. An electrolytic tank developed for obtaining velocity and pressure distributions about hydrodynamic forms. Cylinders. Tuned Circuit Figure 3 - Wiring Diagram of the Electric Circuit Used with the Single Probe The construction of the voltage di- vider R is shown in Figure 4. The resistors in each bank are noninductive precision re- sistors, accurate within ± percent. A slide wire potentiometer is used in the last stage for fine adjustment. Thus the poten- tial at the probe may be read to six figures, with an uncertainty in the fifth or sixth place depending upon the stability of the rest
. An electrolytic tank developed for obtaining velocity and pressure distributions about hydrodynamic forms. Cylinders. Tuned Circuit Figure 3 - Wiring Diagram of the Electric Circuit Used with the Single Probe The construction of the voltage di- vider R is shown in Figure 4. The resistors in each bank are noninductive precision re- sistors, accurate within ± percent. A slide wire potentiometer is used in the last stage for fine adjustment. Thus the poten- tial at the probe may be read to six figures, with an uncertainty in the fifth or sixth place depending upon the stability of the rest of the circuit. Although an accuracy of four significant figures in the potential may be sufficient for obtaining a pressure distribu- tion about a large model with gradual changes in curvature, it is necessary to obtain five and sometimes six significant figures in the potential about small bodies where the curva- ture changes rapidly. The sensitivity and stability of the electrical circuit are improved by eliminating elec- trical pickup and ground loops, by avoiding polarization of the electrolyte at the probe and electrodes, and by eliminating phase shifts in the circuit to the null instrument. To eliminate ground loops and extraneous pickup, isolation transformers are inserted in the input and output circuits and the leads from the probe are shielded. The insertion of a tuned circuit across the leads to the null instrument excludes extraneous frequencies and greatly improves the sensitivity of the null reading. Polarization of the electrolyte about the probe and the electrodes manifests itself as an instability in the null reading. In those experiments where four-place accuracy in the poten- tial is sufficient, polarization was not particularly troublesome even when a 60-cycle power supply was used. If greater precision is needed in the potential readings, precautions have to be taken to eliminate polarization. Polarization may be reduced by increasing the frequency of th
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