Any linear distance sensor like the LM35 output? 0-5V linear output?

Discussion in 'The Projects Forum' started by fiatuno, Apr 4, 2012.

  1. fiatuno

    Thread Starter Member

    Jan 28, 2011
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    Dear members,
    I wish to know if there are any distance sensors which give an output voltage from 0 to 5V to represent the distance like the LM35 does with temperature? I need to measure short distances, such up to 30cm for example, and maybe which are available on market and at a reasonable cost. Thanks in advance for any help.
    Regards
    FiatUno
     
  2. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
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    Sharp makes some analog distance sensors that are IR based. Analog output is not absolutely linear.

    There are also several companies making sonar range finders that output analog voltages based on distance, Maxbotix is one.
     
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  3. fiatuno

    Thread Starter Member

    Jan 28, 2011
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    The sharp ones to tell you the truth I already have, but I ordered them uncorrectly as the first design was changed and couldn't suit my needs anymore. What I need now is a small range distance sensor with an output voltage from 0-5V linear. The minimum should be around 5cm and maximum of about 40cm, from a supply voltage of around 5V. The Maxbotix I can't seem to find on the RS site. Can you please help me out as I have searched upside down our local rs site... Thanks in advance.
    Regards
    Fiatuno
     
  4. fiatuno

    Thread Starter Member

    Jan 28, 2011
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    Is there any better sensor then the Maxbotix which has a 10mV/cm please and begins with a minimum distance of 0cm please? or maybe 2cm? Thanks in advance
     
  5. chrisw1990

    Active Member

    Oct 22, 2011
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    thing is, youre measuring 40cm, thats a lengthy distance for contact linear position..
    non-contact is what you should be looking for, and i dont know where you intend to use this, but if theres a flat reflective surface available, an ultrasonic unit could be implemented..
     
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  6. fiatuno

    Thread Starter Member

    Jan 28, 2011
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    What I wan't to measure the volume of water where I have a tank filled with water and a float surface reflects back the signal to check the distance. The distance difference is multiplied by the volume per cm. I wish to find a sensor which has a linear output as I already told you of around 10mV per cm let us say if possible. so that I can work out the volume from the sensor output. I have sharp sensors using infrared, but they weren't good for my purpose as already stated, as the dimensions changed and need to work on a much smaller area. That is why I would need something like that. Hope this type of sensor exists lol. Thanks in advance for any help. Really appreciate
    Regards,
    Fiatuno
     
  7. John P

    AAC Fanatic!

    Oct 14, 2008
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    Could you do it another way, like with a pressure sensor at the bottom of the tank, or maybe by measuring the apparent weight of a rod hanging into the liquid ("apparent weight" because as the liquid rises, the rod becomes more buoyant)?
     
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  8. fiatuno

    Thread Starter Member

    Jan 28, 2011
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    That would be a problem as the bottom of the tank is fixed and therefore the only way I could do it is send a signal from the top and check what is the distance of the unfilled part so I get an approximate value of it. I have had sharp distance sensors but as already said they don't suit my needs anymore, and I was told that there were much better ones which had a linear output voltage to tell you the distance. Hope I can find a way out if possible. Thanks in advance
     
  9. strantor

    AAC Fanatic!

    Oct 3, 2010
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    What's your budget? I know lots of sensors that will do what you want, but they are industrial parts I have encountered in the line of duty & cost big bucks. Usually hobbyists don't buy that type of stuff.
     
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  10. fiatuno

    Thread Starter Member

    Jan 28, 2011
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    I can manage upto 50 euros, because what I am doing is a part of a project which I can do without but I wish to include it. I wish to keep it in the budget of 50euros. The water tanks aren't big so I need to work for small distances. The linear output would be ideal for my task. Thanks in advance.
     
  11. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Never mind. What I had in mind is going to run about 350 euros.
     
