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INDUSTRIAL AND ENGINEERING CHEMISTRY
These checks (Table IVI show satisfactory agreement between the extinction coefficients determined b y the two instruments. At the meeting of the American Drug Manufacturers’ Association in May, 1939, a report was presented of determinations of the extinction coefficients of six samples of oil, which were circulated among a number of collaborating laboratories. It had been hoped that the instrument described here would be available for use in the survey, but such was not the case. The authors therefore report the values subsequently obtained on this instrument for these samples. Table V lists the data obtained, together with the average values as determined physically by eight of these laboratories which were most consistent and the bioassay figures supplied to the collaborators. Additional data bearing on the same point based on bioassays conducted a t one of the authors’ laboratories on a number of oils, together with the vitamin A potencies computed from measurements with this instrument, are given in Table VI.
Vol. 13, No. 4
Conclusion The instrument here described makes possible rapid and accurate estimation of the amount of preformed vitamin A. It has been economically constructed, is readily portable, and does not require a high degree of technical skill in its operation or in the evaluation of the results. By the use of other light sources and filters, the instrument can be employed for making transmission measurements in other ranges of the ultraviolet; hence its scope is greater than for vitamin A assay alone.
Literature Cited (1) Bills and Wallenmeyer, paper presented before American Society of Biological Chemists, March, 1938. (2) McFarlan, Reddie, and Merrill, IND.ENQ.CHEM.,Anal. Ed., 9, 342 (1937). (3) Morton and Heilbron, Nature, 122, 10 (1928); Biochem. J.,22, 987 (1928). P R ~ B E N Tbefore E D the Division of Biological Chemistry a t the 99th Meeting of t h e American Chemical Society, Cincinnati, Ohio.
A Simple Vacuum Tube Relay EARL J. SERFASS Lehigh University, Bethlehem, Penna.
T
HE successful operation of many recently developed laboratory and industrial instruments depends in a large part upon the operation of a sensitive relay control circuit. The control of heating elements or refrigeration equipment for the regulation of temperature is the outstanding example of the use of vacuum tube relays. Pressure-regulating manometers (1) and liquid-level controls (4) also require control circuits that operate with minute current flow or with a change in high resistance. Several vacuum tube relay circuits have been recently offered (8, 3, 6, 6) and for each is claimed one or more of the B.1
following advantages: simplicity of construction, low control current, wide range, ease of adjustment, continuous service, low cost, high degree of sensitivity, large plate current, power line operation, and alternating and direct current operation. The relay described here has been designed to incorporate all these advantages as well as one or two others. The obvious advantage afforded by small size is realized in this circuit, which consists of one vacuum tube, four resistors, a condenser, and a commercial relay. Schematic diagrams of the relay circuit connected for two
.G-2
D
110v. A.C.OR D.C. FIGURE 1.
SCHEMATIC DI.4GRAM O F S E N S I T I V E
RELAYC I R C U I T
current coils (normally open’
ANALYTICAL EDITION
April 15, 1941
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different type of relay, resistor R-3 may be replaced by a 1000-ohm wire-wound potentiometer. Either relay circuit may be adapted to uses which require the control circuit to operate the relay with a change in control resistance. The relay of the circuit shown in Figure 1, for example, will remain energized so long as the resistance in the control circuit (across X ) does not exceed approximately 500,000 ohms. If the control circuit resistance exceeds this value the relay magnet will open the load circuit. Variation of the critical resistance may be obtained by adjustment of the relay contact spring tension. The simple and compact construction which may be realized with this type of relay is shown in Figure 3. The total cost of parts necessary for this model is less than $7. Standard radio replacement parts are used throughout. The circuit shown in Figure 1 may be adapted for operation as a photoelectric cell relay. The cathode of a high-
I FIGURE 2. SCHEMATIC DIAGFLAM OF SENSITIVE RELAY CIRCUIT Make oontaota t o open load Oirouit
types of operation are shown in Figures 1and 2. Connection of the circuit as shown in Figure 1causes the relay magnet to become energized when the control contacts close or when the resistance between the contacts becomes less than a certain value. The alternative connection in which the relay magnet opens when the contacts close is shown in Figure 2. Both types of circuits will operate with equal efficiency on either alternating or direct current power supply lines. The use of the rectifier-beam power amplifier type tube (type 117L7GT) serves the dual purpose of rectifying an alternating current supply and amplifying the minute control current which flows through the contact points, X . Since rectified and partially filtered alternating current is supplied to the beam power amplifier section of the tube, maximum tube life and e5ciency are assured. The direct current operation of the relay, obtained by this method, eliminates the necessity of placing a condenser across the relay coil to prevent chattering of the relay contacts. Instantaneous positive operation of the relay is thereby assured. The usual condenser may, however, be inserted across the relay coil if delayed action is desired. One of the outstanding features of this circuit is the use of a vacuum tube, the filament of which operates directly from the 110-volt power line. The absence of the usual filament transformer, lamp bulb, or other limiting resistor in the filament circuit further simplifies construction and eliminates one of the major sourcesof trouble in many relay circuits. The very high plate current supplied by the beam power amplifier (45 to 50 milliamperes) eliminates the necessity for the use of a sensitive relay. The inexpensive and rugged commercial type of relay suggested for this circuit assures positive operation a t all times for loads up to 1000 watts. Although high plate current flow is obtained, the current flow across the control circuit contacts, X , is limited to a maximum of about 5 microamperes. If an external resistance is inserted in the control circuit, this control current may he decreased, although the necessity for this precaution seems unlikely. Since fixed resistors are used in the construction of the relay circuit, no electrical adjustments need be made. Mechanical variation of the spring tension on the relay contats may be desired for different types of operation. Should a wider range of adjustment be desired for operation with a
GASE
resistance photocell is connected to G-1 and the anode is connected a t point 2 in Figure 1. Light striking the photoelectric cell will cause the relay to become energized, providing that contact points X are open. Since the circuits described are not isolated from the power supply line, care must be exercised in handling the control circuit contacts. If one side of the regulator is to he grounded, the grounded side of the power line and regulator must be connected as shown in Figure 2. About twenty of these relays have been constructed and installed for various types of operation. A number of these units have been subjected to continuous 24hour operation for 10 months with no apparent change in sensitivity. Not a single failure of any tube or part has been reported during this time.
Literature Cited (1) Ferry. C. W., IND.ENO.Cam&. Anal. Ed.,10, 647 (1938). (2) Hawes, R. C.. Ibid.. 11, 222 (1939). (3) Heisie. C. B.. and Germs. D. C.. Ibid.. 6. 155 (19341. ~, (4) Hersh. Frey, &d Fenske, Im. E". C ~ E L .30,363 , (1938). ( 5 ) Huntress, E. H.. and Herahberg, E . B.. Ibid.. Anal. Ed., 5, 144. 344 (1933). (6) Waddle. H. M., and Saeman, W.. Ibid., 12. 225 (1940) ~
