Data Sheet AS8118

Revision 1.8, 15-Feb-05

Page 17 of 30

Calboard

Reference

Meter

AS8118

Meter

I

Figure 7

Basic calibration setup for comparison calibration method

The standard or reference meter pulses are counted between two or more pulses from the meter to be calibrated. Ideally the

sum of the pulses would exactly be the ratio between standard meter pulse rate and the pulse rate of the meter under test.

From the deviation the corrected Pulse_lev may be calculated.

Nr

Ni

*

)

ideal

(

lev

_

Pulse

)

corrected

(

lev

_

Pulse

=

,

Where Nr is the number of pulses counted from the standard or reference meter and Ni is the ratio between the pulse rates,

which is always >1. The formula for Ni is as follows:

Fcal

*

Fmon

)

ref

(

PR

Ni

=

,

This is assuming that the CAL pulse output is used for calibration. If the LED pulse output is used for calibration, the following

formula should be used:

Fled

)

ref

(

PR

Ni

=

The Pulse_lev (ideal) is calculated using the following formula:

435924

20

230

*

I

A

*

V

V

)

ideal

(

lev

_

Pulse

max

mains

=

It is important to note that the formula for Pulse_lev (corrected) above should not be confused with the formula in the

previous method of calibration for ‘Defined Current and Calibration Time’ method, where Ni and Nr are reversed.

Example

The reference meter has a pulse rate, which is 10,000 times greater than the pulse rate of the AS8118 CAL output. During a

calibration cycle we measure 11,000 pulses between two CAL pulses. Therefore the ideal pulse-level has to be changed by a

factor of 10,000/11,000 = 0.909.