside of the occasional system calibration and model verification tests, the routine maintenance burden of a Raman system is quite low. Optical windows may need to be cleaned, though automatic window cleaning systems can be implemented if it is a known issue. The most likely maintenance activity is laser replacement. Some systems have a backup laser that turns on automatically if the primary laser fails. This lessens the impact of a failure if the unit is being used for closed-loop process control. With a quality instrument and well-developed models, process Raman installations need less maintenance than many competing techniques. 

FIGURE 9.11 Test locations for power quality instrumentation. 

Installing power quality instruments and probes requires special care. It is preferred that voltage and current probe leads do not run in close proximity to high-current cables or bus, especially if they are subjected to large current inrush. This can inductively induce voltages in the leads of the probes and cause erroneous data to be displayed. Voltage and current lead runs parallel to high-current bus or cable... 

The relationship between the solution resistance and the shortest relaxation time of the reaction that can be studied can perhaps be clarified by the following numerical example. Consider a small elec-trode of 0.05 cm, for which C =1.0 pF, and assume that the charge injected is 0.01 pC/cm yielding a value of T = 10 mV. employing high quality instrumentation one can measure the decay of overpotential with, sufficient accuracy if iR is n be expressed by the inequality... 

Figure 26-11 Experimental curves relating relative concentration uncertainties to absorbance for two spectrophotometers. Data obtained with (a) a Spectronic 20, a low-cost instrument (Figure 25-19), and (b) a Cary 118, a research-quality instrument. (From W. E. Harris and B. Kratochvil, An Introduction to Chemical Analysis, p. 384.

Diagnostic Water Quality Instruments for Use in the European Water Framework Directive... 

Critical measuring and test equipment identified as being critical parts of the quality system should be properly calibrated and maintained. Calibration should be traceable to recognized standards. This includes all in-process instruments identified as quality instruments, as well as test equipment used in the laboratory. Test equipment includes laboratory instruments such as spectrometers, viscometers and other apparatus, as well as reagents, buffer solutions and standard solutions. 

Fluorescence spectrometers can be used to measure fluorescence polarization by placing polarizers in the excitation and emission beams. High quality instrumentation for polarized fluorescence measurements is commercially available. 

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