strange LM35 output

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#1
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Hello, I just received 5 LM35DZ temperature sensors. I was quite happy till I tested them and saw that the output voltage doesn't make sense. I powered them with 5 volts and the output is 4.14V in all of them. The temperature is around 20 degrees. As far as I know the Vout should be around 0.2V at this temperature(20*10mV).

Did I buy garbage or someone has any different idea?

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Any chance that you mixed up the top view and bottom view of the TO-92 package?

 

In consideration of others, please RTFM!

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Post a photo of your set up.

Does the voltage change when you warm the sensor between your fingers?

What did you use to measure the voltage? x10 Scope probe?

JC

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the set up is the simplest as follows. Vs is 5v from arduino mega.
https://encrypted-tbn3.gstatic.c...

I measured de voltage with a multimeter and with arduino software using an analogic input. both readings are the same. I heated the sensor with my fingers but nothing changes.

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Quote:
I heated the sensor with my fingers but nothing changes.

That suggests it is a voltage reference.
Still, nice score.

No RSTDISBL, no fun!

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Brutte, I don't understand your suggestion. Do you mean I should change the chip voltage reference? But the Vout shouldn't be 0,2V anyway?

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The photo of your setup clearly indicates that you have swapped pin 1 with pin 3.

 

In consideration of others, please RTFM!

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osaka wrote:
the set up is the simplest as follows. Vs is 5v from arduino mega.
https://encrypted-tbn3.gstatic.c...

I measured de voltage with a multimeter and with arduino software using an analogic input. both readings are the same. I heated the sensor with my fingers but nothing changes.

Show us a Picture of your breadboard. A drawing of pinout is not helpfull. I also think you have swapped pin 1 and 3. Try to fix that.

Peter

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today I bought an lm35 for 2 euro!! very expensive comparing with the ebay purchase of 5pcs for 3.5$!!

I connected it directly and reacted as it was supposed.
I swap the new with the olds... and the voltage is 0.2V with the new and 4.14V with the olds.

I heated the new sensor and works right.

I think I definitely bought a very chip garbage.... :-(

sorry for not posting the picture. With this info is proved that the connection was right.

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Quote:
4.14V with the olds.

Ok, so could you check if these are not "restriped" PNP transistors or darlingtons with base pulled by DVM?
It seems that in your TO-92:
    1 is (E) emitter, 2 is (B) base and
    3 is (C) collector.
Just use an el-cheapo DVM that has hfe. Does it show any reasonable value? Do you own such thing?
If not - switch to diode test, measure all 6 voltages and report.

No RSTDISBL, no fun!

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osaka wrote:
I think I definitely bought a very chip garbage.... :-(

Bad luck. Sometimes there is little difference between cheap and cheat. :!:

I think Brutte could be right: a GP PNP would explain your Measurement.

Peter

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http://upload.wikimedia.org/wiki...

According with the pin number of the image in the link and using the diode test:
negative to 1 and positive to 2=1.131V
negative to 1 and positive to 3=1.101V

negative to 2 and positive to 1=0.721V
negative to 2 and positive to 3=0.567V

negative to 3 and positive to 1=1.022V
negative to 3 and positive to 2=0.870V

I have hfe tool but... I don't have any idea how to use that.

Have you ever used an LM35DZ?what voltage should be measured at Vout pin for 20 ºC?

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I have no idea what that device is. Not a BJT, not a MOSFET, not a JFET.
Did you initially test those with something that had limited current? Because if you applied 5V between emitter and base then these were BJT transistors.

Quote:
Have you ever used an LM35DZ?

I am not sure if that was DZ but sure, I have used LM35 many times. However, I do not have those now.
Quote:
what voltage should be measured at Vout pin for 20 ºC?

IIRC it should have been about 200mV above GND pin when Vcc is above 4V. It has an open emitter output (can only source current but cannot sink).

No RSTDISBL, no fun!

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Ok, thank you to all the helpers. Let's conclude...I received some devices labeled as LM35DZ that weren't LM35, and that was the reason why they didn't work.

End of story :-)