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The start of the demand interval is not synchronized to internal clock or external
source. In the event of loss of power, or when any demand parameter is changed by
the user, the instrument immediately begins to measure the first normal demand
interval. This moment is considered to be a time base reference for any subsequent
demand interval measurements.
Power Demand Interval
For power demands, demand interval measurements can use internal real-time clock
(RTC), or an external source as a time reference.
When using the internal RTC, the demand period time is defined by the user from 1
and up to 60 minutes in preset intervals. For the external source, the external pulse
sensed via an instrument discrete input denotes the start of the new demand interval.
The number of demand periods for the sliding window technique can be defined
from 1 to 15, for either time reference.
Using internal time base, the start of each demand period is always synchronized
with the beginning of the nearest round interval divisible by the demand period,
considering the instrument' s RTC readings. In the event of loss of power , or
changing any demand parameter, the instrument immediately begins a new shorter
demand interval until the first synchronization. For instance, considering demand
interval time being 15 minute, if power up occurred at 13:37, than first
synchronization will be made at 13:45, and be handled at the end of each following
15 minute interval.
The demand interval duration may by slightly shortened or prolonged by RTC time
update. In all cases, the demand interval will be terminated at the nearest round
boundary, assuming new RTC readings. The power demand calculations will be
always correct.
4.3.7 Resetting the Demands
The demand minimum/maximum keeping registers can be cleared simultaneously via
the front panel, communications, or by using a programmable setpoint. The demand
accumulating registers and demand interval synchronization are never affected by
reset, so the user can reset the extreme demands at any point within the demand
interval without the risk of tampering with demand measurements.
IMPORTANT
1. All the demand accumulating registers are always cleared in the event of power up and
when any demand parameter is changed by the user. These do not affect the demand
minimum/maximum keeping registers.
62
Operation Techniques
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