WAGO-I/O-SYSTEM 750
Function Description
35
750-494 3-Phase Power Measurement Module
Manual
Version 1.2.0
All of the energy meter values are saved in the I/O module. These operate
internally with the resolutions mWh / mVARh / mVAh and are reset when 1
billion kWh (kVARh, kVAh) is reached.
The representation of the energy values can be scaled using a defined factor in the
process image (PI). This factor can be set by the user with WAGO-I/O-
CHECK
or
register 35 and can be changed at any time. The two examples below illustrate the
information required for this:
Example 1:
- 750-494, meter:
Active energy acquisition L1 (UInt32 in the PI)
- Scaling (WAGO-I/O-
CHECK
, Register 35): 0 (1 mWh)
- Maximum meter value in the PI: 4 294 967 295 mWh = ~4 295 kWh
A counter overflow can occur for the counter shown in the PI even though the
internal meter has not yet reached the overflow threshold. This is signaled in the
PI by the flag "Overflow process value x". The user must select scaling of the
measured value in accordance with the application being used.
Example 2:
- 750-494/000-001, meter:
Reactive energy, total (Int32 in the PI)
- Scaling (WAGO-I/O-
CHECK
, Register 35): 6 (5 kVARh)
- Maximum meter value in the PI: +10 737 418 235 kVARh (2s complement)
An overflow of the internal meter can occur here, as it can only count to a
maximum of 1 billion kVARh. The meter shown in the PI can, however,
continue to count substantially higher on account of the scaling that has been
set.
The values for the energy meters can be set via WAGO-I/O-
CHECK
. More
information on this is given in the section "Commissioning".
The I/O module also allows you to set thresholds for energy measurement, i.e.,
energy is not metered until these set starting values are reached. This threshold
can be defined for each type of energy using WAGO-I/O-
CHECK
or parameters
40, 41, 42.
You can also define the storing cycle using WAGO-I/O-
CHECK
or Register 46 in
which the energy meter values are saved internally. The valid range for this is 60
… 255 s. With a storing cycle time of 60 s the lifetime of the internal meters is
around 19 years. Each second added to this time increases the lifetime by about
0.3 years.
Determining the Frequency
The phase frequencies are calculated using zero crossing detection of the sampled
signals for each phase. The minimum and maximum frequencies are determined
over a configurable time period (WAGO-I/O-
CHECK
or parameters 37, 38, 39).