LM35 temperature chip

[SteveL]

My previous post concerning thermistors resulted in my sending a thermistor to NI (UK). The engineer wanted to have a go at making it work with a USB-6008.

He is still working on the problem.

In the mean time I need to get an experiment working for our undergraduates to play with in 4 weeks time. I thought I'd try the LM35 because it needs only a 5V supply to work. Sure enough; I had it woking within 5 min's and was getting a reading (10mV/degree C) on my multimeter. OK I thought, connect it to an input on the 6008 and use LV express to create an RSE input: simple!

NO! it gave a constant 3.3mV out, no matter what the temperature. So I disconected it from the DAQ and it worked again. Try it on a different input; same result. Check NI developer forum and discover that it is a known problem with several users. I read all of the messages that had been sent and found one from NI that suggested 2 things. The first one didn't work and the second one tried to explain how to wire it but didn't give a circuit diagram.

Unless anyone has had any experience using the LM35DZ with the 6008 I will have to abandon the temperature experiment.

Anyway, I am going to try and get an electret microphone to work with the 6008 today: I really hope this works (-:

Steve Lawson

P.S although the 6008's were cheap (we bought 30) I am begining to wonder if it would have been cheaper in the long run to go for a better unit.

[peteski]

My previous post concerning thermistors resulted in my sending a thermistor to NI (UK). The engineer wanted to have a go at making it work with a USB-6008.

He is still working on the problem.

Steve,

Did you see the response I posted to your Thermistor inquiry? If not, check it out. In fact, if you need a undergrad experiment, perhaps trying to create a calibration curve with known resistances and checking the results could be a good exercise.

-Pete Liiva (aka peteski)

[thomas2609]

ZITAT(SteveL @ Oct 10 2006, 10:39 AM)

My previous post concerning thermistors resulted in my sending a thermistor to NI (UK). The engineer wanted to have a go at making it work with a USB-6008.

He is still working on the problem.

hi, i know the problem, i guess it depends on the input circuit of the 600x (see http://www.ni.com/pdf/manuals/371303e.pdf page 10) compare with http://www.ni.com/pdf/manuals/371022g.pdf page 37;

a workaround to connect the lm35 to the 6009 would be to use an external power source like battery or other dc power supply.

i did that with a patery pack like http://www.mercateo.com/p/115-970332/Batte...XLR03_AAA_.html (~1,50€)

4 AAA (6V) are ok for the LM35 (supply voltage acording to the data sheet 4 - 30V)

with this configuration you can use the differential mode to measure the temperature.

Bat+ connect to +Vs

Bat- connect to GND and AI4

Output connect to AI0

I am sure there is a better solution, but at least it works ;-)

cheers thomas

[AnalogKid2DigitalMan]

It can be a bear, your are not the only one- battery power does seem to work as thomas2609 pointed out (see Mark's post in 2nd page of this thread). It seems like the front end of the 600x's input is the culprit.

http://forums.ni.com/ni/board/message?boar...ding&page=1

[thomas2609]

ZITAT(AnalogKid2DigitalMan @ Mar 28 2007, 11:45 PM)

It can be a bear, your are not the only one- battery power does seem to work as thomas2609 pointed out (see Mark's post in 2nd page of this thread). It seems like the front end of the 600x's input is the culprit.

http://forums.ni.com/ni/board/message?boar...ding&page=1

as an alternative i figured out a way to drive the lm35 with the ni600x +5V internal power.

see http://cache.national.com/ds/LM/LM35.pdf ( >> FIGURE 5 <<)

so you need 3 additional resistors and can measure in differential mode. (very nice!) ;-)

as i need the lm35 only for demonstration i don't worry how exact resistor values influence the accuracy of the measurement (i used 220 Ohm instead of the 200 Ohm).

my guess is that the error will be >10%

i hope that i could provide some help on the topic

cheers thomas