LM35 data aquisation issue

[dharanikumarsrvn]

i am using a LM35 Ic temperature sensor along with a ADC to detect temperature. LM35 will give a output of 0.35V for 35degC (0.01V for 1degC). The problem i am facing is whenever i connect the LM35 ouput pin to ADC input channel, the output of the LM35 changes to 2.3V. Is there any loading effect by the ADC which causes the change in LM35 output?

 

[crutschow]

The loading should not be a problem.

Post your complete circuit.

 

[schmitt trigger]

Is the ADC a stand-alone device or is it part of a microcontroller?

In the latter case, are you setting the port correctly? With today's controllers, most ports can be congifured as input/outputs, digital/analog, and can have pullups/pulldowns.

A simple experiment you can do is substitute the sensor with a potentiomenter, and verify the behavior.

 

[mretsh91]

I implemented a similar circuit couple of years ago, and it worked correctly I don't think it is a loading problem

 

[dharanikumarsrvn]

apologies for my late response. I have replaced sensor with a potentiometer and it works fine. My ADC is a part of Chipon CC2430 Microcontroller (a zigebee wireless transreciever). The Vcc supply to the LM35 and GND are drawn from the microcontroller lines itself.

 

[neddie]

As far as I can recall , the LM35 could be prone to oscillations. check this is not happening.(I assume you have a scope) Check the rf from the tranciever is not
screwing up the LM35 as well. Put plenty of filtering on the supply lines , maybe a ferrite bead and cap will do.
Just my 2c :0)
Cheers
Neddie