• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 1 answer
  • Subscribers 31 subscribers
  • Views 510 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TMP432 temperature results variation

Karthick ph1
Intellectual 750 points
Other Parts Discussed in Thread: TMP432

Hi there,

I'm working with TMP432 temperature sensor for reading the temperature measurements within the span of -30 to +90degC for our application.  I have done the implementation and able to read the temperature values from tmp432.  However, I noticed that the results are not bound to within +-1 deg C accuracy as mentioned in the datasheet.  Also, I observed that the temperature error is slowly increases with the ambient temperature.  I attached the results for your reference.  Please note that the comparision is done using precised PT100 RTD and tested in thermal chamber.

We are using 2N3906 transistor in GND collector connected mode and the auto n-factor is enabled.  It will be great if you have some of the suggestions to get the accuracy right. 

Regards,

Karthick

7875.ti_tmp432_results.xlsx

  • 0
    Intellectual 750 points

    Is there any TI experts can resolve this problem????  there is no response for this post yest...

  • 0
    TI__Expert 7945 points

    Hello Karthick,

    Thanks for posting detailed information of your findings. I have analyzed and re-attached your data to correlate with  the what I'm about to explain you.4300.tmp432_results.xlsx

    There are 2 things that are affecting your accuracy here:

    1.Average n-factor based on your pt100 setup is 1.0035. Please refer to Table 11 of the data sheet and adjust the n-factor register setting to (hexadecimal)0x08 accordingly. This should considerably increase the accuracy of TMP432.

    2. Response time: Due to the thermal resistance of the BJT because to packaging and possibility of lack of a good thermal connection with the thermal chamber, it seems like the response time of TMP432 is slower compared to PT100. You may observe this effect in comparision chart in tab3 of the excel sheet. Please make sure that BJT is attached just the same way as the PT100 is connected, in terms of its thermal connection and location in the chamber.

    Do let me know how it goes.

    Best Regards,

    Abhi

  • 0 in reply to Abhishek Muppiri
    Intellectual 750 points

    5758.tmp432_ti_forum.xlsxHi Abhi, thanks for your observations and suggestions to improve the accuracy of temperature for tmp432.

    Before reading Your response I was trying to correct the n-factor of the transistor 2N3906.  Then, I read the datasheet completely and I had seen that the default n-correction factor in GND collector connected mode is 1.000 (mentioned in table no.10)....Next, I did correction for n-factor in the software as 0111 ie beta correction disabled and it is now selected to 1.008....For this adjustment I have monitored the results and attached for your reference.

    questions:

    1) Is that the did configuration is correct for n-factor adjustment.  I never seen in the datasheet that describes about this configuration.  Only I seen is "When the beta compensation configuration is set to 1000 (beta compensation is enabled) and sensor is GND collector-connected."----in page no.23

    2)Why the table no.11 is considered only for diode-connected mode?

    3) Is GND collector-connected mode configured to beta compensataion disabled mode?

    4)If Diode connected mode is connected and beta compensation is disabled...I get erratic results..Why?

    5) Why the attached results at various temperature range gives different swings(in - and + variations)..Do we have any point to remove such errors and get minimal linear errors(within +-1 degC) throughout -20 to +70 deg C.

    Please clarify.

    Thanks,

    Karthick

     

     

  • 0 in reply to Karthick ph1
    TI__Expert 7945 points

    Hello Karthick,

    Please understand that Beta compensation and n-factor correction are 2 different things. You can modify the n factor correction register irrespective beta and irrespective of whether you are in  Diode or Collector ground configuration. Please understand the following things:

    1. Automatic Beta correction is only applicable to Collector ground configuration (1XXX )

    2. Beta correction is helpful for BJT's with very low gain(hfe). 

    You do NOT need to worry about adjusting Beta of your transistor. 2N3906 transistor has a Beta of 100-300 so please don't worry about adjusting the beta.

    All you need to change is the n-factor to a suitable value (like i explained in my earlier post) based on your RTD output and it should get good accuracies.

    To answer your question 4: When you changed from Collector ground to Diode configuration the n-factor of transistor may also need to be adjusted to get the best possible accuracies.

    To answer your question 5: I see that the error is well within the temperature spec of the datasheet.Did you add the Cdiff (differential cap) as shown in figure 25. of the data sheet?

    I hope my explanation helped!

    Best Regards,

    Abhi

  • 0 in reply to Abhishek Muppiri
    Intellectual 750 points

    Hi Abhi, Thank your for your response.

    I need clarifications regarding the below questions.  Desperate to hear from you.

    1). Is this possible to set the GND collector connected sensor to beta compensation disabled?

    2). If above statement 1 is true then, it should cancel the resistance upt 1kohms right?

    We did testing based on above statements and connected 470 ohms as series resistance with GND collector connected sensor in beta compensation disabled mode it can't read the temperature results....only throws 0 as read value......

    Then we connected 240 ohms as series resitance and it works.....

    Also, If sensor is operating in diode connected mode with beta compensation disabled it doesn't works.... why???

    please suggest.

    Thanks,

    Karthick

  • 0 in reply to Karthick ph1
    TI__Expert 7945 points

    Hello Karthick,

    Yes you can disable beta correction by configuring '0111'in Beta compensation register,although I don't see the use in adjusting beta compensation for your PNP transistor (for the reason explained in my previous post). Please note that when you change it to manual mode, TMP432 treats it as Diode configuration even though it Ground collector configuration. This will not improve your accuracy and I don't recommend you doing this and this. You don't need to play with Beta Correction - given the specs of your transistor and please stick one configuration.

    Series resistance cancellation applies to both Diode and Ground collector configuration it has nothing to do with Beta compensation. As long as the overall wire resistance is <1KOhms there shouldn't be an issue. Is there a reason why you are adding Series resistance? 

    Can you reset the part when you change the configuration from Ground collector to Diode and let me know if you still get the same error. 

    Your error seems to be within the data sheet specifications and I'm not sure what you are trying to achieve here. Did you correct the n-factor as per my previous post, did your results improve?

    Thanks,

    Abhi