71M6531D_10 Datasheet, PDF (92/120 Pages) Teridian Semiconductor Corporation – Energy Meter IC

Data Sheet 71M6531D/F-71M6532D/F
FDS 6531/6532 005
4.3.7 CE Transfer Variables
When the MPU receives the XFER_BUSY interrupt, it knows that fresh data is available in the transfer
variables. CE transfer variables are modified during the CE code pass that ends with an XFER_BUSY
interrupt. They remain constant throughout each accumulation interval. In this data sheet, the names of
CE transfer variables always end with _X.
The transfer variables can be categorized as:
1. Fundamental energy measurement variables
2. Instantaneous (RMS) values
3. Other measurement parameters
Fundamental Energy Measurement Variables
Table 61 describes each transfer variable for fundamental energy measurement. All variables are signed
32-bit integers. Accumulated variables such as WSUM are internally scaled so they have at least 2x
margin before overflow when the integration time is one second. Additionally, the hardware will not permit
output values to fold back upon overflow.
CE
Address
0x85
0x86
0x87
0x8A
0x8B
0x8C
Name
WSUM_X
W0SUM_X
W1SUM_X
VARSUM_X
VAR0SUM_X
VAR1SUM_X
Table 61: CE Transfer Variables
Description
For EQU[2:0] = 2, this register holds the calculated sum of Wh samples
from each wattmeter element (In_8 is the gain of 1 or 8 configured by
IA_SHUNT or IB_SHUNT).
LSB = 6.6952*10^-13 VMAX IMAX / In_8 Wh.
The sum of Wh samples from each wattmeter element (In_8 is the gain
of 1 or 8 configured by IA_SHUNT or IB_SHUNT).
LSB = 6.6952*10^-13 VMAX IMAX / In_8 Wh.
For EQU[2:0] = 2, this register holds the calculated sum of VARh
samples from each element (In_8 is the gain of 1 or 8 configured by
IA_SHUNT or IB_SHUNT).
LSB = 6.6952*10^-13 VMAX IMAX / In_8 VARh.
The sum of VARh samples from each element (In_8 is the gain 1 or 8
configured by IA_SHUNT or IB_SHUNT).
LSB = 6.6952*10^-13 VMAX IMAX / In_8 VARh.
WxSUM_X is the Wh value accumulated for element X in the last accumulation interval and can be computed
based on the specified LSB value.
For example, with VMAX = 600 V and IMAX = 208 A, the LSB for WxSUM_X is 0.08356 µWh.
Instantaneous Measurement Variables
Table 62 contains various measurement results. The Frequency measurement is computed for the phase
selected with FREQSELn bits in the CECONFIG register.
IxSQSUM_X and VxSQSUM are the squared current and voltage samples acquired during the last accumulation
interval. They can be used to calculate RMS voltages and currents. INSQSUM_X can be used for computing
the neutral current.
Table 62: CE Energy Measurement Variables
CE
Address
Name
Description
Fundamental frequency.
0x82
FREQ_X
LSB ≡ ^FS ≈ 0.587 ⋅10^−6 Hz
2 ³²
0x8F
I0SQSUM_X The sum of squared current samples from each element.
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