PM2002DP
ANALOG SECTION
The analog (metering) interface described in this section is
designed for measuring 220V/80A with precision better than
Class 1.
The most important external components for the SA2002D
integrated circuit are the current sense resistors, the voltage
sense resistors and the bias setting resistor. The resistors
used in the metering section should be of the same type so
temperature effects are minimized.
Voltage Input IVP
The voltage input of the SA2002D (IVP) is driven with a current
of 14µA at nominal mains voltage. This voltage input saturates
at approximately 17µA. At a nominal voltage current of 14µA
allows for 20% overdriving. The mains voltage is divided with a
voltage divider to 14V that is fed to the voltage input pins via a
1MW resistor
Voltage Divider
The voltage divider is (Figure 3) calculated for a voltage drop of
14V. Treat C7 as a short circuit and ignore J16. Equations for
the voltage divider in figure 3 are:
RB = R1 + R2 + R3 + R15 + R10
RB = R12 || ( R11 + P1 / 2)
Combining the two equations gives:
(RA + RB) / 220V = RB / 14V
Values for resistors R10 = 47W, R11 = 22kW, P1=10kW and
R12 = 1MW is chosen.
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Standard resistor values of R1, R2, R3 and R15 are chosen to
be 47kW, 150kW, 47kW and 150kW. The resistor RA is divided
so that the voltage drop across one resistor is within the
specified limits of the resistor type that is used, usually
200VDC. The resistor value ratios are chosen so that shorting
J16 the module could be used on a 110VAC mains system.
CURRENT SENSOR INPUT RESISTORS FIGURE 4 (USING
A SHUNT RESISTOR)
The resistors R6, R7 define the current level into the current
sense inputs the device. The voltage drop across the shunt
should be at least 20mV at rated conditions. A shunt resistor
with a value of 50mV @80A was chosen for the application
module for its ease of use. The resistor values are calculated
for an input current of 16µA on the current inputs at rated
conditions. For a 80A meter the resistor values are calculated
as follows:
R6 = R7 = (I
L
/ 16µA) x R
SH
/ 2
= 80A / 16µA x 625uW / 2
= 1.5625kW
I
L =
Line current
A standard value of 1.6kW is chosen.
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R14
L
R6
R7
Substituting the values result in:
RB = 26.29kW
RA = RB x (220V / 14V - 1)
RA = 386.84kW
Figure 4: Current input configuration
J16
C7
R11
NEUTRAL
R10
R1
R2
R3
R15
R12
P1
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Figure 3: Mains voltage divider
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