. Biophysical research methods. Biophysics -- Research. V. TEMPERATURE DETERMINATIONS 157 The oxides are usually enclosed within ceramic or glass fired under accurately controlled temperature and atmospheric conditions. Lead wires are attached and the resistance unit enclosed or mounted in a manner suitable to the thermal measuring reciuirements. Stability. Fig. 10. Thermistors made in the form of a bead, rod, disc, washer, and flakes. (Courtesy Bell Telephone Laboratories.) tests on thermistor units have disclosed no appreciable change in re- sistance characteristics through 500,000 heating a
. Biophysical research methods. Biophysics -- Research. V. TEMPERATURE DETERMINATIONS 157 The oxides are usually enclosed within ceramic or glass fired under accurately controlled temperature and atmospheric conditions. Lead wires are attached and the resistance unit enclosed or mounted in a manner suitable to the thermal measuring reciuirements. Stability. Fig. 10. Thermistors made in the form of a bead, rod, disc, washer, and flakes. (Courtesy Bell Telephone Laboratories.) tests on thermistor units have disclosed no appreciable change in re- sistance characteristics through 500,000 heating and cooling cycles. 2. Electrical Circuits for Resistance Thernionieters Figure 11 shows a diagrammatic presentation of the most com- monly used circuit for resistance thermometers of the three lead type. The galvanometer is used in this circuit as a null indicator to show when the bridge is in balance. Current flows through the galvanom- eter only when electrical balance is not present. This method is independent of voltage surges from the current source and a dry cell or low voltage alternating current with a copper oxide or selenium rectifier can be satisfactorily used as this source. A double slide wire Wheatstone bridge is represented in the dia- gram. Accuracy of measurement is assured by this circuit design, which places all moving contacts in the galvanometer or batter}^ cir- cuits. Both slide wires are mounted on a single drum and have re- sistance values such that, at all points on the slide wire, the resistances of arms 1 and 2 are equal so that the ratio arms of the bridge will be equal in resistance. Resistance AB will vary as the dial is rotated and since arm 1 equals arm 2, the bridge will be balanced when arm 3. 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
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