Philips PM2519 - Page 28

2-12
2.3.3. RMS Converter
in the RMS converter the difference between the inputs 11 and 12 is converted into current in a dual V-I
converter.
The current is determined by Vin/R and the state of the RNG G signal (where R is either R1405 or
R1406+R1407). This RNG G from D1703 selects the input sensitivity of the RMS converter.
The current in the ac-to-de converter is rectified and then converted into a current again by the RMS section.
This current is proportional to the RMS value of the input signal. Capacitor C1406 is the integrating capacitor
for the RMS section. Capacitors C1404 and C1405 provide the automatic zero (AZC) compensation for the
RMS converter. The output of the RMS converter is converted into a voltage by resistor R1408.
In the RMS converter there is also an output to indicate whether the crest factor has been exceeded. When
point 10 {RNG H) of the RMS converter becomes logic 1 on the CF (point 9) indicates to the microcomputer
that the crest factor is exceeded. If RNG H is low then the output CF is switched to detect zero crossings.
This is used to measure frequencies (see 2.3.2.8.).
RMS CONVERTER
A1400
OQ0066A
-—__——
RMS CIRCUIT
Cos
Ww
RIS
{6x81
R1408
R1306
V1350
BAW 62
CURRENT
CIRCUIT
DUAL V TO |
CONVERTER
Fig. 2.9. RMS converter
¥1450
BAW 62
Vi451
BAW62
“ov
C4 | NGG
it
On
$T4406
840713