Dranetz PowerGuide 4400, Руководство пользователя

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5-16
Nominal Values, continued
Frequency
synchronization
Normal frequency synchronization (sync) of the 4400 analog signal processing circuits
is controlled by analyzing the external AC voltage signal input on channel A. Loss of
external sync causes the 4400 to poll other valid voltage channels (A, B, or C) for an
alternate external sync. If none exists, then internal sync is automatically selected. The
frequency used for internal is entered under Frequency on the Nominal Values screen
(see page 5-14).
Depending on the type of circuit configuration, the instrument will attempt to
autosearch to sync to any valid voltage channel. The autosearch function will be
disabled when users specify sync mode Ch D Volts. Typically, external sync on Ch D is
specified if it is known that signals on A, B or C are inappropriate for use as a sync
source (i.e. the frequency is unstable or DC). A low distortion 50, 60 or 400 Hz signal
can be input to Ch D and used as a sync signal.
NOTE: Failure to connect an external sync or to select an internal sync during current
monitoring will result in erroneous data being collected and displayed.
Frequency
Tracking
Tracking determines how the phase locked loop circuitry responds to sudden changes
in frequency.
Standard mode: On a normal power quality application [Standard], the system is
designed to “ride through” voltage changes to keep tracking the fundamental frequency
even in the absence of voltage.
Fast mode: When operating on a local generator [Fast], the frequency will vary more as
loading changes occur. The Fast mode allows the instrument to follow these changes
more closely.
Internal mode: In cases where no reference signal is available (such as DC monitoring),
the Internal setting is used to set the sample rate.
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