INSTRUMENTATION by Ralph H. Müller
Some Russian Instrumentation Developments
τ
HE JOURNAL, Instrument
Construc-
tion, is, we assume, an adequately descriptive translation for the Russian journal Priborostroenie. It affords an English translation from the January 1959 issue onwards. I t is printed and published for the Department of Scientific and Industrial Research by Messrs. Taylor and Francis, Ltd., of Red Lion Court, Fleet St., London, E. C. 4. More enlightening than its title may be the list of sections, which we find in the contents of No. 2 for February 1963. These deal with Theory and Design, Automatic Control Equipment, Instrument Production Technology, Information and Exchange of Experience, and Reviews and Abstracts.
NICKEL PLATING
Three items which happened to interest us dealt, in one case (p. 19), with hard bright nickel plating using oxalate electrolytes. Hitherto, in the nickel plating of instrument parts, nickel has been deposited from free nickel electrodes and not from electrodes containing complex compounds of nickel. The coats plated in the conventional processes were not very hard and thermal treatment did not increase their hardness. These coats could not be made bright without the use of special organic add : tives, which complicated the composition of the electrolyte. As carefully worked out by V. N . Brusentsova and D. V. Pletnev, the optimum composition of oxalate nickel baths was established as 140 g./l. of nickel sulfate, 300 g./l. of ammonium oxalate, 15 g./l. of sodium or ammonium chloride. Plating was
done at a current density of 10-20 amp./dm 2 , the pH at 7.8 to 8.2, and optimum temperature of 78° to 82° C. Periodically, the electrolyte was "neutralized" to pH 8 with ammonium hydroxide. Heating the plated parts to 300° C. increases the hardness still further and it is then almost equal to that of chromium plate. Chemical analysis of the deposits revealed a constant 0.38% of carbon in the nickel coat and this increases the hardness during the heat treatment. Carbon content is increased by an increase in the quantity of oxalate radical and decreased by increases of pH and temperature or decrease of the current density. The rate of deposition of nickel in oxalate baths is ten times greater than the deposition of chromium. Both the current output and the dispersion are greater in the oxalate-nickel baths than in chromium plating baths. TRANSISTORIZED PHOTO-RELAY
A second development (p. 28) deals with a transistorized photo-relay with temperature compensation. Three transistors are used in a simple circuit powered from a stepdown transformer connected to the line. A diode rectifier and hum filter using a 10 mf. 50 v. electrolytic capacitor provides d.c. potentials. The first stage acts as a preamplifier for the photocell current in the common emitter configuration. The light cell is of the photoconductive type. This stage also acts as an impedance matching element between the high resistance photocell and the low resistance input to the second transistor. The third transistor acts as a power amplifier with a relay connected
to the collector. An MKU-48 relay, as used by authors P. M. Vaisburd and F. G. Vinengauz, requires 30 ma. for pull-up, which seems to us to be unnecessarily insensitive to be used in a circuit which otherwise has very low power consumption. The amplifier, without compensation, exhibits a 10 ma. increase in output current for a temperature rise of 30° C. (20-50°) whereas with temperature compensation, the output seems to be completely independent of ambient temperature from 20° to some 65°. The nature of the temperature compensation is not explained but, presumably, depends upon temperature coefficients of resistance of opposite sign between photoconductor and the transistors and their associated resistor elements. It might be mentioned, in passing, that photoconductors are available in a great variety of sizes—some of them almost microscopic, so that optical arrangements can be extremely simple and utilize such things as vitreous or plastic "light-pipes." TRANSFORMING TEMPERATURE INTO A FREQUENCY SIGNAL
An interesting description of an electro-acoustic unit for transforming temperature into a frequency signal is given by V. V. Kovalevskaya and V. K. Potapkin. The device utilizes the well known principle of acoustic feedback or "ring-around" in which the sound output of a receiver is fed into a transmitter, the output of which, after unit gain amplification, is fed back to the receiver again. Such a system will "ring" at a frequency depending upon the velocity of sound in the medium between receiver and transmitter. A
VOL. 35, NO. 11, OCTOBER 1963 ·
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INSTRUMENTATION
AVCDisTS tube, sealed at the ends with trans mitter and receiver, will resonate at a frequency f0 = nc/21 where c is the velocity of sound, 1 is the length of the pipe, and η = 1, 2, 3, . . .. The velocity of sound in an ideal gas is: c = V ^ v R T / m ) where γ is the ratio of the specific heats, R is the molar gas constant, Τ is the absolute tempera ture, and m is the molecular weight. If this is substituted in the preceding equation, we have:
FROM WESTON
f0 = (1/21) V ( y R T / m )
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hence the resonant frequency is pro portional to -ν/Τ a r ) d is a function of the parameters of the gas. The authors have given details of a transducer of this type for the meas urement of temperature. In their case, the sensitivity attained (depending upon the length of the resonator) was 1 to 9 cycles per second for ° C. Actually, the general technique of such resonators, particularly when used with modern electronic counting techniques, can attain high precision and be employed, as the equations in dicate or imply, for such things as specific heats, the analysis of gases, liquids, or solids, or for determining elastic constants, Young's modulus, etc. Frequency measurements are easily made to 1 part in 108 or better and over a wide range of counting intervals. Once more we mention the fact that during World War I the Germans were analyzing nitrogen-hydrogen mix tures for use in the Haber nitrogen fixation process by blowing them through an organ pipe. For a pipe of fixed dimensions, the pitch or fre quency is a function of the average molecular weight of the gas mixture. The speed of sound in hydrogen is 1260 meters/second and that of nitro gen 337.5 m./sec. In the absence of fancy electronics at that time and to avoid the need for analysts with a sense of absolute pitch, a motor driven siren was used to match the tone to zero beat. TRANSLATIONS OF RUSSIAN INSTRUMENTATION LITERATURE
Another convenient source of current information on Soviet developments in instrumentation, measurement tech niques, and automatic control is Meas urement Techniques, a translation of Izmeritel'naya Tekhnika, a publication of the Academy of Sciences of the U.S.S.R. It is published and distrib uted at nominal subscription rates under a grant in aid to the Instrument Society of America from the National Science Foundation.
