A log-antilog analog control circuit for constant-power warm-thermistor sensors: application to plant water status measurement
Date
2009
Authors
Skinner, A.
Lambert, M.
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Journal article
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IEEE Sensors Journal, 2009; 9(9):1049-1057
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Andrew J. Skinner and Martin F. Lambert
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Abstract
Warm-thermistor sensors are useful for making measurements of flow and the thermal properties of materials. This paper describes a log-antilog analog control circuit capable of monitoring a thermistor's internal temperature in both ambient temperature sensing mode and self-heating mode, while maintaining infinite precision, wide dynamic range and fast sensor response. A single self-referencing thermistor is used to avoid the problems associated with having to match a thermistor pair in order to obtain an over-temperature signal. Instead, thermistor power levels are switched over a range of 1:1000, allowing measurement of both ambient temperature and heated thermistor temperature during the rise and fall of the heat pulse by a single thermistor at the center of the heat field. This provides a sensitive measurement of the thermal diffusivity and advective properties of the surrounding medium. In this paper, such a sensor is used to investigate the thermal properties of a grapevine cane under conditions of irrigation stress.
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© Copyright 2009 IEEE