The instantaneous v samples are used to produce the following information:
• Accumulated squared voltage values
• Accumulated active energy values
• Accumulated reaction energy values (derived by adding a 90phase shift)
These accumulated values are processed by the foreground process (see Section 3.3).
3.2.3 Current
The dc content also must be removed from the current samples. The offset voltage supplied to the CT is also sampled. Subtracting this offset sample from the current sample creates a pseudodifferential effect, which improves crosstalk and noise disturbances and provides a first-stage dc removal effect. An additional dc removal filter completes this process.
The instantaneous i samples are used to produce the accumulated squared values and the two energy values.
3.2.4 Frequency Measurement and Cycle Tracking
The main task of the background process is to measure and process the instantaneous current and voltage signals for each phase. These are then accumulated in 48-bit registers.
A cycle tracking counter and sample counter keep track of how many samples have been accumulated. When approximately one second’s worth of samples have been accumulated in the 48-bit registers by the background process, the foreground process is notified that it can produce the average results, such as RMS and power values. Cycle boundaries are used to trigger the foreground averaging process, because this gives very stable results.
For frequency measurements, a straight line interpolation between the zero crossing voltage samples is used. Figure 9 depicts the samples near the zero-crossing point.