Hi Fr. Tom,

Perhaps I wasn't clear, but that's what I meant to say. I said that it
would get larger when the external pressure decreases.

How expensive/available are standard barometric cells? As I said, I wasn't
proposing this idea as a really serious sensor, just as something
interesting to try.

Sean

At 04:58 PM 3/4/01 -0500, you wrote:
>One small error:
>As external pressure increases the balloon would get
>smaller, not larger.
>
>Pressure sensors can be made in the following way:
>One fixed plate is separated from one plate that is
>mounted to a standard barometric cell (a sealed chamber
>that has a corrugated surface that allows it to expand and
>contract readily. Looks something like a hockey puck
>with circular ripples.) When the chamber expands it
>pushes the moveable capacitor plate towards the fixed
>plate. The changing capacitance is usually used to
>vary the frequency of a high frequency oscillator.
>The frequency is then calibrated to the pressure.
>
>Fr. Tom McGahee
>
>
>

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