24/7 Data Acquisition Wildcard Users Guide

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Calibration Options

The calibration option is only required by Start_Conversion and not by Start_Conv_With_Values. The 24/7 Data Acquisition Wildcard has two basic calibration options, a self calibration and a system calibration. A self calibration performs a calibration that sets the analog to digital converter’s zero point and gain by internally shorting its inputs. A system calibration performs the same calculations as a self calibration but uses voltages at the analog field inputs for the zero and full scale points. All together there are seven calibration options that are variations on a self or system calibration.

Figure 2 displays the different calibration options and their relationship to the two different calibration types. The left side of the figure shows the four different types of self calibration options while the right side shows the three different types of system calibration options. The bottom level contains the four basic calibration options while the next level shows the higher-level calibration options that simply call the basic calibration options in different ways.

Figure 2: Graphical Representation of the Different Calibration Options

Table 4 shows a summary of the calibration options and the associated constants that you must pass to Start_Conversion as well as their execution times. Each calibration option is discussed in the following sections.

*The duration of the calibration operations are rounded up from the times listed in Table XI of the data sheet to account for the pipe line delay as specified in the data sheet.

Table 4: Calibration Options and Their Duration

Full Self Calibration

A self calibration sets the analog to digital converters zero point and gain by internally shorting its inputs. A Full Self Calibration performs both Zero-Scale Self Calibration, that sets the analog to digital converter’s zero point, and a Full-Scale Self Calibration, that sets the analog to digital converter’s gain. Either of these may also be performed separately from a Full Self Calibration. However, a Full-Scale Self Calibration should not be performed unless the analog to digital converter already has valid zero-scale coefficients. The zero-scale coefficients are loaded by calling Start_Conv_With_Values, performing a Full Self Calibration, or performing a Zero-Scale Self Calibration. You can perform a self-calibration in separate steps after a Full Self Calibration for additional offset or gain calibrations. Calibrating one of the parameters, either offset or gain, does not affect the other parameter.

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