1784-PCIC register, with a fixed capacity of ±1.0 TWh. Reading either Present Value always returns a value scaled to the system Energy Units (see MSV173). 1. The Accumulators return an unsigned integer, 0 – Maximum Present Value. When the energy exceeds the Maximum Present Value, the value wraps to 0 (modulo arithmetic). This view most closely corresponds to traditional analog meters, with the primary advantage that the energy resolution is fixed at 1 Energy Unit. If energy overflows, the overflow energy may still be read by setting the next larger Energy Unit. Negative power causes net accumulators (e.g. ACC1706) to run backwards; underflow causes the value to wrap from 0 backwards to Maximum Present Value. 2. The Analog Inputs (see AI700, AI1700 ff.) return a floating point value that does not overflow (unless the internal 1.0 TWh register itself overflows). However, the resolution will gradually degrade as energy accumulates, making it harder to observe small changes in energy over short intervals. Corresponding objects share Out of Service and Reliability. For example, setting the Out of Service of ACC700 sets Out of Service AI700 at the same time. Both properties automatically reset when the meter itself resets, to False and No Fault Detected respectively. To initialize an accumulator, set Out of Service to True, and then write the desired energy to the Present Value of either object. This may be useful when the EM-RS485 replaces an existing meter. Set Out of Service to False to begin accumulating new energy again. WARNING: Energy accumulators left Out of Service will not accumulate new energy! Reliability returns Over Range when any energy accumulates during Over Voltage (see AI1420) or Over Current (see AI1520) conditions. However, accumulators do not otherwise track reliability. EM-RS485 BACnet Protocol Guide Page 13 of 49 154-0022-0C System ACC700 Total Real Energy R/NV Accumulator versions of AI700 – AI706. The default units are kWh (see MSV173). Returns the combined energy of the system phases (see MSV161). For a 3 Phase installation: Total = ACC1700 + ACC2700 + ACC3700 Import = ACC1702 + ACC2702 + ACC3702 Export = ACC1704 + ACC2704 + ACC3704 Net = ACC1706 + ACC2706 + ACC3706 ACC702 Import ● ACC704 Export ● ACC706 Net ACC720 System Real Energy R/NV Accumulator versions of AI720 – AI726. The default units are kWh (see MSV173). Returns the combined energy of the system phases (see MSV161). Unlike Total Real Energy (above), these accumulators derive from Net Real Power (see AI620). For a 3 Phase installation, System = ∫|𝑷𝑵𝑬𝑻| ∙ 𝑑𝑡 = ∫|𝑷𝑹 + 𝑷𝑺 + 𝑷𝑻| ∙ 𝑑𝑡 Compare the order of the absolute value operations in this example with the Total Real Energy derived from the Total Real Power (see AI600): Total = ∫ 𝚺𝑷 ∙ 𝑑𝑡 = ∫(|𝑷𝑹| + |𝑷𝑺| + |𝑷𝑻|) ∙ 𝑑𝑡 When the individual Real Power (see AI1600) of all system phases flows in the same direction (import or export), the System accumulators track the corresponding Total accumulations exactly. However, the System calculation allows opposite phase powers to cancel before accumulation. 𝑃𝑅 𝑃𝑆 + 𝑃𝑇 |𝑃𝑁| |𝑃𝑅| |𝑃𝑆| + |𝑃𝑇| 𝚺 𝑃 ∫=7 ∫=15 Figure 4: System vs. Total Energy The Import and Export accumulations follow the sign of Net Real Power: Import = � � |𝑷𝑵𝑬𝑻| ∙ 𝑑𝑡 𝑖𝑓 𝑷𝑵𝑬𝑻 > 0 0 𝑜𝑡ℎ𝑒𝑟𝑤𝑖𝑠𝑒 Export = � � |𝑷𝑵𝑬𝑻| ∙ 𝑑𝑡 𝑖𝑓 𝑷𝑵𝑬𝑻 < 0 0 𝑜𝑡ℎ𝑒𝑟𝑤𝑖𝑠𝑒 Net Real Energy (see ACC706) equals any possible System Net accumulator, as the calculation does not take absolute values. ACC722 Import ● ACC724 Export EM-RS485 BACnet Protocol Guide Page 14 of 49 154-0022-0C ACC740 Total Reactive Energy R/NV Accumulator versions of AI740 – AI744. The default units are kVARh (see MSV173). Returns the combined energy of the system phases (see MSV161). For a 3 Phase installation: Total = ACC1740 + ACC2740 + ACC3740 Import = ACC1742 + ACC2742 + ACC3742 Export = ACC1744 + ACC2744 + ACC3744 ACC742 Import ● ACC744 Export ACC760 Total Apparent Energy R/NV Accumulator versions of AI760 – AI764. The default units are kVAh (see MSV173). Returns the combined energy of the system phases (see MSV161). For a 3 Phase installation: Total = ACC1760 + ACC2760 + ACC3760 Import = ACC1762 + ACC2762 + ACC3762 Export = ACC1764 + ACC2764 + ACC3764 ACC762 Import ● ACC764 Export R Phase ACC1700 Total R