Long leads on a LM34

Gemsem

I'm working on a temperture sensor for a solar heating project using a LM34 and am wondering which of the following options is possible:
1. Mount the A/D near the stamp and run leads (about 25 ft) to the LM34.
2. Mount the LM34 on the A/D and run leads to BS2.
3. Mount the LM34, A/D and BS2 togather and run signal wires from the BS2 to my PC.
4. Use some other sensor

Fe2o3Fish

Certainly all are possible. Which would be "best"?? That's the question.
At 25', given reasonable wire gauge, the resistance of the wire will be
fairly small and probably won't matter so long as the wire gauge isn't
too small. At 25 or 26 gauge wire, for 25-feet, the total resistance
will be about 1-ohm. You should worry about this ESPECIALLY if you're
sending DC current for power to the sensor over that 25-foot length.

On the other hand, depending on layout and the environment around the
wire path, you can get a fair bit of noise. It's easier to clean up a digital
signal than it is an analog signal. Having said that, the using digital to go
the distance would probably be better so having at least the A/D converter
near the sensor would be better. If you can afford the space and available
power remotely, put the BS2 there as well and pump RS-232 back to your
PC over the 25-feet cable. RS-232 will be more noise immune than TTL or
logic level signals.

Personally, I prefer the later rather than the former method.

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-Rusty-
--
Rusty Haddock = KD4WLZ = rusty@fe2o3.lonestar.org
**Out yonder in the Van Alstyne (TX) Metropolitan Area**
Microsoft is to software what McDonalds is to gourmet cooking

Newzed

I have run LM34s as far as 37 feet from the ADC with no problem, using 22 gauge solid copper.· Be sure you put a 1.2K resistor in series with the LMs sensing lead, and a .1uf bypass as close·as·possible·to the ADC pin the LM is using.
.

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Sid Weaver
Do you have a Stamp Tester yet?
http://hometown.aol.com/newzed/index.html

·

Jonathan

Gem,

I have an LM34 in my hot tub, about 40-50' from the controller. I use a 150uF cap on the output. Since the temperature changes very slowly in a hot tub, the large cap smooths the output without interfering with readings. If you are reading rapid changes, the large cap would be a problem. Use as large a cap as you can without messing up your readings. I have the resistor mentioned above in series with the sensor, soldered right to the leads of the sensors. Has worked fine for years.

Jonathan

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