7-10
IM WT310-02EN
7.4.2 Frequency Measurement
Item
Specifications
Measured item
Voltage and current frequencies applied to the selected input element can be measured.
WT332 (two element model)
Select voltage (U1)/current (I1) of input element 1 or voltage (U3)/current (I3) of input element 3.
WT333 (three element model)
Select voltage (U1)/current (I1) of input element 1, voltage (U2)/current (I2) of input element 2 or
voltage (U3)/current (I3) of input element 3.
Method
Reciprocal method
Frequency measuring range
Varies depending on the data update interval (see description given later) as follows:
Data Update Interval
Measurement Range
0.1 s
25 Hz ≤ f ≤ 100 kHz
0.25 s
10 Hz ≤ f ≤ 100 kHz
0.5 s
5 Hz ≤ f ≤ 100 kHz
1 s
2.5 Hz ≤ f ≤ 100 kHz
2 s
1.5 Hz ≤ f ≤ 50 kHz
5 s
0.5 Hz ≤ f ≤ 20 kHz
Only for the direct current input of the WT310HC, the maximum measurement range is 20 kHz.
Measurement range
Auto switching among six types: 1 Hz, 10 Hz, 100 Hz, 1 kHz, 10 kHz, and 100 kHz
Frequency filter
Select OFF or ON (cutoff frequency at 500 Hz).
Accuracy
Requirements
• When the input signal level is 30% or more of the measurement range if the crest factor is set
to 3 (60% or more if the crest factor is set to 6)
• Frequency filter is ON when measuring voltage or current of 200 Hz or less.
Accuracy: ±(0.06% of reading)
7.4.3 Computation
Item
Specifications
Computing equation of apparent power (S), reactive power (Q), power factor (λ), and phase angle (Φ)
i : Input element number
Single-Phase, Three-
Wire (1P3W)
Three-Phase, Three-
Wire (3P3W)
Three-Phase, Three-
Wire (3V3A)
Three-Phase, Four-
Wire (3P4W)
UΣ[V]
(U1+U3)/2
(U1+U2+U3)/3
IΣ[A]
(I1+I3)/2
(I1+I2+I3)/3
PΣ[W]
P1+P3
P1+P2+P3
SΣ[VA]
Si=Ui×Ii
S1+S3
)
3
1
(
2
3
S
S +
)
3
2
1
(
3
3
S
S
S
+
+
S1+S2+S3
QΣ[var]
Qi=
2
2
i
i
P
S
−
Q1+Q3
Q1+Q2+Q3
λΣ
λi = Pi/Si
S
P
Σ
Σ
Φ[°]
Φi =
)
(
cos
1
i
i
S
P
−
)
(
cos
1
−
S
P
Σ
Σ
• On the WT300 series, S, Q, λ, and Φ are derived through the computation of the measured values of voltage, current, and
active power. Therefore, for distorted signal input, the value obtained on the WT300 series may differ from that obtained on
other instruments that use a different method.
• If the voltage or current is less than 0.5% (less than or equal to 1% if the crest factor is set to 6) of the rated range, zero is
displayed for S or Q, and error is displayed for λ and Φ.
• For Q[var], when the current leads the voltage, the Q value is displayed as a negative value; when the current lags the voltage,
the Q value is displayed as a positive value. The value of QΣ may be negative, because it is calculated from the Q of each
element with the signs included.
7.4 Features
