Specifications

August 2010
G4500 BLACKBOX PORTABLE OPERATIONAL MANUAL
116
PQZip Recording | Elspec
ory becomes full, the oldest files are deleted automatically to free required space
for the newest data.
Fixed Quality versus Fixed Ratio
The most important parameter defining the actual compression ratio, (which de-
termines the amount of storage required and maximum time continuous data can
be stored) is a PQZip threshold value or Tolerance as it referred on the WEB
page.
The Tolerance defines what change in an individual harmonic would be defined
as significant enough to store and being reproduced afterwards. The tolerance
value is defined in percentage to the full scale or nominal reading for the specific
channel.
It is assumed that changes within 0.1% of nominal would have no importance in
further power quality investigation, and the values within that range are averaged
to store the representative value only. The basic and factory default tolerance
value is normally defined as 0.1%. However, on some sites/networks that value
can still be considered too tight, for example, a highly fluctuating load or voltage
lines.
It is most likely that a user would prefer increasing a tolerance value for currents
or voltages or even both in order to achieve better compression ratios on highly
polluted network locations. The BLACKBOX Portable provides the possibility
of automatic adjustment of the actual tolerance value presuming a compression
ratio defined as amount of data being stored per month.
That option is called Fixed Ratio. When selected, the user is requested to define
the amount of data to be stored per month (Monthly Ratio) in MB.
Usually, slight voltage spectral changes have higher importance than current
changes. Therefore, the amount of data which could be stored for voltages may
be determined as greater than for currents. The V/I Relation parameter defines
the relationship between the data (a part of the Monthly Ratio) reserved for volt-
age. If the voltage portion is larger than currents, the system will define a tighter
tolerance for voltages than for currents.