BL0921

BL0921

BL0921

BL0921

http://www.belling.com.cn

- 8 -

3/15/2007

Total 13 Pages

Single Phase Energy Meter IC

Single Phase Energy Meter IC

Single Phase Energy Meter IC

Single Phase Energy Meter IC

with Integrated Oscillator

with Integrated Oscillator

with Integrated Oscillator

with Integrated Oscillator

power will result in measure error, and the component brought to the frequency of ω will also

affect the output of the average active power when the next low-pass filter cannot restrain the ac

component very completely.

When the offset on the one of the voltage and the current channels is filtered, for instance, the

offset on the current channel is removed; the result of multiplication is improved greatly. There is

no dc error, and the additional component at the frequency of ω is also decreased.

When the offsets on the voltage channel and the current channel are filtered respectively by two

high-pass filters, the component at the frequency of ω (50Hz) is subdued, and the stability of the

output signal is advanced. Moreover, in this case, the phases of the voltage channel and the current

channel can be matched completely, and the performance when PF equal 0.5C or 0.5L is improved.

In BL0921, this structure is selected. Though it is given in the system specification that the ripple

of the output signal is less than 0.1%, in real measure of BL0921, the calibration output is very

stable, and the ripple of the typical output signal is less than 0.05%.

Additionally, this structure can ensure the frequency characteristic. When the input signal changes

from 45Hz to 65Hz, the complete machine error due to the frequency change is less than 0.1%. In

such, the meter designed for the 50Hz input signal can be used on the transmission-line system of

electric power whose frequency is 60Hz.

Voltage Channel Input

The output of the line voltage transducer is connected to the BL0921 at this analog input. As

Figure4 shows that channel V2 is a fully differential voltage input. The maximum peak differential

signal on Channel 2 is ±660mV. Figure4 illustrates the maximum signal levels that can be

connected to the BL0921 Voltage Channel.

V1

V2

+660mV

-660mV

V1

V2

AGND

V1A

V1N

+

-

V1B

+

-

V1

GAIN

GAIN

Maximun input differential voltage

±660mV

Maximun input common-mode voltage

±100mV

Figure 4.

Voltage Channels

Voltage Channel must be driven from a common-mode voltage, i.e., the differential voltage signal

on the input must be referenced to a common mode (usually GND). The analog inputs of the

BL0921 can be driven with common-mode voltages of up to 100 mV with respect to GND.

However, best results are achieved using a common mode equal to GND.

Figure5 shows two typical connections for Channel V2. The first option uses a PT (potential

transformer) to provide complete isolation from the mains voltage. In the second option, the

BL0921 is biased around the neutral wire and a resistor divider is used to provide a voltage signal

that is proportional to the line voltage. Adjusting the ratio of Ra and Rb is also a convenient way

of carrying out a gain calibration on the meter.