TMP007 datasheet(14/55 Pages) TI

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{

}

OBJ

DIE

ƒ V

+ ç

SENSOR

OBJ

DIE

(

)

SENSOR

ABSORBED

RADIATED

OBJ

DIE

= es

Rad

OBJ

Energy

= es

TMP007

SBOS685C – APRIL 2014 – REVISED JULY 2015

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Feature Description (continued)

7.3.4 Object Temperature Calculation

The TMP007 generates a sensor voltage, VSensor, in register 00h that is related to the energy radiated by the

object. For an ideal situation, the Stefan-Boltzman law relates the energy radiated by an object to its temperature

by the relationship shown in Equation 5:

where

•

σ = Stefan-Boltzman constant = 5.67 × 10

-12 W/(cm2K4)

•

ε = Emissivity, 0 < ε < 1, an object dependent factor, ε = 1 for a perfect black body

(5)

A similar relationship holds for the sensing element itself that radiates heat at a rate determined by TDIE. The net

energy absorbed by the sensor is then given by the energy absorbed from the object minus the energy radiated

by the sensor, as shown in Equation 6:

(6)

In an ideal situation, the sensor voltage relates to object temperature as shown in Equation 7:

(7)

where

•

S is a system-dependent parameter incorporating the object emissivity (

ε), FOV, and sensor characteristics.

The parameters S0, A1, and A2 are used in determining S.

•

f(VOBJ) is a function that compensates for heat flow other than radiation, such as convection and conduction,

from nearby objects. The parameters B0, B1, and B2 are used to tune this function to a particular system and

environment.

(8)

The coefficients affect object temperature measurement as described in Table 1.

Table 1. Calibration Coefficient Definitions

COEFFICIENT

PURPOSE

CALIBRATION

COMMENT

FOV and emissivity of object

Application and object

Default values based on black body with

ε = 0.95, and

dependent

110° FOV

A1, A2

Device properties

Factory set

Default values based on typical sensor characteristics

Device properties

Factory set

Default values based on typical sensor characteristics

B0, B1, B2

Corrects for energy sources

Environment dependent

Calibrate in end-application environment

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