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  12. fiatuno

    Thread Starter Member

    Jan 28, 2011
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    wowww lol, no thats more than I could afford, anyone thinks I could do with a sensor from a fuel tank which works with a lever. What output do these sensors normally have, are they linear. Do they need 12V or do they work with 5V if someone could help. because I think this could be a good solution. Maybe I can even use a potentiometer. these are just ideas I am coming up with.
    Regards
    Fiat uno
     
  13. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Oh, didn't know that you were open to other ideas. Yeah you could definately sense it with float; mount a float on an arm that swivels on a pot. Your output wouldn't linear, but you could linearize it in your code if you're clever. You could mount a float on a rod that slides straight up & down, maybe with a pull cord on the top of the rod that spins a pot - that would require a little more mechanical complexity, but would be linear.

    Do you really need an anolog absolute value of the volume of water in the tank? or would a low limit & high limit suffice?
     
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  14. fiatuno

    Thread Starter Member

    Jan 28, 2011
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    The complexity of the mechanical is not the thing that boders me most as I prefer solving it mechanically, rather than having to solve it programmaly as I already did the program for a linear voltage output and don't wish to change the program again. Can you explain to me better how can I get a linear output maybe there is a picture on the web please. Yes I am open to new ideas, my problem was I was focusing on that solution only. Thanks in advance for any help.
    Regards
    Fiatuno
     
  15. MrChips

    Moderator

    Oct 2, 2009
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  16. fiatuno

    Thread Starter Member

    Jan 28, 2011
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    The below link would have been the best solution if it began from 0 cm or atleast 2cm as it gives an analog linear voltage. But thats not the case unfortunately for me

    http://www.robotshop.com/maxbotix-ez0-ultrasonic-ranger-1.html

    That is why I am analysing newer solutions for me which could give me an analog linear voltage. I also checked for slide potentiometers, but I don't know if this could work as the ones I have found have a 20% tolerance which is to much for my application.
     
  17. MrChips

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    Oct 2, 2009
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    I am not sure what problems you are experiencing with ultrasonic range finders.
    They have a resolution of about 2cm and range from cm to m. The results are extremely linear since they are based on the velocity of sound in air.

    Measuring liquid levels in tanks is one of the most common applications.
     
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  18. fiatuno

    Thread Starter Member

    Jan 28, 2011
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    Hi Mr Chips, I got that website upside down, but the ones I found with what I need where the Maxsonar and still they aren't good enough as under 6 inches they do not function well. And that one also gives the output voltage needed linearly. I have sent my local RS store, and they don't have any similar component to the one I need. I don't mind which form the sensor is or what it uses, as long as it gives me a linear output voltage. Thanks to all of you for your help uptill now mates.
     
  19. John P

    AAC Fanatic!

    Oct 14, 2008
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    If the ultrasonic sensors won't go down to the range you need, can you just mount the unit so it's standing off from the top of the tank, say operating down a tube that's 12 inches long? I doubt if the smooth walls of the tube (PVC pipe?) would create echoes--the sound would need a surface to bounce off, like the liquid.

    However, I think you should consider a rod hanging into the liquid as I suggested earlier. Look how cheaply you can get a force sensor:
    http://www.ebay.com/itm/Load-Cell-5...559?pt=LH_DefaultDomain_0&hash=item519e9734cf
     
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  20. strantor

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    Oct 3, 2010
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    I think that might your problem. In my plant we use lots of ultrasonic sensors. Whenever I have a problem with one, the first thing I check is the surface of the reflector. Generally we will have an adjustable piece of flat plate steel that the sensor looks at, and if this plate has been knocked a few degrees off of alignment, I adjust it and it usually fixes the problem. Ideally your surface should be a flat plane that is exactly perpendicular to your sensor on both axis. If it is at an angle other than perpendicular, it reflects the ultrasonic vibrations from the sensor off into never-never land and not back to the sensor. If you are trying to read a round float object, forget about it, the float is going to do nothing but diffuse the ultrasonic vibrations in every direction except back to your sensor. You would be better off to focus the ultrasonic sensor directly at the surface of the water. It's not perfectly flat, but it will be perpendicular, and will probably work a lot better than focusing it at a float. Ultrasonic sensors usually work fairly well in this application.
     
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