MLX90614_15 Datasheet, PDF (24/51 Pages) Melexis Microelectronic Systems – Single and Dual Zone Infra Red Thermometer in TO-39

MLX90614 family
Single and Dual Zone
Infra Red Thermometer in TO-39
Example: (see Figure 17 above):
Configuration:
Sensor1 = Ta, Sensor2 = T_obj1 Config Reg[5:4] = 00b,
T_{A _ MIN} = 0°C
( ) _{( ) TA_ RANGE _ L EEPROM = 100 ×}
T_{A _ min} + 38.2
64
= 59.6875 ≈ 60d = 0x3C
T_{A _ MAX} = 60°C
( ) _{( ) TA _ RANGE _ H EEPROM = 100 ×}
T_{A _ max} + 38.2
64
= 153.4375 ≈ 153d = 0x99
( ) { } T_{A _ RANGE} EEPROM ,0x03 = T : T _{A _ RANGE _ H A _ RANGE _ L} = 0x993C
( ) T_{O _ MIN} = 0°C T_{O _ MIN} (EEPROM ,0x01) = 100 × T_{O _ min} + 273.15 = 27315d = 0x6 AB3
( ) T_{O _ MAX} = 50°C T_{O _ MAX} (EEPROM ,0x00) = 100 × T_{O _ min} + 273.15 = 32315d = 0x7E3B
Captured high durations are:
Sensor
1
–
t
=
16.875ms
at
period
T
=
100ms
thus
the
duty cycle
is
Duty _S1
=
16.875
100
=
0.16875
Sensor
2
–
t
=
73.125ms
at
period
T
=
100ms
thus
the
duty cycle
is
Duty_{S 2}
=
73.125
100
=
0.73125
The temperatures are calculated as follows:
( ) ( ) T_A = 4 × Duty_S1 − Start1 × T_{A _ MAX} − T_{A _ MIN} + T_{A _ MIN}
T_A = 4 × (0.16875 − 0.0625)× (60 − 0)+ 0 = 25.5°C
( ) ( ) T_O1 = 4 × Duty_{S 2} − Start 2 × T_{O _ MAX} − T_{O _ MIN} + T_{O _ MIN}
T_O1 = 4 × (0.73125 − 0.5625)× (50 − 0) + 0 = 33.75°C
8.5.3 Customizing the temperature range for PWM output
The calculated ambient and object temperatures are stored in RAM with a resolution of 0.01°C (16 bit).
The PWM operates with a 10-bit word so the transmitted temperature is rescaled in order to fit in the desired
range.
For this goal 2 cells in EEPROM are foreseen to store the desired range for To (To_min and To_max) and
one for Ta (Ta_range: the 8MSB are foreseen for Ta_max and the 8LSB for Ta_min).
Thus the output range for To can be programmed with an accuracy of 0.01°C, while the corresponding Ta range
can be programmed with an accuracy of 0.64°C.
The object data for PWM is rescaled according to the following equation:
T = ^T _K^{− T} , K = ^T ₁₀^−₂^T_{3 PWMobj}
RAM
MIN_EEPROM
PWM obj
PWM obj
MAX _EEPROM
MIN_EEPROM
3901090614
Rev 009
Page 24 of 52
Data Sheet
June 29, 2015