EVB90620 Datasheet, PDF (14/39 Pages) Melexis Microelectronic Systems – High precision non-contact temperature measurements

MLX90620
16x4 IR array
7.3 Calculation
7.3.1 Calculation of absolute chip temperature Ta (sensor temperature)
The output signal of the IR sensors is relative to the cold junction temperature. That is why we need to know
the temperature of the die in order to be able to calculate the object temperature ‘seen’ by each pixel.
The Ta can be calculated using the formula:
Ta
K_{T 1}
K_T
2
1
4K_{T 2} V_TH 25
PTAT _ data
25,[ C]
2K_{T 2}
ConstantsV_TH (25) , Error! Objects cannot be created from editing field codes.and K_{T 2} are stored in EEPROM
at following addresses as two’s complement values:
EEPROM address
0xDA
0xDB
0xDC
0xDD
0xDE
0xDF
Cell name
V_TH_L
V_TH_H
K_T1_L
K_T1_H
K_T2_L
K_T2_H
Stored as
2’s complement
2’s complement
2’s complement
Parameter
V_TH0 of absolute temperature sensor
K_T1 of absolute temperature sensor
K_T2 of absolute temperature sensor
Table 5 EEPROM parameters for Ta calculations
V_TH 25 256.V_{TH _ H} V_{TH _ L}
K_T1
256.K_{T1_ H} K_{T1_ L}
2¹⁰
K_{T 2}
256.K_{T 2 _ H} K_{T 2 _ L}
2²⁰
7.3.2 Example for Ta calculations
Let’s assume that the values in EEPROM are as follows:
EEPROM address
0xDA
0xDB
0xDC
0xDD
0xDE
0xDF
Cell name
V_TH_L
V_TH_H
K_T1_L
K_T1_H
K_T2_L
K_T2_H
Cell values (hex)
0x78
0x1A
0x33
0x5B
0xCC
0xED
Table 6 EXAMPLE for Ta calibration values
3001090620
Rev 4.0
Page 14 of 40
Datasheet IR16x4
19 September 2012