WAGO-I/O-SYSTEM 750 XTR
Function Description 49
750-495/040-00x 3-Phase Power Measurement Module 690 V
Manual
Version 1.2.0
4.3
Description of the Measured Values
Calculation for current and voltage
The I/O module calculates the
true RMS value
for the voltage and current per
period applied at the measurement inputs. See the figure below.
𝐼𝐼
𝑅𝑅𝑅𝑅𝑅𝑅
=
�
1
𝑁𝑁
×
� 𝑃𝑃
𝑁𝑁
2
𝑁𝑁−1
𝑁𝑁=0
𝑈𝑈
𝑅𝑅𝑅𝑅𝑅𝑅
=
�
1
𝑁𝑁
×
� 𝐶𝐶
𝑁𝑁
2
𝑁𝑁−1
𝑁𝑁=0
i
k
: Sampling value of current
I
rms
: RMS of current
u
k
: Sampling value of voltage
U
rms
: RMS of voltage
N: Number of sampling values
Figure 9: RMS Calculation (Example – Not to Scale)
The current and voltage RMS values are calculated for each period in the I/O
module. The RMS values can be exported with every second period with the
specified measuring accuracy via the process image (2T). In a 50 Hz power
system, this corresponds to a refresh rate of 40 ms.
The
arithmetic mean value
for the phase current and voltage is calculated on
the basis of the RMS values. The time interval for which the mean value should
be calculated can be set via WAGO-I/O-
CHECK
or parameters 34, 35 and 36.
The
minimum and maximum RMS values
for the current and voltage are also
determined over a configurable time interval (WAGO-I/O-
CHECK
or parameters
37, 38 and 39).
Peak values
for current and voltage can be captured for a selectable phase (with
“3-Wire Wye/Delta”, the module does not support the peak voltage value for L2).