24
Operation
4.3 Power Measurement
Power Measurement
Object #2
Power
Output
Configuration
Properties
nvoPower_f
SNVT_power_f
nv1
nciWMaxSendT SNVT_elapsed_tm
nciWMinSendT SNVT_elapsed_tm
nciWMinDelta SNVT_power_f
nciPowLimHi SNVT_power_f
nciPowLimLo SNVT_power_f
nciPowAlmSetT SNVT_elapsed_tm
nciPowAlmClearT SNVT_elapsed_tm
nciPowLimHystHi SNVT_power_f
nciPowLimHystLo SNVT_power_f
nciPowAlarmInhT SNVT_elapsed_tm
nc22
nc24
nc27
nc9
nc18
nc5
nc2
nc11
nc13
nc4
nvoPowerW
SNVT_power
nvoPowerKW
SNVT_power_kilo
Manufacturer
Specific
Variables
Figure 4.3: Power Measurement Object
The WattNode measures power over two second intervals by averaging the power over the preceding two
seconds. The WattNode can be configured to update the power output network variables at intervals from 1
to 65,000 seconds. Every five seconds, the WattNode checks to see if any power alarms have been tripped
or cleared.
4.3.1 Power Output
The power value is available in three different units:
Network Variable
Resolution
Range
nvoPowerW
0.1 watt
0 to 6553.5 watts
nvoPowerKW
0.1 kilowatt
0 to 6553.5 kilowatts
nvoPower_f
1.2e-7 × measurement
0 to 1.0e38 watts
Table 4.4: Power Output Network Variables
Any of these output units may be used, depending on the application. The
nvoPower_f
variable is a
floating point variable that has a resolution of one part in 8 million of the current measurement value.
The update time interval of these power output variables is controlled by three configuration properties: the
minimum interval between updates, the maximum interval between updates, and the change in power that
triggers an update. The first configuration variable
nciWMinSendT
sets the minimum time that must elapse
between updates to the power. This can be used to prevent the WattNode from overloading the network.
The second configuration variable
nciWMaxSendT
sets the maximum time that may elapse between
updates. Finally,
nciWMinDelta
may be used to force an update if
nciWMinSendT
time has elapsed since
the last update and the power has changed by
nciWMinDelta
watts. The units for
nciWMinDelta
are
floating point watts.
