1-14
IM 253710-01E
When inputting voltage or current signals via an external PT or CT
The output from the secondary side of the potential transformer can be connected to
the same voltage input terminal used for direct input and the output of the secondary
side of the current transformer can be connected to the same current input terminal
used for direct input. Set the PT ratio, CT ratio, and power coefficient (coefficient
multiplied by power determined from the voltage and current). Then, the input signal
can be made to correspond to the numerical data or display data that are obtained
when the current is directly applied to the input terminals.
Measurement Function
Transformation Ratio
Conversion Result
Voltage U
U
2
(secondary output of PT)
U
2
×
P
P : PT ratio
Current I
I
2
(secondary output of CT)
I
2
×
C
C : CT ratio
Active power P
P
2
P
2
×
P
×
C
×
SF
SF : power
Apparent power S
S
2
S
2
×
P
×
C
×
SF
coefficient
Reactive power Q
Q
2
Q
2
×
P
×
C
×
SF
Max./Min. current value Ipk
Ipk
2
(secondary output of C)
Ipk
2
×
C
Input Filter (Line Filter and Zero Crossing Filter) «For procedures, see section 5.6.»
There are two types of filters. This instrument makes measurements by synchronizing to
the input signal. Therefore, the frequency of the input signal must be measured
accurately. These filters are used for this purpose.
Line filter
This filter is inserted into the measurement circuit. It removes the noise from the
inverter and from distorted waveforms. The cutoff frequency can be selected.
Zero crossing filter
This filter is inserted only into the frequency measurement circuit. Zero crossing
refers to the point at which the input signal crosses the center level of the amplitude.
This filter is used to accurately detect the zero cross point. The cut-off frequency can
be selected. This instrument can detect the zero crossing point with a hysteresis of
approximately 3.5% of the measurement range. The zero crossing detection is used
to determine the measurement/computation period, measure frequency, determine
the period of a PLL source, and is used as a trigger condition for the HF auto mode
and HF normal mode (explained later).
1.3 Acquiring Data (Voltage and Current Signals)