7 Maximum Demand Calculation
The maximum power consumption of an installation is an important measurement as most
power utilities base their charges on it. Many utilities use a thermal maximum demand
indicator (MDI) to measure this peak power consumption. An MDI averages the power
consumed over a number of minutes, such that short surges do not give an artificially high
reading.
The Integra 1540 uses a sliding window algorithm to simulate the characteristics of a thermal
MDI instrument, with the demand period being updated on a minute by minute basis.
The demand period can be reset, which allows synchronisation to other equipment. When it is
reset, the values in the Demand and Maximum Demand registers are set to zero.
Time Integration Periods
8, 15, 20 and 30 minutes
The number of sub-intervals, i.e. the demand time in minutes, can be altered either by using the
“Demand Integration Time” set-up menu (see Section 5.2.3 Demand Integration Time Edit) or
via the RS 485 port using the Modbus‚ protocol.
Note: During the initial period when the “sliding window” does not yet contain a full set of
readings (i.e. the elapsed time since the demands were last reset or the elapsed time since the
Integra 1540 was switched on is less than the selected demand time) the maximum demands
(HiAd and HiPd) will remain at zero and not follow the instantaneous demands.
The Time Integration Period can be altered either by using the “Demand Integration Time” set-
up menu (see Section 5.2.3 Demand Integration Time Edit ) or via the RS 485 port using the
Modbus‚ protocol.
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