Phase Real Energy R/NV Accumulator versions of AI1700 – AI1706. The default units are kWh (see MSV173). Returns the accumulation of Real Power 𝑷 (see AI1600). Note the absolute value operation in the accumulation of Total but not Net: Total = ∫|𝑷| ∙ 𝑑𝑡 Net = ∫ 𝑷 ∙ 𝑑𝑡 ∫A = 4 ∫B = –8 ∫C = 2 Total = 14 Import = 6 Export = 8 Net = -2 Figure 5: Real Energy The Import and Export accumulations follow the sign of Real Power: Import = � � |𝑷| ∙ 𝑑𝑡 𝑖𝑓 𝑷 > 0 0 𝑜𝑡ℎ𝑒𝑟𝑤𝑖𝑠𝑒 Export = � � |𝑷| ∙ 𝑑𝑡 𝑖𝑓 𝑷 < 0 0 𝑜𝑡ℎ𝑒𝑟𝑤𝑖𝑠𝑒 Accumulation stops during Phase Loss conditions (see AI1420). ACC1702 Import ● ACC1704 Export ● ACC1706 Net EM-RS485 BACnet Protocol Guide Page 15 of 49 154-0022-0C ACC1740 Total R Phase Reactive Energy R/NV Accumulator versions of AI1740 – AI1744. The default units are kVARh (see MSV173). Returns the accumulation of Reactive Power 𝑸 (see AI1640): Total = ∫|𝑸| ∙ 𝑑𝑡 The Import and Export accumulations follow the sign of Real Power 𝑷 (see AI1600): Import = � � |𝑸| ∙ 𝑑𝑡 𝑖𝑓 𝑷 > 0 0 𝑜𝑡ℎ𝑒𝑟𝑤𝑖𝑠𝑒 Export = � � |𝑸| ∙ 𝑑𝑡 𝑖𝑓 𝑷 < 0 0 𝑜𝑡ℎ𝑒𝑟𝑤𝑖𝑠𝑒 Accumulation stops during Phase Loss conditions (see AI1420). Although Reactive Power itself is signed, the accumulators capture only the magnitude without distinguishing between capacitive and inductive modes. Consider calculating this from average power (one of AI1648 – AI1652) over an interval instead: Net = 𝑸 ∙ Δ𝑡 ACC1742 Import ● ACC1744 Export ACC1760 Total R Phase Apparent Energy R/NV Accumulator versions of AI1760 – AI1764. The default units are kVAh (see MSV173). Returns the accumulation of Apparent Power 𝑺 (see AI1660): Total = ∫ 𝑺 ∙ 𝑑𝑡 = ∫ 𝑽 ∙ 𝑰 ∙ 𝑑𝑡 The Import and Export accumulations follow the sign of Real Power 𝑷 (see AI1600): Import = � � 𝑺 ∙ 𝑑𝑡 𝑖𝑓 𝑷 > 0 0 𝑜𝑡ℎ𝑒𝑟𝑤𝑖𝑠𝑒 Export = � � 𝑺 ∙ 𝑑𝑡 𝑖𝑓 𝑷 < 0 0 𝑜𝑡ℎ𝑒𝑟𝑤𝑖𝑠𝑒 Accumulation stops when the RMS Voltage becomes invalid (see AI1420). ACC1762 Import ● ACC1764 Export S Phase ACC2000– ACC2999 S Phase Accumulators parallel the R Phase, offset +1000. For example, read AI2700 for Total S Phase Real Energy. T Phase ACC3000– ACC3999 T Phase Accumulators parallel the T Phase, offset +2000. For example, read AI3700 for Total T Phase Real Energy. EM-RS485 BACnet Protocol Guide Page 16 of 49 154-0022-0C Analog Inputs • Object Identifier R • Object Name R • Object Type R • Present Value W Only writable when Out Of Service is TRUE • Status Flags R • Event State R Always NORMAL • Reliability W Only writable when Out Of Service is TRUE • Out of Service W • Units of Measure R • Update Interval R • Minimum Present Value R • Maximum Present Value R • Resolution R • Property List R For statistical purposes, analog input values are organized into groups. By convention, the primary object leading each group provides the most accurate, up-to-date reading possible. Secondary objects within a group provide statistical measurements in time that may support some simple logging applications with less overhead for setup and bandwidth. Typical statistical values include: • Smoothed: Returns the value after applying a first-order exponential filter (see AV134). • Minimum: Returns the single lowest valid reading taken since last reset. • Maximum: Returns the single highest valid reading taken since last reset. • Average: Returns the average of all valid readings taken since last reset. Except for the energy accumulators, each analog input group shares common Out Of Service and Reliability properties. Setting Out Of Service to True disables all statistical calculation, so that any group value may be arbitrarily set. Statistics will be reset after setting Out Of Service to False again. Once recorded, there are a few methods to reset statistics records (Minimum, Maximum, Average): • Manually for a single object, by writing 0 to the Present Value (W0 in the Access Legend). • Manually for an individual group, by setting Out Of Service to True and then False again. • Manually for multiple objects, by writing one of the Statistics Reset keys (see AV192, AV1192). • Automatically for single values, by configuring Auto Reset Statistics (see BV195). Most statistical values reset with a value equal to the Present Value of the primary object (see Figure 6). Demand statistical values reset to 0 until the end of the current demand windo |
