Instrument automatic, principles

Instruction sets (programming), 71 Instrumentation (automatic control system), 158 Instrument Society of America (ISA), 1772 Insufficient reason principle, 2380 Insurance industry ... 

As an example, consider the automation efforts for chemical laboratories in the last decades. Chemical laboratories of today are equipped with instruments that, in principle, can run automatically for 24 hours a day. This results in a higher productivity, since more samples can be analysed with an equal technical effort. Decisions about the analysis itself, how many and which samples must be analysed with what method or technique, etc., are still the responsibility of the laboratory personnel. Since experience can be incorporated into expert systems, they can provide significant benefits as decision-supporting tools. Therefore, the main ideas of expert systems and their development are explained in this chapter. More detailed information can be found in the numerous textbooks on expert systems [7-10]. 

Many instruments utilize a double beam principle in that radiation absorbed or emitted by the sample is automatically compared with that associated with a blank or standard. This facilitates the recording of data and corrects for matrix effects and instrumental noise and drift. Instrumentation for the generation of radiation is varied and often peculiar to one particular technique. It will be discussed separately in the relevant sections. Components (b) and (c), however, are broadly similar for most techniques and will be discussed more fully below. 

Mitsubishi also supply a microprocessor-controlled automatic total halogen analyser (model TOX-IO) (Fig. 1.8 (b)) which is very similar in operating principles to the Dohrmann instruments discussed above, i.e. combustion at 800-900°C followed by coulometric estimation of hydrogen halide produced. 

A recent brief review showed the working principles of various automatic analyzers6. A modified account of N and O analysis will be presented here. Today there exist in the market instruments that perform organic elemental analyses in a few minutes. The ease and speed of such analyses enable the use of such instruments for routine analysis. Although some operational details vary from model to model and between one manufacturer and another, all these instruments can be considered as exalted versions of the classical Pregl determination of C and H by conversion to CO2 and H2O, together with Dumas method for N by conversion to N2, the calorimetric bomb method for S by conversion to SO2 and SO3 and Schultzes method for O by conversion to CO. This is combined with modern electronic control, effective catalysts and instrumental measuring methods such as IR detectors and GC analyzers. 

Automation has been applied for a number of years in process control instrumentation, but the major impetus to introduce automatic devices into laboratories stems from three sources (1) the introduction of the continuous-flow principles as outlined by Skeggs [1] (2) the general demand for clinical chemical measurements, which represents a ready and sizeable market for instrument companies, and, more importantly, (3) the abihty to handle large volumes of data and package them in a form suitable for presentation to analysts and customers, through the use of mini- and micro computer systems hnked to a control computer. 

Planar chromatography, also known as Thin Layer Chromatography (TLC), is a technique related to HPLC but with its own specificity. Although these two techniques are different experimentally, the principle of separation and the nature of the phases are the same. Due to the reproducibility of the films and concentration measurements. TLC is now a quantitative method of analysis that can be conducted on actual instruments. The development of automatic applicators and densitometers has lead to nano-TLC, a simple to use technique with a high capacity. 

ANALYZER (Reaction-Product). Chemical composition may be determined by the measurement of a reaction product—in an automatic fashion utilizing the basic principles of conventional qualitative and quantitative chemical analysis. Two steps usually are involved in this type of instrumental analysis (1) the formation of a target chemical reaction, and (2) the detennination of one or more of the reaction products. 

These are typically based on the principle of the hydrometer. For automatic measurement and control an inductance bridge may be employed to detect the position of the hydrometer. The level of the liquid in which the hydrometer is floating must be maintained constant. The float or displacer may be partially or totally immersed in the liquid (similar to the float systems used to measure level—Section 6.5.1 and Fig. 6.28). A schematic diagram of an instrument using a totally immersed displacer is shown in Fig. 6.35. 

For more information on this subject, consult some of the following references l)J.C.Peters Th.R.Olive,ChemMerEngrg 50, 95-107 (May 1943) (Fundamental principles of automatic control) 2)Editorial Staff Review, Ibid 50, 108-24 (May 1943) (Instruments for measuring and controlling process variables) 3)Editorial Staff Review, Ibid 50,. 125(May 1943) (Automatic control ther-minology) 4)E.S.Smith, "Automatic Control Engineering, McGraw-Hiii,NY(1944) 5) D.P.Eckman, "Principles of Industrial Proc-... 

Reference to Table 4.1 indicates that olefins can be determined by the electrochemical generation in situ of halogens. Bromine is effective for both olefins and sulfur compounds and is the basis for an automatic coulometric titrator for continuous analysis of petroleum streams.17 The basic principle of this instrument is a potentiometric sensing system that monitors bromine concentration in a continuously introduced sample stream. The bromine in the solution reacts with the sample components and causes a decrease in the concentration of bromine. When this decrease is sensed by the potentiometric detection electrodes, the electrolysis current producing bromine adjusts itself to maintain the bromine concentration. Because the sample is introduced at a constant rate, the electrolysis current becomes directly proportional to the concentration of the sample component. Thus, the instrument records the electrolysis current as concentration of sample component and provides a continuous monitor for olefins or sulfur in petroleum streams. 

In principle it might be a Pavlovian habit related to the establishement of a direct association between a Pavlovian CS and an UR (see Cardinal et ah, 2004). Another possibility is that automatic responding is an instrumental habit related to learning of an instrumental stimulus-response (S-R) association. An instrumental habit is more likely to account for the relative flexibility of the behavior as indicated by the ability to rapidly switch to an explicit goal-oriented mode when the automatic responding is impaired. 

The indicating instniments which are connected to the thermocouple are of three general types, those operating upon the galvanometric principle, as an ordinary voltmeter those operating upon the potentiometric principle and those operating upon a combination of these two principles. The first two types of instrument have been made automatically recording, as will be discussed elsewhere. 

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