Functional Description; Overview; Gnss Synchronization; Current Inputs - Arbiter Systems Power Sentinel 1133A Operation Manual

Chapter 11

Functional Description

11.1

Overview

The Arbiter Systems Model 1133A Power Sentinel consists of several blocks. They are: GNSS
receiver and synchronization; voltage and current inputs; programmable-gain amplifiers, multiplex-
ers, and analog-to-digital converter; digital signal processor; host processor; display and keyboard;
I/O functions; and power supply. The button features of the instrument and its measurement
functions are described in the sections, which follow.
Two microprocessors are required to handle the many tasks being performed each second in such
a highly integrated instrument. A Texas Instruments TMS320C32 floating-point DSP unit performs
the digital signal analysis tasks. Instrument I/O functions and interface to the "real world" are
handled by an SGS-Thomson ST10F167 16-bit micro-controller. Both of these processors have
significant additional processing power, which is not used in the initial version of the 1133A. This
will allow for the future expansion of features, which is sure to come, with a minimum amount of
upset; indeed, many future enhancements should be possible with only a firmware upgrade.
11.2

GNSS Synchronization

To provide accurate time synchronization for power measurements, the 1133A uses a twelve-
channel global positioning system (GNSS) receiver and proprietary technology developed by Arbiter
Systems and refined in several generations of GNSS timing products. By comparing the internal
10-MHz crystal oscillator to the 1-PPS output of the GNSS receiver, the 1133A can maintain its
frequency at any time within a few parts in 10
internal timing signals are derived from this accurate time-base.
11.3

Current Inputs

A three-phase, current input section is designed to be accurate to a few ppm over time and
temperature (see "Error Analysis"). This current input section uses a two-stage process, similar to
a two-stage current transformer except that the first stage is dc-coupled. Each of these two stages
has an accuracy of a few tenths of one percent; together, they have an accuracy of a few parts per
million.
10
, and time within one microsecond. All of the