CS5464 datasheet(39/46 Pages) CIRRUS

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CS5464

DS682F3

9. SYSTEM CALIBRATION

9.1 Calibration

The CS5464 provides DC offset and gain calibration

that can be applied to the voltage and current measure-

ments, and AC offset calibration which can be applied to

the voltage and current RMS calculations.

Since the voltage and current channels have indepen-

dent offset and gain registers, offset and gain calibra-

tion can be performed on any channel independently.

The data flow of the calibration is shown in Figure 10.

The CS5464 must be operating in its active state and

ready to accept valid commands. Refer to 7.6 Com-

mands

on page 24.

The value in the Cycle Count register (N) determines

the number of output word rate (OWR) samples that are

averaged during a calibration. DC offset and gain cali-

brations take at least N + TSETTLE samples. AC offset

calibrations take at least 6(N)+ TSETTLE samples. As N

is increased, the accuracy of calibration results tends to

also increase.

The DRDY bit in the Status register will be set at the

completion of Calibration commands. If an overflow oc-

curs during calibration, other Status register bits may be

set as well.

9.1.1 Offset Calibration

During offset calibrations, no line voltage or current

should be applied to the meter. A zero-volt differential

signal can also be applied to the voltage inputs VIN

 or

current inputs IIN1

 (IINof the CS5464.

(see Figure 11.)

9.1.1.1 DC Offset Calibration

The DC Offset Calibration command measures and av-

erages DC values read on specified voltage or current

channels at zero input and stores the inverse result in

the associated offset registers. This will be added to in-

stantaneous measurements in subsequent conver-

sions, removing the offset.

Gain registers for channels being calibrated should be

set to 1.0 prior to performing DC offset calibration.

9.1.1.2 AC Offset Calibration

The AC Offset Calibration command measures the re-

sidual RMS values read on specified voltage or current

channels at zero input and stores the inverse result in

the associated AC offset registers. This will be added to

RMS measurements in subsequent conversions, re-

moving the offset.

AC offset registers for channels being calibrated should

first be cleared prior to performing the calibration.

Modulator

V1, I1, V2, I2

Filter

I1RMS, V1RMS,

I2RMS, V2RMS



I1DCOFF, V1DCOFF,

I2DCOFF, V2DCOFF

I1GAIN, V1GAIN,

I2GAIN, V2GAIN

0.6

= READABLE/WRITABLE REGISTERS.







DCAVG

RMS

I1ACOFF, V1ACOFF,

I2ACOFF, V2ACOFF

N

DC Gain

DC Offset

AC Offset

RMS

AC Gain

Negate

DC AVG

Negate

Figure 10. Calibration Data Flow

XGAIN

External

Connections

AIN+

AIN-

CM +

Figure 11. System Calibration of Offset

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