NOTES ON ANALYTICAL PROCEDURES A
Versatile Electronic Relay
JOSEPH G. BAIER, JR., AND PAUL E. M I L L I N G T O N , T h e University of Wisconsin in Milwaukee, Milwaukee, Wis. cell for light activation of the relay, to operate either alone or in conjunction with the usual type of regulator. The relay will open or close the 117-volt alternating current control contacts either upon opening or closing of the regulator contacts, or with increase, decrease, or interruptions in the light striking the photocell. Using the low resistance range, the regulator contact current does not exceed a few microamperes and is as low as a fraction of a microampere for photocell operation or in using the highest resistance range. Series resistances are provided to protect the operator from accidental shock by body contact with the regulator terminals.
A n electronic relay is described which i s variable in sensitivity, requires at most only a few microamperes of contact current, can b e adjusted to the inherent resistance of the regulator circuit, and incorporates a photocell for light activation of the relay.
A
NUMBER of electronic relay circuits have been described in the literature (1, 3-6) during the past few years. The
general trend has been toward the development of a relay requiring regulator contact current in the order of a few microam’ peres, so as to prevent deterioration of the mercury-platinum ‘or the bimetallic strip regulator contacts. I n using these relays, it is necessary that the regulator elements be well insulated and their connecting leads short and with good insulation, since any reduction in the necesmrily high open circuit resistance, due to high humidity or insulation leakage, may prevent normal use of the relays. Moreover, these relays are usually of fixed types, each serving only one purpose, so that, for different uses, either several specific types of relays must be present in the laboratory or circuit changes in the existing instruments must be made. The relay described in this paper offers the following features not found as a group in the usual electronic relay:
RELAY CIRCUIT
The relay circuit shown in Figure 1illustrates the use of a type 2050 gas tetrode (interchangeable with type 2051), operating on alternate half waves of the alternating current cycle, in a conventional circuit (a) modified for the purpose. This type of tube was chosen for its high current-carrying capacity and for the triggering action of the grid where, when the critical grid-firing voltage is reached, the tube conducts to its maximum capacity. The necessary voltages for plate and grid operation are obtained from the voltage divider, R, to R4, with the voltage developed across R1 and Rz supplying the plate a voltage positive with respect to the cathode, and the voltage across Ra and R, negative with respect to the cathode on the same half cycle for grid control. R3 gives a minimum negative grid bias voltage just in excess of cutoff, while R, allows for an additional grid bias voltage, By means of a six-point selector switch in conjunction with a variable to the grid through potentiometer Rs. The use of repotentiometer, the relay can be adjusted rapidly for use with sistors Rs to R13 allows for the ranges of sensitivity desired for any type of regulator having contact and connecting wire lead operation of the relay. resistances from approximately 0 ohm to 250 megohms. With SIin position 6 and the control on R6 moved all the way It is provided with a socket to receive an emission-type photoup (minimum setting), the relay will operate xith contact resistances across TRof as much as 280 megohms, while with SI in position 1and the I I control of R6 all the way down (maximum setting) practically a zero resistance is necessary. On adjusting Szto intermediate contact points and varying R6 for each position of 8 2 , a complete range in between is available. The plate circuit relay, RE, is of 1500 ohms’ resistance requiring approximately 8 ma. for operation. Under the conditions of available 0 plate voltage, a relay requiring up t o 35 ma. and of lower resistance could have been used. N7VAC However, under these conditions and especially if the circuit is to be turned o f fand onfrequently, P a switch should be inserted in the plate circuit to provide a minimum delay of 10 seconds after turning on SIbefore applying the voltage to the plate of the tube. This is recommended by the manufacturer of the tube, since turning on the heater and plate voltages a t the same time may result in reduced tube life. The authors have not experienced this difficulty in the use of the instrument as described. The holding condenser, C, is necessary to prevent chattering of the plate circuit relay, since the operation of the relay depends upon half-wave plate rectification. The plate circuit relay has a set of single-pole singlethrow contacts connected to a pilot lamp to indicate operation and a set of single-pole doublethrow contacts to deliver up to 6 amperes a t Figure 1. Circuit Diagram of Relay 117 volts alternating current to a dual outlet reVI PO50 gal tetrode, Vz = 8 6 8 gar photocell, r midget filament tnnsformer 117, 6.3-volt ceptaclc, so that “normally open” or “normally Thordarson T19F80; R E = plate circuit relay, PI, Pn = 6.3-volt pilpt lamp:, Marda NO.44, jn Drake closed” relay service is available for operation of No. PO ieweled sockets SI= midget toggle switch, Ss = six-position Mallory selector swltch NO. 1916L C 10-pld. electrolytic condenser, 50-volt DCWV. RI 10 000ohmr; Rt 5000 ohms, the desired control device. If a greater load R 400 ohms. R, = 1750 ohms Rs = wire-wound potdntiometer bf 10,000 ohms Mallory NO. is to be operated, a heavy-duty alternating curM’lOMP, Re 2 250 000 ohms, d, = 5 megohms, RI = 100,000 ohms, R I n’50,WO ohms, rent relay can be placed in the control contact Rs 500,000 ohms: Rii 1 megohm, Ria = 5 mesohmr. Ria = 1 0 megohms. Resistors Ri to Rd T R = thermoR e to Ria arol0.5-watt carbon resistors. are Brown Devil 1 0-watt wire-wound resistors. circuit or a plate circuit relay vith suitable conregulator, NC and NO are normally closed and normally open relay contact:. Pilot lamp Pz indicates tacts can be substituted. when relay i: enersired, A i l e PI indicates contlnually while instrument Is in u:e
a
-
-
- -
-
-
-
-
-
152
.
