MLX90323 Datasheet, PDF (13/25 Pages) Melexis Microelectronic Systems – 4 – 20 mA Loop Sensor Interface with Signal Conditioning and EEPROM

MLX90323
4 – 20 mA Loop Sensor Interface
with Signal Conditioning and EEPROM
8 Temperature compensation
The MLX90323’s temperature compensation algorithm is piece-wise with up to 4 temperature segments, see
figure 2. Within each temperature segment (‘gap’), the correction is a first order calculation. There are
separate temperature coefficients for gain and offset. The first temperature gap is slightly different than the
other three. The compensation is based on the temperature difference between the current temp and the T1
point (the upper end of the gap). The other gaps use the lower end of the gap to measure the temperature
difference. For instance in the second gap, the temperature difference is current temperature minus T1. This
difference has to be accounted for in the compensation procedure.
Temperature
Compensation
OF & GN
OFTC3
OFTC4
OFTC2
OFTC1
GNTC3
GNTC4
1 Gap
GNTC2
i4
GNTC1
i3
i2
i1
Application's temperature
range
0
T1
T2
T3
3FFh
Temperature
Figure 2. Temperature Compensation.
Temperature Gaps
There are four temperature gaps possible with the
MLX90323. The gaps are defined with respect to
the filtered digitized temperature value saved in
RAM locations 58 and 59. The first temperature
gap is always bound at the low end by a digitized
temperature value of zero. The fourth
temperature gap is bound at the high end by a
digitized temperature value of 1023₁₀ (3FF_hex).
Whenever fewer than four gaps are used, the last
gap should have an upper bound of 1023₁₀. This
is to ensure that if the temperature exceeds the
last point it won’t enter into an undefined
temperature gap.
Temperature Points
The temperature points T1, T2 and T3 are defined
by the user to differentiate between the four
possible temperature compensation ranges. The
low endpoint T0 is defined as the minimum
digitized filtered temperature value, zero. This
means that the coefficients for the first gap,
OFTC1 and GNTC1, will apply to the signal until
the digitized filtered temperature reaches zero.
The high endpoint T4 is defined as the maximum
digitized filtered temperature value, 1023₁₀. This
means that the coefficients for the last gap,
OFTC4 and GNTC4 will apply to the signal from
the T3 point and up until the digitized filtered
temperature reaches its maximum, 1023₁₀.
When defining these points, the number that is
used is simply copied from the ‘Temp Value’ box
(see “MLX90323_software_descroption.pdf”) at
the desired temperature (contents of ram locations
58 and 59).
3901090323
Rev 003
Page 13 of 25
Data Sheet
Feb/12