Operating principle

The energy meters calculate the energy from the input power consumed by the counting function (AddPositivePwr, AddNegativePwr or AddPwr) and from the call frequency. The calculated value is added to the actual value and the result value is output via a counter variable (rEAct_InWs, rEAct_Cmpl_InWs, rEAct_Neg_InWs or rEAct_Pos_InWs).

Counting variables

The following counting variables are available:

• AddPositivePwr
• Counts only positive power values. Negative power values are ignored (return inhibited).
• AddNegativePwr
• Counts only negative power values. Positive power values are ignored (advance inhibited).
• AddPwr
• Counts negative and positive power values, taking into account the sign. This means that negative energy values can also result and a positive energy balance can be distinguished from a negative energy balance.

Memory

The function blocks of the energy meters themselves have no remanent memory. In order to avoid losing information when transferring the initial value during initialization, the output can be connected to a remanent memory and its value can be used as the initial value.

Implementation

All blocks of the energy meters must be cyclically supplied with power. Since the counting function records the power value, the appropriate counting function must run in a synchronous task or be called synchronously. Maximum accuracy is achieved if this synchronous task simultaneously operates the fieldbus or is connected to it. If a lower resolution is selected, the call cycle of the counting function should be a multiple of the task that provides the power value.