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Old 09-03-2013, 02:38 PM   #1
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Default Piezo electric differental pressure sensor

Hi

I'm in the process of automating my new 55 gal RIMS brewrig.

I had the misfortune to have my brand new Blichmann false bottom, sucked ball shaped by my pump. :-(

I order to avoid that, i have installed to small sight glasses on the MT, made of 850mm x 8mm ID glas pipes. One with input below the, now straight again, false bottom and the other just above. Now it's at least visual if the pressure is different below or above the false bottom. :-)

Then i got the idea to use a differential pressure sensor, to automate the recirculation.

...and then, why not use the measured pressure to determine how much liquid i have in my kettles?

Well, now i need help. I have absolutely no idea, how to calculate, the minimum and maximum pressure i could expect in the sight glasses/pipes.

For now the pipes are open in the top, but here must the pressure sensor be connected air tight.

So, do you think it will work?

Can you help me with a formula / spreadsheet to calculate the possible pressure levels in the pipes/sight glasses?

Do you thing that this cheap differental pressure sensor can work: http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=MPXx10&fsrch=1&sr=1

The sensor will feed an input port on a Siemens Logo! analog port i use to control the process.

Thank you

/lars

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Old 09-03-2013, 08:15 PM   #2
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It tells you that you have a range of 0-10kPA. If we can somehow convert this into a height of water column that would be perfect. There is a way. 1 kPA ~ 4.015 "h2o. Or a vessel containing x inches of water will produce y kPa of DP.

Lets say your kettle is 30 inches tall. Using water (SG=1.000) you should read from 0 - 30 "h2o or 0 - (30/4.015) kPa.

Just keep in mind that this is for water, not wort. If you want to measure wort, it may be useful to have a corrected input for your measured SG.

How tall is your kettle? What vessels need measurement?

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Old 09-09-2013, 03:53 PM   #3
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Short answer is yes, the BrewTroller uses MPX5010DP, why not check out their implementation.

https://www.oscsys.com/projects/brewtroller/system-design/volume-measurement

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Old 09-27-2013, 02:31 AM   #4
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Thats the sensor that I used and it worked fine. I just had to calibrate it using a linear fit equation. I just added 32oz at a time and measured the output through it into excel and done.

I used arduino tho if it makes a difference.

I tried to get SG but it wasn't accurate enough and turned to be a bit "noisy".

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Old 10-07-2013, 12:28 AM   #5
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Quote:
Originally Posted by heapyjeepy View Post
Thats the sensor that I used and it worked fine. I just had to calibrate it using a linear fit equation. I just added 32oz at a time and measured the output through it into excel and done.

I used arduino tho if it makes a difference.

I tried to get SG but it wasn't accurate enough and turned to be a bit "noisy".
Can you share some more info on how you went about your level sensing? And what you tried to get SG measurements?
I'm guessing the linear fit was due to the shape of the kettle/keggle?
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Old 10-07-2013, 12:50 AM   #6
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I used a differential pressure sensor attached to the bottom of my keggle about 2 inches off the bottom. the sensor was plugged into the analog pin on my arduino. The I added water 32 oz at a time from my nealgene bottle.

I did a serial print (displays the input on a range from 0-256 on my laptop running the arduino software) and recorded the values in excel. To get a linear equation to interpulate the in between values I plotted these values and used the graph-show equations in excel.

Sooo.... to get my value of gallons/oz/pints/qts..... just take the input analog value run it thru the linear equation and bammm. Output for volume.

Now the specific gravity I used two sensors and used the differance in pressures and determined the gravity. Estentually I used (p1-p2)/g*h=specific gravity. The sensors weren't sensitive enough. I could only equate gravity numbers to a tenth or so. I might continue lookin into this.

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Old 10-07-2013, 12:53 AM   #7
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Sorry yeah the linear equation is because of the keggle shape. Its nearly linear as far as the accuracy I'm looking for for volume.

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Old 10-07-2013, 02:55 AM   #8
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Quote:
Originally Posted by heapyjeepy View Post
I used a differential pressure sensor attached to the bottom of my keggle about 2 inches off the bottom. the sensor was plugged into the analog pin on my arduino. The I added water 32 oz at a time from my nealgene bottle.

I did a serial print (displays the input on a range from 0-256 on my laptop running the arduino software) and recorded the values in excel. To get a linear equation to interpulate the in between values I plotted these values and used the graph-show equations in excel.

Sooo.... to get my value of gallons/oz/pints/qts..... just take the input analog value run it thru the linear equation and bammm. Output for volume.

Now the specific gravity I used two sensors and used the differance in pressures and determined the gravity. Estentually I used (p1-p2)/g*h=specific gravity. The sensors weren't sensitive enough. I could only equate gravity numbers to a tenth or so. I might continue lookin into this.
Thanks, so you were using 2 sensors for trying to determine SG? Why not a single DP sensor - that should remove some of the noise. But I can see accurancy being a issues since the difference you are trying to measure would be about 5% of the value.
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Old 10-07-2013, 01:03 PM   #9
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I could have used a single DP sensor but they were kinda cheap and i was trying to figure out how they would respond when the water went over the second sensor port in the keggle. This was kind of a learning experience.

The noise/error is also because of the change in pressure in the tube due to heat. (increase in temp yields increase in pressure). I found this slick setup that I might try using to eliminate this difficult "not so linear" equation of pressure/temp change. It uses a small air pump into the line at a constant rate and forces bubbles out the air port. The pressure will change but the noise from the bubbles can be more easily filtered out buy averaging over some time.

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Old 10-07-2013, 01:04 PM   #10
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Yeah, that pic didn't work. try this:

https://www.oscsys.com/projects/brewtroller/system-design/volume-measurement

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