Vaisala FD12P Uživatelská příručka stáhnout pdf (Strana 91)

Chapter 4 _________________________________________________________________ Operation

VAISALA ________________________________________________________________________ 91

Type

AN AMBL ↵

↵↵

↵

WAITING FOR MULTIPLEXER

ANALOG INPUT, AMBL

118 0.1

119 0.3

Analog Output Commands

Analog Output Calibration

The DAC output voltage is converted to current, 0 to 22 mA unscaled.

This current is then software-calibrated to give 4 mA at the minimum

visibility and 20 mA at the maximum visibility. The minimum and

maximum visibility values are set in the configuration session. A

hardware error is indicated by 0 mA.

The ACAL command sets two-bit values, 4000 and 800, to the

digital-to-analog converter. The corresponding currents measured by a

multimeter must be given as answers to the questions asked in the

commands. The analog output scaling factors, which define the

bits/mA relation, are then calculated by the software. The scaling

factors are Scale 0 and Scale 1. The FD12 calculates them as follows:

Scale 0 = 4×((4000-800)/(high current - low current))

The bit value that gives 4 mA. Scale 1 depends on the mode.

In linear mode:

Scale 1 = bits16mA / (maximum vis - minimum vis)

In logarithmic mode:

Scale 1 = (ln(max vis) - ln(min vis)) / bits16mA

bits16mA = (3200 / (high current - low current)) × 16

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Vaisala FD12P Uživatelská příručka Strana 91