Proper sensor attachment

Discussion in 'General Electronics Chat' started by vladtess, Nov 29, 2015.

  1. vladtess

    Thread Starter Member

    Jan 5, 2011
    43
    1
    Hello. So we have have programmed everything to have the hardware to sense a temp. Now how do I attach the waterproof sensor to the boiler tank in such a way that temp is accurate?

    Do we just tape to the device that we are measuring, or is there a better method techniques?

    Thanks much!!
     
  2. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    Tape a wad of insulation on top of the sensor so it doesn't measure the air temperature in the room.
    Anything foamy or fluffy will do, depending on whether you want this to last for years or decades.
     
  3. vladtess

    Thread Starter Member

    Jan 5, 2011
    43
    1
    Do I need a thermal paste between the two?
     
  4. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    The two whats? The two sensors? The tank and the sensor?
    Depends on how fast you want it to respond.
    Anything in an insulated pocket will arrive at the temperature of the uninsulated side...eventually.
    You want 5 seconds, use a thermocouple. You want 90 seconds, use a thermistor. You need 5 minutes? Use a Klixon switch.

    Think about it. How many boilers do you know that change by 20 degrees in 5 seconds?

    All you need is a sensor that is way faster than the thermal time constant of the mass.
    I assume you haven't answered in 20 minutes because you're calculating how fast you can heat water.
     
    Last edited: Nov 29, 2015
  5. AnasMalas

    Member

    Nov 27, 2015
    66
    10
    is the sensor inside the boiler or outside? why is it waterproof? is the boiler made of metal?
    if you want to measure the water temp, your sensor should not touch the metal. if measuring the temp of the metal it has to touch it with nothing else to influence the temp.
     
  6. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    Outside. That's why you can tape the sensor on the boiler.
    Because the sensor might get wet if you use it in a place where hot water is actively being used.
    Most of them are, unless you're talking about a chemistry lab.
    Really? That sounds like an idea for a career. You can spend the rest of your life retrofitting 100 million water heaters and boilers that don't have submerged sensors.
    Nothing else? Not atmospheric air? Not insulation? Not the wires which connect it? That sounds like a battery powered transmitter in a vacuum cavity. No. The battery power will be inside the vacuum cavity. I guess this is where you tell how to measure temperature of a metal tank without anything touching the sensor or powering the sensor.

    I think I have it: An infrared non-contact thermometer which is calibrated to the emissivity of the tank...or a 10 cent thermistor.

    http://www.mouser.com/search/Refine.aspx?N=18356393&Ns=Pricing|0
     
    Last edited: Nov 29, 2015
    Hypatia's Protege likes this.
  7. AnasMalas

    Member

    Nov 27, 2015
    66
    10
    How do you know it is not submerged?! he said he needs the best method. and my questions where directed at him.
    he needs to get accurate temp. he never said he had 100 million water boilers and heaters. its like telling someone that because he spent 1 hour salvaging components that his work is impractical. guess what? that is what DIY is about!
    I said nothing else TO INFLUENCE THE TEMP. such as air or possibly water if it does get wet like you imply or even tape that can conduct heat. But even if he uses insulation he wont get an accurate temp! why? because when you are trapping heat, this heat raises the temp for the reading. so you might get a reading of 80 when it is really 70.

    again, you are not the thread starter. why are you answering questions that are not directed to you by mere assumptions about HIS own project?!
     
  8. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    Because I have been doing this kind of work for 45 years, 30 of them with a State License as an OEM designer, Certified to testify in court as an Expert Witness. I know you can't get a perfect temperature measurement except under laboratory conditions and I know you can't measure 80 degrees on a 70 degree tank by insulating the sensor from outside influences.

    What I want you to realize is that simple problems don't need laboratory quality solutions. I can use a thermocouple or a thermistor to get a temperature reading within a couple of tenths of an F using nothing but a wad of dead leaves and a piece of electricians tape. I can not, however, get a pipe or a tank to measure 10 degrees hotter than it really is by insulating my sensor from outside influences. If you're going to go all, "High Precision" with your advice, you should start by understanding the basics. Follow that up with avoiding blanket statements and words that suggest absolutes. If vladtess needs better precision than a couple of tenths of an F, he will ask a follow-up question.
     
    Hypatia's Protege and cmartinez like this.
  9. AnasMalas

    Member

    Nov 27, 2015
    66
    10
    Isnt it basic physics that if you measure the temp of the water it will be different to that of the container it is due to diffrent head capacity?
    Isnt it basic understanding that if you insulate part of a hot metal sheet and leave the rest uninsulated then after time remove insulation that the previously insulated area would be warmer than the remaining space? Or is it that when you go to be an "OEM designer" that they tell you
    Sike! Nothing of what you've studied ia remotely correct!!!

    Why dont you try it? Get some metal. Heat it. Place cotton on part. Leave for 10 minutes, which is warmer?
     
