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-50c temperature controller using BS2P? — Parallax Forums

-50c temperature controller using BS2P?

l8_apex_itl8_apex_it Posts: 16
edited 2009-02-10 23:37 in BASIC Stamp
I am hoping to control a chiller as the current analog control system is rather limiting and does not provide tight enough controls for our process. I was originally thinking of using the DS2760 Thermocouple Kit but noticed the range as listed on the device is from 0°C to +127°. So that will not work. One great thing about the DS2760 is that I could easily get special thermocouples per my requirements from Omega. The other option was using the LM34 as I've played around with that before. However, I just found on the specs that the min. temperature is -40C. Since I will be using it between -15C and -50C that is no longer a viable option.

What are some other options? My goal would be to use off the shelf thermocouples.

Thanks,
Scott

Comments

  • Tracy AllenTracy Allen Posts: 6,664
    edited 2009-02-10 00:54
    The AD590 is a good choice. It is rated to -55 deg. Celsius, and it is easy to use as a current source with a linear output of 1 microamp per Kelvin.

    I bet the DS2760 Kit could be coaxed to work. The BS2P would be located outside of the chiller, right, and the DS2760 too. Therefore, the "cold junction" aka "reference junction" would be at room temperature. And the measurement junction, which would be colder than the reference junction in this case, would be down at -15 to -55. The DS2760 itself is capable of measuring both positive and negative temperatures and also both positive and negative voltages on the input where the thermocouples go. I am not sure, but I think the program provided with the kit uses a thermocouple table that covers only positive temperatures, so if you need the negative temperatures, you would have to dig into it. It is not a trivial program. The AD590 would be much easier to calculate.

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    Tracy Allen
    www.emesystems.com
  • Mike2545Mike2545 Posts: 433
    edited 2009-02-10 01:08
    The DS1620 has the range of -55c to +125c.

    Parallax has some sample code to help get you started.

    Mike2545
  • l8_apex_itl8_apex_it Posts: 16
    edited 2009-02-10 23:37
    Thanks Tracy and Mike. You gave me enough information to pursue all three options a bit more.
    I think I will look into the AD590 and DS1620 first. The DS2760 has some advantages and I have used it before. However, I will have to look into the table and see if I have a firm grasp on how to modify it for use with the negative temperatures.

    -Scott

    Post Edited (l8_apex_it) : 2/11/2009 2:13:00 AM GMT
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