CS5461 datasheet(26/46 Pages) CIRRUS

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CS5461

DS546PP2

be set to a value much higher than the EOUT pulse

rate.

The FOUT pin outputs negative and positive ener-

gy, but has no energy direction indicator. The max-

imum FOUT pulse frequency is set by the value in

the PulseRateF Register.

5.4 Anti-Creep for the Pulse Outputs

Anti-Creep can be enabled/disabled for both

EOUT/EDIR and FOUT pulse output systems in

the Control Register. Anti-creep allows the elec-

tronic meter to maintain a “buffer” energy band,

defined by positive/negative energy threshold lev-

els, such that when the magnitude of the accumu-

lated energy is below this level, no energy pulses

are issued. The anti-creep feature is especially use-

ful when the meter demands that the energy pulse

outputs are set to relatively high frequency. A high-

er frequency pulse rate means that less energy reg-

istration is required to generate a pulse; and so it is

more likely that random noise present in the power

line and/or current-sense circuit can generate a

pulse that does not represent billable energy.

5.5 Design Examples

EXAMPLE #1: For a power line with maximum

rated levels of 250 V (RMS) and 20 A (RMS), the

pulse-frequency on the EOUT pin needs to be

‘IR’ = 100 pulses-per-second (100 Hz) when the

RMS-voltage and RMS-current levels on the power

line are 220 V and 15 A respectively. To meet this

requirement, the pulse-rate frequency (‘PR’) in the

Pulse-Rate Register must be set accordingly.

After calibration, the first step to finding the value

of ‘PR’ is to set the voltage and current sensor gain

constants, KV and KI, such that there will be accept-

able voltage levels on the CS5461 inputs when the

power line voltage and current levels are at the

maximum values of 250 V and 20 A. KV and KI are

needed to determine the appropriate ratios of the

voltage/current transformers and/or shunt resistor

values to use in the front-end voltage/current sen-

sor networks.

For a sinewave, the largest RMS value that can be

accurately measured (without over-driving the in-

puts) will register ~0.707 of the maximum DC in-

put level. Since power signals are often not

perfectly sinusoidal in real-world situations, and to

provide for some over-range capability, the RMS

Voltage Register and RMS Current Register is set

to measure 0.6 when the RMS-values of the

line-voltage and line-current levels are 250 V and

20 A. Therefore, when the RMS registers measure

0.6, the voltage level at the inputs will be

0.6 x 250 mV = 150 mV. The sensor gain con-

stants, KV and KI, are determined by demanding

that the voltage and current channel inputs should

be 150 mV RMS when the power line voltage and

current are at the maximum values of 250 V and

20 A.

KV = 150 mV / 250 V = 0.0006

KI = 150 mV / 20 A = 0.0075

Ω

These sensor gain constants are used to calculate

what the input voltage levels will be on the CS5461

inputs when the line-voltage and line-current are

220 V and 15 A. These values are VVnom and VIn-

om.

VVnom =KV * 220 V = 132 mV

VInom =KI * 15 A = 112.5 mV

The pulse rate on EOUT will be at ‘PR’ pulses per

second (Hz) when the RMS-levels of voltage/cur-

rent inputs are at 250 mV. When the voltage/cur-

rent inputs are set at VVnom and VInom, the pulse

rate needs to be ‘IR’ = 100 pulses per second. IR

will be some percentage of PR. The percentage is

defined by the ratios of V

Vnom/250 mV

and

Inom/250 mV with the following formula:

PulseRate

Vnom

250mV

-------------------

Inom

250mV

-------------------

⋅⋅

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