Operation
21
4.1.3 Time of Day
The time of day variable
nviTimeSet
is an input that the WattNode uses to timestamp alarms, peak demand,
energy clear time and peak demand clear time. It also keeps demand intervals synchronized. It is not
necessary to bind this variable, but if it is not set, then alarms will be reported with time fields set to zero,
and the demand measurements will be timed off the WattNode’s internal crystal. The internal crystal is
stable to 0.02%, and will not contribute a significant error to demand measurements. Regular updates to the
time of day prevent long term demand drift. Without updates to the time of day a timing error of 0.02%
could result in a drift of up to 8 minutes per month. If the demand intervals of several WattNodes are
supposed to stay synchronized, this may not be acceptable.
The
nviTimeSet
variable may be bound to a time stamp network variable in a monitoring computer, or it
may be bound to a separate clock node on the network. The WattNode internally tracks time, so if
nviTimeSet
is bound, it does not need to be updated frequently. Updating the time of day hourly or daily
should be sufficient.
Tampering with the
nviTimeSet
variable can affect the timing of demand measurements that may be used
for billing. To prevent unauthorized tampering, authentication should be enabled for
nviTimeSet
.
4.1.4 Alarms
The WattNode has both power and demand alarms. The power alarm can be configured for an over-power
alarm and an under-power alarm. The demand alarm can be configured for two levels of over-power
alarms. Whenever an alarm occurs, or is cleared, the Node object alarm SNVT
nvoAlarm
is updated. The
alarm SNVT contains the following fields:
location – The 6 character location of the WattNode.
object_id – The number of the object reporting the alarm (2 - Power, 3 - Demand).
alarm_type – The alarm condition:
Alarm Type
Number
Description
AL_NO_CONDITION
0
No alarm condition present
AL_LOW_LMT_CLR_1
5
Clear alarm low 1
AL_LOW_LMT_CLR_2
6
Clear alarm low 2
AL_HIGH_LMT_CLR_1
7
Clear alarm high 1
AL_HIGH_LMT_CLR_2
8
Clear alarm high 2
AL_LOW_LMT_ALM_1
9
Set alarm low 1
AL_LOW_LMT_ALM_2
10
Set alarm low 2
AL_HIGH_LMT_ALM_1
11
Set alarm high 1
AL_HIGH_LMT_ALM_2
12
Set alarm high 2
Table 4.2: Alarm Types
priority_level – The priority of the alarm. Lower numbers indicate lower priority.
index_to_SNVT – The SNVT number of the variable that caused the alarm. This is needed so that the
value
field can be properly interpreted. Both the power and demand alarms use SNVT_power_f
to report the value that caused the alarm.
value – The value of the variable that caused the alarm.
alarm_limit – The configured value at which the alarm is triggered.
timestamp – Year, month, day, hour, minute, and second fields indicating the time at which the alarm
occurred. If the time of day has not been set, then all timestamp fields will be zero except year
which will be 65535 to indicate that the time is not known.
