PT100 to 0-10V analog input

Discussion in 'General Electronics Chat' started by kop, Oct 19, 2007.

  1. kop

    Thread Starter Member

    Oct 19, 2007
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    Can anyone help me make a circuit, so as I can connect a 2-wire Pt100 to an 0-10V analog input or to a 24V digital input (with a ADC circuit) of a plc???
    Sorry for my engish...!
     
  2. cumesoftware

    Senior Member

    Apr 27, 2007
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    2 wire Pt100? What is that?
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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  4. kop

    Thread Starter Member

    Oct 19, 2007
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    Right SgtWookie! I'm talking about PT100 Platinum Resistance Thermometer.
    Can anyone help make a circuit (transmitter or tranducer), so as I can connect a pt100 to an 0-10V analog input or a 24V digital input of a plc?
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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  6. kop

    Thread Starter Member

    Oct 19, 2007
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    Thank you very much beenthere, but can you help me more please?
    Which of this circuits converts the calibration of pt100 to 0-10V?
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    None of those do, as shown. You would have to add another amplifier stage.

    Start with figure 4 on that page. Add another op amp from the output. Use appropriate components to get the gain you need to scale the range you want to measure to values reading 0-10v. Read the documentation for the op amp you're going to use.
     
  8. kop

    Thread Starter Member

    Oct 19, 2007
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    Can you help me a little bit more please...?
    What is your opinion for this beenthere....?
    Thank you for your replies guys!
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    How can we help you? You haven't given us the temp range that you want to measure.

    That's going to greatly affect the design of the amplifier stage.
     
  10. kop

    Thread Starter Member

    Oct 19, 2007
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    I want to measure temp between -50C - 200C, or if it is easier between 0C - 100C.
     
  11. kop

    Thread Starter Member

    Oct 19, 2007
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    Any advice please....?
     
  12. thingmaker3

    Retired Moderator

    May 16, 2005
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    Calculate minimum and maximum Vout from your MAX4236 based on the temperature range you choose. Compare this to the output range you choose in order to know the gain and offset (if any) of the additional amp stage.

    Right now there are four possibilities based on what you have told us so far. You need to narrow the field by choosing your requirements.
     
  13. kop

    Thread Starter Member

    Oct 19, 2007
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    Thank you thingmaker3! Can you help me a little bit more please? Which mathematic types should I use in order to make the choice of resistances?
     
  14. thingmaker3

    Retired Moderator

    May 16, 2005
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    Which resistances?:confused:
     
  15. kop

    Thread Starter Member

    Oct 19, 2007
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    I must change the resistances in the following circuit so as I can have Vout=0-10V. I must change Vin=12V too! Any idea?
     
  16. thingmaker3

    Retired Moderator

    May 16, 2005
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    You have not specified your temperature range yet. Pick one. Until you make that decision, no one can help you.
     
  17. kop

    Thread Starter Member

    Oct 19, 2007
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    The temperature range that I want to measure, is between -100 Celcius degrees and 200 Celcius degrees. The following circuit gives 0.97V-2.97V Vout, with 5V input.[​IMG]
    If i change the input to 12V, will i have bigger output than the output that gives the circuit with 5V input?
    I have one more problem too. I can't find MAX4236 at the stores to buy. They told me that they don't have maxim's amplifiers. Can you give me a type from another amplifier that can helps?
    Sorry for my english!
     
  18. kop

    Thread Starter Member

    Oct 19, 2007
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    Any help please....?
     
  19. thingmaker3

    Retired Moderator

    May 16, 2005
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    Using the formula supplied by Maxim in the link provided by Beenthere, we see that o/p is directly proportional to V1. If V1 is changed from 5v to 12v then Vout will change from 0.97V-2.97V to 2.33V-7.13. This would be in the 0-10V range you specified as i/p for your PLC. For a wider range of Vout with 12v as V1, alter the values in the formula supplied in the link.

    Instead of playing guessing games with what components you can get locally, why don't you choose either of these options:
    1) order the Maxim amp online, or
    2) let us know what amps you have access to.
     
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