SA4120A
Reverse Energy Flow Indication
resistance should also be significantly smaller than the DC
resistance of the current transformers secondary winding.
The SA4120A assesses the phase difference between the
voltage and current channel signals. If this phase difference
is greater than 90 degrees then the reverse energy indicator
is activated. This facility is designed to detect the wrongful
connection or possible tampering of the meter. The operation
of the direction output is fully described in the Output Signals
section.
When using a shunt resistor as a current sensing element the
voltage drop across the shunt resistor RSH at maximum rated
mains current (IMAX) should not be less than 5mVRMS and not
exceed 100mVRMS
.
The resistors R1 to R4 define the current flowing into the
device. For best performance the SA4120A requires anti-
alias filters on the current sense inputs. These filters are
realized by means of the capacitors C1 and C2. The typical
cut-off frequency of these filters should be between 10kHz
and 20kHz. The optimum input network is achieved by setting
the input resistors equal, i.e. setting R1 = R2 = R3 = R4 = RC.
This sets the equivalent resistance associated with each
capacitor to RC/2.
Starting Current
The SA4120A generates pulses on the pulse output for an
input power greater than 0.02% of FMAX. This is to comply with
the IEC requirement where the meter is required to generate
pulses for currents greater than 0.4%Ib.
Power-On Reset
The SA4120A has a power-on reset circuitry that activates
whenever the voltage between VDD and VSS is less than
3.6V ± 8%.
R1
R2
Current In
IIP
IIN
IIP
IMAX
16µARMS
C1
C2
GND
RSH
Power Consumption
The power consumption of the SA4120A integrated circuit is
less than 25mW.
GND
GND
R3
R4
Current Out
Compatibility with SA2002H
R1
R2
The SA4120A can be used as a functionally compatible
replacement for the SA2002H. It should however be noted
that the value of the reference resistor on the VREF pin has
to be changed from 24k to 47k
16µARMS
CT1
C1
C2
Current In
RA
RB
IMAX
GND
R3
Current Out
IIN
INPUT SIGNALS
Voltage Reference (VREF)
A bias resistor of 47k sets optimum bias and reference
conditions on chip. Calibration of the SA4120A should be
done on the voltage input and not on the VREF input.
R4
Figure 8: Current sense input configuration
Voltage Sense Input (IVP)
Figure 9 shows the voltage sense input configuration. The
voltage sense input saturates at an input current of
±17.6µARMS (±25µAPEAK). The current into the voltage sense
input should be set to 14µARMS at nominal mains voltage
(VNOM) to allow for a mains voltage variation of up to +25%
without saturating the voltage sense input.
Current Sense Inputs (IIP and IIN)
Figure 8 shows the typical connections for a current sensor
input when using a shunt or a current transformer as a current
sensing element. A typical single channel meter can be
designed with either a current transformer or a shunt resistor
as a current sensing element. At maximum rated mains
current (IMAX) the resistor values should be selected for an
input current of 16µARMS. The current sense inputs saturate
at an input current of ±17.6μARMS (±25μAPEAK), so this allows
about 10% headroom until saturation occurs.
R1
R2
R3
VNOM
Voltage In
Neutral
P1
R4
IVP
14µARMS
GND
(P1 + R5) << R4 << (R1 + R2 + R3)
C1
R5
For a current transformer application the resistors RA and RB
form the termination resistor. The reference level is
connected in the centre of the termination resistor to achieve
purely differential input currents. The voltage drop across the
GND
GND
Figure 9: Voltage sense input configuration
termination resistors at maximum rated mains current (IMAX
)
should be in the order of 100mVRMS. The termination
SPEC-3094 (REV. 2)
29-09-2017
8/14
SAMES [ SAMES ]
