Measurement-computing PCI-DAS6402/16 Instrukcja Użytkownika Pobierz pdf (Strona 20)

Chapter 4

Calibrating the PCI-DAS6402/16

Overview

The PCI-DAS6402/16 provides self-calibration of the analog inputs and outputs, eliminating the need for

external equipment and user adjustments. All adjustments are made via 8-bit calibration DACs and digital

potentiometers that are referenced to an on-board factory-calibrated standard. The board is fully calibrated at the

factory with calibration coefficients stored in nvRAM. At run time, these calibration factors are loaded into

system memory and are automatically retrieved each time a different DAC/ADC range is specified.

You can recalibrate any time using factory voltage standards by selecting the

Calibrate option in InstaCal. A

full calibration typically requires less than two minutes. We strongly recommend that you turn your computer

on, and allow at least 60 minutes for the internal computer case temperature to stabilize prior to calibrating the

board.

Calibration theory

Offset calibration for the analog front end is performed via adjustments of the ADC itself. Front-end gain

adjustment is performed only via the ADC reference. This strategy was chosen since the gain tolerance of the

in-amp circuit is quite good and there is adequate gain tuning range using only the ADC.

Analog input calibration is shown in . Figure 4-1

Figure 4-1. Analog input calibration

Calibration

Reference

nalog In

Offset

Adjust

Unipolar/

Bipolar

Offset

Adjust

Ref.

Digital offset

potential

Digital gain

potential

4-1

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