SNOAA47A September   2024  – October 2024 TMP116 , TMP117 , TMP119

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Sensor - Object Surface Thermal Resistance and the Importance for Measurement Precision
  6. 3Testing
    1. 3.1 Hardware Setup
    2. 3.2 Test Setup
    3. 3.3 Test Method
      1. 3.3.1 Measurement Results
  7. 4Thermal Parameters Calculations
  8. 5Summarizing and Interpreting Test Results
  9. 6Summary
  10. 7References
  11. 8Revision History

4 Thermal Parameters Calculations

If the DUT temperature change is known as the corresponding dissipated power changes, there is the possibility to calculate the thermal resistance (RT​) between the sensor and the thermal head.

This parameter is calculated as:

Equation 2. R T = T 1 - T 2 P 1 - P 2

where

  • P1 and P2 are the dissipated power on step 1 and 2 in Section 3.3
  • T1 and T2 are sensor settled temperature on step 1 and 2 in Section 3.3

Estimating the 95% of step final temperature as a 3×τ point, it is possible to estimate the system time constant. Despite this self-heating and cooling process not fully matching the ideal Gaussian curve, the time constant remains a convenient way to estimate the process speed. Knowing the time constant and thermal resistance (RT), there is the possibility to calculate the sensor's effective thermal mass for each soldering case as:

Equation 3. MT=τRT

There is importance in understanding that Equation 3 calculates the effective thermal mass, which is larger than the package thermal mass, because thermal mass also includes the connected PCB area around the soldered device.