YOKOGAWA PZ4000, Руководство пользователя

Страница: 143 / 417

6-8
IM 253710-01E
Explanation
Select the PLL source (phase locked loop source) to be used for determining the
fundamental frequency for the analysis of the hermonics.
Selecting the PLL source
Select the PLL source from the following choices.
• CH1 to CH8 : The voltage or current of the element that has a measurement
module installed becomes the PLL source. The numbers of the channels that do
not have measurement modules installed are not displayed.
• Ext Clk : The clock signal applied to the external clock input connector becomes
the PLL source.
When setting the PLL source to [Ext Clk]
Apply a clock signal to the external clock input connector (EXT CLK IN) on the rear
panel that meets the following specifications.
EXT CLK IN
Item Specification
Connector type BNC connector
Frequency range 20 Hz to 6.4 kHz
Input level CMOS
CAUTION
Applying a signal to the external clock input connector (EXT CLK IN) that is
outside the 0 to 5 V range may damage the instrument.
Note
• Specify a signal that has the same period as the signal being measured. Selecting a signal
with little distortion for the PLL source will result in a stable harmonic measurement. If the
fundamental frequency of the PLL source cannot be determined due to fluctuations and
distortion of the signal, correct measurement results cannot be obtained. It is recommended
that the PLL source be set to a voltage that has little distortion as compared to the current.
There are cases when the specifications cannot be satisfied if all input signals are distorted or
their amplitudes are small with respect to the measurement range. In order to measure the
harmonics of higher orders more accurately, set the PLL source to external clock and apply a
signal to the external clock input connector that has the same period as the input signal.
• If the fundamental frequency is less than or equal to 500 Hz and the signal contains high
frequency components, we recommend the zero crossing filter be set to [500 Hz]. This filter
has a cut-off frequency of 500 Hz and is effective only for the frequency measurement circuit.
• When the amplitude of the signal selected for the PLL source (CH1 to CH8) is small
compared to the range, PLL synchronization may fail. In this case, set the measurement
range so that the amplitude of the PLL source signal is larger than 30% of the range rating.
• When setting the external clock signal to PLL source, input an external clock signal having
the same frequency as the fundamental frequency of the signal being measured.
• The harmonics of higher orders can be measured more accurately by using an external clock
signal that has a frequency that is an integer multiple of the fundamental frequency of the
signal being measured.
• The external clock must be a continuous clock. Burst signals cannot be used.
• There is no function available to frequency divide the external clock signal on this instrument.
• When acquiring sampled data with the time base set to external clock and the frequency of
the PLL source is lost (cannot be detected), the acquisition of the sampled data may not
operate properly.
6.4 Selecting the PLL Source for Harmonic Measurement