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SA9109BFA

MONOCHIP SINGLE PHASE BIDIRECTIONAL KILOWATT HOUR METERING IC

South African Micro Electronic Systems 

SA9109B

Display resolution

From the above formula for fP it can be derived that the slope constant, Ks, is given

by the following expression:

K

=

626

*

3600

*

1000

*

E

kWL

S

VL * IL

Where

E

= energy for 1 display increment in kWh

kWh

VL

= rated line voltage

IL

= rated line current

This formula is valid only if 16µARMS flows into the current sense input for rated line

current (IL) and 14µARMS flows into the voltage sense input for rated line voltage (VL).

Offset Adjustment

The precision of this device does not require any offset adjustment for Class 1

metering. This facility has been provided to compensate for poor PCB layout or

circumstances requiring precision well beyond a Class 1 rating.

The offset of the device may be adjusted by programming a different offset into the

device during calibration. To calculate the offset the following procedure should be

followed:

Measure the linearity error at the current where offset correction is needed.

KO =

IM * ERR

IR * 6 * 10-6

Where

IM = Measured current on the current sensor

IR = Rated current on the current sensor

E = Error ratio between the device and the Wh standard

RR

KO = Offset constant (-127 ...127)

(The default value is 0)

Note that K must be programmed as a integer value.

O

Meter/Manufacturers Identification Data

A total of eleven 4 bit words are available to store relevant data such as the meter

and manufacturer identification codes. For the optical interface protocol, the 4-bit

words are converted to 8-bit words (ASCII-format).

Writing to RAM

The memory is configured as ten 32 bit words. The programming data must be

written to the device as a bitstream containing a total of 320 bits. ROM-locations

will not be overwritten.

10/18

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