Gas bottle monitoring system

Discussion in 'The Projects Forum' started by pking01, Apr 21, 2015.

  1. pking01

    Thread Starter New Member

    Apr 21, 2015
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    hi good afternoon,
    I am currently undertaking a project to create a monitoring system for gas bottle monitoring systems for the vulnerable person
    currently they have no indication when the bottle were to run out.

    an idea of creating a scale on which the gas bottle would sit and when the gas bottle reached a set weight an indicator (led) would flash inside alerting them that they are low on gas and need to order a new bottle

    I am looking at using a battery source rather than a mains supply thus eliminating finding a mains supply and any other legislations around that

    so far I an thinking of using a solar panel to charge my battery how big solar cell?how bigger battery (9v) the cell would feed through a charger controller to regulate when it would feed the battery and when not to thus preventing overcharging and damaging the battery, there would be a voltage regulator leading to a load cell/ scale

    this is where i become stuck....

    i now need some sort of micro controller or data reader or somesort of software to take the reading and work then emit wirelessly to a display inside??the display i need to read what % is left of the bottle and also some led display (RAG) to show green when over 50% amber 10-50% and red under 10%

    any help on any aspects would be appreciated

    thanks in advance

    Pete
     
  2. wayneh

    Expert

    Sep 9, 2010
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    There's no pressure gauge? That's the conventional solution for non-condensible gasses like oxygen or nitrogen. For fuels that condense into liquid, there are other solutions.
     
  3. pking01

    Thread Starter New Member

    Apr 21, 2015
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    the pressure gauge would be where the bottle is situated, I am looking to take the risk out of lets say an elderly person to go outside in winter to check the level of their bottle, thinking the scale solution as posted above, thus eliminating the risk out of reading the gas bottle gauge and they are able to read it indoors ie the display could be placed on the window sill or kitchen worktop
     
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    you mean actually LOOK at a pressure gage?
    They should make an app for that....
    so how long is this hose that people can wander so far away they no longer are in sight of the O2 bottle?
     
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
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    there are solid state pressure sensors available. be carefull if this is on an oxygen system, there are various dangers involved.
     
  6. wayneh

    Expert

    Sep 9, 2010
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    You could look at a load cell with a detached (but wired) display. These are widely used in industrial settings, so they are made to endure pressure washing and so forth. It should be no problem to set one outside and place the display/controller wherever you like.

    But, a remote wifi camera aimed at the pressure gauge might be cheaper. The wifi-based home security systems generally come with several cameras, so you'd get a security system along with your pressure-monitoring system.
     
  7. ebeowulf17

    Active Member

    Aug 12, 2014
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    I like Wayne's idea: A camera on the existing gauge seems like a simpler, more reliable solution than load cells and such.
     
  8. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    what about a digital or analogue bathroom scales, as the bottle gets low the weight also decreases, put a buzzer circuit on the desired weight .
     
  9. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    What is the weight of a) an empty bottle and b) a full bottle of gas? If the difference is only small then a weight-based sytem may require sophisticated signal processing.
     
  10. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    the weight of a gas bottle is the size you buy, for example a 13kg propane bottle has 13kg of gas in at new, the bottle weighs 19kg, total weight 32kg full .
     
  11. Reloadron

    Active Member

    Jan 15, 2015
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    Please tolerate my use of the US measuring system. :)

    I assume we are talking about oxygen bottles? A typical large gas bottle for oxygen here in the US is about 9" OD at the base and is about 54" tall. The empty weight can vary between around 105 to about 140 Lbs depending on the steel used and manufacture wall thickness. When charged to 2,200 PSI of oxygen you have about 244 cubic feet of oxygen weighing around 20 LBs. I guess all we care about is the weight of the oxygen in the bottle. You would just have to know the weight of an empty bottle and all of the bottles would need to be the same. Since the weight of an empty can vary between 105 to 140 LBs you have a large span so the bottles all need to be the same. The oxygen bottle game is not a new rodeo for me, been there and done that for years with an invalid mother-in-law. OK, let's say the empty bottles are identical. So we have a platten of a scale the bottles are placed on. Will this scale be in a neat clean environment or will it be exposed to the elements? Will each end user have their own bottle and scale? What distance is the oxygen piped to the user from the storage point?

