Wireless Temperature Measurement of a Sample in Vacuum
The temperature of a sample suspended from a microbalance is difficult to measure without interfering with the weighing process. A device is described in which the sample temperature causes a change in frequency of the infrared emitted from a gallium arsenide photodiode. The oscillator unit is mounted in a small hermetically sealed box which in turn is moiunted on the microbalance as part of the sample weight. A thermistor is buried in the sample, attached by fine wires at any convenient distance from the box to minimize circuit thermal sensitivity. Power to operate the oscillator is derived from a silicon solar cell, activated by a light exterior to the chamber. The gallium arsenide cell output can be detected at distances ranging from a few inches to several hundred feet by a suitable photocell. The detected signal is fed into a frequency meter.
Experimental data for frequency change vs. temperature are shown. A range of 400 C is easily attained. The accuracy of temperature measurement is ±0.15%.
KeywordsSolar Cell Sample Temperature Gallium Arsenide Silicon Solar Cell Furnace Wall
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