Microprocessor-controlled instruments

Liquid crystals, commonly referred to as the fourth state of matter, are materials which are intermediate in character between the solid and liquid states. Unlike normal isotropic liquids, they show some time-averaged positional orientation of the molecules, but they retain many of the properties of liquids, such as the ability to flow. In recent decades, liquid crystals have played an increasingly important part in our lives. Probably their most familiar application is in the information displays which provide the visual interface with microprocessor-controlled instrumentation. Liquid crystal displays have superseded more traditional display technology, such as light-emitting diodes and cathode ray tubes, for many appliances principally because of the advantages of visual appeal, low power consumption, and their ability to facilitate the miniaturisation of devices into which they are incorporated. They are encoun-... 

With the introduction of computers and microprocessor-controlled instrumentation, it has become possible to use spectrophotometry to obtain far more accurate determinations of color. The tristimulus values are obtained after integration of the data according to Eqs. (7)—(9). This degree of sophistication permits the use of more advanced methods of color quantitation, such as the 1976 CIE L u v system [41] or other systems not discussed in the present chapter. 

Modern, microprocessor-controlled instruments often have an internal standard , with the instrument undergoing an automatic verification check every time the instrument is used. This may be perfectly satisfactory if the standard can be related to traceable calibration standards. To do this, it is usually necessary... 

Programming of microprocessor-controlled instruments has so far not been possible this makes the systems inflexible. 

Microprocessors control instruments (e.g., wavelength, scan rate). They may collect data and process it. 

Today s laboratories —particularly the larger ones— use a variety of intelligent, microprocessor-controlled, instruments with analogue output and (micro)computers interfaced to one another. It is the fashion in which the interfacing Is done that ensures efficient laboratory computerization (automation). Ziegler [31] established three categories of computerized configurations, namely (Fig. 2.14) ... 

Metrohm markets microprocessor-controlled Instruments for routine coulo-metric (KF 652 Processor) and amperometrlc-voltammetrlc (EP/KF 678 Processor) analyses. These Instruments are frequently used for research purposes. Thus, the Mettler Memotltrator and the Metrohm Tltroprocessor 636/Rod Stirrer 622 were used by Johansson et al. [62] to demonstrate that potentiometric two-phase titrations can be carried out in an automatic fashion. The typical background noise from the electrodes can be reduced by Introducing hydrophobic anions or cations in the aqueous phase. These ions also affect the acid-base equilibrium by extracting the sample ions as ion-pairs into the organic phase, which allows the conditional acidity constant (apparent K ) to be manipulated to make selective titrations possible. 

Figure 5.22. Tecator Aquatec Analyzer. Designed for determination of ammonia, nitrate, nitrite, and phosphate in aqueous samples, the microprocessor controlled instrument (left)-employs dedicated modules comprising microconduit based Chemifolds and furnished with prepacked reagent solutions (right), facilitating rapid change of function and simplifying the operation of the system.

Hierarchical control is another current concept in which large-scale computers can communicate directly with medium-sized computers which, in turn, communicate with microprocessor control instrument systems and even analog backup instruments. 

Subsequently Ishibashi and Fujinaga in Japan pursued a line of development based also on mechanical switching of potential, while in England Barker and coworkers built the first electronic instruments. The advent of solid-state electronics made possible broad commercial development of instruments which in turn extended pulse techniques to other electrodes and stimulated applications. Computer-and microprocessor-controlled instruments have expanded the use of pulse techniques and encouraged development of specialized waveforms. 

A microprocessor controlled instrument, Sargent Welch Model 7001, also performs pulse techniques. A 20-character alphanumeric display and a 30-touch button keypad allow the user to specify the experiment. After recording a voltammogram, smoothing, averaging, and background subtraction are options. The price in 1980 was 8800. Pulse widths from 1 to 1000 ms may be chosen, with sampling from 100 x3 after pulse initiation to 500 ps before the end of each pulse. 

In order to be able to record and analyse data continuously, in collaboration with Dr N. J. Goddard of our Microprocessor Unit, we have developed the microprocessor controlled instrumentation shown in Figure 18 [23]. Without microprocessor instrumentation it was difficult to monitor the rats continuously and almost impossible to analyse the quantities of data spewing out on roll after roll of chart paper. 

Instruments and apparatus used for analytical work must be correctly maintained and caUbrated against reference values to ensure that measurements are accurate and leUable. Performance should be checked regularly and records kept so that any deterioration can be quickly detected and remedied. Microcomputer and microprocessor controlled instrumentation often has built-in performance checks that are automatically initiated each time an instrument is turned on. Some examples of instrument or apparatus calibration are... 

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