LM35 (DZ) problem with output

[geobabu]

Hi,
Please help me regarding the problem facing with LM35 (DZ) temperature Sensor interfacing. Normally the LM35 provides an o/p @ 10mV/°C .

I had connected a LM35, V+ to 5V, and with a DMM , Vout pin shows around 2.7V ~ 2.85V, while I am expecting around .26 ~ .29mV @ room temperature. Other thing is when the temperature increases , the voltage is gradually decreasing and vice versa. When I connected a 1K resistor across, Vout & GND, the 2.7V ~ 2.85V range reduced to ~ .54, its decreases as temperature rises.

Also I didn't connect the o/p to any other device like opamp/ADC.

I got the same results with another sensor also. I think, something wrong over here. Please help me to find out the issue.

Thanks in Advance.
Geo

 

[crutschow]

Is the LM35 ground terminal connected to circuit ground? Post a schematic.

 

[groeber0]

Check the pins. I'm betting you reversed Vcc and ground.
It's possible the ones you tried are not dead yet.

 

[geobabu]

no.. its not reversed. and I connected as simple as mention in the datasheet for the Celsius Centigrade measuring
Pin 1 -> 5V
Pin 2 -> Vout (now connected a 1K resistor to the GND)
Pin 3 -> Power supply GND

 

[groeber0]

I don't have any lm35's right now, but I remember this happening: me getting confused by the angle of the which-pin-is-which illustration in the datasheet, and reading several volts from Vout. The chips were connected to 5V and did not die. If all else fails, try it.

 

[geobabu]

anyway I just reversed the connection ..and the Vout is giving around 4.7V. I think now its reversed ..

 

[MikeMl]

Pin out of LM35Dz

 

[geobabu]

thanks Mike for sharing the image. Yes, same pin connection only I had followed. and Vout pin gives ~2.7V @ room temperature.

 

[MikeMl]

Are the parts form National or from a Chinese Copy Cat?

 

[geobabu]

NS's symbol is there on the flat surface.
If its a perfect one, it will only give around ~.25V at room temp. with this simple simple connection , am I correct ?

 

[Vizier87]

a mistake I committed when using the LM35 before is that the figure provided by MikeMl is seen from ABOVE rather than BOTTOM. That means a world of difference.

 

[davenn]

a mistake I committed when using the LM35 before is that the figure provided by MikeMl is seen from ABOVE rather than BOTTOM. That means a world of difference.

his supplied image is BOTTOM view

Dave

 

[Vizier87]

yes that's what i meant in my post. I mistakenly took the figure to be from ABOVE rather than BOTTOM.