INSTRUMENTATION Environment, maintenance, and numerous factors other than mechanical precision contribute to the over-all performance and reliability of modern instruments by Ralph, ' T ' H E pace in modern i n s t r u m e n t a - 1 tion is breathless a n d bewildering. If one stops to contemplate our assets, so much t h a t is new h a s gone by, t h a t it is difficult t o catch u p with progress. Nevertheless, t h e r e are several continuing problems which require our a t t e n tion. Current Practices in Instrumentation Numerous questions can be raised a b o u t current practices in instrument a t i o n . One of these is t h e m a t t e r of reliability. There was a time when t h e few i n s t r u m e n t s a t t h e disposal of t h e analyst depended upon t h e skill of a master mechanic. T h e analytical balance, t h e refractometer, a n d t h e microscope were dependable and precise t o t h e extent t h a t a conscientious craftsm a n h a d executed a good design. A modern infrared spectrophotometer, to select a n example a t random, involves optics, electronics, servo-mechanisms, recorders, a n d some control of environment. There are t h u s a dozen or more factors, other t h a n mechanical precision, which contribute t o over-all performance. Lest someone hastily point a n accusing finger a t electronics, m a y we point out t h a t a recent editorial [Electronics, 25, 97 (1952)] s t a t e d : "Causes of r a d a r failure were recently recorded aboard a cruising American n a v a l vessel. Arranged in order of 'down-time' hours, t h e y turned out to be (1) mechanical, (2) electrical, a n d (3) electronic. Fewest failures, in other words, were classified as electronic in t h e narrow sense of t h e w o r d . " As t h e editor pointed out, such failures could h a v e been avoided if the manufacturer, skilled in electronic circuitry, h a d been equally experienced mechanically a n d electrically. P e r h a p s
one might generalize a n d say t h a t , whenever a large n u m b e r of skills is involved, t h e precision a n d reliability of each component should be comparable to t h a t of all other components. F o r a long time, t h e military h a s imposed extremely severe performance requirements on acceptable equipment. This has been due, n o t only t o unusual operational conditions, b u t to a realistic appreciation of h u m a n factors. W e were told, during t h e war, t h a t after a n instrument h a d been "frozen" a n d almost "boiled," subjected t o 10 g of shock, and immersed in brine for 1 hour, t h e final and most crucial of all tests was applied. This was t o give t h e equipm e n t t o two sailors with t h e injunction : " F o r H e a v e n ' s sake—Be careful!" I n m a n y respects, t h e chemical l a b o r a t o r y is a hazardous environment for instruments. M a n y , if n o t all, manufacturers of i n s t r u m e n t s are aware of this, particularly if their instruments are primarily for chemical measurem e n t s . I n t h e early d a y s of p H meter development, a prominent manufacturer whose instruments are noted for careful design a n d faultless construction, delivered t h e latest model t o a customer. Within 2 weeks, indignant requests to "remove t h e j u n k " were received. U p o n inspection, t h e intricate wiring was found to b e a verdant mass of cupric chloride crystals. I t was a d m i t t e d t h a t t h e control laboratory atmosphere h a d a n almost lethal concentration of chlorine, t h a t t e m p e r a t u r e s were high, and t h e average h u m i d i t y was 8 0 % , b u t t h e customer still took a dim view of equipm e n t t h a t could n o t w i t h s t a n d those rigors as well as his chemists. I n s t r u m e n t manufacturers are prepared to build equipment to withstand almost a n y specific hazard or unusual conditions b u t , unless t h e condition is 23 A
by Ralph,
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Müller
MM. 3Mulier
