5/16

A 10K trimpot (P2) is used in the voltage channel for meter

calibration (for the SA2007M). The center position on the pot is

used in the formulae, so P2 = 10K.

Combining the two equations gives:

( RA + RB ) / 230V = RB / 14V

Values for resistors R4 = 10 , R5 = 22k

and R6 = 1M

is

chosen.

Substituting the values result in:

RB = 23.437k

RA = RB x ( 230V / 14V – 1 )

RA = 361.607k .

Standard resistor values of R1, R2, R3 and R4 are chosen to

be 120k , 120k , 120k

and 10 .

Device calibration is done on the voltage input of the

SA2007M. P2 can be varied for precise meter calibration.

Calibration using P2 is not necessary when using the

SA2007P as device calibration data is read from the external

EEPROM. P2 can be removed, the footprint short circuited and

R5 replaced by a 24K resistor.

The capacitor C4 is used to compensate for phase shift

between the voltage sense inputs and the current sense inputs

of the device, in cases where CTs with phase errors are used.

The phase shift caused by the CT may be corrected by

inserting a capacitor in the voltage divider circuit. To

compensate for a phase shift of 0.18 degrees the capacitor

value is calculated as follows:

C = 1 / (2 x x Mains frequency x R6 x tan (Phase shift angle))

C = 1 / ( 2 x x 50 x 1M

tan (0.18 degrees ))

C = 1.013µF

The VREF pin of the SA2007 is connected to a resistor (R17)

that determines the on chip bias current. With R17 = 24K

optimum conditions are set.

The GND pin of the SA2007 is connected to the neutral phase,

which is halfway between VDD and VSS. Note that supply

bypass capacitors C1 and C2 are positioned as close as

possible to the supply pins of the device, and connected to a

solid ground plane.

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W

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Reference Voltage VREF

Ground GND

sames

PM2007M/PPE

Protection

A MOV together with R4 protects the transformer and the

voltage divider circuit against voltage transients.

Common mode and asymmetrical transients are attenuated

by the current setting resistors R8, R9 R10 and R11.

The PM2007M/PPE module uses a transformer based power

supply to ensure flexibility for different counter drive

configurations. The current indicated in table 4 is worst-case

peak pulse current. The normal operating current of the

module is closer to 15mA. A 78LC05-voltage regulator is used

to regulate the voltage from the transformer. Two resistors R18

and R19 generate the analog ground voltage for the SA2007.

The SA2007 operates between 5 Volt and 0 Volt with its GND

pin connected to mid-rail.

POWER SUPPLY

Table 4: Maximum peak current drawn by components on

the module

http://www.sames.co.za

Source

SA2007M/P IC

DIR LED

SEL1 LED

ELT LED

Pulse LED

Counter

GND ref

EEPROM

Total

Max current

5

5

5

5

5

11

3

2

41

Unit

mA

mA

mA

mA

mA

mA

mA

mA

mA