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   On 2024-03-27, The Natural Philosopher  wrote:   
   > On 26/03/2024 19:16, David Higton wrote:   
   >> In message    
   >>            The Natural Philosopher  wrote:   
   >>   
   >>> On 26/03/2024 18:16, Ahem A Rivet's Shot wrote:   
   >>>> On Tue, 26 Mar 2024 17:33:50 +0000 Jim H  wrote:   
   >>>>   
   >>>>> Assuming the "oil" you're talking about is kerosene/heating fuel, the   
   >>>>> speed of sound is 1330 m/sec so 0.5cm takes 3.76 micro-sec.   
   >>>>   
   >>>> 	I would have thought it's measuring the distance to the surface of   
   >>>> the oil from above the oil so it would be the speed of sound in air that   
   >>>> matters 300m/s.   
   >>>>   
   >>> Correct, Mrs Shot. Anyway it's died within 30 minutes of going back on   
   >>> 'short echo'... So its definitely sensitive to that in some way.   
   >>>   
   >>> I'll add more debug code tomorrow   
   >>   
   >> Are you sure the sensor isn't malfunctioning as a result of being in   
   >> oil vapour?   
   >>   
   > Since it is operating on the desk in front of me, fairly sure :-)   
   >   
   > I haven't let it anywhere near the oil tank yet. The plan is to have it   
   > installed by the fall. ready for next winter.   
   > So it is being hammered to check for problems *before* it gets to a cold   
   > wet inaccessible oil tank.   
      
   On the off chance an alternative sensing architecture might be of   
   some use: Instead of using sound to measure distance, have you   
   considered possibly using fluid pressure to measure the height of   
   the stack of liquid above a pressure sensor?  If you put a   
   pressure sensor near the bottom of the tank, and if the air space   
   above the liquid is at atmospheric pressure, the gauge pressure   
   reading will be directly proportional to the height of liquid   
   above the sensor.   
      
   For water, the pressure reading will be ~0.43 psi per foot of   
   height.  Oil is almost certainly less dense, so you might need a   
   very sensitive pressure sensor--unless the tank is very large.   
      
   Anyway, just in case you hadn't considered that idea...   
      
   --   
   Robert Riches   
   spamtrap42@jacob21819.net   
   (Yes, that is one of my email addresses.)   
      
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