ANALYTICAL
34 A
INSTRUMENTATION
MODEL 230
AUTOMATIC FRACTION COLLECTOR
alternately admitting air or other gases to a system and connecting the system to exhaust at rates varying between 5 and 40 cycles per minute. A double-ended piston in the pump is driven by solenoids. The latter are excited alternately by recti fied a.c. which is switched to the solenoids by a relay. The relay is in the anode cir cuit of a 6J5 tube, which is controlled by the output pulses from a controlled multi vibrator. Rate stabilization is obtained by an OD3 voltage regulator (ube. A modification is suggested by the authors, in which two 6L6 power tubes can be controlled by the multivibrator to drive the solenoids directly and thus dispense with the relay.
BOTH TIME AND DROP COUNTING OPERATION FOR THE MOST PRECISE FRACTION CUTTING REQUIREMENTS OF CHROMATOGRAPHIC WORK
• One outstanding feature is the phototube arrangement for drop counting. Drops from the column fall directly into the test tubes without touching anything. There are no intermediate glass arms and funnels to cause mixing, contamination, evaporation, etc. This is especially important when accurate separations are required. Turntable, phototube housing, etc., are made of Stainless Steel.
Price complete for time and drop counting $795.00
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INSTRUMENT COMPANY
PACKARD
INFORMATION-
RESEARCH EQUIPMENT AND SERVICE
LA GRANGE, ILLINOIS
P. O. BOX 428
rfutoeUve NO-LEAK Speed 1/aive HELD AT 6 0 0 0 PSI FOR 3 0 DAYS PRESSURE DROP BiGISTIREP T h i s valve was photographed t w i c e . . . 30 days apart. As y o u c a n see, pressure was c o n s t a n t over t h e test period. Dependable performance is t y p i c a l of AUTOCLAVE E N G I N E E R S ·
products. Another i m p o r t a n t AE feature is service. T h e valve a n d all fittings used for t h e test are i n stock i t e m s . A p o i n t t o r e m e m b e r w h e n y o u t h i n k of h i g h pressure equipment. JAN. 10, 1953
For more about SPEED VALVES. WRITE FOR BULLETIN 6152
FEB.
AUTOCLAVE ENGINEERS, INC. ERIE, PENNSYLVANIA EXPORT DEPT.
751 DREXEL
BLDG.
CHEMISTRY
PHILADELPHIA
10,
1953
Further developments in vacuum tube voltmeters are concerned with attempts to increase stability, raise the input imped ance, and lower the input capacitance. The most recent improvement in this direction, described by A. W. Brewer of the Clarendon Laboratory in Oxford [/. Sci. Instr., 30, No. 3, 91 (1953)], utilizes an electrometer tube in conjunc tion with an ordinary pentode or triode, both acting as cathode followers. A volt age gain of 0.90 is attained with input leak age current of the order of 1 0 _ H A. and input capacitance which is a small frac tion of 1 microfarad. By the further addi tion of two pentodes acting as "tail tubes," the input range can be extended to ± 5 0 0 volts, although a power supply of 1200 volts is required for this range. The power dissipated by the second tube is great enough to operate an ordinary voltmeter or recorder. Another logarithmic amplifier extend ing over a range of 1 to 106 has been de scribed by M. Briere, A. Rogozinski, and J. Weill [J. phy.i. radium, 12, 144 (1951)]. It has been known for a long time that a logarithmic relation exists between the current through a diode and its anode voltage when the latter is negative. This phenomenon has been reinvestigated in the region of very weak currents. A cir cuit is described using a multigrid elec trometer tube in diode connection, and operated at subnominal rating. It is fed from various sources such as ionization chambers or phototubes. The logarithmic portion of the current-voltage curve ex tends over five decades. The lower limit depends upon the tube, but in some cases currents as small as 10™14 A. follow this relationship. The importance of logarith mic elements or circuit is much greater than one might suspect, because they enter into several of the prevailing meth ods for high-speed multiplication in which logarithmic terms are fed into sum ming or difference amplifiers. Oscillators
β, ΡΑ.
The intentional introduction of jitter or oscillations into measuring instruments
