INSTRUMENTATΙΟΝ by Ralph H. Müller
Recording Systems. Recent Developments in Transducers and Diodes
A
MOST USEFUL SURVEY of recording
techniques has appeared in the current issue of Instruments and Control Systems 35, No. 7, July 1962. The lead article by Robert Nelson is a survey of nearly 1000 recorders offered by more than 200 suppliers. In a set of 14 tables, the author specifies the class of recorders manufactured by each company followed by classifications according to type. These include directwriting galvanometers, special galvanometer types, galvanometer lightbeam, X-Y recorders, potentiometer (voltage), potentiometer (force) event recorders, high-speed multiple-styli, sweep recorders, oscilloscope-camera, pressure recorders, filled-system temperature, special purpose recorders, and recorder accessories. Under each category a recorder is described by the particular technique which is employed ; the channels and peak to peak amplitude, frequency response, and special features. These are sufficiently informative that a fairly exact opinion can be obtained about the suitability of the recorder for a particular application. An extension of recorder techniques is required when process information has to be analyzed and evaluated. B. Blum, in this series of articles, discusses data recording and handling systems to link the computer and the process. One basic system has been de-
veloped consisting of the following equipment: 1. a multiple point millivolt potentiometer recorder; 2. a brush-type encoder for the analog-todigital conversion; 3. a translator which converts the cyclical binary code from the encoder to a decimal code and diode matrix which converts this decimal code to the binary code necessary for the digital computer being used; 4. a tape punch; 5. a programmer which sequences the tape punch, initiates, and terminates scan cycles, and provides necessary commands. A transient waveform recorder is described by E. S. Mathisen. This system uses a display scanner which translates any repetitive high-frequency signal into low frequency signals suitable for an X-Y recorder. The display scanner is built into a special oscilloscope, called a sampling oscilloscope. By combining two sampling oscilloscopes, an X-Y recorder, and a delay line, a unique and useful instrument called the waveform recorder is obtained. Its principal use is in testing and evaluating digital computers and associated equipment. Other articles in the series deal with a potentiometric recorder which computes—i.e., multiplication, division, squaring, square-rooting, etc. A short paper on recording papers and charts contains much really valuable information not ordinarily considered or ap-
preciated by the users of recorders. Although several treatises are concerned wholly or in part with transducers, occasional reviews are useful because the design and development of new and better transducers is an active field. The recent survey by Donald Leibowitz of the Kearfott Division, General Precision, Inc., is helpful. In Product Engineering 33, No. 15, 47 (1962) his classification and description of transducers is preceded by a list of definitions, the precise understanding of which is essential for performance appraisal. Some recent developments in solidstate physics may soon find applications in the optical techniques useful to the analyst. Zinc-diffused gallium arsenide diodes, recently developed at the Lincoln Laboratory, convert modulated electrical input signals into a beam of modulated infrared light [Electronics 35, No. 30, 24 (1962)1. It is thought that the diode may allow early realization of many applications proposed for optical masers, although the output of present diodes is not coherent. Television signals have been transmitted over such beams at small distances. Peak power in these experiments was 3 watts but larger diodes may yield 15 kilowatts. At a temperature of 77° K., the output of the diode is concentrated in a spectral band 100 angstroms wide centered at 8600 A. VOL. 34, NO. 10, SEPTEMBER 1962 · 1 3 7 A
