Instrument function

Some other designation systems indicate the recording or indicating function in front of rather than behind the instrument function. For example ... 

In a GLP-compliant laboratory, a data system must meet explicit requirements guaranteeing the validity, quality, and security of the collected data. Operational qualification (OQ) must be performed after any new devices are installed in the laboratory system and whenever service or repair are performed. The role of OQ is to demonstrate that the instrument functions according to the operational specifications in its current laboratory environment. If environmental conditions are highly variable, OQ should be checked at the extremes in addition to normal ambient conditions. Performance qualification (PQ) must be performed following any new installation and whenever the configuration of the system has been changed. PQ demonstrates that the instrument performs according to the specifications appropriate for its routine use. 

When appropriate, require that operators be capable of performing mechanical repairs of their own instruments. This is the simplest way of teaching instrumental function and greatly improves operator self-confidence. With the highly-computerized systems of today, it is likely that supplemental assistance from the manufacturer will be necessary for instrumental maintenance. 

Principles and Characteristics Instead of thermal initiation, microwave decomposition may be of use for sample preparation involving combustion or acid digestion. The advantages over thermal initiation lie in the shorter time needed (minutes instead of hours). Microwave oven digestion (MOD) systems are not analytical instruments. Functionally, they are chemical... 

Bolhar-Nordenkampf, H.R., Long, S.P., Baker, N.R., Oquist, G., Schreiber, U. and Lechner, E.G. (1989). Chlorophyll fluorescence as a probe of the photosynthetic competence of leaves in the field a review of current instrumentation. Functional Ecology 3 497-514. 

LOPA is a semi-quantitative tool for analyzing and assessing risk. This method includes simplified methods to characterize the consequences and estimate the frequencies. Various layers of protection are added to a process, for example, to lower the frequency of the undesired consequences. The protection layers may include inherently safer concepts the basic process control system safety instrumented functions passive devices, such as dikes or blast walls active devices, such as relief valves and human intervention. This concept of layers of protection is illustrated in Figure 11-16. The combined effects of the protection layers and the consequences are then compared against some risk tolerance criteria. 

The concept of PFD is also used when designing emergency shutdown systems called safety instrumented functions (SIFs). A SIF achieves low PFD figures by... 

General References Guidelines for Hazard Evaluation Procedures, Second Edition with Worked Examples, American Institute of Chemical Engineers, New York, 1992 Layer of Protection Analysis A Simplified Risk Assessment Approach, American Institute of Chemical Engineers, New York, 2001 ISA TR84.00.02, Safety Instrumented Functions (SIF)—Safety Integrity Level (SIL) Evaluation Techniques, Instrumentation, Systems, and Automation Society, N.C., 2002. 

Safety instrumented function (SIF) A safety function allocated to the safety instrumented system with a safety integrity level necessary to achieve the desired risk reduction for an identified process hazard. 

Safety instrumented system (SIS) Any combination of separate and independent devices (sensors, logic solvers, final elements, and support systems) designed and managed to achieve a specified safety integrity level. An SIS may implement one or more safety instrumented functions. 

Safety integrity level (SIF) Discrete level (one out of a possible four SIL categories) used to specify the probability that a safety instrumented function will perform its required function under all operational states within a specified time. 

These are remarkably few in current commercial simulation packages (though they do differ in the extent to which they incorporate all the effects discussed in this chapter). The main sources of error are in the incorporation of the instrument function in which there is a significant trade-off between speed and accuracy for large data sets. 

For laboratory-based systems the instrument function given by the effect of the beam conditioner must now be introduced. In Chapter 2 we discussed beam conditioners in detail and showed that they may be characterised in terms of an intensity which is a function of both divergence and wavelength. 

Add the instrument function. If this is large it affects widths and relative peak intensities, but not integrated intensities. 

Add curvature (if physically reasonable). This has the same effect as the instrument function... 

Standardization The instrument response function can vary from analyzer to analyzer. If calibration transfer is to be achieved across all instrument platforms it is important that the instrument function is characterized, and preferably standardized [31]. Also, at times it is necessary to perform a local calibration while the analyzer is still on-line. In order to handle this, it is beneficial to consider an on-board calibration/standardization, integrated into the sample conditioning system. Most commercial NIR analyzers require some form of standardization and calibration transfer. Similarly, modem FTIR systems include some form of instrument standardization, usually based on an internal calibrant. This attribute is becoming an important feature for regulatory controlled analyses, where a proper audit trail has to be established, including instrument calibration. 

Use Level of Protection Analysis to evaluate the reliahility needed for safety instrumented functions. (Before startup for all serious consequences identified in the process hazards analysis)... 

Even if perfectly narrow spectral lines are not available, we may take a clue from this approach and measure a spectral line of known shape. De-convolution should then yield the instrument function. This technique does indeed work (Chapter 2, Section II.G.3). Some of the information needed to generate the known line shape can even be obtained directly from the observed data. 

We may convert this relationship to half-width form by remembering that aL = 2 AxL/3 and expressing aR in terms of the Gaussian instrument function half-width AxR ... 

The resolution of overlapping spectral peaks depends on their separations, intensities, and widths. Whereas separation and intensity are predominantly functions of the sample, peak width is strongly influenced by the instrument s design. The observed line is a convolution of the natural line, a function characteristic of inelastically scattered electrons that produces a skewed base line, and the instrument function. The instrument function is, in turn, the convolution of the x-ray excitation line shape, the broadening inherent in the electron energy analyzer, and the effect of electrical filtering. This description is summarized in Table I. 

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