DESK AND POWER SUPPLY FOR THE BECKMAN SPECTROPHOTOMETER' ANTON B. CARLSON, A. 5. AYERS, and CHARLES V. BANKS Iowa State College, Ames, Iowa
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following description of accessory equipment for the Beckrnan Model DU spectrophotometer is the result of considerable effort directed toward devising an arrangement which would permit nearly constant use of this instrument with a minimum of maintenance. Since the Model DU is used so extensively, it was felt that publication of this report would be of value to other users of this instrument. The desks and power supply described herein have been in daily use for over a year and have given excellent service. I n these laboratories two instruments were available, one being reserved for use with the tungsten lamp and the other being reserved for use with the hydrogen discharge light source. This arrangement eliminates changing lamp housings and the subsequent refocusing of the light beam. The power supply described helow is suitable for use with both the tungsten and the hydrogen discharge lamps. DESIGN OF THE DESK
One of the few disadvantages of the Beckman instrument is that the position of the dials and controls on the horizontal top makes continuous work a t this instrument extremely tiring. To overcome this difficulty, two desks were designed and constructed. The general design is similar to a standard double pedestal office desk, the essential feature being that there is no drawer or other obstruction on the under side of the top in the center section. This permits placing of the instrument a t a lower level with respect to the operator, i. e., the instrument is very nearly "sitting in the operator's lap." The desk top is cut out a t the center section in such a way that i t is possible to get close to the instrument. These innovations permit the analyst to sit erect in a chair and read the instrument by simply bending his head downward. Figure 1 shows the desks and location of the power supplies. The left pedestal of each desk contains the storage batteries, charger and other electrical components of the circuit. The right pedestal of the desk in the background has a deep drawer in the position corresponding to the hydrogen discharge lamp power supply which is visible in the foreground. The drawers visible in Figure 1do not extend to the rear panel of the desk, thereby leaving space to bring the lamp leads through the desk top. All leads to the instruments are
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Contribution No. 135 from the Institute far Atomic Research, Ames, Iowa. Work was performed in the Ames Laboratory of the A. E. C.
Figure 1.
View .f Speetrophotornetor Desks
brought through - small holes which were made in the desktops. The desks were constructed of oak and plywood. The over-all dimensions are: 29 in. wide. 55 in. lone. -, and 26 in. high. The dimensions of the top are such that the flame photometer attachment may he installed. Sufficientspace is available, for a notebook in which to record data, a t either side of the operator. The length of the plywood instrument cover is such that i t can be closed when the large cell compartment accessory is in position for use. This cover lacks many aesthetic qualities, but was necessitated by cost consideration: The possibility of sloping the instrument toward the operator by means of wedges was considered, hut not put into use because it increases the hazard of solution spillage from the cuvettes. ~~
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Figure 3 shows the actual connections which mere made to the storage batteries. Each battery lead was attached to the proper post by a separate screw. The use of two metal screws on each terminal is a distinct advantage as shown by an oscilloscope connected across the output, leads. When the battery S,,e,,-DPST TOGGLE SWITCHES post connections were made P,.s-l10 Y, 6 WATT CANDELABRA BASE PILOT LAMP as indicated in Figures 2 and P.-6 V, 1.5WATT MINIATURE BASE PILOT LAMP 3, no a.-c. ripple could be A-0-10 AMMETER R-3D 2 5 WATT OHMITE RHEOSTAT detected in the output. For U-15 AMP, 110 VOLT MERCURY PLUNGER. H-B INSTRUMENT CO. spectrophotometerstability, CH-MALLOW 6AC6 DRY PLATE BATTERY CHARGER this is a prime requisite. 