EVAL-ADE7752EB Analog Devices Inc, EVAL-ADE7752EB Datasheet - Page 5

• Manufacturer Part Number: EVAL-ADE7752EB
• Manufacturer: Analog Devices Inc

Specifications of EVAL-ADE7752EB

• Lead Free Status / Rohs Status: Not Compliant

REV. PrB 06/02
SETTING UP THE EVALUATION BOARD AS AN
SETTING UP THE EVALUATION BOARD AS AN
SETTING UP THE EVALUATION BOARD AS AN
SETTING UP THE EVALUATION BOARD AS AN
SETTING UP THE EVALUATION BOARD AS AN
ENERGY METER
ENERGY METER
ENERGY METER
ENERGY METER
ENERGY METER
Figure 5 shows a typical set up for the ADE7752 evaluation
board. In this example a kWh meter for a 4 wire, three phase
distribution system is shown. Current Transformers are used
to sense phases' current and are connected as shown in Figure
5. For a more detailed description on how to use a CT as a
current transducer see the Current Sense Inputs section of this
documentation. The line voltage is connected directly to the
evaluation board as shown. Note JP23, JP24 and JP25 should
be left open to ensure that the attenuation networks are not
bypassed. Also note the use of two power supplies.
The second power supply is used to power the optical
isolation. With JP26 left open, this will ensure that there is no
electrical connection between the high voltage test circuit and
the frequencies outputs. The power supplies should have
floating voltage outputs.
Setting up the evaluation board for the ADE7752
The configuration of the jumpers on the ADE7752 evaluation
board for operation with the ADE7752 are detailed in Figure
5. The selection of the outputs frequencies of CF, F1 and F2
is done by configuring SCF, S1 and S0 with jumpers P16,
P12 and P14 respectively.
three active energies (arithmetic sum or sum of the absolute
values) can also be selected on the evaluation board with
Jumper P3. Table III details the action of each jumper.
If CTs have a turn ration of 1:1800, the burden resistance of
the CTs can be placed on the evaluation board at SH1A,
SH2A, SH1B, SH2B, SH1C and SH2C.
The meter is intended to be used with a line - neutral voltage
of 220 V and a maximum current per phase of 40 A. The
frequency outputs F1 and F2 can be used to drive a mechani-
cal counter. These outputs will be calibrated to provide
100imp/kWhr. The logic output CF can be used for calibra-
tion purposes and is shown connected to a frequency counter
via the opto-isolator in Figure 5.
PRELIMINARY TECHNICAL DATA
Signal State
S C F
S 1
S 0
TABLE III : ADE7752 frequency setting
1
0
1
0
1
0
1
0
Jumper position
P16 - RIGHT
P16 - LEFT
P12 - LEFT
P12 - RIGHT
P14 - RIGHT
P14 - LEFT
P3 - LEFT arithmetic sum
P3 - RIGHT Sum of absolute values
The mode of summation of the
PRELIMINARY TECHNICAL DATA
– 5 –
At maximum current (40 A) the power seen by the meter will
be 26.4 kW. This will produce a frequency of 0.733 Hz on
the logic outputs F1 and F2 when these outputs are calibrated
to 100 imp/kWhr (100 imp/hr = 0.0277 Hz, 0.02777 x 26.4
= 0.733 Hz). From Table III in the ADE7752 datasheet, the
closest frequency to 0.733 Hz in the half scale ac inputs
column is for F1-5 = 4.77 Hz. Therefore this frequency is
selected by setting S0 = 1 and S1 = 0. The choice of CF
frequencies in this mode (see Table IV of the ADE7752
datasheet are 16 times F1 or 160 times F1. For this example
16 times F1 is selected by setting SCF = 1.
Since the voltage on the current inputs (IAP/IAN, IBP/IBN
and ICP/ICN) are fixed, the only possible way of calibrating
(adjusting) the output frequency on F1 and F2 is by varying
the voltage on the voltage channels. This is carried out by
varying the attenuation of the line voltage using the trim pots.
First we can calculate the voltage required on the voltage
channels in order to calibrate the frequency on F1 and F2 to
100 imp/kWhr. The ADE7752 datasheet gives the equation
which relates the voltage on the current channels and voltage
channels to the output frequency on F1 and F2.
With a burden resistor of 7.6 Ω, the current channels' levels
for 5 A is 5 A / 1800 X 2 X 7.6 = 0.042 V rms. The output
frequency at 5A on F1 and F2 should be 0.02777 Hz (100
imp/kWhr) x 3.3 (3 x 220 V x 5 A) = 0.0917Hz.
From Equation 1 the voltage on voltage channels should be
set to 139.8 mV rms. The attenuation network as shown in
Figure 3 is used to attenuate 220 V to 139.8 mV.
R41 = R42 = R45 = R46 = R48 = R49 =786 kΩ,
R43= R44 = R47 = R10 = R8 = R14 = R16 = R20 = R22
= 500Ω
and trim pots = 500 Ω.
Freq
=
. 6
82
×
(
V
AN
×
I
A
+
V
V
BN
REF
×
EVAL-ADE7752EB
2
I
B
+
V
CN
×
I
C
)
×
F
1
−
5
(1)