EVB90620 Datasheet, PDF (16/39 Pages) Melexis Microelectronic Systems – High precision non-contact temperature measurements

MLX90620
16x4 IR array
7.3.3 Calculation of To
Following formula is used to calculate the temperature seen by specific pixel in the matrix:
T_{O(i, j )}
Where:
V_{IR(i, j ) _ COMPENSATED}
4
(i, j)
T_a 273.15 ⁴ 273.15,[ C]
V_{IR(i, j) _ COMPENSATED} is the parasitic free IR compensated signal as calculated in 7.3.3.1
(i, j) ^{is a individual pixel sensitivity coefficient stored in EEPROM as calculated in 7.3.3.2}
T_a is the ambient temperature calculated in 7.3.1
7.3.3.1 Calculating V_{IR(I,j)_COMPENSATED}
1. Offset compensation
V V _{IR(i, j) _ OFF _ COMP}
IR(i, j)
A_{i(i, j)}
B_{i(i, j )}
2 ^{Bi _ scale}
T_a
T_{a _ 0}
Where:
V_{IR(i, j)} is a individual pixel IR_data readout (RAM read)
A_{i(i, j)} is a individual pixel offset stored in EEPROM as two’s complement value
B_{i(i, j)} is a individual pixel offset slope coefficient stored in EEPROM as two’s complements
value
B_{i _ SCALE} is a scaling coefficient for slope of IR pixels offset and is stored in the EEPROM as
unsigned value
T_a is ambient temperature calculated in 7.3.2
T_{a _ 0} 25 C is a constant
NOTE: This applies to the compensation pixel as well ( A_CP and B_CP while B_{i _ SCALE} is the same)
2. Thermal Gradient Compensation (TGC)
V_{IR(i, j ) _ TGC _ COMP}
Where:
V_{IR(i, j ) _ OFF _ COMP}
TGC
32
.V_IR
_
CP
_
OFF
_
COMP
V_{IR _ CP _ OFF _ COMP} is offset compensated IR signal of the thermal gradient compensation pixel
TGC is a coefficient stored at EEPROM address 0xD8 as two’s complement value
3. Emissivity compensation
V_{IR(i, j) _ COMPENSATED}
V_{IR(i, j) _ TGC _ COMP}
Where:
is emissivity coefficient. The scaled value is stored into EEPROM as unsigned value
256. _ H _ L
32768
3001090620
Rev 4.0
Page 16 of 40
Datasheet IR16x4
19 September 2012