8
3.2
Meassuring system
3.2.1
Phase-Locked loop - PLL
The measuring system use a phase-locked loop (PLL) between 10-120 Hz. All quantities are being
measured. The number of samples per period is deppending of the frequency.
3.2.2
Soft mode
A fixed sample rate of 1800 samples/second (soft mode) is used when the frequency is lower than
10 Hz or higher than 120 Hz. Measured quantities in soft mode are voltage (U), current (I) and
frequency (F).
3.2.3
Block diagram
Schematic block diagram of measure process.
*
Soft mode = 1800 samples / second
3.2.4
Frequency filter
The frequency measurement is low-pass filtered with a binomial filter. This setting determines the
length of the filter in periods of the measured frequency. A shorter length gives a more responsive
measurement. A longer length gives a slower, more stable measurement.
Frequency filter is adjustable between 0
–
10.
