Specificity, measurement instruments

For interpolation between these points, the IPTS specifies the use of specific measuring instruments, equations and procedures 261. The highest reproducibility of the IPTS is at the triple point of water. The accuracy falls at lower or higher temperatures than the triple point. 

Instrumentation normally is denoted by a circle in which the variable being measured or controlled is denoted by an appropriate letter symbol inside the circle. When the control device is to be located remotely, the circle is divided in half with a horizontal line. Table 1.3 gives various instrumentation symbols and corresponding letter codes. The specific operating details and selection criteria for various process instrumentation are not discussed in this book. The reader is referred to earlier works by Cheremisinoff [1,2] for discussions on essential control and measurement instrumentation. 

Different available measurement instruments and evaluation methods are described in Chapter 12. Some specific methods to evaluate local ventilation systems are described in this section. All local ventilation systems should be evaluated regularly. The evaluation procedures can be divided into detailed and simple, as well as direct and indirect, procedures. The detailed procedures need special instruments and competence, whereas it should be possible to use the simple procedures every day. Since the simple procedures do not measure directly the performance of the exhaust, it is usually necessary to calibrate a simple procedure by using a detailed procedure. ... 

The character and the degree of automation in chemical control may have been covered in the above treatment of semi-automatic or completely automatic, and of discontinuous or continuous analysis, but something more should be said about the means by which automation proper has been performed in recent times. Whereas in the past automated analysis involved the use of merely, mechanical robots, to-day s automation is preferably based on computerization in a way which can best be explained with a few specific examples. Adjustment knobs have been increasingly replaced with push-buttons that activate an enclosed fully dedicated microcomputer or microprocessor in line with the measuring instrument the term microcomputer is applicable if, apart from the microprocessor as the central processing unit (CPU), it contains additional, albeit limited, memory (e.g., 4K), control logics and input and output lines, by means of which it can act as satellite of a larger computer system (e.g., in laboratory computerization) if not enclosed, the microcomputer is called on-line. 

There is no clear, specific analyte signal the instrument response (T) does not change adequately with a variation in the analyte value (X). This phenomenon indicates that small changes in analyte concentration are not detected by the measurement instrument. Different or additional instrument response information is required to describe the analyte (the problem is underdetermined). 

Measurement of relative humidity depends on the system used. Systems employing vacuum are usually evacuated prior to introduction of water vapor [29]. For cases in which there is not a gas-forming reaction occurring, measurement of total pressure in the system can be used as a measure of water vapor pressure. Systems in which air is not evacuated require specific measurement of water vapor pressure. (For the latter type of system, caution should be taken to assure that the relative humidity source is in close proximity to the solid, since the diffusion of water vapor through air to the solid is required to maintain a constant relative humidity in the immediate vicinity of the solid.) A wide variety of pressure measuring instrumentation is commercially available with varying accuracy, precision, and cost. 

Systematic errors usually arise from specific shortcomings in the measuring instrument, the observer, or the way in which the measurement is taken. Sources of systematic error include a badly calibrated measuring device, a faulty instrument movement, an incorrect action by the experimenter (e.g., misreading a volume measurement), or the parallax effect when incorrectly viewing a scale. Repeating the measurement does not necessarily help, because the error may be repeated, and the analyst may... 

I have also chosen the interest domain to illustrate a simple but important methodological principle—the importance of measurement error and specificity. Measurement error and specificity saturate all psychological instruments and failure to take them into account results in theoretically misleading conclusions1. 

The pH can be measured instrumentally using a pH meter, a potentiometer, and an ion-selective electrode. The pH meter should be calibrated using buffers obtained from commercial sources. All pH meters come with model-specific instructions for calibration. The following protocol gives a basic overview of the calibration procedure and subsequent measurement for all pH meters. Review the instructions of the specific model in your laboratory to insure proper calibration. 

The selection of the most suitable instrument for a required measurement from a range of commercially available instruments necessitates the knowledge of certain important factors. These can be divided into the static and dynamic characteristics of the instrument. The dynamic properties of instruments are fundamentally no different from those of any other system or process and are described, therefore, by the analysis of system dynamics presented in Chapter 7. Static properties, which are specific to instrumentation, are discussed in this section. 

In the direct competitive ELISA, the analyte specific antibodies are first coated on a solid phase. The sample or standard solution of analyte is generally incubated simultaneously with the analyte enzyme conjugate or incubated separately in two steps. The amount of enzyme bound to the plate is then determined by incubation with a chromogenic substrate solution. The resulting color/fluorescence, which is inversely proportional to the analyte concentration present in the sample, is then measured instrumentally or by visual comparison with the standards. 

To evaluate aspects of HRQL that are specific to a particular disease or condition, specific measures also may be used. Specific measures include only important aspects of HRQL that are relevant to the patients being studied, such as the loss of function patients experience from asthma or the amount of pain they have from arthritis. Disadvantages of using specific measures are that they are not comprehensive and cannot be used to compare across conditions. They also cannot measure unforeseen side effects or conditions. Examples of specific instruments for heart failure are the Minnesota Living with Heart Failure Questionnaire and the Chronic Heart Failure Questionnaire (Guyatt et al., 1989 Rector, Kubo, and Cohn, 1987). 

Analyses are performed in accordance with standardized methods issued under the responsibility of a Technical Committee within the Health Ministry. Usually such measurements rely on a comparison of the measured quantity in the unknown sample with the same quantity in a standard , i.e. an RM, according to a specific measurement equation [6], after calibrating the instrument. Calibration of a photometric system for clinical analyses usually means the set of operations that establish, under specific conditions, the relationship, within a specified range, between values indicated by the instrument and the corresponding values assigned to the RMs at the stated uncertainty. Calibration of the photometer itself implies the calibration of wavelength and absorbance scale by means of proper wavelength and absorbance RMs [5], traceable to national standards. A calibration of the instrument is still needed in concentration units to check the indicated provided value. The measurement result is then verified by application of that method of measurement to a certified reference material (CRM). Both the comparator - a photometric device with narrow or wide bandwidth, and the RMs should thus be validated. 

Conduct type approval of measurement instruments used by the field laboratories for the conformity evaluation to the specific regulations under their responsibility... 

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