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Temperature sensor — Parallax Forums

Temperature sensor

harry_sharry_s Posts: 7
edited 2007-07-20 04:34 in BASIC Stamp
Hi everyone

I want to make temperature measurements with a BS2. I have an rtd and a transmiter that outputs 4-20ma.
If i use an adc0831 and a 250Ohms resistor am I ok? I read somewhere that I may need a differential adc...

If a want to use a sensor on a chip like ds1620...how far away from the stamp can I place it?? I have to place the sensor a few meters away from the stamp...Is there a better solution??

Thank you

Harry

Comments

  • NewzedNewzed Posts: 2,503
    edited 2007-07-13 11:54
    Harry, if you use an LM34DZ sensor, it can be placed up to 40 feet away.· Be sure to use a 1.2K resistor in series with the sensing lead, and put an .1uf cap as close as possible to the ADC pin you are using.

    Sid

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  • Philip GamblinPhilip Gamblin Posts: 202
    edited 2007-07-13 14:30
    This sounds a lot like what I do at work all day with·the exception of the Stamp. I should be more up to speed on the particulars, but I believe·the trasmitter you are using will want 24 volt DC loop power on the 4-20 mA loop. The ds1620 is a much more appropriate (easier to implement) application for the Stamp. It is a serial device, while I'm sure there is a physical limitation to the distance, I don't know what that is.

    Happy Stampin'smile.gif
  • harry_sharry_s Posts: 7
    edited 2007-07-16 08:12
    Thank u both for your answers...

    After some thinking I prefer the digital output of the ds1620...

    how can I find the distance limitation?
  • FranklinFranklin Posts: 4,747
    edited 2007-07-16 14:39
    You would look at the data sheet for the device and find the spot that tells you the maximum distance at which the device will function.

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  • Tracy AllenTracy Allen Posts: 6,664
    edited 2007-07-16 16:11
    A few meters should work fine with the DS1620 on the BS2. Be sure that you put a bypass capacitor between the power supply pins on the DS1620. Aside from that, the limit on cable length is due to the capacitance of the cable. With shiftout on the BS2, that is similar to the limit for RS232 at 9600 or 19200 baud. But don't forget the bypass capacitor, 1uF tantalum.

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  • denodeno Posts: 242
    edited 2007-07-20 03:55
    Hello to all...regarding the distance one can remotely wire a DS1620 temperature sensor, I have one running 100 feet away.· I am using a 5 wire, 22 gauge cable.· I have put a .1ufd, and a 22ufd across 4 and 8 of the DS1620.· The 1k resistor in the DQ line is back mounted on the PCB, not at the DS1620 location.

    The five wires are: DQ, CLK, RST, 5volts, and ground.

    Just in case someone wants to know....

    Deno
  • Philip GamblinPhilip Gamblin Posts: 202
    edited 2007-07-20 04:34
    That is good to know. I often thought about using serveral for mapping thermal issues at home
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