LM35 Sensitivity

[TedO]

Hi guys,

Now I have, with the help of Dazz, sorted out the minus temperature readings on my fridge controller using the LM35 sensor connected as per Fig 18 of the datasheet. When I use the LM35DZ sensor in positive temperature applications, the output from the sensor via the PIC to the LCD is very stable, the numbers of degrees change very positively up or down.
What I find now with using the LM35C in the minus range, with the sensor now having two outputs instead of one, is that the display is very jittery. When the number of degrees changes, the readings would sometimes jump and down over 3 numbers ie if the reading is for example -15......then the display will "oscillate" between -14 and -16.
This jittery output is a problem as it triggers the cutoff temperature when the actual temperature has not really been reached by the fridge.
Is this jittery output as a result of the "negative" output being above ground? I have tried unsuccessfully to try and stabilize the output using small caps and resistors on the sensors. Can one stabilize these outputs in software???

Would appreciate it if somebody in the know can assist me with the above.

Thank you
Regards
Ted

[medelec35]

Hi Ted,
Instead of GetInt, you could try GetAverageInt.
Start off with high values like 250 for both entries.

Another way could be using Rolling Average method.
I have found this old thread which may help

Martin

[TedO]

Hi Martin

Thanks so much.........once again you have come to my rescue, I entered the 250 number as suggested and it is absolutely stable as can be, I did not for one moment think about the GetAverageInt option, have definitely learnt from this.

Much appreciated, it feels so good when one can have such experienced people looking at our novice problems and come up with good sound advice!!!

Regards
Ted

[AbhijitR]

Hello! Martin
good evening

I used below solution and it turned out to be life saver for me for the moment, many many thanks.

Instead of GetInt, you could try GetAverageInt.
Start off with high values like 250 for both entries.

Martin

Abhi

[medelec35]

As we have not got the thanks button to use yet.
Thank you Abhi,
I'm glad i have helped you to resolve your issue.
I really appreciate the feedback.