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measuring efficiency of a solar thermal panel


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#1 Max

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Posted 11 November 2005 - 11:49 AM

I want to measure the efficiency of asolar thermal panel, which means recording samplings from four probes (one sample per minute would be enough), with an accuracy of +/- 1C. The temperature range is 0C to 100C. I am a newby in the field, my question is : should I use thermistors or thermocouples, themperatures above 100C should not occur, but it would be nice if the sensor (termistor or thermocouple) could survive higher temperature... Thanks Max

#2 Max

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Posted 11 November 2005 - 01:10 PM

is it possible to this thermistor for my application :

http://www.ussensor....DO-35_inter.htm

Max

#3 LabJack Support

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Posted 11 November 2005 - 01:29 PM

The first thing you should do is search this forum on the term "temperature". You will find lots of topics, and the recommendation that for 0-100 degrees C you use a silicon type sensor such as the EI-1022, LM135, or LM34/LM35. Then you can do searches on "thermistor" and "thermocouple" to find more topics about those specific types. Start with that and see what comes up.

#4 Max

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Posted 11 November 2005 - 02:40 PM

I decode your answer : do your homework and come back with
a more refined question ! B)

Ok, I've searched, and I think that I can rule out the thermocouple.

would this sensor do the thing :

http://www.omega.com...D590&Nav=temd10

Max

#5 LabJack Support

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Posted 11 November 2005 - 04:43 PM

Yes, unless you have mechanical requirements that rule out a semiconductor type of package, I would not use a thermocouple or thermistor. Your range is perfect for a silicon temp sensor.

The part you pointed out could be made to work, but it is not particularly accurate and it has a current output that you would have to convert to voltage. A better choice is the LM34 from national.com. The LM34CAZ is very accurate and easy to use. National will send you a couple free samples from their web site. The LM34 is better than the LM35 because you get more volts/temp, and also because with a single +5 volt supply you get a range of +5 to +300 deg F (-15 to +149 deg C).

Another good option is the EI-1022 sold by us. It works from -40 to +100 degrees C, and comes as a handy probe assembly. The absolute accuracy is not as good, but it can be calibrated to provide good results.

http://www.labjack.com/products.html

#6 LabJack Support

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Posted 15 November 2005 - 12:14 PM

Since the analog input bias currents on the U12 get negative with decreasing voltage, I did some testing with the LM34CAZ connected to the U12 at low temperatures. With nothing added, the LM34CAZ could not measure below 56 degrees F. With a 9k resistor from signal to ground (AI0 to GND), I could measure to 9 degrees F. With a 4.7k resistor I could get below the minimum rated temp of 5 degrees F. Did the same testing with a UE9, which has much lower analog input bias current, and the LM34CAZ did not need any load resistance to reach 5 degrees F.

#7 [email protected]

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Posted 04 March 2013 - 08:14 AM

Since the analog input bias currents on the U12 get negative with decreasing voltage, I did some testing with the LM34CAZ connected to the U12 at low temperatures. With nothing added, the LM34CAZ could not measure below 56 degrees F. With a 9k resistor from signal to ground (AI0 to GND), I could measure to 9 degrees F. With a 4.7k resistor I could get below the minimum rated temp of 5 degrees F.

Did the same testing with a UE9, which has much lower analog input bias current, and the LM34CAZ did not need any load resistance to reach 5 degrees F.



I ran a test with the U12 and a 10k resistor, it got down to 5deg F but it was reading 49 deg F at room temp!


Guys! is there any way to get the full range on the U12?

#8 LabJack Support

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Posted 04 March 2013 - 05:45 PM

I just did a test with a 10k resistor and did not see that it had any effect at higher temperatures. I connected the LM34 to AI0 and added a 10k resistor from AI0 to GND. I pulled on both connections to AI0 to make sure they were both in there securely. I was able to take the other end of the resistor in/out of GND and it made no difference with my 65 degree F readings.


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