A simple multiscaler interface for Mossbauer spectroscopy has been constructed for the Apple I1 microcomputer. The interface collects two simultaneous spectra.
Apparatus and techniques J. Phys. E: Sci. Instrum., Vol. 17, 1984. Printed in Great Britain
Mossbauer data collection using an Apple II microcomputer J Linarest and T Sundqvistt Institute of Physics, University of Uppsala? Box 530, S-75 1 21 Uppsala, Sweden Received 30 March 1983, in final form 21 November 1983
Abstract. A simple multiscaler interface for Mossbauer spectroscopy has been constructed for the Apple I1 microcomputer. The interface collects two simultaneous spectra to allow the use of a double-ended spectrometer.
1. Introduction Mossbauer spectra have mostly been recorded by means of multichannel analysers, where each channel of the spectrum is open during a predetermined: constant interval of time. With the advent of microcomputers, the alternative of replacement of the multichannel analyser by a microcomputer system has been employed (see, for example, Sundqvist and Wappling (1983), Player and Woodhams (1 978)). In this Note we describe a very simple interface, which is working as a two-input multiscaler, recording two Mossbauer spectra simultaneously, thus turning the Apple I1 microcomputer into a Mossbauer data-collection system. The interface uses 10 low-cost low-power integrated circuits. The two spectra are collected as 3-byte integers, giving a count capacity of 16 x 10 counts/channel and thus there is no risk of overflow in a typical Mossbauer spectrum. To increase flexibility and allow the optimum performance under different experimental conditions, provisions are included for operating at different numbers of channels ranging from 256 to 1024. The interface can also be used for different channel advance rates, thus making it possible to tune the vibrator frequency to fit the transducer used. One major limitation is the minimum channel dwell time given by the execution time of the data-collecting
t Work done while on leave from Universidad Catolica, Lima, Peru; now returned.
f Author to whom correspondence should be addressed.
routine; when using 512 channels this limits the vibrator frequency to about 15 Hz (by recording only one spectrum this value is increased to about 20 Hz).
2. The Mossbauer interface The interface is built on a standard-size Apple interface card, using CMOS and LSTTL integrated circuits. It is designed so that it can be used in two different basic arrangements (figure 1). If set in the internal oscillator mode, the vibrator timing is controlled by the crystal clock of the Apple I1 microcomputer (Ql). In the external oscillator mode, the timing is controlled by Channel Advance and START signals from an external function generator. 2.1. Pulse counters The two inputs each have one 8-bit prescaler to count, during one interval time, the incoming pulses. For this purpose the CMOS IC 14040 is used in order to reduce the power consumption and the number of ICS. At the end of the time interval, given by the channel advance or by the internal oscillator, the number of pulses counted are loaded into the internal latches of a programmable peripheral interface circuit Intel 8255 (operating in mode 1 input). After the counters are cleared they immediately start counting for the next channel. The dead time obtained by this technique is about 1%. A GATE input enables the counting to be stopped by an external TTL signal. This option could be used to inhibit the counting, when e.g. the temperature controller fails to keep the temperature within an acceptable range.
2.2. Mode of operation The address of the channel currently open is obtained from a 10-bit binary counter. The ‘clock’ signal increasing the value of this counter is derived from an external channel advance pulse or from the internal timer. The ’clock’ signal triggers a monostable to give a 1 ps ‘latch’ signal, which loads the data into the 8255. and a ‘clear’ signal to clear the pulse counters before starting with the next channel. An interrupt signal (IRQ) is sent to the microprocessor. which halts the execution of the main program and jumps to the data-collection routine written in 6502 machine language. After reading the channel address, it reads inputs A and B respectively and adds them to the contents of the corresponding channels in the memory. When the addition is finished the computer returns to the main program. This is repeated until the START signal appears. The START signal resets the address counter and restarts the process from the beginning. Since the data collection is run under interrupt it is not necessary to have the main program (written in BASIC)running
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Figure 1. System arrangement: ( a ) internal and (b) external timing.
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Apparatus and techniques all the time. Once the interface is started, the computer can be used to run other programs.
3. The microcomputer The spectrometer is based on an Apple I1 Plus microcomputer equipped with 48 k RAM memory. A disc drive is used to store programs and data on 5 in diskettes. The Apple computer has a graphic display capability with 192 x 280 points resolutions which is well suited for the present application. The main drawback of the Apple I1 computer is the rather low computing power of the microprocessor involved (6502 running at I MHz). The microcomputer is equipped with a printer for listings and a pen-plotter for plotting of spectra.
