Computers instrument interfaces

A brief description of computers, microprocessors and computer/instrument interfacing in the context of analytical chemistry is given in the following sections. 

The late 1960s saw the appearance of dedicated laboratory mini-computers and the third generation of instrument systems (Fig. 8.4). The computers were interfaced to existing instruments and were used primarily to log and process data. In some cases, simple instructions could be sent to the instrument by programs resident in the minicomputer. It was also possible for the computer to optimize instrument conditions in real time by monitoring output data. 

Instrument interface for data interchange. -Computational support. 

Commercial processor-based electrochemical instruments are available in two forms. In the first configuration, a general-purpose laboratory or personal computer is interfaced to the analog instrumentation. In the other approach, the package is integrated in such a way that the processor is dedicated to the electrochemical experiments. Several dedicated, processor-based pulse polarographs... 

Data System. An IBM-PC desktop computer is interfaced to the instrument control module to provide automated data collection and analysis. The data collection and analysis programs are menu driven. A data management facility is an integral part of the data system. A modeling utility is provided to aid the operator in chosing the operating conditions (rotational speed, spin fluid volume, fluid density, etc.) for a sample. Programming is done in compiled BASIC and the 8087 math coprocessor is used to improve computational speed. 

A fully-automated lab may need to contain both types of systems. For instrument automation systems it is important to note that not all instruments (and experiments) can or should be interfaced to a computer. There are some whose accuracy or utility can be impaired by adding an interface. With some instruments there is also the problem of having to go inside the device to gain access to an analog signal, that could void any equipment warranty. One of the choices you may have to face is the early obsolescence of equipment due to the need for easier, and supported, computer-to-instrument interfacing. 

The computer is an integral part of the instrument. Is there a good software and is it growing What will the software updates cost Who will service the computer The interface Does a single warranty cover the entire package including the computer ... 

CAMAC is an international standard for modular computer instrumentation. It specifies the electrical, mechanical, and functional characteristics of modular instruments to be plugged into a standard multi-receptacle "crate" which, in turn, can be interfaced to a minicomputer. The unique feature of CAMAC systems, as opposed to other modular systems, is that the modules not only get power from the crate but the "data-way" between the modules and the crate "controller" can carry 24-bits of data in each direction in addition to various function, address, and flag signals. The controller resides in the crate as a module and acts as an interface between the modules and a specific computer. Some of the lines in the dataway are location-specific so that a module in a given slot can be addressed by the controller. The modules (except for the controller) cannot communicate with other modules except through the controller. 

Many other areas of analytical instrumentation have benefited greatly from computerization, and the reader is referred to review articles describing various applications in detail [1]. The objective of this chapter is to introduce the fundamental principles of on-line computer instrumentation, focusing attention on the characteristics of digital devices important for interfacing laboratory instruments to digital computers. These fundamentals include a consideration of number systems. 

An important consideration for troubleshooting activities is to be aware that the control loop consists of a number of individual components sensor/transmitter, controller, final control element, instrument lines, computer-process interface (for digital control), as well as the process itself. Serious control problems can result from a malfunction of any single component. On the other hand, even if each individual component is functioning properly, there is no guarantee that the overall system will perform properly. Thus, a systems approach is required. 

Electrochemical experiments were carried out with an EcoChemie Autolab 30 multipurpose instrument interfaced to a personal computer. 

The effects of trace amounts of interstitial elements (H2,02, and N2) on the chemical and physical properties of materials have been widely recognized. From among the many techniques—activation analysis, mass spectrometry, spectroscopy, wet chemical, vacuum fusion, and inert gas fusion—the latter two have probably found widest application. Horton and Carson describe advances in instrumentation for solid samples that have increased the daily output from a few samples to 60 samples. This in turn permits better evaluation of the experimental parameters and leads to the improvement of precision. However, the accuracy is still dependent upon the availability of appropriate standards. Furthermore, when the concentration of gases is very low, below 1 ppm, one must distinguish carefully between that portion present on the surface and that in the bulk of the material. Systems with computer-controlled interfacing... 

