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ADE7169ASTZF16 Datasheet(PDF) 49 Page - Analog Devices |
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ADE7169ASTZF16 Datasheet(HTML) 49 Page - Analog Devices |
49 / 140 page Preliminary Technical Data ADE7169F16 Rev. PrD | Page 49 of 140 PKV bits are set in Interrupt Enable Register 3 SFR (MIRQENH, 0xDB), the 8052 core has a pending ADE interrupt. Peak Level Record The ADE7169F16 records the maximum absolute value reached by the voltage and current channels in two different registers— IPEAK and VPEAK, respectively. VPEAK and IPEAK are 16-bit unsigned registers. These registers are updated each time the absolute value of the waveform sample from the corresponding channel is above the value stored in the VPEAK or IPEAK register. The contents of the VPEAK register correspond to the maximum absolute value observed on the voltage channel input. The contents of IPEAK and VPEAK represent the maximum absolute value observed on the Current and Voltage input respectively. Reading the RSTVPEAK and RSTIPEAK registers clears their respective contents after the read operation. PHASE COMPENSATION The ADE7169F16 must work with transducers, which could have inherent phase errors. For example, a phase error of 0.1° to 0.3° is not uncommon for a current transformer (CT). These phase errors can vary from part to part, and they must be corrected in order to perform accurate power calculations. The errors associated with phase mismatch are particularly noticeable at low power factors. The ADE7169F16 provides a means of digitally calibrating these small phase errors. The ADE7169F16 allows a small time delay or time advance to be introduced into the signal processing chain to compensate for small phase errors. Because the compensation is in time, this technique should be used only for small phase errors in the range of 0.1° to 0.5°. Correcting large phase errors using a time shift technique can introduce significant phase errors at higher harmonics. The phase calibration register (PHCAL[7:0]) is a twos comple- ment signed single-byte register that has values ranging from 0x82 (–126d) to 0x68 (104d). The register is centered at 0x40, so that writing 0x40 to the register gives 0 delay. By changing the PHCAL register, the time delay in the Voltage channel signal path can change from – 231.93 μs to +48.83 μs (MCLK = 4.096 MHz). One LSB is equivalent to 1.22 μs (MCLK/5) time delay or advance. A line frequency of 60 Hz gives a phase resolution of 0.026° at the fundamental (i.e., 360° × 1.22 μs × 60 Hz) or 0.00732% of the line period. Similarly, a line frequency of 50Hz gives a phase resolution of 0.022° at the fundamental or 0.0061% of the line period. Figure 33 illustrates how the phase compensation is used to remove a 0.1° phase lead in Current channel due to the external transducer. To cancel the lead (0.1°) in Current channel, a phase lead must also be introduced into Voltage channel. The resolution of the phase adjustment allows the introduction of a phase lead in increment of 0.026°. The phase lead is achieved by introducing a time advance into Voltage channel. A time advance of 4.88 μs is made by writing −4 (0x3C) to the time delay block, thus reducing the amount of time delay by 4.88 μs, or equivalently, a phase lead of approximately 0.1° at line frequency of 60 Hz. 0x3C represents –4 because the register is centered with 0 at 0x40. 1 1 0 1 0 0 1 70 PGA1 IPA IN I ADC 1 HPF 24 PGA2 VP V V ADC 2 DELAY BLOCK 1.22 μs/LSB 24 LPF2 V I 60Hz 0.1° I V CHANNEL 2 DELAY REDUCED BY 4.48 μs (0.1°LEAD AT 60Hz) 0Bh IN PHCAL [5.0] PHCAL [7:0] --231.93 μs TO +48.83μs 60Hz 1 1 Figure 33. Phase Calibration ADE7169F16 RMS CALCULATION Root mean square (rms) value of a continuous signal V(t) is defined as VRMS = ∫ × = T rms dt t V T V 0 2 ) ( 1 (2) For time sampling signals, rms calculation involves squaring the signal, taking the average and obtaining the square root. The ADE7169F16 implements this method by serially squaring the input, averaging them and then taking the root square of the average. The averaging part of this signal processing is done by implementing a Low Pass filter (LPF3 in Figure 35 and Figure 36). This LPF has a -3dB cut-off frequency of 2Hz when MCLK = 4.096MHz. V(t) = ) sin( 2 t V ω × where: V is the rms voltage. ( )t V V t V ω 2 cos ) ( 2 2 2 − = When this signal goes through LPF3, the cos(2ωt) term is attenuated and only the DC term Vrms2 goes through – see Figure 34. V LPF3 INPUT V(t)= ( )t V V t V ω 2 cos ) ( 2 2 2 − = V t V ) ( 2 2 = ) sin( 2 t V ωω ⋅ Figure 34. ADE7169F16 RMS Signal Processing |
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