Fluke 5790B, Руководство по обслуживанию

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2-1
Chapter 2
Theory of Operation
Introduction
The Product is an automated ac-dc transfer standard. The following elements are
among those critical to establishing the accuracy of the Product.
•
The FTS (Fluke RMS Thermal Sensor) is the transfer element. It
compares a precisely known adjustable dc voltage (or a square wave
derived from dc) to an unknown ac voltage. If the FTS output remains
unchanged when the input switches from the unknown ac voltage to the
known dc voltage, the RMS value of the ac voltage is equal to the dc
voltage. The FTS has extremely flat frequency response and has short
term stability approaching 1 part per million (ppm).
•
Highly stable resistor networks scale the 7 V range and higher to the FTS
2 V operating level and to scale the precision reference to the 0.7 mV
level.
•
An ADC (analog to digital converter) measures the FTS output.
•
A high-resolution DAC (digital to analog converter) generates precisely
variable dc for the ac-dc transfer.
•
An ultra-stable dc voltage reference establishes DAC accuracy.
•
A dc-to-square-wave converter chops the DAC output to eliminate dc
reversal error in the RMS sensor.