Most of the experimental information concerning copolymer microstructure has been obtained by physical methods based on modern instrumental methods. Techniques such as ultraviolet (UV), visible, and infrared (IR) spectroscopy, NMR spectroscopy, and mass spectroscopy have all been used to good advantage in this type of research. Advances in instrumentation and computer interfacing combine to make these physical methods particularly suitable to answer the question we pose With what frequency do particular sequences of repeat units occur in a copolymer. 

Instrumentation is rapidly becoming more electronic. However, many users prefer pneumatic, and computer compatibility is available with either although electronic interface with computers is generally preferred. One coal gasification company prefers pneumatic because they feel the inherent corrosive atmosphere around such plants is not kind to electronic equipment. 

The first set of case studies illustrates errors due to the inadequate design of the human-machine interface (HMI). The HMI is the boundary across which information is transmitted between the process and the plant worker. In the context of process control, the HMI may consist of analog displays such as chart records and dials, or modem video display unit (VDU) based control systems. Besides display elements, the HMI also includes controls such as buttons and switches, or devices such as trackballs in the case of computer controlled systems. The concept of the HMI can also be extended to include all means of conveying information to the worker, including the labeling of control equipment components and chemical containers. Further discussion regarding the HMI is provided in Chapter 2. This section contains examples of deficiencies in the display of process information, in various forms of labeling, and the use of inappropriate instrumentation scales. 

Ensure that the instrument has appropriate output ports to drive other devices such as storage and computational facilities. Wherever possible, these ports should conform to the IEEE interface standards. 

Computer monitoring and control systems have recently been introduced. These are designed to operate in place of conventional instrumentation. Using intelligent interface outstations connected to a desktop computer, many plant functions may be programed into the computer and controlled centrally. 

Once the best method of dealing with interferences has been decided upon and the most appropriate method of determination chosen, the analysis should be carried out in duplicate and preferably in triplicate. For simple classical determinations the experimental results must be recorded in the analyst s notebook. However, many modern instruments employed in instrumental methods of analysis are interfaced with computers and the analytical results may be displayed on a visual display unit, whilst a printer will provide a printout of the pertinent data which can be used as a permanent record. 

Many modern instruments used in the analytical laboratory are interfaced with a computer and a printer provides a permanent record of the experimental data and the final result may even be given. This printout should be permanently attached to the observations page of the laboratory record book, and it should be regarded as normal practice to perform a rough calculation to confirm that the printed result is of the right order. 

Room-temperature fluorescence (RTF) has been used to determine the emission characteristics of a wide variety of materials relative to the wavelengths of selected Fraunhofer lines in support of the Fraunhofer luminescence detector remote-sensing instrument. RTF techniques are now used in the compilation of excitation-emission-matrix (EEM) fluorescence "signatures" of materials. The spectral data are collected with a Perkin-Elraer MPF-44B Fluorescence Spectrometer interfaced to an Apple 11+ personal computer. EEM fluorescence data can be displayed as 3-D perspective plots, contour plots, or "color-contour" images. The integrated intensity for selected Fraunhofer lines can also be directly extracted from the EEM data rather than being collected with a separate procedure. Fluorescence, chemical, and mineralogical data will be statistically analyzed to determine the probable physical and/or chemical causes of the fluorescence. 

T.F. Niemann, M.E. Koehler, and T. Provder, "Microcomputers Used as Laboratory Instrument Controllers and Intelligent Interfaces to a Minicomputer Timesharing System," in Personal Computers in Chemistry> p- Lykos, Ed,... 

Overall control is provided by the PDP-11/44, running DEC S RSX-llM operating system. RSX-llM is a multi-user multi-task operating system, and a number of other analytical instruments are interfaced to this computer system and are running concurrently. The automated Instron software is menu-driven because our experience has shown that menu-driven software is particularly effective for applications of this type. To perform either test the user accesses a main menu from which separate menus for instrument calibration, tensile tests, and flexure tests can be reached. The tensile and flexure menus have equivalent options the choices pertaining to automated testing are as follows ... 

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