ADE7758ARWRL datasheet(41/68 Pages) AD

41 / 68 page

ADE7758

Rev. A | Page 41 of 68

ENERGY REGISTERS SCALING

The ADE7758 provides measurements of active, reactive, and

apparent energies that use separate signal paths and filtering for

calculation. The differences in the data paths can result in small

differences in LSB weight between the active, reactive, and

apparent energy registers. These measurements are internally

compensated so that the scaling is nearly one to one. The

relationship between the registers is shown in Table 11.

Table 11. Energy Registers Scaling

Frequency of 60 Hz

Frequency of 50 Hz

Integrator Off

VAR = 1.004 × WATT

VAR = 1.0054 × WATT

VA = 1.00058 × WATT

VA = 1.0085 × WATT

Integrator On

VAR = 1.0059 × WATT

VAR = 1.0064 × WATT

VA = 1.00058 × WATT

VA = 1.00845 × WATT

WAVEFORM SAMPLING MODE

The waveform samples of the current and voltage waveform, as

well as the active, reactive, and apparent power multiplier out-

puts, can all be routed to the WAVEFORM register by setting

the WAVSEL[2:0] bits (Bit 2 to Bit 4) in the WAVMODE

setting the PHSEL[1:0] bits (Bit 0 and Bit 1) in the WAVMODE

waveform sampling. Four output sample rates may be chosen by

using Bit 5 and Bit 6 of the WAVMODE register (DTRT[1:0]).

The output sample rate may be 26.0 kSPS, 13.0 kSPS, 6.5 kSPS,

or 3.3 kSPS (see Table 16).

By setting the WSMP bit in the interrupt mask register to

Logic 1, the interrupt request output IRQ goes active low

when a sample is available. The 24-bit waveform samples are

transferred from the ADE7758 one byte (8 bits) at a time, with

the most significant byte shifted out first.

The interrupt request output IRQ stays low until the interrupt

routine reads the reset status register (see the ADE7758 Interrupts

section).

CALIBRATION

A reference meter or an accurate source is required to calibrate

the ADE7758 energy meter. When using a reference meter, the

ADE7758 calibration output frequencies, APCF and VARCF,

are adjusted to match the frequency output of the reference

meter under the same load conditions. Each phase must be

calibrated separately in this case. When using an accurate source

for calibration, one can take advantage of the line cycle accu-

mulation mode and calibrate the three phases simultaneously.

There are two objectives in calibrating the meter: to establish

the correct impulses/kW-hr constant on the pulse output and to

obtain a constant that relates the LSBs in the energy and rms

registers to Watt/VA/VAR hours, amps, or volts. Additionally,

calibration compensates for part-to-part variation in the meter

design as well as phase shifts and offsets due to the current

sensor and/or input networks.

Calibration Using Pulse Output

The ADE7758 provides a pulsed output proportional to the

active power accumulated by all three phases, called APCF.

Additionally, the VARCF output is proportional to either the

reactive energy or apparent energy accumulated by all three

phases. The following section describes how to calibrate the

gain, offset, and phase angle using the pulsed output

information. The equations are based on the pulse output from

the ADE7758 (APCF or VARCF) and the pulse output of the

reference meter or CFEXPECTED.

Figure 76 shows a flow chart of how to calibrate the ADE7758

using the pulse output. Since the pulse outputs are proportional

to the total energy in all three phases, each phase must be cali-

brated individually. Writing to the registers is fast in order to

reconfigure the part for calibrating a different phase, therefore

Figure 76 shows a method that calibrates all phases at a given

test condition before changing the test condition.

ADE7758ARWRL 数据表(PDF) 41 Page - Analog Devices

ADE7758ARWRL 数据表(HTML) 41 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68

数据表下载