AVR465 datasheet(19/40 Pages) ATMEL

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AVR465

2566A-AVR-07/04

Here P is active power in watts and MC is the meter constant in impulses/kilowatt-

hour. Note, that the pulse frequency also depends on the system clock. The above

equation assumes a system clock of 4MHz.

The calibration coefficient is treated as a 16-bit, unsigned integer.

The Energy Pulse output is typically wired to an LED and used for calibration and

verification purposes. The pulse must be sufficiently long to light the LED for an

optical reader to register it, but also sufficiently short to allow a reasonably high output

frequency. The default is 50ms active time, which limits the frequency to about 10Hz.

At 4MHz system clock, 10A max current and 230V nominal voltage, this means the

maximum meter constant is about 15000 imp/kWh. To increase the meter constant

above this, the maximum current and the pulse length must be decreased.

Another limitation is the quantization of the pulse interval. At default system clock

(4MHz) and default T/C prescaler (1024), the timer is updated once every

1024/4000000 = 0.256ms. Assuming highest default pulse rate (10Hz) the pulse

interval is 100ms and the highest quantization inaccuracy is +/-(0.256/100) = +/-

0.256%. For practical purposes it is recommended to scale system clock, maximum

current and meter constant such that the timer/counter interval never goes below,

say, 500 timer ticks. By default (4MHz, 10A, 230V, 10000imp/kWh) the pulse interval

will not go below 500 ticks.

A pulse pair is provided to drive a stepper-motor counter. Typically, the required

display pulse rate is much lower than the energy pulse rate. The pulse rate, fDP, can

be adjusted using the DPC calibration coefficient, as follows:

Equation 26.

Effect of Display Pulse Constant.

DPC

DP =

Here fEP is the energy pulse rate. The 16-bit display constant is treated unsigned.

The EEPROM layout of calibration coefficients is shown in the table below. All

coefficients are 16-bit wide and stored with high byte first, then low byte.

Table 6.

Calibration Coefficient Layout in EEPROM.

ADDR.

+ 0x00

+ 0x01

+ 0x02

+ 0x03

+ 0x04

+ 0x05

+ 0x06

+ 0x07

0x00

PCC0

PCC1

PCC2

ILG0

0x08

ILG1

ILG2

ING0

ING1

0x10

ING2

DPC

0x18

CRCW

CRC16

PCC is the phase calibration coefficient and ILG and ING are the current gain

coefficients for live and neutral wires, respectivelty. UG is the voltage gain coefficient,

MC the meter constant and DPC the display pulse constant. CRC16 contains the

checksum for the low 32 bytes of the EEPROM. If CRCW is set to to 0x4357 then the

checksum is calculated by the firmware and written to CRC16.

Limitations

Display Constant

Coefficient Layout

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