TMP007 datasheet(39/55 Pages) TI

39 / 55 page

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

Object Temperature (

SC)

0°C-C

20°C-C

40°C-C

60°C-C

0°C-U

20°C-U

40°C-U

60°C-U

C015

0.00

0.05

0.10

0.15

0.20

0.25

Object Temperature (

SC)

0°C-C

20°C-C

40°C-C

60°C-C

0°C-U

20°C-U

40°C-U

60°C-U

C016

Accuracy

Mean Calibration Error

3 Standard Deviations

(

)

MEAN

OBJ_PREDICT

OBJ_ACTUAL

TMP007

www.ti.com

SBOS685C – APRIL 2014 – REVISED JULY 2015

8.2.1.2.2

Verifying the Calibration

The next step is to use the generated coefficients to verify the calibration, and determine the accuracy of the

system. For common calibration (C) , the same coefficients are used for all devices; in unit calibration (U) the

coefficients are calculated for each device. Common calibration includes device-to-device variation, and thus is

less accurate, but much easier to implement. Unit calibration is more accurate, and eliminates device variation,

but requires more effort to implement. The choice depends on the application requirements for accuracy versus

implementation effort.

Mean calibration error at each point is defined as shown in Equation 13:

where

•

TOBJ_PREDICT is the temperature based on the calibration coefficients.

•

TOBJ_ACTUAL is the known object temperature, measured independently.

•

N is the number of devices in the calibration set.

(13)

The mean error graph (see Figure 54) provides an efficient method of understanding how the systematic errors

vary across the temperature ranges of interest. This graph also provides a means of weighing the benefits and

efforts of common versus unit calibration for a particular application.

Note that calibration does not affect the temporal random noise observed, as shown in Figure 55. The standard

deviation of the temperature error is independent of the calibration if the random error is dominated by the sensor

noise and not external system factors, such as convection and conduction. For common calibration, the total

standard deviation increases because of the effects of device-to-device variation. This standard deviation is

calculated in the usual way, by substituting TOBJ_PREDICT for the mean in the standard deviation formula.

The accuracy is then defined as the mean calibration error plus the random errors from all sources. For this

example application, use the criteria shown in Equation 14:

(14)

The resulting accuracy over TOBJ and TDIE is shown in Figure 10 and Figure 11 for the unit- and common-

calibration approaches, respectively. Clearly, the unit calibration results in higher accuracy, though common

calibration is applicable for many application requirements.

8.2.1.3 Application Curves

Figure 54. Mean Calibration Error, Wide Range Over TDIE

Figure 55. Noise in Temperature Measurement, Wide

Range Over TDIE

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