TMP007 datasheet(43/55 Pages) TI

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SENSOR

OBJ

DIE

det

cos

TMP007

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SBOS685C – APRIL 2014 – REVISED JULY 2015

8.3 System Examples

8.3.1 Use of NEP, NETD, and Responsivity in Estimating System Performance

It is often necessary to estimate system performance as part of the design process. A key system parameter is

temperature accuracy for a given set of parameters. Table 16 lists example parameters for estimating system

performance.

Table 16. Estimating System Performance Parameters

DESIGN PARAMETER

EXAMPLE VALUE

COMMENT

Object distance

10 mm

Distance to object

Object diameter

15 mm

Object size and geometry

0.95

Object emissivity

TDIE

23°C

Die temperature

TOBJ

30°C

Maximum expected object temperature

FOV

110°

Field of view subtended by object

Responsivity (R0)

10.8 V/W

Responsivity for TDIE = 25°C, θ = 0°

Responsivity (R)

9 V/W

Responsivity for 110° FOV

Sensor rms noise

0.20 µV

RMS sensor noise at TDIE = 25°C

NEP

30 nW

Thermal power equivalent to rms sensor noise

Conversion rate

1 SPS

SPS = samples per second

The system accuracy is a function of TOBJ, TDIE, ε, and radiation transfer.

The radiation transfer factor is system dependent, and is affected by the object distance and geometry (for

example, planar versus curved surfaces, or presence of lenses). For an planar object perpendicular to the

detector axis (see Figure 19), the radiation transfer follows the well-known sin2(

θ) result. This expression can be

used with a radiation transfer function responsivity value of 9 V/W to estimate system performance.

Because of the angular dependence of the TMP007 detector response, a more accurate representation for the

same radiative transfer function geometry is shown in Equation 19:

where

•

R0 is the responsivity of the detector to a point source at an angle normal to the detector (θ = 0 in Figure 19.

R0 has a value of ~10.8 V/W at 25°C.

(19)

The responsivity value of 9 V/W is based on a system with a 110° FOV.

Using the device-specific radiation transfer expression and R0, the detector response is shown in Equation 20:

where

•

εOBJ is the emissivity of the object (0.95).

•

σ is the Stefan-Boltzmann constant (5.67 × 10

-12 W/(cm2K4).

•

TOBJ is the object temperature (273 K + 30°C).

•

TDIE is the detector temperature (273 K + 23°C).

•

Adet is the detector active area (1.09 × 10

-3 cm2)

•

θ is the half-angle subtended by the object as viewed from the detector.

•

R0 is the responsivity (~10.8 V/W for the specified temperatures).

(20)

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