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CS5463: Determining No-load Condition Without

Violating Starting Condition Standards

1. INTRODUCTION

When the CS5463 is used in power meter applications, some customers use the I

RMS

residual value as the

threshold for the exte rnal microprocesso r to decide if the meter is under th e no-load condition, and then find

the meter can not pass the starting test. This applications note gives the reason and the correct solution.

2. NO-LOAD AND STARTING CONDITIONS

According to the standa rd IEC 62053 -22, the definitio n of a no-load condition is defined a s: "When the vo lt-

age is applied with no current flowing in the current circuit, the test output of the meter shall not produce

more than one pulse.". The test of starting condition is defined as: "The meter shall start and continue to

To meet these requireme nts, a power meter has to use th e correct no-load threshold in order to restrain the

pulse output and energy accumulation when there is no load current but resume pulse output and energy

accumulation when the load is above the starting current (I

3. DETERMINING A NO-LOAD CONDITION CORRECTLY

The CS5463 has three ene rgy pu lse outp uts (E1, E2, an d E3). T he p ulse outputs un der no-loa d o r starting

condition has been well manipulated by the CS5463. In addition, the CS5463 has a no-load threshold reg-

ister (LOAD

Min

) to help disable the active energy pulse output under some specified condition. When the

magnitude of the P

Active

Min

, the active energy pulse output is disabled.

Different from the energy pulses, the energy register, either mechanical or electronic, is normally manipu-

lated by a microcontroller. T he microcontroller need s to use a variable and a th reshold value to decide if the

meter is under a no-load condition, in which case the values in the power registers should be discarded.

There are two options to select the variable and the threshold.

Table 1: Variable & Threshold Values Comparison

Because I

RMS

exhibits much more system noise than P

Active

, I

RMS

should not be used as a variable

to determine the no-load condition.

Variable

Used

Threshold Value

Com pare

Result

RMS

R es idu a l v a lu e (AC of fset ) w ith

inputs of U

an d no c u rre nt

BAD

Active

Less than the valu e with inputs of U

and starting current

GOOD

AN337

DEC '08

AN337REV1

Summary of content (2 pages)

PAGE 1
AN337 CS5463: Determining No-load Condition Without Violating Starting Condition Standards 1. INTRODUCTION When the CS5463 is used in power meter applications, some customers use the IRMS residual value as the threshold for the external microprocessor to decide if the meter is under the no-load condition, and then find the meter can not pass the starting test. This applications note gives the reason and the correct solution. 2.
PAGE 2
AN337 For example, assume a 10(60)A Class 0.5 watt-hour meter using a 200 uΩ shunt as the current sensor. The voltage on the CS5463 I-channel input (IIN±) with the starting current (Ist = 0.1% Ib) will be 2 uV which is well below the I-channel noise level. Therefore, if IRMS was used to decide the no-load condition, the meter will not pass the no-load and starting tests.