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Will a LM335Z work as a LM34? — Parallax Forums

Will a LM335Z work as a LM34?

Microman171Microman171 Posts: 111
edited 2006-02-07 01:27 in Learn with BlocklyProp
I want to build my own Industrial Control kit so I can make the heater but in the NZ this is as close as I can get to the Temperature sensor IC: LM335Z smile.gif Will that work as the same thing?? Please ask about the question if there is somthing you need to know... I'm desperate here sad.gif
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Post Edited (Microman171) : 2/11/2006 4:58:09 AM GMT

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-02-06 17:50
    You should probably edit your subject line so people know what your post is about.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2006-02-06 19:15
    · The temp sensor provided in the Industrial kit is a LM34; its output is 10mV / deg. Fahrenheit.· The LM335 has an output of 10mV / deg. Kelvin.· So, NO, they aren't swappable.
    · You may be able to get hold of an LM35, all part of the same family -- its output is 10mV / deg. Celsius.
    · You should look up Kelvin, Celsius, and Fahrenheit.· A change of 1 degree Kelvin is the same as that of 1 degree Celsius.· However, Kelvin is referenced to "absolute zero", but 0 deg. Celsius is the freezing point of water.
    · If you're resourceful, you should be able to "re-tool" the program example to work with the LM335 or LM35.· I think that the values/outputs of the LM35 might be more manageable.

    ******
    Celsius -- from freezing to boiling are 100 degrees [noparse][[/noparse]sensor deviation = 1,000 mV]
    Fahrenheit -- from freezing to boiling are 180 degrees [noparse][[/noparse]sensor deviation = 1,800 mV]

    Post Edited (PJ Allen) : 2/6/2006 7:19:31 PM GMT
  • Andy Lindsay (Parallax)Andy Lindsay (Parallax) Posts: 1,919
    edited 2006-02-06 19:30
    Well, the LM335 is not a “drop-in” replacement for the LM34, but it can be made to work. Whereas the LM34 has an output voltage that’s proportional to the degree-Fahrenheit temperature, the LM335 has an output current that is proportional to the Kelvin degree measurement. However, the LM335 datasheet http://cache.national.com/ds/LM/LM135.pdf also shows how to put a resistor in series with the sensor to convert its current to voltage output. (See left circuit in Typical Applications on page 5.) So long as you use the voltage output circuit from the datasheet instead of what’s shown in the book, and so long as you adjust your code for degrees-Kelvin instead of degrees-Fahrenheit, the experiments should still work.

    Note: Applied Sensors, which is available for download from www.parallax.com -> Downloads -> Stamps in Class Tutorials, demonstrates a more effective way to measure the LM335. The sensor it uses is the AD592, but the principle is the same.
  • Microman171Microman171 Posts: 111
    edited 2006-02-06 19:50
    Thanks guys

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  • Microman171Microman171 Posts: 111
    edited 2006-02-06 20:05
    I figured out the formular to convert kelvin to celsius:

    C = K - 273.15

    So the BS2 should find that easy smilewinkgrin.gif

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  • Tracy AllenTracy Allen Posts: 6,658
    edited 2006-02-06 20:21
    The LM335 has a voltage output of 10 mV per Kelvin, while the LM334 has a current output proportional to Kelvin, and the scale constant is set by one resistor. I see that Dick Smith carries both.

    When the AD592 became hard to find for a while, I wrote up an article about how to use the LM334 and a resistor to output 1 uAmp per Kelvin (the same as the AD592). www.emesystems.com/EarthM/TK334fab.pdf. That can be used with the RCtime circuit in Applied Sensors.

    The thing about Kelvin is the 273 degree offset. The output of the LM335 at 0 Celsius is 2.73 volts. That is not a problem with a 12 bit AD converter, but it might be an issue with an 8 bit converter, depending on how the reference is set. But in theory, it is simply a matter of subtracting the offset, and you could use the LM335.

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    Tracy Allen
    www.emesystems.com
  • Microman171Microman171 Posts: 111
    edited 2006-02-07 01:27
    I've just looked at the DSE website and I cant find the LM334 Sensor in your article would the LM335Z do the same thing??

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