The Elimination of Temperature Effects in Microbarometers

Barrie W. Jones Physics Department, The Open University, Milton Keynes, United Kingdom

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Abstract

A microbarometer based on a differential-pressure transducer has been developed, in which an air chamber provides a near-ambient reference pressure. This differential mode ensures high sensitivity to ambient-pressure changes but suffers from the drawback that the reference pressure is sensitive to temperature. The basic principle of this microbarometer design is not new, and in many earlier cases it is clear that measures have been taken against the effects of temperature on the reference pressure. Here we report what seems to be a new approach to the design of such measures and to their evaluation.

The approach is to stabilize the temperature of the reference chamber, and this is done in two stages. First, the reference chamber is enclosed in a passive jacket to provide a thermal gain function, such that temperature variations external to the jacket are attenuated by more than a factor of 1000 at all periods of interest (below 60 min). Figures of merit are developed to guide the choice of jacket materials. Second, these external temperature variations are kept within a peak-to-peak range of about 0.3 K (at about 303 K) for days on end.

The actual thermal gain function of the jacket plus chamber is obtained by Fourier transforming the smoothed thermal impulse response function. This function is obtained by numerically differentiating the measured thermal step response function.

Abstract

A microbarometer based on a differential-pressure transducer has been developed, in which an air chamber provides a near-ambient reference pressure. This differential mode ensures high sensitivity to ambient-pressure changes but suffers from the drawback that the reference pressure is sensitive to temperature. The basic principle of this microbarometer design is not new, and in many earlier cases it is clear that measures have been taken against the effects of temperature on the reference pressure. Here we report what seems to be a new approach to the design of such measures and to their evaluation.

The approach is to stabilize the temperature of the reference chamber, and this is done in two stages. First, the reference chamber is enclosed in a passive jacket to provide a thermal gain function, such that temperature variations external to the jacket are attenuated by more than a factor of 1000 at all periods of interest (below 60 min). Figures of merit are developed to guide the choice of jacket materials. Second, these external temperature variations are kept within a peak-to-peak range of about 0.3 K (at about 303 K) for days on end.

The actual thermal gain function of the jacket plus chamber is obtained by Fourier transforming the smoothed thermal impulse response function. This function is obtained by numerically differentiating the measured thermal step response function.

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