extreme, t h e customer often fails t o mention factors, which to h i m seem u n important. There is one practice in which t h e industrial user of i n s t r u m e n t s is usually more careful and systematic t h a n t h e research m a n . T h a t is in t h e m a t t e r of periodic inspection, maintenance, replacement, a n d repair. This is n o t solely a m a t t e r of extending i n s t r u m e n t life, b u t largely due to t h e fact t h a t ins t r u m e n t failure m a y result in very costly product failure in a production line. A research m a n is n o t too u n h a p p y if h e succeeds in locating a defective t u b e which outlived its usefulness, even though t h e " r u n " was spoiled. U n d e r similar circumstances, t h e i n s t r u m e n t m a n in a p l a n t chides himself for poor housekeeping a n d knows he will h a v e t o answer a lot of embarrassing questions. Some of t h e practices which h a v e been adopted b y t h e electronics i n d u s t r y in t h e interest of increased reliability a r e : water- or moistureproofing, t h e use of fungicides, hermetic sealing of relays, embedding of circuit elements in plastic (plotting), careful ventilation, either b y convection or blowers, shock mounting, a n d improved shielding. M o s t of these precautions are m a n d a t o r y in military equipment, b u t often we do not find t h e m in scientific instruments. There is a n increasing t r e n d t o furnish carefully packaged electronic units in plug-in form. This reduces replacement problems to a m a t t e r of seconds. With one or two notable exceptions, including recorders, this practice is not too widely used in instruments. T h e Red Series R C A tubes are rated for 10,000 hours of life compared with t h e nominal 1000 hours of ordinary tubes. Their use in instruments is another aid in reliable, u n i n t e r r u p t e d performance. Too m a n y of our electronic devices
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YOUR PRODUCTION AND PROFITS ARE BEING LOST HERE!
Are You Wasting Critical and Expensive Materials In Your Slag Heap? Steel producers know that up to 20% of the alloying elements used in special steels, which have to be present, often are lost in the slag. Constant and tedious laboratory analysis of both the steel and the slag is necessary to maintain proper production control. In addition to loss of money in replacing these elements, much time can be wasted in actual production.
HERE'S WHAT YOU CAN DO ABOUT I T . . . The ARL Production Control Quantometer—long used for chemical analysis of steel and other alloys—has now been adapted for the analy sis of slags! Accurate percentages of elements present in both steel and slags-are recorded permanently in pen-and-ink in less than two minutes.... a great saving in production time and money. This makes it possible to prevent material loss before it occurs. Individual Quantometers are not limited to a single type of analysis, but can be designed to meet the requirements of many plant problems. As many as 25 elements as selected by the user can be accurately measured on the instrument—up to 20 simultaneously. The ARL Quantometer is the most advanced type of spectrometer yet developed, and its use can mean a great saving to you in production control costs and vital materials conservation. Write for complete information. THE ARL UNE ALSO INCLUDES 1.5 AND 2-METER SPECTROGRAPHS, PRECISION SOURCE UNITS, RAMAN SPECTROGRAPHS AND RELATED ACCESSORIES.
Applied Research Laboratories f
t
S P E C T R O C H E M I C A l
E Q U I P M E N T
3717 PARK PLACE G L E N D A L E 8, CALIFORNIA NEW YORK · PITTSBURGH · DETROIT · CHICAGO · DALLAS · LOS ANGELES
are still housed in sheet metal bread boxes. They all look alike, rarely make efficient use of space, and rarely fit anywhere except on a table top. It is surprising what can be done, in the way of making such equipment more compact and rugged by the use of strong fuse boxes or cutout boxes plus a few flanges and pipe couplings. Equipment so enclosed can be bolted to a wall, under a table, or in other unobtrusive places. The result is not so impressive to a visitor, but it is a practice which industry insisted upon long ago. A good designer could have a field day with much of our electronic equipment. A good beginning would be the redesign of pilot lamps to illuminate and inform rather than to blind one. Improved Precision through Jitter On several occasions, we have mentioned the improved precision which can be obtained in meters and recorders by the intentional introduction of jitter. This trick reduces stiction errors and improves the reproducibility of readings. A definitive treatment of the subject is given by R. L. Ives [Electronics, 25, 161 (1952)]. Ives has pointed out that relay oscillators with a frequency of 5 to 15 cycles are so successful that they are being incorporated in all modern field meteorological instruments. However, for fixed