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LM35A/LM60 erading correction

SIDDHARTH MOHAN
Genius 3205 points
Other Parts Discussed in Thread: LM60, LM35, LMT70

 need to read the temperature from LM35A/LM60 through ATMEGA328-PU micro controller, i see that LM35 has an error of 1.5deg C and LM60 3-4 Deg C, HOW can this error be reduced to accurate input into the micro controller 

regards

  • 0
    TI__Mastermind 31410 points
    Hi Mohan,

    LM35A and LM60 have a temperature accuracy of ±1.5°C and ±3-4°C respectively as specified in the datasheets. If you want a better temperature accuracy, we have other analog temperature sensors with super accurate ±0.1°C LMT70.

    In order to provide you a correct temperature sensor, I need more information from you.

    1. What type of application you are planning to use with analog temperatue sensors?
    2. What is the hotspot you are tyring to measure the temperature?

    Hope this helps! Please let me know if you have further question.

    Aaron
  • 0 in reply to Aaron Heng
    Genius 3205 points

    Thank you for the reply.

     

    1. We want to check the temperature rise of SMT resistor packages and as of now I have only LM35 available with me hence kindly suggest what hardware and software changes can I do to get accurate reading even with the error specified in the datasheet. I am getting a much higher error that that mentioned in datasheet for LM35. What should be the spacing between the Device under test and LM35. The analog voltage from LM35 is being read into Arduino through ATMEGA328P-PU controller hence kindly suggest software changes I can do to minimize the error due to sensor. Most critical part which I see is the spacing between the LM35 and my SMT resistor (attached image) – plz suggest
    2. Also if I have to interface LM35 with TI MSP430 launchpad – what is the way – I mean can you suggest suitable links/notes which demonstrate the circuit connection and program ?

    Regards 

  • 0 in reply to SIDDHARTH MOHAN
    TI__Mastermind 31410 points
    Hi Mohan,

    Most of our temperature sensors are sensing the element through device’s package and its metal leads. The majority contribution of the thermal path is the leads itself. By looking at your picture, you have a huge gap of thermal gradient from your SMT resistor to the LM35. Basically, you are measuring the temperature of the breadboard as well as the ambient air temperature. You mentioned that there was a large gap temperature error. Do you have the reference temperature? Was the SMT resistor is the thermistor? What is the heat dissipation of the SMT resistor?

    With your current setup, you are still getting the large error due to the heat loss where the difference in temperature between your SMT resistor and the surrounding environment. The tiny SMT resistor will not able to heat up the LM35 which is 5x bigger than the resistor. There is a disconnected heat transfer here.

    My suggestion is to get a smaller temperature sensors equal package size and place them in a enclosed box without the helping element such as air flow. Attach them as close as possible. The best way to clue with together with fast thermal conductive epoxy.

    In my opinion, it doesn't matter if you switch to a different MCU; you will get the same error. If you want to use MSP430 launchpad, you can use the internal ADC provide with launchpad.

    Hope this helps!

    Aaron