PPA45xx Quick User Guide
Page 14
Frequency Lock
In a very noisy application, where the frequency of
the signal is known but the instrument is unable to
measure the frequency even with PWM filters or low
frequency mode filters applied, it is possible to
manually enter the frequency to be used for analysis
Normal
Utilises N4L unique signal processing techniques for
fundamental frequency synchronisation including
hysteresis to increase frequency noise immunity
Constant
Constant selection will allow the user to overwrite the
present measured frequency with the known
frequency. This entered frequency is then used for all
the analysis and the frequency of the input signal is
not measured
Dynamic
As per “Normal” without hysteresis. This option
should not be used when DC only coupling is selected
in the Coupling menu.
High Speed
High speed mode can be selected for data log speeds
less than 100ms
Disabled
Disable high speed function
Enabled
Activate high speed data log function
COUPLING
Coupling
There are three coupling options - AC only, AC+DC,
or DC only. AC+DC coupling is the default option and
should be used where possible. AC coupling should be
used for measuring signals that are biased on a dc
level (such as an amplifier operating on a single
supply or the output of a dc PSU). DC coupling should
be selected when making DC measurements as it
prevents noise from resetting the frequency
measurement algorithm. The coupling option does not
affect the bandwidth of the instrument only the
frequency detection
ac + dc
Will allow both ac and dc signals to be calculated in all
measurements
ac
AC Coupling only allows ac signals to be measured
and will filter out all dc components
dc
DC coupling should be selected when making DC
measurements as it prevents noise from resetting the
frequency measurement algorithm, the bandwidth of
the instrument is not affected. When DC coupling is
selected “Dynamic” Frequency lock has no meaning
and so should not be used.