Problem encountered when using LM35DZ

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cjhaw

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Hi, I am new in using the LM35DZ. I had encountered when measuring a temperature of boiled water by using the connection of basic centrigrade temperature sensor (Fig 1) from LM35 data sheet. Supposed the temperature measured by thermometer is more than 90 'C. But the measured temperature from LM35 is 55 'C which is shown in multimeter 550 mV.

Is there any solution to improve the result? I hope that I can get help from you all.

Thank you.
 

hi,
I assume you powered the LM35 from 5V thru 9v.??

How did you bring the LM35 body into contact with the boiling water.?

Usually they are accurate to +/-0.5C,
 
ericgibbs said:
hi,
I assume you powered the LM35 from 5V thru 9v.??

How did you bring the LM35 body into contact with the boiling water.?

Usually they are accurate to +/-0.5C,
Click to expand...

Hi, I used power supply with only 2V to tune until 280mV which indicate the room temperature. I didnt tune it to 4V or more because the multimeter will show higher value of voltage output which is not same as room temperature. just contact the top surface of LM35 on the surface of aluminium cup. I also tried to immersed the body of LM35 into the boiled water. Is there any solution?
 
atferrari said:
You did the test at sea level or up there somewhere in the mountains?
Click to expand...

I did the experiment with the room temperature of 28 'C, sea level. I also used thermometer to measure the boiled water. By right the divice should show the result near to the thermometer. Thanks.
 
Angry Badger said:
Hi,

Are you applying sufficient supply voltage?

**broken link removed**

**broken link removed**
Click to expand...


Hai, thank you for the post. The figure in attachment is the 2 ways I used to connect the LM35 to power supply. The left one show the direct connect of LM35 legs to the power supply. The second one I just connect the two V+ and V- to power supply then from the power supply, the V- connect to GND.

I actually try to follow the value in data sheet. But with the connection, when I tuned my voltage input to 4V, I need higher current (could be up to 0.3 A) and the LM35 itself is getting very hot and give high voltage output than expected. Is there anything wrong with my connection? Thanks.
 

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Last edited:
I use the LM34, TO-92 package (same device except it reads in F instead of C) right out of the box with regulated 5 volts. Temp readout on DMM will constantly track within .5 degrees my $500 indoor and outdoor thermometers.

Generally, if a part is behaving irradically, it isn't the part.
 
eric: you are fast replying while I manage to find the options. Yah, should be in microamps but when I increasing the voltage the CC light is on back from power supply. Is there any problems? Or is it better if I use three 1.5 V of battery to do the measure? The attachment is the power supply I used.
 

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cjhaw said:
I posted my connection of LM35 as well.
Click to expand...

Where did you get those connections? Attached is the proper connection from the LM35 data sheet. Very simple. Plus and ground from your power supply, DMM red probe to out and black probe to ground. No problem.
 

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Re-reading

cjhaw, I think that rereading the datasheet again will show you what you are not doing properly.

Just in case you like to see a more complete design (still working after 10 years) peek here **broken link removed**

Go to Circuits and look for Politemp832.

Now that I think of it, you did not show any complete circuit yet.
 
Hi there, thank you for all of you help. I made the correction of connection of the circuit.

Actually, I made two mistakes before that. First is I thought the LM35DZ in data sheet is top view (didn’t notice there is a ‘BOTTOM VIEW’ there. The second mistake is I misunderstood the connection shown in Figure 1. Next time I will be more careful.

The V+ of LM35DZ should connect to + at power supply whereas the GND connected to -. Then use multimeter to connect at GND and Vout of the LM35DZ. Logic result will then be shown on the multimeter. Haha.

Many thanks for you all. Have a nice day
 

Hi, thanks for the website posted. I will refer to it
 
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