ANALYTICAI EDITION
February, 1946
153
The transformer, T,is a midget filament transformer t o supply 6.3 volts to the heater of the 2050 tube. Resistor RTis a currentlimitingresistor for the type868 photocell. Rsis a regulator contact protective resistance and should be spproximately 250,000 ohms. Figure 2 is a photograph of the instrument. BASIC O P E R A T I O N OF THE CIRCUll
The circuit operates in the following manner. With the regulator terminals Tn,open or the phototube dark (or at some PIP determined light intensity depending on the setting of S%and Rs),the grid of the 2050 is at a voltage more negative than the critical mid firins voltage as determined by Rs and the setting ~~~~
~~~
0~~~~
~
~
~
energiee the plate circuit relay. O P E R A T I O N OF THE R E L A Y
After connecting the relay t o a thermoregulator or similar activatins mechanism and with contacts T Bopen. switch 8,can be mavedbrogressively from contact 1 toward contact 6 and if the relay operates, owing t o leakage across the wire leads from the regulator, switch S, can be backed off one position (or the setting of Rslowered) until the plate circuit relay does not become energized except when contacts Tz are closed. Actually for most u8es of the relay, except under conditions of very high humidity (IT when using the photocell, switch 89 can be left permancntl; in positions 3 or 4. For excitation of tha relay using the photocell, the procedure described previously can be amployed. When the position of S p is found where the relay operates for any given light intensity on the photocell, backing o f f8,one step will cause i t to cease operation. A position of Rscan then be found where slight movement one way will cause the relay to operate, and movement in the opposite direction will caum it to be nonenergized. If Rs is now left in the position where the plate circuit relay does not operate a slight increase in the light will cause i t t o be energized and with a decrease it will again be inoperative. The instrument is made very flexible in its use by simply adjusting SBand Ra as outlined. The relay is easy to assemble, requires no preliminary adjusb ments, and should cost approximately $13.50 for all parts. I1 photocell operation of the relay is not desired, V , and R, can be
Figure
2. Photograph of R e l a y
omitted, reduoiug the total cost to $10. relay has been iu almost continuous use without any 2tcmnliiun for more th an two years, controlling the temperature of a coustanI& hrmidity chamber using a toluene-mercury-platinum thermoregUl ator. LITERATURE CITED
..
* m.. 000,.n.,n\ I., ,'".Oil,. RCA Data Sheet for type 2050,2051 tubes (1939). Redfern.Sutton, IND. ENO. CHEM., ANAL.ED., 14, 64 (19429. Rudy, C. E., Jr., and Bugassi, P., Zbid., 12, 757 (1940).
Tr
n n
n.__n
(1,I
n*.Wva, a.U., IN"_YP(". U m I m . . b n A Y .
(2) (3) (4) (5) (6)
Serfass, E. J..Ibid., 13, 262 (1941). Waddle. H. M., and Saeman. E., Ibid.. 12, 225 (1940).
T.
Y".,
**/I
Kettle for Measuring Small Residues iin Low-Temperature Fractional Distillation GRAY T. HAMBLEN AND JC Continental Oil Cotnpan
s
OME samples for low-temperature fractional analyseyses re-
q u r e the measurement of very small liquid residues, when under the Conditions of the analysis, it is impossible t o vaporize the residue and memure i t as a gas. If it is necessary t o pour the residue from the kettle before measuring it, very large samples must be taken, so that the liquid remaining in the kettle will not be a large psrt of the total residue. A kettle in which i t is possible to measure accurately small residues is advantageous, since time is saved by the use of samples of moderate size. Two types of sample which contain a very small proportion of heavy material are the effluent from a polymerization plant and the raw gasoline stream from a natural gasoline plant which recovers a large amount of propane and butane. The figure shows 8. kettle made from the lower end of a California-type 100-ml. graduated centrifuge tube. The heating ooil is wound upon a 19-mm. piece of capillary tube, which js fused to the end of the centrifuge,tube. The volume of the capillary is determined by adding hqwd from a buret to the centnfuge tube; if the buret reads 1.1 ml. and the centrifuge tube reads 1.0 mi., the volume of the capillary is 0.1 ml. The heater consists of 23 cm. of No. 28 resistance wire, which is wound between two layers of closely wound asbestos or glass string. The wire may be threaded through a Fiberglas sleeve before, winding. The string and the wire are fixed by the liberal application of water glass.
i n e upper section ot tne centntuge tuDe IS puiiea on at a m u t the 30-ml. mark, and an 18/9 female hall joint is sealed to the rounded end. The male part of the joint is sealed t o the distilling tube of the low-temperature fractionating column. The sample is introduced ,thmu,ph the ,oapillary connection which is sealed , , three-way stopcock is atled t o the capillary by Lns of a short Diece of ,l
Nitrogen contained in a Dekar lask during introduction of he sample. After distillation is comdeted, the kettle isimmersed 1 ice water. in order t o condense vapor and cause the eflux liquid to leave the Nacking of the distilling tube ndeollectinthekettle. The ettle is then immersed in rater a t 60' F. and the olume of the residue is read+
