AS8168 Ver la hoja de datos (PDF) - austriamicrosystems AG

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AS8168

Single Phase Average Energy Metering IC with On-Chip Calibration, Stepper Motor Drive and LED Output

austriamicrosystems AG 

Data Sheet AS8168

- Defined current and calibration time method

- Comparison method

It is also possible to perform:

- Calibration without on-chip programming

Defined Current and Calibration Time Method

The AS8168 generates a pulse whenever the internal energy accumulator contains a value, which is greater than a

programmed threshold. This threshold is the parameter Pulse_lev. This parameter depends on the basic meter properties,

the mains voltage Vmains and the maximum current to be measured, Imax. Furthermore, it is assumed that through a resistor

divider Vmains is scaled down to match the maximum input range of the VP input.

Firstly, an ideal value for Pulse_lev is calculated. This is the value, which would have to be programmed into the AS8168

device if the meter system was perfect.

The following formula calculates this ideal value of Pulse_lev:

Pulse _ lev(ideal) = 230V * 20A * 435924

Vmains Imax

A calibration is performed to compensate for system non-idealities like resistor tolerances etc. The effect of these non-

idealities is that with the ideal Pulse_lev value the pulse rates will not be correct. In order to calibrate the meter, a new

Pulse_lev value has to be found. Figure 6 shows the basic calibration setup. CAL pulses from a meter built with the AS8168

are counted during a defined time period tc, while an accurately defined calibration current Ical, is being measured.

AS8168

Meter

time

base tc

Ical

Calboard

Figure 6 Basic calibration setup for defined current and calibration time method

Again, if the system was perfect we would expect a certain number of pulses to be counted, the ideal number of pulses, Ni:

Ni = PR * tc * Vmains * Ical

3600 * 1000

where tc is in seconds.

PR is the pulse rate on pin CAL, which can be calculated from the PROM parameters F_mon_sel and F_cal_sel:

PR = Fmon * Fcal

where Fmon [imp/kWh] is the pulse rate selected by F_mon_sel and Fcal is the multiplier selected by F_cal_sel.

If pin LED is used for calibration then PR is the pulse rate on pin LED (selected by F_led_sel).

The corrected value for Pulse_lev can now be calculated using the following formula:

Revision 1.2, 11-Feb-05

Page 15 of 30

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