BL0921

BL0921

BL0921

BL0921

http://www.belling.com.cn

- 10 -

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

V1A

V1N

+

-

CF

RF

CT

±660mV

AGND

V1B

+

-

CF

RF

CT

Rb

Rb

GAIN

±660mV

GAIN

Phase Neutral

IP

IN

V1A

V1N

+

-

AGND

Phase Neutral

V1B

+

-

CF

RF

CT

Rb

±660mV

GAIN

IP

IN

AGND

CF

Ra

Rb

Rv

AGND

±660mV

Ra >> RF

Rb+Rv=RF

Figure 7.

Typical Connections for Current Channels

Fault Detection

The BL0921 incorporates a novel fault detection scheme that warns of fault conditions and allows

the BL0921 to continue accurate billing during a fault event. The BL0921 does this by

continuously monitoring both the phase and neutral (return) currents. A fault is indicated when

these currents differ by more than 12.5%. However, even during a fault, the output pulse rate on

F1 and F2 is generated using the larger of the two currents. Because the BL0921 looks for a

difference between the signals on V1A and V1B, it is important that both current transducers are

closely matched. On power-up the output pulse rate of the BL0921 is proportional to the product

of the signals on Channel V1A and Voltage Channel. If there is a difference of greater than 12.5%

between V1A and V1B on power-up, the fault indicator (FAULT) will go active after about one

second. In addition, if V1B is greater than V1A the BL0921 will select V1B as the input. The fault

detection is automatically disabled when the voltage signal on Channel 1 is less than 0.5% of the

full-scale input range. This will eliminate false detection of a fault due to noise at light loads.

If V1A is the active current input (i.e., is being used for billing), and the signal on V1B (inactive

input) falls by more than 12.5% of V1A, the fault indicator will go active. Both analog inputs are

filtered and averaged to prevent false triggering of this logic output. As a consequence of the

filtering, there is a time delay of approximately one second on the logic output FAULT after the

fault event. The FAULT logic output is independent of any activity on outputs F1 or F2. Figure 8

illustrates one condition under which FAULT becomes active. Since V1A is the active input and it

is still greater than V1B, billing is maintained on VIA, i.e., no swap to the V1B input will occur.

V1A remains the active input.