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Calculating Power Availability: Number of Nines ION 7500 / ION 7600 User’s Guide
Page 158 Chapter 5 - Features and Applications
Calculating Power Availability: Number of Nines
Power availability is becoming an increasingly important topic in today’s
electronic world. As the use of electronic equipment increases in industry and the
home, the degree of tolerance for power outages has decreased. In some cases, a
very short loss or reduction of supply voltage can have a large economic impact.
The purpose of calculating the “Number of Nines” is to provide a measurement of
the time that power was available at the point the meter is monitoring. This value
can be used alone or incorporated into other reliability calculations. Availability
can be calculated as a percentage of total time (since the last reset).
A typical utility distribution system provides an availability of approximately
99.9%. Many applications require better availability than this: up to 99.9999% or
better. It has become common to refer to high availability using the “Number of
Nines”: 99.9% corresponds to 3 nines; 99.9999% is 6 nines.
Once the meter is installed, the availability calculations must be reset to ensure
valid time counts. You can reset the availability calculations with Vista software,
ION Setup software, or through the meter’s front panel.
For more information on the power availability, refer to the technical note Power
Availability.