. Biophysical research methods. Biophysics -- Research. 146 LAWRENCE R. PROUTY AND JAMES D. HARDY mocouple is determined by adjusting the slide wive contact until the potential drop in resistor BC equals the potential of the thermocouple. The slide wire is provided with a scale divided into suitable units. The galvanometer serves only as a null indicator in this type of poten- tiometer. Potentiometers may be used with great accuracy. They may be operated manually or they may be made self-recording. If the stand- ard junction temperature changes, the galvanometer must be ad- standard Cell. Ther
. Biophysical research methods. Biophysics -- Research. 146 LAWRENCE R. PROUTY AND JAMES D. HARDY mocouple is determined by adjusting the slide wive contact until the potential drop in resistor BC equals the potential of the thermocouple. The slide wire is provided with a scale divided into suitable units. The galvanometer serves only as a null indicator in this type of poten- tiometer. Potentiometers may be used with great accuracy. They may be operated manually or they may be made self-recording. If the stand- ard junction temperature changes, the galvanometer must be ad- standard Cell. Thermocouple Fig. 3. Potentiometric circuit for thermocouples with standard cell. justed. It is possible to compensate automatically for these tempera- ture changes by installing the standard junction within the potenti- ometer and attaching a bimetallic spring to the control spring of the galvanometer coil. A second type of potentiometric circuit for use with thermocouples is shown in Figure 4 (^). Materials for the circuit are available in most laboratories and it may be constructed readily at little expense. It has the advantage of not requiring a standard cell. Basically, the circuit employs a galvanometer as a null instrument to balance a known current supplied by a v. dr^^ cell against the thermoelectric current. The current is set at a constant value on the milliammeter by adjustment of a 200 ohm (coarse) and a 20 ohm (fine) variable resistor. The galvanometer is brought to the null point on each temperature determination by means of a 7 ohm slidewire resistance calibrated to read either in divisions or degrees of temperature. As. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Uber, Fred Murray, 1905-. New York : Interscience Publishers
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