| 摘要 |
An improved apparatus for temperature measurement which minimizes sensing element self-heating error and instrument ambient heating error when used as an oceanographic thermometer includes a frequency-selective network having a thermistor as a temperature sensing element thereof. The network is connected in the feedback loop of an AC amplifier whose output voltage is stabilized by an automatic gain control circuit at a predetermined, low value. In one embodiment, the output voltage is connected to the apparatus output terminal through an isolation circuit, and the AGC circuit comprises a second thermistor in shunt with the output voltage. In a second, improved embodiment, the output voltage is amplified by a second amplification stage and applied to a level detector circuit and to an isolation circuit from which the apparatus output is taken. The level detector in turn controls the impedance of a field effect transistor in shunt with the output voltage. The requirements for a successful oceanographic thermometer design are discussed and related in detail to the embodiments noted, and the performance of working models of each embodiment with regard to these requirements is set forth.
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