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전자부품 데이터시트 검색엔진 |
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전자부품 데이터시트 검색엔진 |
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ADE9078 데이터시트(PDF) 43 Page - Analog Devices |
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ADE9078 데이터시트(HTML) 43 Page - Analog Devices |
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43 / 108 page  ADE9078 Data Sheet Rev. 0 | Page 42 of 107 Energy Accumulation Details Internal Energy Register Overflow Rate There are 42-bit internal signed energy accumulators for each phase of each energy accumulation, as shown in Figure 61. These accumulators update at a rate of fDSP = 4 kSPS. To calculate the time until the internal accumulator overflows with full-scale inputs and all digital gain and offset factors at zero, use the following equation. Maximum Internal Energy Accumulator Time (sec) = × DSP f SCALE FULL AT AWATT _ _ _ 241 where AWATT_AT_FULL_SCALE refers to the nominal AWATT value with full-scale inputs. For example, with MTEN = 0, for single-point gain compensation and AIGAIN, AVGAIN, APGAIN, and AWATTOS all equal to zero, the Phase A total active energy has a digital gain of 1. Thus, the Phase A total active energy accumulated in the internal accumulator overflows in 26.4 sec with the nominal full-scale AWATT value of 20,823,646. Maximum Internal Energy Accumulator Time (sec) = sec 4 . 26 4000 20,823,646 241 = × User Energy Register Update Rate, EGYRDY As shown in Figure 61, the internal energy accumulator is latched into a user accessible energy register or added to a user accessible register at a rate of EGYRDY. Figure 63 further shows how the EGYRDY update rate is generated. The EGYRDY update rate occurs after EGY_TIME + 1 fDSP samples or EGY_TIME + 1 half line cycles, according to the EGY_TMR_ MODE bit in the EP_CFG register. If EGY_TMR_MODE = 0, select the sample-based accumulation as follows: Internal Energy Accumulator Time (sec) = + DSP f TIME EGY 1 _ The EGY_TIME[12:0] register allows up to (8191 + 1) = 8192 samples to be accumulated, which corresponds to 8192/4000 = 2.048 sec if EGY_TMR_MODE = 0. Internal Energy Accumulator Time (sec) = sec 048 . 2 4000 1 8191 = + If EGY_TMR_MODE = 1, select the half line cycle-based accumulation as follows: Internal Energy Accumulator Time (sec) = + RATE ZX TIME EGY _ 1 _ With a 50 Hz line frequency and a zero-crossing interrupt rate of 100 Hz, the maximum accumulation time is 81.92 sec with EGY_TIME equal to 0x1FFF (8191d). Internal Energy Accumulator Time (sec) = 92 . 81 100 1 8191 = + If EGY_TMR_MODE = 1, the zero-crossing source to monitor is selected in the ZX_SEL bits in the ZX_LP_SEL register, as shown in Figure 63. Note that the internal energy register overflows in 26.4 sec with full-scale inputs so EGY_TIME must be set lower than 2640d to prevent overflow when EGY_TMR_MODE = 1. ENERGY POWER 0 ZX_SEL 1 11 10 ZXVA ZXVB ZXVC ZXCOMB 00 01 CF3_CFG CF3 0 1 EGY_TMR_MODE CF3/ZXPIN COUNTER EGY_TIME[12:0] + 1 EQUAL? EGYRDY UPDATERATE EGYRDY COUNTER PWR_TIME[12:0] + 1 EQUAL? PWRRDY UPDATE RATE PWRRDY fDSP fDSP Figure 63. EGYRDY and PWRRDY Update Rates Reloading or Accumulating User Energy Register When an EGYRDY event happens, the internal energy accumulation is either directly loaded into the xWATTHR register or added to the existing accumulation based on the state of the EGY_LD_ACCUM bit in the EP_CFG register. If EGY_LD_ACCUM = 0, the internal energy register is added to the user accessible energy register. If EGY_LD_ACCUM = 1, the internal energy register overwrites the user accessible energy register. Finally, the internal energy accumulator resets and starts counting again from zero. User Energy Register Overflow Rate There are 45-bit user accessible signed energy accumulators for each phase of each energy accumulation. These accumulators update at a rate according to EGYRDY, as described in the User Energy Register Update Rate, EGYRDY section. The following equation shows how to calculate the time until the user accessible accumulator overflows with full-scale inputs and all digital gain and offset factors at zero. For this example, assume that the energy register is updating at every fDSP = 4 kSPS sample. Maximum User Energy Accumulator Time (sec) = × DSP f SCALE FULL AT AWATT _ _ _ 244 where AWATT_AT_FULL_SCALE refers to the nominal AWATT value with full-scale inputs. |
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