imxrt1052 Temperature Sensor Module - temperature reading vs Infra Red probe reading

[Cindy]

Dear expert,

I am checking temperature reading from 2 setups

a) setup - 1: IMXRT1052 on MIMXRT1050-EVK

   use Infrared Thermometer to point to the central of the chip and recorded reading: 

        34 degree Celcius

    software reading: 44.6 [NOTE: using the SDK example code to read temperature ]

    Different in readings = 44.6 - 34 = 10.6 degree C

b) setup - 2: IMXRT1052 on custom design board

     Use Infrared Thermometer to point to the central of the chip and recorded reading: 

            46 degree Celcius

    Use software(TEMPMON_GetCurrentTemperature) to read temperature, software reading: 73.4.

    Different in readings = 73.4 - 46 = 27.4 degree C 

Question:-

I understand that there will be different between the reading from thermometer and the software reading, why the different is so big on SETUP-2?

Thank you!

Best Regards,

Cindy

For your information:-

I am the following library file for temperature monitoring:-

fsl_tempmon.c, .h

I have read AN5215 and have tried 2 equations mentioned in the notes:-

a) original equation (please refer to the attachment)

b) updated equation (please refer to the attachment)

Both equations gives similar results for both setups.

[lucas_cao]

Hi,

There is a potential reason. I see you said you are using the RT1050-EVK, not EVKB. For EVK, it is using A0 silicon, and for A0 silicon, the internal temperature sensor may bot be trimmed.

So i suggest you using 2 custom board test again and compare the resuts.

[Miguel04]

Hi @Cindy 

The custom board is the reason the values are so different  with setup 2, any difference between the EVK and your custom board causes this lack of accuracy.

Best Regards, Miguel.

[Cindy]

Can you suggest what differences can cause this big difference in readings?

Both of the iMXRT core clock frequency on EVK and custom board are the same, at 600MHz.

Can the PCB layout causes this difference?

Thanks!

Best Regards,

Cindy

[Miguel04]

Hi @Cindy 

It is difficult for us to verify the cause of the issue, however, mainly the PCB layout is the cause of this type of errors.

Best Regards, Miguel.