AT73C500 Просмотр технического описания (PDF) - Atmel Corporation

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AT73C500

Chip Set Solution for Watt-Hour Meters

Atmel Corporation 

In multi-channel mode the active exported energy of each

three meters (phases) is stored in registers 12-14. REG15

is not in use.

The maximum value of different power registers differs,

depending on the calculation formulas used. The scaling of

registers is described below.

If a full scale sine signal is applied to voltage and current

inputs and the voltage and current channels are exactly in

the same phase, a value of 258F C2F7H will be produced

in the 32-bit P1, P2 and P3 registers. The LS bit will corre-

spond to about 34 microwatts in nominal input conditions of

270V maximum phase voltage and 80A maximum current.

If the load is fully reactive (± 90° phase difference) and full

scale signals are applied, the Q1, Q2 and Q3 register con-

tent will be 2231 594DH positive or negative, and the LSB

will represent about 38 µVAr. The maximum value of the

16-bit S registers is 258EH and this value is obtained if a

full scale amplitude is produced to the current and voltage

inputs. LS bit of the S registers correspond to about 2.25VA

power.

The following formula is used to calculate the power factor:

PF = sign(Q) × -aa---bb---ss---(-(--PS----))

The PF register contents 7FFFH represents power factor

value one and the contents 0000H value zero. Negative PF

values are stored correspondingly as negative binary num-

bers. It should be noted that the sign of power factor result

indicates whether the loading is inductive (+) or capacitive

(-).

The contents of frequency register (REG17) actually repre-

sents a 16-bit figure which corresponds to the duration of

50 line frequency cycles. The measurement is made by

comparing the line frequency with one of the sampling

clocks of AT73C500 and therefore the result depends on

the crystal frequency used. With default 3.2768 MHz crys-

tal, the resolution of time value is 1.25 ms. To get the fre-

quency, the following calculation has to be made:

f = R--4---E0----0G---0-1--0--7--Hz

If the master clock frequency (MCLK) of AT73C500 is not

nominal, the following formula gives frequency results:

f = R--4---E0----0G---0-1--0--7-- × 3----.-2--M--7---6C---8--L--M-K----H----z--Hz

In the default condition, value 7FFFH of register 17 corre-

sponds to 1.22 Hz frequency, value 0320H represents

50Hz and 0001H 40 kHz. However, in practice, the band-

width of frequency measurement is limited to 20 Hz to 350

Hz.

The frequency measurement is locked with one of the

phase voltages. If this voltage disappears, AT73C500 tries

to track one of the other phases. The frequency measure-

ment works down to about 10% level of the full scale volt-

age range. The harmonics content of phase voltage should

be below 10%. If it is higher, erroneous frequency results

may be obtained.

The voltage registers (REG19-REG21) are scaled so that

full scale sinusoidal input signal at AT73C501/AT73C502

voltage channels will produce 7A8BH value into voltage

registers. This means that the resolution of the registers is

about 8.6 mV. Accordingly, full scale current will produce

7DA4H to current registers (REG22-REG24) providing a

resolution of about 2.5 mA. In practice, the voltage can be

measured down to about 25V level and current down to

about 100mA.

If either voltage or current, or both, contain a considerable

amount of harmonics producing a square wave type wave-

form, it is recommended to scale the input range so that the

maximum peak-to-peak value is at least 10% below the full

scale range of inputs. This is to avoid overflow in the calcu-

lations performed by AT73C500.

Energy Counters

Four 32-bit counters (REG12-REG15) measure energy

consumption. In nominal situations, the counters are

always incremented when 0.4Wh (0.4VArh) energy is con-

sumed. The counters can store minimum of 1100 days con-

sumption, provided that AT73C501/AT73C502 and

AT73C500 are used with default settings.

Impulse outputs are generated from these counters. The

meter constant rate represents 2 LSBs of a counter which

equals 0.8 Wh (0.8 VArh) and produces 1250

impulses/kWh. (1250 impulses/kVArh). In modes 1 to 4, the

display pulses are generated from 25 LSBs of a counter.

This corresponds to an impulse rate of 100 impulses/kWh

(100 impulses/kVArh). It is possible to adjust this rate with

MCC calibration coefficient. In mode 7, 250 LSBs of the

energy register is needed to generate one impulse (10

impulses/kWh).

The default values above are based on 80ARMS full scale

current, 270VRMS full scale voltage and 3.2768 MHz clock

rate.

The crystal frequency will affect the values of energy regis-

ters (REG12-REG15) and time register (REG 16). It will

also change the pulse rates of the impulse outputs.

10

AT73C500

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