From: liz@poppyrecords.invalid.invalid   
      
   Don Y  wrote:   
      
   > On 12/26/2025 3:27 AM, Liz Tuddenham wrote:   
   > > Don Y  wrote:   
   > >   
   > >> Any pointers regarding deployment of pressure sensors measuring   
   > >> air pressure?  I'm looking at nominally an inch of water   
   > >> (pressure/vacuum)...   
   > >   
   > > Washing machine/diswasher water-level switches?   
   >   
   > No, I'm looking at pressures in air handling systems.   
      
   They operate on air pressure.  The rising water level closes off the   
   bottom end of a chamber; thereafter any further increase in water level   
   causes an increase in air pressure within the chamber.  A very flexible   
   rubber diaphragm presses aginst a spring and eventually operates a   
   microswitch.   
      
   By substituting a movement sensor for the microswitch (and with the use   
   of a suitable spring) you could make a proportional air pressure sensor   
   of good sensitivity which held its calibration to a reasonable degree of   
   accuracy.   
      
   I have also used a differential air pressure sensor that used a thin   
   silvered tensioned plastic diaphragm as a concave/convex mirror with a   
   light emitter and sensor on each side, connected to a balancing circuit.   
   It was exceptionally sensitive but not particularly robust or   
   repeatable.   
      
      
   --   
   ~ Liz Tuddenham ~   
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