SA9109B

10/18

sames

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.

K

O

=

I

M

*

E

RR

I

R

* 6 *

Where

I

M

= Measured current on the current sensor

I

R

= Rated current on the current sensor

E

Error ratio between the device and the Wh standard

K

O

= Offset constant (-127 ...127)

(The default value is 0)

Note that K

Display resolution

From the above formula for f

by the following expression:

K

626 * 3600 * 1000 * E

kWL

V

Where

E

kWh

= energy for 1 display increment in kWh

V

L

= rated line voltage

I

L

= rated line current

This formula is valid only if 16µA

current (I

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.