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Oil temperature sensor, help?

Discussion in 'Sensors and Actuators' started by AlenZGB, May 21, 2014.

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  1. AlenZGB

    AlenZGB

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    Feb 19, 2014
    Helloo
    im trying to build oil temperature sensor for my scooter. I have one wire temperature sensor, how can i get
    reading from it and then transfer it to the LCD screen or something like that.
     
  2. Supercap2F

    Supercap2F

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    Mar 22, 2014
    There is no such thing as a one wire component. A component has to have at least two wires. If the sensor you have has a metal case then thats most likely to be the second pin. Do you have a meter? If so then (assuming it has a metal case) turn your meter to the ohm range and put one probe on the wire and one on the case. If your reading changes with temperature then it's a resistor that changes resistance with temperature (I can't think of the real name right now).

    Dan
     
  3. AlenZGB

    AlenZGB

    174
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    Feb 19, 2014
  4. Supercap2F

    Supercap2F

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    Mar 22, 2014
    Do you have its data sheet or its part No.? Can I see them?

    Dan
     
  5. AlenZGB

    AlenZGB

    174
    5
    Feb 19, 2014
  6. Supercap2F

    Supercap2F

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    Mar 22, 2014
    It looks like it's a thermistor (yay! I thought of the name) but I can't be sure. If it is then I might be able to draw you up a circuit so you can have a relay or some thing turn on when it senses 120 C. Do you have a meter if you do then goto post #2 and do what I said and tell me the results. Then we can know what it is.

    Dan
     
  7. AlenZGB

    AlenZGB

    174
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    Feb 19, 2014
    It is thermistor, you are right. I didnt connect it but the resistance is changing during heating and cooling. Friend is on some trip, will come in a few days and bring me sensor.
    My question is,how can i connect it so that i can get reading on LCD screen, small one just to see if theres any overheating in the oil segment.
    If not then the warning lamp on some temperature will be also good, but lcd would be nicer :D


    EDIT:
    maybe use this cheap LCD and somehow convert it to what i need
    it this is possible, without turning the world upside down :D
    http://www.ebay.com/itm/New-Digital...195?pt=LH_DefaultDomain_0&hash=item2ecf2b071b
     
    Last edited: May 22, 2014
  8. Supercap2F

    Supercap2F

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    Mar 22, 2014
    Ok I need some more info on the thermistor. Get out a meter and hook one probe to the case and one to the wire. Tell me what the meter says. Then warm up the sensor (like rub it in your hand) then hook it up to the meter again and tell me what it reads this time. I need to know to these readings to determine what components to use in the circuit I will draw for you. I can make a LCD display 120 C when the sensor reads that value and higher and blank when it does not (like if it is > 119 C then the display will be blank. When it reads < 120 C it will display 120 C). You will have to have a way to get the sensor to 120 C to fine tune the circuit. Will that be OK?

    All the Best :)

    Dan
     
  9. AlenZGB

    AlenZGB

    174
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    Feb 19, 2014
    Yeah that will be OK :D
    Ill let you know the reading as soon as my friend give me the sensor.

    thanks :))
     
  10. duke37

    duke37

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    Jan 9, 2011
    The classic temperature reference near where you want is boiling water, 100degC

    The boiling point will rise with dissolved salt, you could try to find out the temperature rise with a concentrated solution.

    The resistance of a thermistor is very non linear so you will need to calibrate at 120degC.
     
  11. Supercap2F

    Supercap2F

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    Mar 22, 2014
    I know thats what I meant when I said:

    Dan
     
  12. AlenZGB

    AlenZGB

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    Feb 19, 2014
    You are right. :D
    soo ill have to use cemistry and mix salt with water to boil at 120degC :D
    maybe il get some sensors from work tomorrow, from some VW so that i can get accurate reading.
    i see this will be busy weekend :D
     
  13. duke37

    duke37

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    Jan 9, 2011
    I looked up 'boiling point elevation' on wikipedia and this says 0.17degC with 1% salt solution so you will not get more than 3 or 4 degrees.

    Acetic acid boils at 118degC but you would need to do this outside !

    Thermistors can be described with a suitable equation. The constants can be determined with a thermometer up to 100degC and then the curve can be extrapolated.

    You should calibrate the sensor that you are going to use.
     
  14. AlenZGB

    AlenZGB

    174
    5
    Feb 19, 2014
    Ill get sensor tomorrow and boil it and read the resistance, before and in boiled water. Then ill send some readings.
     
  15. Supercap2F

    Supercap2F

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    Mar 22, 2014
    Type in: "thermistor switch circuit" to google images. There are a lot of circuits out there that will do what you want.

    Dan
     
  16. duke37

    duke37

    5,342
    753
    Jan 9, 2011
    Wikipedia gives an equation that thermistors fit.
    I have a 1989 Maplin catalogue which gives this equation

    ln(Rt1) = ln(Rt2) + B(T2-T1)/(T1/t2)
    where temperatures are in Kelvin
    B values are given for the thermistors they sell and are about 4000.

    You should measure the resistance at various temperatures and fit the values to the equation to find B. Then you can extrapolate to find the resistance at 120degC (393K).
    Use this resistance to set up your display.
     
  17. AlenZGB

    AlenZGB

    174
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    Feb 19, 2014
  18. duke37

    duke37

    5,342
    753
    Jan 9, 2011
    Taking the Bosch data, then B = 3534 and the resistance at 120degC is 70 ohms.

    Bosch data says 5V supply but 1mA maximum. I do not know how this can be done.

    You will need an op-amp to sense the thermistor output and provide say 1.2V at 120C which can be displayed on a simple voltmeter. It may be difficult to get it to track temperature without a log convertor.
     
  19. AlenZGB

    AlenZGB

    174
    5
    Feb 19, 2014
    Guess it will be harder then i tought :/
    its a thermistor not a electric motor, this shouldnt draw more current or am i mistaking ?
     
  20. duke37

    duke37

    5,342
    753
    Jan 9, 2011
    The point is that with a 5V supply and a resistance of 70 ohms, then the current will be 71mA. The maximum current is given as 1mA. Have I read the data wrong?

    One way would be to supply it with 1mA and measure the voltage across it, that would be well below 5V.
     
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