How often should a AD779x calibration be implemented in a system ?
To determine the frequency of calibrations within a system, consider
• What accuracy is required from the converter?• How does drift performance of the ADC limit performance?• Over what temperature range does the system operate?
Taking these three questions into account will give some indication as to how often a calibration is required. Other system parameters should also be considered when determining how often to calibrate. These are all related to circuit sensitivities to temperature change as follows:
• Parasitic thermocouple effects• Gain drift due to the reference temperature coefficient• Drift sources external to the converter
In general, the higher the accuracy requirement, the more often a calibration will be required in order to maintain system accuracy. After a calibration has been performed, high resolution converters like the AD779x will have some offset and gain drift associated with them. The AD779x’s offset drift due to temperature is typically 10 nV/°C, and the gain drift is typically 1 ppm of full-scale range/°C.
In accessing the complete effects on accuracy due to temperature, the temperature effects due to parasitic thermocouples and drift sources external to the converter also need to be factored into the equation.
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