0 -NON-POLARIZED RECEPTACLE FOR ULTRAVIOLET POWER SOURCE 8-2-120 AMPERE HOUR STORAGE BATTERIES An attempt was made to F-I0 AMP 3 AG FUSE employ an &dinary toggle Figvro 2. Schemetic Diagram and Parts List for SpeoMphotometer Power Svpply switch in the storage battery output. However, the DESIGN OF THE POWER SUPPLY combined voltaee d r o of ~ the relativelv high resistance lamp was SUBThe power supply described below is simply an switch togetheruwith 'that of the cient to appreciably lower the voltage supplied to the adaptation of well-known concepts of electricity. The spectrophotometer. Under the condition of low input actual design is probably quite similar to commercially voltage, it was sometimes impossible to balance the available power supplies. Figure 2 shows the circuit diagram together with a instrument satisfactorily. Substitution with the merlist of its integral parts. The approximate cost of the cury relay switch as indicated in Figure 2 overcame this power supply, less the two storage batteries and charger, difficulty. All electrical connections were made with No. 12 is $30. This sum is very small when compared to the plastic insulated wire. Care was exercised to ensure original investment for the Beckman instrument. A Sorenson voltage regulator is in use in these labora- well-soldered connections in the output leads from the tories to provide a constant 115-volt a.-c. source for storage batteries. The three leads to the spectrophovarious instruments including the spectrophotometers. tometer were sufficiently long to permit inverting the Tests have indicated that voltage regulation is unneces- instrument to provide access to the internal "C" batsary when operating the charger in conjunction with the teries. tungsten lamp. Usually i t is possible to charge the OPERATION storage batteries when using the hydrogen discharge The following is a list of the manual operations lamp; but since the current drain is very small, it is probably best to carry out the charging operation a t a necessary to turn on the spectrophotometer, when the time when the instrument is not in use. A consider* tungsten lamp is to be used. tion of local power conditions must determine the neces(1) Turn on switch No. 1 (see Figure 2), which supplies power to the battery charger, the hydrogen dissity of voltage regulation. It can be seen from Figure 2 that the three switches charge lamp power supply, and switch No. 3. turn off all power t o the instrument except, of course, (2) Turn on switch No. 2, which supplies charging the 71/pvolt batteries located in the bottom of the current to the storage batteries. If switch No. 2 is on instrument case. These switches, together with their when switch No. 1 is off, the batteries will discharge pilot lights, help to eliminate the chance that the through the charger. instrument and lamps will be left on unnecessarily. (3) Turn on switch No. 3, which supplies power directly to the relay coil and indirectly to the spectrophotometer. (4) Turn the instrument switch to check and turn on the tungsten lamp. (5) Balance the charge and discharge ammeters by means of the rheostat. The above stew are carried out in reverse order (omitting step 5) 'when turning off the power supply. When the hydrogen discharge lamp is to be used, steps 2 and 5 may be omitted, thereby permitting
APRIL. 1951
operation of the instrument without concurrent charging of t,he storage batteries. However, experience has indicated that the power supply is sufficiently stable to permit charging the storage batteries during use of the hydrogen discharge lamp; this procedure is being used in these laboratories. About once every month, the charge on the storage batteries should be checked with a hydrometer. If the charge is low, a period of free charging (steps 1 and 2 above) should be instigated and the storage batteries returned to full charge. At the same time, when necessary, the elect,rolyte level should he adjusted by the addition of distilled wat,er. Proper care of t,he storage batkries, as described above, will ensure a longer useful life. A dated record of all maintenance work should he kept as an aid in locating any trouble which may arise. Figure 4.
storage containers
for Accessory Equipment
ADDITIONAL ACCESSORIES
Figure 4 shows some accessory equipment also constructed in these laboratories. The large cell compartment was purchased from Beckman Instruments, Inc. The thermostatted cell compartment was constructed from plans supplied to us by Bell and S t ~ y k e r . ~ The plywood boxes have proved very valuable. These accessories (cells, etc.) are quite expensive and justify adequate provision for their storage when not in use. The box which contains the large cell compartment was designed to hold the small cell compartment as well, thereby providing suitable storage space for either assembly. %BELL, P.H., AND C. R. STRYKER, Science, 105,415 (1947).
The small block, which holds the 1-cm. cells in an upright position in their box, contains round holes which do not permit the optical surfaces of the cells to touch the sides of t,he holes. This arrangement permits the cells to drain and immobilizes them, thus preventing breakage. Furthermore, the optical surfaces are protected from becoming scratched. Following a suggestion by Moeller and B r a n t l e ~ , ~ slide rule hairline indicators were cemented to the wave length and the transmission-density scales. This simple modification minimizes the errors due to parallax and increases the accuracy of the measurements. MOELLER,T.,AND J. C. BRANTLEY, Anal. Chon., 22, 433 (1950).
