MLX90621 datasheet(2/44 Pages) MELEXIS

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MLX90621

16x4 IR array

Datasheet

39001090621

Page 2 of 44

Datasheet IR16x4

Rev 3.0

15 September 2016

General Description (continued)

The results of the infrared sensor measurements are stored in RAM:

•

15...18-bit result of IR measurement for each individual sensor (64 words)

•

15…18-bit result of PTAT sensor

Depending on the application, the external microcontroller can read the different RAM data and, based on the

calibration data stored in the EEPROM memory, compensate for difference between sensors to build up a thermal

image, or calculate the temperature at each spot of the imaged scene.

These constants are accessible by the user microcontroller through the I2C bus and have to be used for external post

processing of the thermal data. This post processing includes:

•

Ta calculation

•

Pixel offset cancelling

•

Pixel to pixel sensitivity difference compensation

•

Object emissivity compensation

•

Object temperature calculation

The result is an image with NETD better than 0.1K RMS at 1Hz refresh rate.

The refresh rate of the array is programmable by means of register settings or directly via I2C command. Changes of

the refresh rate have a direct impact on the integration time and noise bandwidth (faster refresh rate means higher

noise level). The frame rate is programmable in the range 0.5Hz…512Hz and can be changed to achieve the desired

trade-off between speed and accuracy.

The MLX90621 requires a single 2.6V…3.2V although the device is calibrated and performs best at VDD=2.6V.

The MLX90621 is factory calibrated in following temperature ranges:

•

-40˚C…85˚C for the ambient temperature sensor

•

-50˚C…300˚C for the object temperature.

NOTE: The sensor can detect higher temperatures, but is not calibrated for temperatures above 300°C.

See Table 21 for configuration specific properties.

Each pixel of the array measures the average temperature of all objects in its own Field Of View (called nFOV).

It is very important for the application designer to understand that the accuracy of the temperature measurement

is very sensitive to the thermal equilibrium isothermal conditions (there are no temperature differences across

the sensor package). The accuracy of the thermometer can be influenced by temperature differences in the

package induced by causes like (among others): Hot electronics behind the sensor, heaters/coolers behind or

beside the sensor or by a hot/cold object very close to the sensor that not only heats the sensing element in the

thermometer but also the thermometer package.

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