On-Line Data-Acquisition Systems in Nuclear Physics, 1969: Chapter 2 - DATA-ACQUISITION SYSTEMS

On-Line Data-Acquisition Systems in Nuclear Physics, 1969, by H. W. Fulbright et al. National Research Council is part of the HackerNoon Books Series. You can jump to any chapter in this book here. Chapter 2: DATA-ACQUISITION SYSTEMS

A. INTRODUCTION

1. History

The movement toward computer systems began in earnest about 1962. Much of the early work depended on the use of magnetic tape for storage of data, either raw or partially digested, the analysis of data being carried out later, off-line. More recently, computers have been used increasingly for on-line processing. The early work is well known and will not be described here. Some of the more recent systems are basically very close descendants of one or another of the early systems.

Many varieties are now in service. Most incorporate small or medium-sized computers, however, extensive new experience has been gained during the past two or three years of operation of a few large time-shared systems, in particular those in the tandem Van de Graaff accelerator laboratories at Yale and at Rochester, perhaps the first large systems in operation which were planned systematically for nuclear research. Both operate with multiprogramming monitor control, background calculations being possible, on a low-priority basis, simultaneously with data acquisition.

2. Possible Systems

Simple rules for the design of various types of data-acquisition systems cannot be stated, but some examples of possible systems can be given. (See Figure 1.)

a. A simple system for pulse-height analysis work can be assembled from a small computer, a 5-in. Tektronix CRO, an ADC unit, and a teletype with paper-tape attachment for a cost of about $30,000, providing that a competent engineer is available, not counting programming and engineering costs. A Calcomp plotter could be added for about $6000. To maintain and operate the system at least a half-time technician-programmer would be required.

FIGURE 1 Basic data-acquisition system.

b. A general-purpose system for use in an accelerator laboratory can be assembled from a medium-sized computer, two typewriters, four 13-bit (0-8192) ADC's, six 18-bit (0-262,144) counters, a 10 in. x 10 in. CRO display unit with light pen, two tape drives (for IBM tape), a Calcomp plotter, and a fast paper-tape reader for about $175,000 plus the cost of engineering service and programming. At least one full-time technician-programmer would be needed for maintenance and programming.

c. A large shared-time system of the smallest configuration which makes much sense consists of a large computer with a 16k memory, two typewriters, a fast punched-tape reader, four DEC tapes (or the equivalent), one IBM-compatible magnetic tape, one CRO with light pen, one incremental plotter, input devices for experimental data (ADC's, counters, etc.), plus an interfacing system to link the external input-output devices to the computer.

The interfacing system may include a fixed-wired "front end," such as that used at Yale, a small computer, such as that used at Rochester, or both. The hardware would probably cost over $400,000 exclusive of engineering, and to this must be added a large expense for programming, even if the manufacturer supplies a satisfactory shared-time monitor plus all the usual software. Three men would be needed to assemble, maintain, and operate the system: an engineer, technician-programmer, and a full-time programmer, or some equivalent combination, assuming use of the system in a large laboratory with an active and continually developing research program.

Thus the cost of this "stripped-down" system must be expected to reach $500,000 before it is in full operation, and the cost of keeping it going, including salaries, overhead, and replacement parts will likely exceed $50,000 per year, although this could perhaps be trimmed somewhat once the system is running. Furthermore, to run efficiently, the system would need additional components: another 16k (at least) of core memory, another IBM-compatible magnetic-tape drive, and a line printer. A rotating memory device would also be helpful. These would raise the cost by well over $100,000. It is apparent that large time-shared systems are so expensive that they can ordinarily be justified only in the largest, most lively research establishments.

3. Small Computers as Satellites

In medium and large systems the use of small computers for coupling input and output devices to the main computer offers a number of attractive advantages, especially now that mass production and competition have brought the prices down so low that a large amount of hardware nearly ideal for the purpose is available at a bargain. Some advantages:

(1) The small machine can control data acquisition, accumulating blocks of data while the large machine is doing background calculations, interrupting those calculations only occasionally to transfer raw or partially processed data.

(2) The small machine can continuously control the monitor CRO.

(3) It can control output devices such as a plotter, line printer, rotating memory, or tape drive.

(4) It can carry out many logic operations on the incoming data. Experience has shown that such operations are numerous, and from the economic point of view they should not be allowed to tie up the larger machine, which, at the same time, can better be engaged in complicated calculations. In some cases the use of two small satellite computers can easily be justified. The chief disadvantage: Programming can be complicated. However, if the larger machine already has a time-shared monitor which recognizes the small machine as a typical input-output device (as is the case with the PDP-6 plus PDP-8 system at Rochester) the programming problem is not bad.

In the following five sections descriptions of a number of data-acquisition systems of various types and sizes will be given in order to illustrate concretely some practical system configurations. In each case a breakdown of costs and a discussion of the lessons learned in connection with planning, construction, and operation will be included. The systems are of the following types: two small, one medium, one large, two multiple-CPU, and one process control.

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H. W., Fulbright et al. 2013. On-Line Data-Acquisition Systems in Nuclear Physics, 1969. Urbana, Illinois: Project Gutenberg. Retrieved May 2022 from https://www.gutenberg.org/files/42613/42613-h/42613-h.htm#Page_16

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