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TMP126: Air flow temp measurement - Response time <20ms

Vineeth CN
Prodigy 20 points
Part Number: TMP126
Other Parts Discussed in Thread: TMP117,

Hello TI Team,

We are now working for a global medical product company (cannot disclose the name now). We are doing an end to end development of Spirometer.

We have a requirement for measuring the air temperature  (Inhaled and Exhaled) in our flow tube. We need a temperature sensor with ~ <20ms response time. It is critical for us to measure the moving air temperature at every 20ms ie, we cannot do averaging(8 samples) and go for sleep for reducing the self heating effect. Our measurement temperature range will be from 20 to 40 degree Celsius. 

Do you have any temp sensor in our company portfolio that can measure the flowing air temperature at ~<20ms? 

Thanks and Regards,

Vineeth

  • 0
    TI__Mastermind 39805 points

    Hi Vineeth,

    TMP126 has a conversion time of 5.5ms, so you can retrieve a new temperature measurement at that interval. Our highest accuracy sensor, TMP117, can also be configured for 15.5ms conversion time, which meets your requirement. The TMP117 will still be more accurate than TMP126 when configured this way.

    You're likely to encounter more trouble with response time than conversion time. Response time is a function of mass and thermal transfer. You should use the sensor with the least mass and mount it on a flex PCB to minimize mass. The TMP117DRV has a mass of 9.5mg compared to TMP126DCK's 7mg.

    thanks,

    ren

  • 0
    Prodigy 20 points

    Hi Ren,

     Thank you very much for your quick help and detailed explanations. 

    I understand the thermal response of the temperature sensor is how fast the device responds to a sudden change in temperature and the temperature sensor response speed is determined by the amount of thermal mass surrounding the sensor. But my concern is on other parameters mentioned in the datasheet. Details below. 

    Multiple conversion and averaging is required for reduced noise in the conversion result. And also for reducing self heating effect we should provide enough stand-by time. In our application we cannot average the results and we need to scan the temp changes continuously at <20ms interval.  

    The thermal response of the TMP117/TMP126 is same for moving air? Our application is Spirometer, so patient will be exhaling through a flow tube and we will be placing the temp sensor in the flow path to measure the exhaled air temperature.  

    I just want to understand these sensors are still feasible for our application? 

    Looking forward for your inputs.

    Thanks and Regards,

    Vineeth

  • 0 in reply to Vineeth CN
    TI__Mastermind 39805 points

    Hi Vineeth,

    You don't need to be concerned about datasheet parameters. The devices are capable of resolving a change in temperature in the 20ms you require. The only question is whether the breath is physically capable of inducing the temperature change in the sensor in the time required. I cannot advise you on this; you will have to test it or simulate it.

    thanks,

    ren