Unstable stretch sensor

Discussion in 'The Projects Forum' started by Amp_noob, Jun 29, 2012.

  1. Amp_noob

    Thread Starter New Member

    Jun 25, 2012
    5
    0
    Got this stretch sensor from adafruit , and it was highly unstable.
    Measured with both ohm meter and by sending AC thru it to measure the current.

    Adafruit states that the resistance will be approximately 350ohm/inch, I got like 300-700ohm/inch.

    Can someone recommend me with an accurate stretch sensor?
    Would this one be more accurate?
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    You did read the part about its response time being VERY slow..

    Why not describe your application or intended use for this sensor?
    I've never seen nor heard of a "stretch" sensor in a real world professional application.
    That's a gimmicky toy basically where stability/accuracy/quick response is not required.

    There are numerous other ways to measure displacement..
     
    strantor likes this.
  3. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    +1
    You'll never see a "stretch sensor" used in industry.

    Tell us what you're doing and we can find a reliable way to do it.
     
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    Depending on several factors, I can see it used for a cheap, disposable, around-the-chest respiration transducer. Offsets and gain could be automatic in the electronics.

    Ken
     
  5. Amp_noob

    Thread Starter New Member

    Jun 25, 2012
    5
    0



    Yeah I know it has a decay time, but the thing is when I stretch it to lets say from 1inch to 2inch and holds it still I get different values each times, and the value is not stabilized even after 30minutes.
    Here are the values after 30 minutes, before each try the rubber is shrunken back to it initial value(320-380omh)
    First try : 988ohm
    Second try:1200ohm
    Third try:775ohm
    Fourth try:680ohm
    Fifth try: 1044ohm
     
  6. Amp_noob

    Thread Starter New Member

    Jun 25, 2012
    5
    0


    Stage 1.
    I want to measure the length variations of "something", that "something" can curve and expand in any directions.
    Wish to measure down to millimetre.


    Stage 2.
    In realtime the data is sent to TI USB-6008 and then Labview for graph processing.


    Stage 2 is completed, problem is inaccuracy in stage 1, can't even calibrate that thing.
     
  7. panic mode

    Senior Member

    Oct 10, 2011
    1,320
    304
    when interested in precision, consider products that have datasheet. that way you get precision, repeatability etc specified properly instead of "about"...

    and then ensure you are always within limits. for example going from 1 to 2 inch is 100% stretch while link states that you should not exceed 60%. the product is likely already damaged and out of spec, whatever that was.

    you can use wire draw encoder for example
     
    Last edited: Jun 30, 2012
  8. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    It sounds like you're trying to measure flubber.
    Are being intentionally vague? I won't play the 100 questions game. If you want help you need give a reasonable description, and a picture is worth 1000 words.
     
  9. WBahn

    Moderator

    Mar 31, 2012
    17,731
    4,789
    Given that they think that stretching something that is 6" to a length of 12" is a 50% elongation, I wouldn't put a lot of stock in their specs or their expertise.
     
  10. Amp_noob

    Thread Starter New Member

    Jun 25, 2012
    5
    0
    Sorry for this mysteriousness.
    But I've signed a confidentiality agreement, so I can not give out the exact object to be measured and the whole procedure.

    The nearest thing I can compare to is a balloon, when it is filled with air the surface will expand in all directions.
    Or temperature dependent tape that is taped to something curved, as the temperature changes, it will increases or decreases.
     
  11. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    What about a string pot?
    What sort of accuracy/precision do you require?
    What is the measurement delta?
    Must you measure distance? Maybe pressure (for your balloon example)
    stain gauge maybe?

    Sounds like an interesting problem but if you've signed an NDA then I'm afraid the necessary information cannot be exchanged properly here and all we would be doing is taking random guesses to solve a virtually unknown problem to us.

    But I'd make a guess that a string pot would work for this if a junk "stretch sensor" was attempted. Its MUCH more precise.
    Good luck...
     
    strantor likes this.
  12. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    sorry for the lack of tact. Its just that we get an overwhelming amount of posters around here who are just too lazy to provide enough information to help them, and it gets irritating after a while.

    so I guess I will entertain the 100 question game.

    is this object circular? are you trying to measure circumference?
     
Loading...