71M6533 Datasheet, PDF (91/124 Pages) Teridian Semiconductor Corporation – Energy Meter IC

FDS_6533_6534_004
71M6533/71M6534 Data Sheet
4.3 CE Interface Description
4.3.1 CE Program
The CE performs the precision computations necessary to accurately measure power. These computa-
tions include offset cancellation, phase compensation, product smoothing, product summation, frequency
detection, VAR calculation, sag detection and voltage phase measurement. All data computed by the CE
is dependent on the selected meter equation as given by EQU (in I/O RAM). As a function of EQU, the
element components V0 through I2 take on different meanings.
The CE program is supplied by Teridian as a data image that can be merged with the MPU operational
code for meter applications. Typically, the CE program covers most applications and does not need to be
modified. Other variations of CE code may be available from TERIDIAN. The description in this section
applies to CE code revision CE34A02D, which functions for both the 71M6533 and the 71M6534. This
version of the CE code does not process the ID current channel. CE codes capable of calculating and
measuring the ID channel are available from Teridian.
4.3.2 CE Data Format
All CE words are 4 bytes. Unless specified otherwise, they are in 32-bit two’s complement format
(-1 = 0xFFFFFFFF). Calibration parameters are defined in flash memory (or external EEPROM) and
must be copied to CE data memory by the MPU before enabling the CE. Internal variables are used in
internal CE calculations. Input variables allow the MPU to control the behavior of the CE code. Output
variables are outputs of the CE calculations. The corresponding MPU address for the most significant
byte is given by 0x0000 + 4 x CE_address and by 0x0003 + 4 x CE_address for the least significant byte.
4.3.3 Constants
Constants used in the CE Data Memory tables are:
• Sampling Frequency: F_S = 32768 Hz/13 = 2520.62 Hz.
• F₀ is the fundamental frequency of the mains phases.
• IMAX is the external rms current corresponding to 250 mV pk at the inputs IA, IB and IC.
• VMAX is the external rms voltage corresponding to 250 mV pk at the VA, VB and VC inputs.
• NACC, the accumulation count for energy measurements is PRE_SAMPS*SUM_CYCLES. This value
also resides in SUM_PRE (CE address 0x23) where it is used for phase angle measurement.
• The duration of the accumulation interval for energy measurements is PRE_SAMPS*SUM_CYCLES/F_S.
• ln_8 is a gain constant of the current channel, n. Its value is 8 or 1 and is controlled by In_SHUNT.
• X is a gain constant of the pulse generators. Its value is determined by PULSE_FAST and PULSE_SLOW.
• Voltage LSB for sag detection = VMAX * 7.879810^-9 V.
The system constants IMAX and VMAX are used by the MPU to convert internal digital quantities (as used
by the CE) to external, i.e. metering quantities. Their values are determined by the scaling of the voltage
and current sensors used in an actual meter. The LSB values used in this document relate digital quanti-
ties at the CE or MPU interface to external meter input quantities. For example, if a SAG threshold of 80
V peak is desired at the meter input, the digital value that should be programmed into SAG_THR would be
80 V/SAG_THR_LSB, where SAG_THR_LSB is the LSB value in the description of SAG_THR.
The parameters EQU, CE_E, PRE_SAMPS, and SUM_CYCLES essential to the function of the CE are stored
in I/O RAM (see Section 4.2 I/O RAM Description – Alphabetical Order).
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