MULTI-CAL-SYSTEM: PGA309 Temperature Calibration

Hello Avi,

When creating the EEPROM lookup table of the PGA309, the temperature index values in the lookup table must be monotically increasing from minimum to maximum for the Lookup table to function properly.  The lookup table must still be built from minimum Temp ADC reading to the maximum Temp ADC reading. The pre-cal examples provided with the multi-cal PGA309 system software also show temperature readings starting from minimum temperature to maximum temperature. Please review section 3.2 page 62-64 of the PGA309 User Guide.

If your sensor requires the linearization calibration vs pressure, the 50% pressure point reading will be required at the first temperature.  The PGA309 linearization circuitry can compensate for the parabolic-shaped portions of a sensor’s nonlinearity with applied pressure. The PGA309 contains a dedicated circuit for sensor voltage excitation and linearization, as shown in Figure 2-10 of the PGA309 User Guide. The Linearization Circuit scales the selected VREF and sums it together with a portion of the output voltage (VOUT) through the feedback pin (VFB) to compensate for the bow-shaped nonlinearity of the bridge sensor output versus pressure. By adjusting the excitation voltage, the bridge non-linearity vs pressure is corrected.

Therefore, the mid-scale or 50% span measurement along with minimum pressure and max pressure readings are required to estimate the bow-shaped non-linearity of the sensor by measuring the bridge output at minimum pressure, mid-scale (or 50%) pressure and maximum pressure.  The nonlinearity vs pressure is assumed to be constant over temperature variation; therefore, only one linearization DAC register coefficient is stored on the EEPROM at the first temperature reading. 

Thank you,

Luis