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Show Temperature Telemeter This instrument permits direct reading of air or snow temperature at long distances from the observation point. It was developed for observing air temperature in Squaw Peak Bowl, high above the regular snow observation station on the Squaw Valley floor, but may be extended to any application where a single temperature must be measured at a distance. In essence, a simple Wheatstone bridge is used to read the resistance of a thermistor exposed in whatever temperature environment must be monitored. The Fenwall G378 thermistor is the same one used in the settlement- temperature gauge, and the circuitry is similar, with a more sensitive galvonometer substituted for greater precision, along with a higher- resistance Micropot. See schematic diagram, A three- wire circuit between bridge and thermistor is required to cancel out temperature variations of resistance in the cable, which would introduce substantial errors if only two wires were used. If the connecting cable is sound, and free of bad joints or leaks to ground, the distance at which the thermistor can be located is theoretically limited only by effects of cable resistance on bridge sensitivity. The cable length at Squaw Valley is approximately three miles, and operation has been satisfactory. Any effects, such as deterioration of poorly soldered joints or intrusion of water, which cause cable resistance or circuit insulation to change, will adversely affect instrument calibration. The thermistor must be coated for protection and calibrated against a thermometer in the same manner as those used for snow temperatures. The calibration curve of dial readings versus temperature will in this case be distinctly non- linear, but the scale is sufficiently expanded to permit readings to the nearest 0.5° F., or even closer. For measurement of air temperature, the thermistor should be exposed with the same care as a thermometer to avoid radiation errors. Exposure in a standard - 8 - |