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Pressure Sensor for water level measurement

Discussion in 'General Electronics Chat' started by premkumar9, Apr 1, 2015.

  1. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi Jim,
    As you have got the program set up, any chance you could post a composite plot of series1 and 2 ie: PTX water and PTX air combined.?
    Eric

    EDIT: algebraically of course.:)
     
  2. premkumar9

    premkumar9 Member

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    Thank you very much Jim. Unable to conclude anything. I will repeat my experiments once my set up is ready. Will try to conclude whether this sensor can be used or I have to go for something better.
     
  3. alec_t

    alec_t Well-Known Member Most Helpful Member

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    I would conclude that there is no definite correlation between the three series of data, within the limits of measurement accuracy.
    I speculate that the apparently consistent drop in the water pressure sensor readings might be due to some gradual 'settling-in' process, e.g. a permanent slight deformation of some part of the sensor. Repeating the measurements, over a longer time period, might help to prove/disprove that theory.
     
    Last edited: Apr 23, 2015
  4. dave

    Dave New Member

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  5. JimB

    JimB Super Moderator Most Helpful Member

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    Eric, you are a hard taskmaster!

    Here it is:

    Water depth 2.JPG
    Again, the traces are:
    Yukky green - Temperature
    Purple - (50m+ext)/2
    Light Blue - (50m - ext +1)

    JimB
     
  6. JimB

    JimB Super Moderator Most Helpful Member

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    What, not even that they make big jumps up and down at the same time?

    JimB
     
  7. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    Hi Jim,
    Hardness is a relative term, I knew you would find it easy, many thanks for the plot.:rolleyes:

    I would like to know why the OP wants this degree of accuracy for a water level that can fluctuate over 40 mtrs in depth.

    ie: Water in a dam. 50 Meters.
    E
     
  8. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    and your conclusion is?
     
  9. JimB

    JimB Super Moderator Most Helpful Member

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    Possibly because someone in an office far far away just picked some numbers out of thin air, without thinking of the practicalities of such a measurement.
    While I am wearing my cynical hat, he also probably wanted the data logged at 1 second intervals.

    Even Barnes Wallace did not need it that accurate! (The devil made me say that).

    JimB
     
  10. premkumar9

    premkumar9 Member

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    This minimum to maximum variation will be over a period, say a year. In a particular day change may be less than even 5 cm. 5 cm level change means a big change in the volume of water.
     
  11. premkumar9

    premkumar9 Member

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    May be even many years.
     
  12. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Not even then. Meter accuracy is 0.5% + 3 digits. Besides, some jumps up coincide with other jumps down.
     
  13. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    "5" has to be. Just has to be the answer.

    That aside.

    Note that the inflection points all generally-coincide. Temperature or turn-on/turn-off spike co-incident with the air conditioning turning on and off?
     
  14. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    maybe a power dip to AC also caused supply issue to sensors. in addition to RF noise and temp shift . All easily solvable problems.
     
  15. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    The % difference is well within the range of what might be considered barometric pressure.

    So,in the absence of anything else, I'd say poor power supply regulation and that it reads absolute rather than gauge pressure. The shape also suggests barometric pressures.

    The water and air sensors "track" somewhat shape wise suggest barometric pressure.

    The meter suggests that you don't have enough accuracy to resolve the height resolution required. I would "think" that a 4-20 mA sensor that reads in gauge pressure and has a port to the air atmosphere is required.

    4-20 mA allows the sensor to be powered by the same lines used for readout and the lines can be arbitrarily long.

    Powering a sensor with a constant voltage supply over long distances, there is a voltage drop across the leads and the measurement usually has to be differential.
     
  16. premkumar9

    premkumar9 Member

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    Thank you all for the guidance. Is there any way to mark the important posts and filter them later?
     
    • Informative Informative x 1
  17. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    Click on Informative (i) icon lower right.. might be indexed somehow

    1) you will always need a more stable reference Voltage 100 ppm, or an ADC with 14 bit accuracy
    2) You must make a list of ALL possible error sources , simulate them or observe them and find the contribution to output result with at least 12 bit resolution preferably 14 bit.
    e.g. Voltage, RF, air Pressure, Temperature, ripple, AC quality ( transients, brown out, surges , noise)
    3) Learn Sensitivity Analysis Δx/Δy and Correlation techniques or curve fitting
    Excel does 6 kinds of curve fitting easily, and you can hide data that ought to be excluded .
    - plot xy data format then add curve fit and display formula)
    - then use the formula in code for correction and calibration to compensate for any known sensitivity as long as it is stable. or make it stable.
    4) thus your reference voltage or current source for the sensor must be equal in stability to your ADC or DMM.
    5) write a design spec so you can test against your requirements. in future, do this 1st !!
    6) Write a Design Verification Test (DVT) Plan with 1 page per test based on above specs. with rejection criteria. and setup.. in top and fill in results in bottom. with left side using photos or diagram.
    7) After you follow this design methodology it is harder to fail.
    ( or as I was taught.. get it Right the First Time )
     
    Last edited: Apr 24, 2015
  18. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Suggestion:

    Make a document in a word processor with a title and then link directly to the post.

    The post above is: http://www.electro-tech-online.com/...-level-measurement.144260/page-5#post-1218144

    I went to the #96 and "Copied the link location"

    If you want, you could create a post, with your own index.

    Post #96 - Tony's suggestions

    For an example line. If you want help on the latter, yell. As you loose editing ability, you can keep moving the index to the last post.

    I did a variant on this on a thread that lasted more than a year where I would put the links to the latest scematics and important posts.
     
    Last edited: Apr 23, 2015
  19. premkumar9

    premkumar9 Member

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    Thank you :)
     
  20. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    The link with a name is done with this syntax:

    [url=http://www.somewhere.com/]The link name[/url]

    which will show up as:

    The link name
     
  21. premkumar9

    premkumar9 Member

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    Oh. Thanks. I was also thinking how that is done:)
     

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