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programming the temperature compensation for the first gap is slightly different than the other
gaps. The compensation coefficients for the first gap (OFTC1 and GNTC1) apply to digitized
filtered temperature values from T1 down to zero. The fourth gap coefficients apply to digitized
filtered temperature range from T3 to 1023 (decimal).
The temperature points T1 thru T3 should always be in increasing order from T1 to T2 to T3. If
the temperature sensor has increasing signal with increasing temperature then the compensation
procedure is intuitively easy. This is the case with the internal temperature sensor. If the
temperature sensor has decreasing signal with increasing temperature then the compensation will
start at a hotter temperature and go towards cold. The procedure below is written with regard to
the filtered digitized temperature not the real physical temperature.
4.3) Procedure
1) Set the desired operating mode and number of gaps. It is also helpful to set T2 and T3 to
1023.
2) At the T1 temperature do a baseline calibration, the span then the offset by using CSGN[2:0]
and GN[9:0] then CSOF[1:0] and OF[9:0]. The T1 temperature is somewhat arbitrary, typically
its room temperature. If the temperature sensor goes down with increasing temperature then the
T1 value will be towards the high end of the application’s temperature range. Update the
Temp/Signal values. Copy the digitized temperature reading to the T1 box. If one temperature
gap is desired then T1 will be the highest digitized temperature value.
3) Lower the temperature to the lowest operating temperature and recalibrate the output using
GNTC1 and OFTC1 only. If the temperature sensor goes down with increasing temperature then
raise the temperature to its maximum value and re-calibrate the output using GNTC1 and
OFTC1. Do not change the T1, OF, or GN values.
4) Raise the temperature until the second temperature point, T2. If the temperature sensor goes
down with increasing temperature then lower the temperature to the T2 value. This point may be
arbitrary and can be based on how far the output has deviated from it's desired value. Re-
calibrate the sensor by adjusting GNTC2 and OFTC2 only.
5) Update the Temp/Signal values displayed on the screen. Copy the digitized temperature value
to the T2 box. This must happen AFTER step 4.
6) Repeat steps 4 and 5 for T3 and setting GNTC3, OFTC3. T1, T2, and T3 must be in ascending
order.
7) For the last temperature gap, raise the temperature to the highest operating temperature
point and re-calibrate the output using GNTC4 and OFTC4. There is no T4, it is assumed to be
1023 (the maximum value of the digitized filtered temperature).
MLX90308CCC & MLX90314AB Software Users Manual
Rev 2.0
20
11/28/01