22
Operation
The alarms are reported through the Node object, but they are configured by the Power and Demand
objects. Full descriptions of the configuration and operation of the alarms are in sections
4.3.2 Power
Alarms
and
4.4.4 Demand Alarms
.
4.2 Energy Measurement
Energy Measurement
Object #1
Energy Output
Configuration
Properties
nvoElecWH_f
SNVT_elec_whr_f
nv1
nciWHMaxSendT SNVT_elapsed_tm
nciGain SNVT_muldiv
nc22
nc31
nvoElecKWH
SNVT_elec_kwh
nvoEngyClrT
SNVT_time_stamp
nciCTAmps
SNVT_amp
Manufacturer
Specific
Variables
Figure 4.2: Energy Measurement Object
Many installations will only measure energy. It is used for sub-metering, or tracking the kilowatt-hours
used by the measured circuit. Because of its accumulating behavior, this object can be used on networks
that are accessed infrequently. For example, this measurement could be used in a sub-metering application,
where the energy value was read monthly, either by manually connecting to the network or via a modem
interface to a central monitoring office.
The energy total will always increase as long as the WattNode is online. The energy total is reset to zero by
an override request, or when either
nciGain
or
nciCTAmps
is changed. For most metering applications, the
best control choice is to let the energy total increase from the time of installation, or to reset the total to
zero only once a year. It is possible to zero the total every time it is read out, but if a measurement is lost, it
cannot be recovered. Whenever energy is zeroed,
nvoEngyClrT
will be set to the current time and date.
This helps security, since tampering with the energy will update
nvoEngyClrT
.
During a power outage, the energy consumed will not be measured. Whenever the line voltage drops below
60–80% of nominal, the WattNode will shut down until power is restored. To preserve the energy
measurement across power outages, the WattNode writes the current energy to non-volatile memory every
30 seconds. When power returns, the last stored value stored is recovered.
4.2.1 Energy Output
The energy value is available in two different units:
Network Variable
Resolution
Range
nvoElecKWH
1.0 kilowatt-hour
0 to 50,000 kilowatt-hours
nvoElecWH_f
1.2e-7 × measurement
0 to 1.0e38 watt-hours
Table 4.3: Energy Output Network Variables
