| 摘要 |
A new method and apparatus for the measurement of thermal conductivity of gases employs a single katharometer element, which preferably is a thermistor, but may be a heated filament. In a preferred circuit the element is part of a first potential divider whose output voltage is compared to that of a second reference potential divider by applying them to the inputs of a differential amplifier supplying heating current to the element. If the temperature of the element changes, changing its resistance, the amplifier output changes the amount of power supplied to the katharometer element to restore it to the predetermined temperature. Passage of a gas with a different thermal characteristic over the element changes its temperature which is corrected by the circuit so that the element operates at a constant temperature. The output of the amplifier to maintain the constant temperature is therefore a measure of the gas thermal conductivity. Operation of the apparatus is therefore independent of the resistance/temperature characteristic of the thermal element and is virtually insensitive to ambient temperature changes. The invention also provides new methods of operating katharometers to reduce the sensitivity of measurement to thermal leakage, to reduce the deleterious effect of temperature changes to the Katharometer, and to provide a simple but effective model for their operation.
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