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From: The Natural Philosopher <tnp@invalid.invalid>
Newsgroups: comp.sys.raspberry-pi
Subject: Re: Need help with PI PICO...
Date: Thu, 28 Mar 2024 07:07:52 +0000
Organization: A little, after lunch
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On 28/03/2024 03:44, Robert Riches wrote:
> On 2024-03-27, The Natural Philosopher <tnp@invalid.invalid> wrote:
>> On 26/03/2024 19:16, David Higton wrote:
>>> In message <utv5e7$29onh$2@dont-email.me>
>>>             The Natural Philosopher <tnp@invalid.invalid> wrote:
>>>
>>>> On 26/03/2024 18:16, Ahem A Rivet's Shot wrote:
>>>>> On Tue, 26 Mar 2024 17:33:50 +0000 Jim H <invalid@invalid.invalid> 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.
> 
Never thought of that. Cute.

> 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...
> 
I hadn't.
Actually it looks like this idea is going to work fine, I just need to 
zero in on what the problem actually is, and get some form or 
reliability at short range. The sensor appears to work at far greater 
distances than its rated for, so against an orthogonal  flat oil surface 
it should be just fine

I won't be able to get much done in the next few days so will attack the 
code again next week.

-- 
"It is an established fact to 97% confidence limits that left wing 
conspirators see right wing conspiracies everywhere"