J. Phys. E: Sci. Instrum., Vol. 17, 1984. Printed in Great Britain
Automation of surface cleaning and sample addition for surface balances H L Brockman, J M Smaby and D E Jarvis The Hormel Institute, University of Minnesota, 801 16th Avenue NE, Austin, Minnesota 55912. USA Received 4 October 1983. in final form 30 November 1983
4. Software A data-acquisition control program is written in BASIC which is used to start and stop the data collection and to display and manipulate the collected spectra. Spectra can be listed on a printer, or plotted on a pen-plotter and can be saved on or loaded from the diskette memory. The short machine-language routine which is activated once for each interrupt request will read data and update the spectrum stored in memory. This program first reads the channel address from the interface, which is also the address to the memory cell where the first byte of the channel is tor be stored. The number of counts is read and added to memory, first counter A and then counter B. In this way the two spectra are interleaved in the memory.
5. Conclusions The system described is a flexible high-performance system, which is of low cost compared to conventional multichannel analyser systems. The system has been in use for some time and has proved to be reliable and easy to operate. The interrupt structure makes it possible to utilise the power of the computer fully. At the same time as a Mossbauer spectrum is stored by the system, a least-squares analysis program, specially adapted to the Apple I1 microcomputer (Ericsson and Linares 1983, Sisson and Boolchand 1982) can be run. Detailed circuits and program listings are available on request. Acknowledgments W e are very grateful to D r Roger Wappling for his critical reading of the manuscript. References Ericsson T and Linares J 1983 in preparation Player M A and Woodhams F W D 1978 A simple microprocessor Mossbauer spectrometer J . Phys. E: Sci. Instrum. 1 1 19 1-2 Sisson K J and Boolchand P 1982 A microcomputer system for the analyses of Mossbauer spectra Nucl. Instrum. Meth. 198 3 17 Sundqvist T and Wappling R 1983 A microcomputer controlled Mossbauer spectrometer Nucl. Instrum. Meth. 205 473-8
Abstract. An apparatus is described for surface cleaning and sample addition for the measurement of physical properties of insoluble molecules at the air/water interface. To clean the surface the subphase liquid level is increased to engage aspirators positioned above the surface. These also adjust the liquid level by reproducibly breaking contact with the liquid during aspiration. Sample is added via an autosampler of the type used in high-pressure liquid chromatography. The advantages of the apparatus are the reduced chance of surface contamination and oxidation. When used in conjunction with a computer-controlled film balance, the system can be fully automated with a 25 sample capacity.
1. Introduction Changes in interfacial tension and surface potential properties are useful for characterising the states of molecules at the air/water interface. Routinely, these are measured by determining the interfacial tension before and after addition of surfactant or the difference in interfacial tension. i.e. the surface pressure, between a working surface and a reference surface (Adamson 1982). As discussed by Gaines (1972), early instrumental developments in this field centred on devices for continuous recording of surface tension and for continuous variation and recording of the area of the working surface. More recent improvements have emphasised novel ways to measure surface pressure using new materials (e.g. Stenberg and Lofgren 1979, Albrecht and Sackmann 1980). for transferring films to other solid or liquid substrates (e.g. Fromherz 1975, Uphaus 1981, Roberts et a1 1981, Barrand and Vandevyver 1983) or for computerised instrument operation and data acquisition in digital form (e.g. Brockman et a1 1980, Albrecht 1983). In spite of these technological improvements the basic techniques for cleaning of the aqueous subphase prior to sample addition and the addition of sample itself have been performed manually (e.g. Kuhn el a1 1972). Moreover, contamination of the surface during these procedures is a major source of error in film balance studies (Davies and Rideal 1963). With the advent of computer-controlled film balances and the development of computer-compatible valves and equipment for liquid sample dispension, such functions can now be automated relatively simply. This allows unattended collection of surfacepressure-surface-potential-area isotherms in an inert atmosphere. thereby reducing chances for surface contamination and sample oxidation.
2. Design criteria and construction Most of the modifications necessary within the film balance itself for automated cleaning and sample addition are mounted on a simple metal bridge which spans the floating barrier/transducer that separates the working and reference surfaces of a Langmuir-type instrument (Lauda Filmwagge, Brinkmann 0022-3735/84/05035 I
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