Figure 6: Rms Value Calculation (Example, Not To Scale) - WAGO SYSTEM 750 User Manual

36 Function Description
Calculating the RMS Values for Current and Voltage
The I/O module measures the true RMS of the voltages and currents applied to the
measurement inputs per period. See figure below.
i : Scan value of the current
k
u : Scan value of the voltage
k
N: No. of scan values

Figure 6: RMS Value Calculation (Example, Not to Scale)

In a 50-Hz-supply network, the RMS value can be read with the specified
measuring accuracy with every second period via the process image. Therefore,
the default setting of the measuring cycle time is 39 ms.
For applications where voltage and current drops have to be evened out, a mean of
the RMS values for current and voltage can be generated by the measuring cycle
time setting. If a time of 40 ms is set in WAGO-I/O-CHECK, there is averaging of
2 RMS values, a value of 500 ms is set, there is averaging of 13 RMS values
(500/39 = 12.82).
The maximum measuring cycle time can be 24375 ms. The update rate in the
process image corresponds to the time set.
N-1
∑
2
I = i
1
eff k
N
k 0
=
I
eff
U
750-493 3-Phase Power Measurement Module
U =
1
eff
N
: RMS value of the current
: RMS value of the voltage
eff
WAGO-I/O-SYSTEM 750
N-1
∑
2
u
k
k 0
=
Manual
Version 1.2.0