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Depending on the sign, the incoming pulses are totalled in a positive or a
negative register. In the case of a simple sum (only positive inputs) the
positive register contains the sum and the negative register contains the
value 0.
In the case of frequent changes of the direction of energy flow (e.g. be-
tween export and import forward/backward), the hysteresis (slack) can be
used to activate the function “Differential total calculation” (for energy regis-
ters only). Here pulses will only be added to the positive or negative energy
registers once they have exceeded a minimum amount of energy after a
change of energy flow direction. The function of the hysteresis is one of an
intermediate storage register. Each pulse in positive direction will increase
the value of that register, whereas each pulse in negative direction will de-
crease its value. Pulses only appear at the output of the hysteresis register
once its programmable maximum content is exceeded in either direction.
An integrated energy direction pointer ensures correct output to either
“positive” or “negative” target registers. The purpose of the hysteresis regis-
ter is to prevent unnecessary totalling of pulses in the “positive” and “nega-
tive” registers, when the flow of energy in both directions is almost in
balance. A meaningful guideline for the content of the hysteresis is double
the sum of the absolute value of all weighted inputs of the related total reg-
ister.
Example:
Total Energy
Result with
Hysteresis = 0 kWh Hysteresis = 4 kWh
Export (+) 100 kWh 100 kWh 98 kWh
Import (-) 2 kWh 2 kWh 0 kWh
In addition, the energy increment since the end of the last registration pe-
riod is calculated for both the positive and negative registers of each sum
and for each registration period (Tm1 and Tm2). If the function “balance
calculation” is activated (possible only for demand or energy increment),
then the difference between the positive and negative total registers is cal-
culated at the end of the registration period and only the result is stored in
the relevant register. This value is then multiplied with the time factor (TF =
60/registration period length), which results in the demand value. At the be-
ginning of each new registration period, the energy increment register (and
therefore also the demand register) will be set to 0.
Example:
Demand
Result
Without balance
calculation
With balance calcula-
tion
Export (+) 100 kW 100 kW 98 kW
Import (-) 2 kW 2 kW 0 kW