Self-Balancing System for Continuous Control of Current or Voltage

Abstract

An autotransformer was preferred for the heater, as a transformer does not heat up as readily as a rheostat and, thus, provides a more constant volt-amperage supply to the heater.An exploded view of the heater (rated at 110 watts and 115 volts, in Figure 2 shows how it may be disassembled for replacement of burned out heating units (available from American Instrument Co., Silver Spring, Md., as replacement parts of an electric micro-Kjeldahl digestion apparatus). When assembled, the small plate (containing side vents for air cooling) which has the heater attached to it, fits into the box and the lid fits tightly over the top.The details of the heater construction are shown in scale drawings in Figure 3. This box and support plate are made of Transite. The heater unit, A, is fastened to the support plate beneath it with four small spacing nuts. A similar set of spacing nuts fastens the electrical contacts to the unit: the nuts are easily removed to replace a heater unit. As the heating unit never becomes extremely hot during an analysis, ordinary coated wire was found to be satisfactory for lead wire from the heater to the power control.

Electroanalysis

“…Apparatus involving a vibrating electrode has been used by Lindsey (122) and Harris and Lindsey (56). Apparatus suitable for dead-stop titrations was devised by Dubois, Maroni, and Walisch (38) and by van Pelt and ICeuker (141)• Circuits designed to give warning of the approach of a dead-stop end point have been described by Collier and Fricker (25) and by Glastonbury (52). Automatic titrations have been described by Juliard and van Cakenberghe (73) and Stock (174)• An apparatus for automatic coulometric titrations involving amperometric end points was devised by Richter (154)• Kolthoff and Jordan have investigated "convection electrodes" of platinum (104) and mercury (105) w'hich should have exceptionally favorable characteristics (rapid attainment of steady state, efficient stirring, high sensitivity, reproducibility) for certain types of amperometric titrations.…”

“…Although an instrument of this type does not respond as rapidly as an electronic regulator, its response is adequately rapid for all practical purposes. A similar instrument has been designed by Dunn, Mann, and Mosley (38) for another purpose, but it should function satisfactorily for use in coulometric titrations also. Gerhardt and coworkers (52) and Ehlers and Sease (40) have described modified versions of the Reilley, Furman, and Adams (124) electronic constant current supply.…”

Separation of Mixtures of Tritium and Hydrogen Using Hertz Pumps

“…For the thermal conductivity measurements, Leeds and Northrup thermal conductivity bridges, with the cells modified to reduce their volume to 10 ml., were used. An improvement in this apparatus w'as the addition of a photoelectric servo-mechanism, which made precise control of the bridge current possible (1).…”

A simple amperostat for coulometric titration

“…While small variations in the relatively low cell resistance had little effect on the current, the series resistance values varied because of heating, the battery voltage decayed with time, and recourse had to be made to manual adjustment of the current. Servo mechanical systems have since been devised (e.g., 3,4) which give currents constant to better than 0.01% over long periods, although their response times are not fast. A number of electronic current regulators using vacuum tubes have also been described (e.g., [5][6][7][8][9] generally involving dc amplifiers with feedback.…”