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MX Foundation 4
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MX Foundation 4
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Reference signals for analog input calibration have been provided to improve measurement accuracy. The use of software calibration allows the elimination of hardware calibration potentiometers traditionally used in precision analog front ends.
Very accurate calibration of the IPM-ADC can be accomplished by using calibration voltages present on the module. The five voltages and the analog ground reference are used to determine two points of a straight line, which defines the analog input characteristic. The calibration voltages are precisely adjusted at the factory to provide optimum performance.
When sampling the calibration value, the user should use a lower rate (uniform sampling at 50kHz) to obtain the highest precision and stability. The calibration value can be rechecked periodically to obtain excellent accuracy over temperature changes. Finally, when sampling the calibration data, several readings (recommended 64 to 128) should be taken and averaged to lower as much as possible the measurement uncertainty.
The following table can be used to select the ideal calibration low and high value
| Input Range (V) | PGA Gain | Voltage Range | Ideal Cal Low | Ideal Cal High |
|---|---|---|---|---|
| -2.5 to 2.5 | 1 | -2.5 to 2.5 | 0 | 2.45 |
| -2.5 to 2.5 | 2 | -1.25 to 1.25 | 0 | 1.225 |
| -2.5 to 2.5 | 4 | -0.625 to 0.625 | 0 | 0.6125 |
| -2.5 to 2.5 | 8 | -0.3125 to 0.3125 | 0 | 0.30625 |
| -5 to 5 | 1 | -5 to 5 | 0 | 4.9 |
| -5 to 5 | 2 | -2.5 to 2.5 | 0 | 2.45 |
| -5 to 5 | 4 | -1.25 to 1.25 | 0 | 1.225 |
| -5 to 5 | 8 | -0.625 to 0.625 | 0 | 0.6125 |
| -10 to 10 | 1 | -10 to 10 | 0 | 4.9 |
| -10 to 10 | 2 | -5 to 5 | 0 | 4.9 |
| -10 to 10 | 4 | -2.5 to 2.5 | 0 | 2.45 |
| -10 to 10 | 8 | -1.25 to 1.25 | 0 | 1.225 |
| 0 to 2.5 | 1 | 0 to 2.5 | 0.30625 | 2.45 |
| 0 to 5 | 1 | 0 to 5 | 0.30625 | 4.9 |
| 0 to 10 | 1 | 0 to 10 | 0.30625 | 4.9 |
The example below shows how to implement software calibration.