    If I were to do something like this I would think about what Kermit2's mention was. I can buy a pile of 0 to 2500 PSIG pressure transducers with a 4 to 20 mA two wire output for under $150 each. If I assume a 2200 PSIG full bottle with a 0 to 2500 PSIG gauge I only need a two wire loop easily powered from where the user is. I guess if for some reason I want to power the loop from the bottle storage location I can but I see no reason to? There are countless way to power a single loop or a dozen or more loops. I would take my 4 to 20 mA and run it through a 1% 250 Ohm resistor giving me 4 to 20 mA = 1 to 5 Volts. Take the 1 to 5 volts and offset it by 1 volt and amplify it to 0 to 5 volts and drive a LM3914 type circuit. Then 3 LEDs Green, 3 LEDs Amber and 3 LEDs Red followed by a blinking LED where the oxygen is history. Something like that anyway.

    There are so many variables to this and so many unanswered questions. My reply is based purely on a mix of assumption and speculation. If this is for any sort of a medical application or the end users are invalid patients or nursing home patients then this is a whole new game requiring a new game plan. :) However, based on my read I would be thinking sensing pressure rather than weight.

    Ron
     
  12. pking01

    Thread Starter New Member

    Apr 21, 2015
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    0
    Thanks for all responses it was for domestic heating propane supply some rural houses don't have a fixed has supply so rely on bottles a full gas bottle weighs 95kg and empty 47kg! I was looking and bathroom scales but they have an auto off feature which doesn't Help....great idea with cctv camera this could work potentially maybe fixed on the scale reading! More responses welcome

    Thanks in advance
     
  13. strantor

    AAC Fanatic!

    Oct 3, 2010
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    How about suspend the bottle from a spring-loaded arm; I would use a piece of scrap wood with a $3.50 gate hinge and a $3 screen door spring, attached to a fence post. Attach a $1 potentiometer fixed to the pivot point of the arm, and run a cord (old ethernet cable or 3-wire extension cord will work, or whatever you already have) from the potentiometer into the house.

    tankweight.png
    scale2.png

    Before attaching the pot, fine-tune the spring positioning/tension so that an empty bottle is lifted significantly higher than a full bottle. At least 90 degrees of travel from empty to full would be best, but less should be OK. Then drill a hole into the wood that is a tight fit for the potentiometer shaft. Center the pot so that it is mid-resistance (5K for a 10K pot) and press it in, aligned with the connection points pointing up. Then hang a rigid weight from the potentiometer body to keep it aligned up/down ( a hose clamp around the body securing it to a bent coat hanger with a small weight should work). Tape a zip-lock bag over the pot & connections to keep out moisture. Putting some discarded desiccant packs from pill bottles inside would be a good idea too.



    Inside a small enclosure (altoids tin, tupperware, whatever you laying around), place (2) 9V batteries (or an appropriate number of AA or AAA or coin cells or whatever), one of these $2 voltmeters, a $0.15 button, and this circuit:

    scale.png

    The precision voltage reference (v. ref) is a low-power signal regulator, not a power voltage regulator; it's purpose is to present the pot with an unchanging voltage as batteries drain. It can be a cheap part like this $0.46 12V reference, and the trim pots are only about $0.10.

    Make sure the pot is connected so that a fuller bottle gives a higher output voltage and an emptier bottle gives a lesser voltage.

    Hang a full bottle on the arm and hold down the button; adjust the top trim pot so that the display reads exactly 10V out. Then hang an empty bottle and adjust the bottom trim pot until the display reads zero. Then go back and fine tune the top pot with a full bottle, then the bottom pot with an empty bottle again. You might have to repeat again one or more times to get the calibration perfect so that full = 10.0 (100%) and empty = 00.0 (0%).

    When the button is pressed, the circuit energizes, and the elderly can see the bottle charge level in "percent." The meter draws 8mA, the voltage ref draws about 4 mA, and the pots' series resistance will draw maximum of about 10mA. That's 22mA, achievable by coin cell batteries. This could probably fit inside a tic tac box if you wanted it to.:
    [​IMG]

    When the button is not pressed, no current is drawn from the circuit and the batteries' charge level will not drain. It should last a very long time on batteries even if checked several times daily.

    This project could cost you as little as $6.50 for hardware and $3.80 for electronics, not including shipping. Even less if you already have some of the stuff. $10.30 is not a bad price.
     
    Last edited: Apr 22, 2015
  14. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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  15. Reloadron

    Active Member

    Jan 15, 2015
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    Location? Knowing we are looking at LPG is great but location is important because here in the US and also in for example GB and other Euro countries there are Legislation / Regulations that govern how the gas must be stored and managed right down to construction of the storage container. For example in GB:

    Also, what environmental conditions? Areas where the storage is exposed to for example snow and rain or freezing ice may effect a scale operation? Do the bottles have automatic changeover?

    Ron
     
  16. wayneh

    Expert

    Sep 9, 2010
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    OK, that rules out pressure methods.
     
  17. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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  18. Reloadron

    Active Member

    Jan 15, 2015
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