Measurement Specialties PCI-DAS1002 manual Calibrating the Board, Introduction, Calibration theory

Chapter 4

Calibrating the Board

Introduction

Calibrate the board using the InstaCal utility after the board has fully warmed up. The recommended warm-up time is 15 minutes. For best results, calibrate the board immediately before making critical measurements. The high resolution analog components on the board are sensitive to temperature. Pre-measurement calibration ensures that your board is operating at optimum calibration values.

Calibration theory

The PCI-DAS1002 is shipped fully calibrated from the factory with calibration coefficients stored in nvRAM. When using Universal Library at run time, these calibration factors are loaded into system memory and are automatically retrieved each time a different DAC/ADC range is specified.

The analog input circuits are calibrated for both offset and gain (Figure 3).

ƒOffset calibration for the analog input is performed directly on the input amplifier (PGIA) with coarse and fine trim DACs acting on the amplifier.

ƒFor input gain calibration, a precision calibration reference is used with coarse and fine trim DACs acting on the ADC.

Analog In

PGIA

Variable Gain

A/D

Trim DAC	Pre-Gain
Coarse
	Offset

Trim DAC

Fine

Figure 3. Analog input circuit calibration

The analog output circuits are calibrated for both offset and gain (Figure 4). This circuit is duplicated for both DAC0 and DAC1.

ƒOffset adjustments are made in the output buffer section. The tuning range of this adjustment allows for max DAC and output buffer offsets.

ƒGain calibration is performed via DAC reference adjustments.

		D/A		Analog Out
		Ref
	Gain			Offset
Trim DAC	Adjust		Trim DAC	Adjust
Coarse
Trim DAC
Fine

Figure 4. Analog output circuit calibration

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