Maxim Integrated 71M6541 Demo Board - Manual (Page 17)

71M6541 Demo Board REV 3.0 User’s Manual
17 Rev 4.0
1.8.2 USING THE DEMO BOARD FOR ENERGY MEASUREMENTS
The 71M6541 Demo Board was designed for use with shunt resistors connected directly to the IAP/IAN pins of
the 71M6541 and via the Remote Sensor Interface and it is shipped in this configuration.
The Demo Board may immediately be used with a 50
µΩ
shunt resistor (ANSI) or a 120
µΩ
shunt resistor (IEC).
It is programmed for a kh factor of 1.0 (see Section 1.8.4 for adjusting the Demo Board for shunts with different
resistance).
Once, voltage is applied and load current is flowing, the red LED D5 will flash each time an energy sum of 1.0
Wh is collected. The LCD display will show the accumulated energy in Wh when set to display mode 3 (com-
mand
>M3 via the serial interface).
Similarly, the red LED D6 will flash each time an energy sum of 1.0 VARh is collected. The LCD display will
show the accumulated energy in VARh when set to display mode 5 (command
>M5 via the serial interface).
1.8.3 ADJUSTING THE KH FACTOR FOR THE DEMO BOARD
The 71M6541F Demo Board is shipped with a pre-programmed scaling factor Kh of 1.0, i.e., 1.0 Wh per pulse.
In order to be used with a calibrated load or a meter calibration system, the board should be connected to the
AC power source using the spade terminals on the bottom of the board. The shunt resistor should be connected
to the dual-pin header labeled J3 on the bottom of the board.
The Kh value can be derived by reading the values for IMAX and VMAX (i.e., the RMS current and voltage val-
ues that correspond to the 250mV maximum input signal to the IC), and inserting them in the following equation
for Kh:
Kh = 109.1587* VMAX * IMAX / ( SUM_SAMPS * WRATE *X),
See the explanation in section 1.10.4 for an exact definition of the constants and variables involved in the equa-
tion above.
1.8.4 ADJUSTING THE DEMO BOARDS TO DIFFERENT SHUNT RESISTORS
The Demo Board is prepared for use with 120
µΩ or 50 µΩ (ANSI option) shunt resistors in both current chan-
nels. For the Demo Board, a certain current flowing through the 120
µΩ shunt resistor will result in the maximum
voltage drop at the ADC of the 71M6541. This current is defined as IMAX.
IMAX will change when different values are used for the shunt resistor(s) which will require that WRATE has to
be updated as shown in section 1.10.4.
1.8.5 USING THE PRE-AMPLIFIER
In its default setting, the 71M6541 is applies a gain of 1 to the current input for phase A (IAP/IAN pins). This
gain is controlled with the
PRE_E bit in I/O RAM (refer to the IC data sheet). The command line interface (RI
command) can be used to set or reset this bit. It is recommended to maintain the gain of setting of 1
(RI2704=0x90).
1.8.6 USING CURRENT TRANSFORMERS (CTs)
Phase B of the 71M6541 Demo Board can be equipped with a CT that may be connected at header J8. A bur-
den resistor of 1.7
Ω, or any other value may be installed at the R33 and R34 locations. With a 2000:1 ratio CT,
the maximum current fort phase B will be 208 A.
Note: The CT configuration will require a different version of the Demo Code.
Current measurements can be displayed for phase B by the demo code, and the corresponding currents can be
extracted by the MPU from the CE registers for tamper detection when using the Demo Code for EQU 0.
1.8.7 IMPLEMENTING A SINGLE-PHASE 3-WIRE METER (EQU 1)
This application will require two identical current sensors for each phase. The simplest approach is to use iden-
tical shunt resistors for each channel.
1.8.8 ADJUSTING THE DEMO BOARDS TO DIFFERENT VOLTAGE-DIVIDERS
The 71M6541 Demo Board comes equipped with its own network of resistor dividers for voltage measurement
mounted on the PCB. The resistor values (for the D6541 REV 3.0 Demo Board) are 2.5477M
Ω (R15-R21, R26-
R31 combined) and 750
Ω (R32), resulting in a ratio of 1:3,393.933. This means that VMAX equals
176.78mV*3,393.933 = 600V. A large value for VMAX has been selected in order to have headroom for