station operation, their life is too short. A good telephone-type relay is dependable for 10,000,000 operations. At 10 cycles per second, this is used up in about 11.6 days (of 24 hours). Wherever uninterrupted service is required over months or years, another solution is required. Exhaustive tests have shown that the "keep-alive" frequency should be between 5 and 15 cycles per second, and that the wave form should be nonsinusoidal, but symmetrical. Frequencies of less than 5 cycles per second require excessive amplitude to be effective and insert sawteeth into the record. Frequencies of much more than 15 cycles per second interfere with ink flow in pens of several designs, converting the recorder into a very efficient ink thrower! Frequencies in excess of 400 cycles per second make continuous excavations in the chart. Ives describes an all-electronic, lineoperated, keep-alive circuit which employs a 10 cycles per second multivibrator which feeds 4 cathode follower output stages. The latter are so connected to the driving multivibrator that the load in the power supply is equalized. Typical recordings on an EsterlineAngus recording milhammeter are shown for a square wave, with and without the
ANALYTICAL
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Free Data File
superimposed jitter. A noticeable sharpening of the corners is evident. The author points out that his circuit will yield 40 days of continuous service when ordinary tubes are used. When red tubes (10,000 hours) are used, monthly checking is advisable and tube replacement is indicated every 13 months. These considerations apply to all meters or recorders which employ a D'Arsonval movement. The situation is somewhat different when applied to an electronic self-balancing potentiometer. The above author has not been concerned with this case, and we wish to point out that the situation is somewhat different. In this case, response to an artificially introduced jitter is a function of servo response time. The minimization of stiction is much more easily introduced by turning up the gain on the servo amplifier until random noise is detected by the system. At that point, the recorder trace shows jitter or tremors and one can be assured that persistent, unidirectional stiction forces are minimized.
For i n f o r m a t i o n o n t h e A u t o m a t i c T i t r a t o r a n d t h e a b o v e a p p l i c a t i o n see y o u r Beckman D e a l e r , or W r i t e For D a t a File 4 3 - 1 5 .
H O W Y O U C A N USE THE BECKMAN AUTOMATIC
TITRATOR!
The Beckman Automatic Titrator performs accurate potentiometric titrations (neutralization, oxidation-reduction, precipitation a n d complex-formation types) with average time of 2 minutes—accuracy to 0.1 %. Greater speed and accuracy than indicator methods and no special skill required.
BECKMAN INSTRUMENTS control modern industries
BECKMAN
INSTRUMENTS, INC.
SOUTH P A S A D E N A 1 , CALIFORNIA Factory Service Branches: New York - Chicago - U s Angeles
Beckman Instraments include : pH Meters and Electrodes — Spectrophotometers — Radioactivity Meters — Special Instruments
Voltage-Regulator Tubes Voltage regulator tubes have long been convenient means of stabilizing d.c. voltage supplies. A most useful and practical means of computing circuits for their rapid utilization is given by R. C. Miles [Electronics, 25, 135 (1952)]. In addition to curves for the operational characteristics for all common voltage regulator tubes, the author has most obligingly listed the tubes in the old and the new notation. There was a time when V.R. 105 meant a voltage regulator tube operating at 105 volts. Two decades of alphabetical confusion have reduced this to an OC 3 tube whereby "he who reads can falter." In the same vein, we have often wondered why the R.M.A., in sponsoring the color coding of resistors and capacitors, even permitted the elimination of the printed value. To be sure, the practice was justified on a production line where witless operators could identify colors at a glance and where the reading of numbers in excess of the number of fingers on two hands would have been an exhausting mental and physical process. The converse process, for the intelligent but occasional user of resistors, is a degrading lip-moving process of spelling out color values. Do we have any sympathy or support for the imminent design of a computer, analog or digital, which will translate "officialese" into Basic English?