  10. AnasMalas

    Member

    Nov 27, 2015
    66
    10
    Also wouldn't an "OEM" boiler be made to lose minimum amounts of heat? Then how will the reading of a sensor mounted outaide be remotely correct?
     
  11. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    Like I said, Learn the Basics. Conjuring artificial scenarios only obfuscates the matter and creates an extended detour from serving the Thread Starter. That is called, "Hijacking the Thread" and is not allowed here. Giving incorrect information is also frowned upon, and is usually corrected within a few hours by a person with personal expertise specific to the question. This site is rife with brilliant people comprising centuries of education and experience. There are at least a couple of dozen regulars that can put me to shame in fields like, math, high energy physics, and radio frequency devices. The trick is to know your limitations and forsake the idea that you can be, "right" all the time. I understand that you are enthusiastic and you want to be helpful, but you're playing with the big boys now.

    If you want to explore the specifics of Thermodynamics, please start a Thread of your own. It can be very simple, like 1,2,3, Thank you, or it can take several days and more than a hundred posts. This is a teaching site, and you are more than welcome to participate.
     
    Last edited: Nov 29, 2015
    Hypatia's Protege and cmartinez like this.
  12. AnasMalas

    Member

    Nov 27, 2015
    66
    10
    I never said i was correct. if this is called hijacking the thread then alright. this will be my final reply.
    at first i asked some simple questions. these questions are based on all the lab work we have been doing over at school which teaches IGCSE for 4 years. if all these questions were incorrect then the educational system is beyond seriously flawed.
    i was talking out of what we normally do in the lab. touch the thermometer to the container and the temp changes by 5 C than that which is floating in water. thus i wanted to ask if he needed it to measure purely the water temp because if that is the case i have a solution to do that easily.
    when i asked my question you started replying with sarcasm
    then i asked you why are you answering what i was asking the thread starter. That is not hijacking?
    then you assumed that he doesnt need single degree accuracy. despite him saying he wants accuracy (despite him not giving any parameters for accuracy, so i took what we define as accurate in the lab)
    i then asked two questions, you replied with "learn the basics" and went on about how no one is an expert and all that. where did you point the inaccuracy out?

    where in this whole conversion did i put anything but questions? were any answered appropriately? or is this just a "I am older and have experience thus i am superior" type of conversion?
     
  13. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    {quote} But even if he uses insulation he wont get an accurate temp! why? because when you are trapping heat, this heat raises the temp for the reading. so you might get a reading of 80 when it is really 70. {end quote} (Emphasis added)
    WOW! If that is true ,when I need to heat something up, all I need to do is pretend that it is a sensor and insulate it. Sounds a lot like something for nothing.
     
    Hypatia's Protege and cmartinez like this.
  14. AnasMalas

    Member

    Nov 27, 2015
    66
    10
    We are talking in the context of relative heat. the heat rises relative to the rest of the boiler
     
  15. AnasMalas

    Member

    Nov 27, 2015
    66
    10
    put a blanket over your leg. compare its temp with your arm after 15 minutes. which is higher relatively?
     
  16. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    I'm just trying to wrap my head around where the extra 10 degrees came from. Again, sounds like over unity or something for nothing.
     
  17. ISB123

    Well-Known Member

    May 21, 2014
    1,239
    527
    He is talking about slower heat loss when something is insulated. I think he meant to say that if you isolate the sensor with some kind of material its going to lose some of its responsiveness because if you just had 80C in your room and if it was to suddenly drop to 50C the sensor would still read 80C for some short time until the insulation "cools down".
     
    cmartinez likes this.
  18. AnasMalas

    Member

    Nov 27, 2015
    66
    10
    The water has high heat capacity. (again, relative to metal). When you place a piece of metal and a cup of water of equal mass the water would be cooler. Because its high heat capacity allows it to take more heat energy before gaining a degree of temperature. Metal also lose temp faster because again. Lower energy required to raise the temp.

    So in a situation where the metal is loosing heat to the surrounding, it loses heat energy. The insulated area would not lose heat. Meaning that it would have a higher temp than the rest of the boiler. Because it is accumulating heat energy (gaining faster than losing comparitivly) it is like having two heat sinks. One is just having still air and the other has a powerful fan. Both are gettimg the same amount of heat energy. Which will have a lower temp?

    What I am trying to imply is that heat energy =/= temperature. Insulation doesnt allow heat energt to esacape, thus when more of it is introduced the temp go up.

    This is where I got my statement from. This is what I have understood in class and written in my exams. Could they be teaching incorrect info? Possible!
     
  19. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    Here is a thought experiment.
     
    cmartinez likes this.
  20. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
    2,778
    1,211
    Which, in turn, would more accurately reflect the temperature of the water - hence @#12 's suggestion of insulating the probed area!

    Best regards
    HP
     
    cmartinez likes this.
Loading...