Platinum Z5 CD, Manual

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4-36 888-2408-002
WARNING: Disconnect primary power prior to servicing.
Overall System Theory
4.7.2.2 Forward Factor and A/D_FWD_PWR
The Forward Factor is a calibration factor that is calculated during forward power
calibration. To check the Forward Factor press [HOME, MORE,
CONFIGURATION C,A,A]. All Z5 transmitters are factory calibrated with a
forward sample voltage of 8.9vdc at 5kW, as measured at TP9 on the Life Support
Board. This sample voltage is low pass filtered on the Master Controller and then A/
D converted in the micro for metering. This A/D value shows up as A/
D_FWD_PWR [HOME, MORE, CONFIGURATION C,B], which at 8.9V should
be very close to 806 (the A/D converter is 10 bit for 0 to 1024 range, but the input to
the A/D is not actually 8.9V). By setting the FWD PWR CAL screen to 5kW and
calibrating we are telling the micro that 806 represents 5kW. The micro now
calculates the Forward Factor by dividing the 5kW by the square of 806 or
Forward Factor = FWD PWR CAL (kW) / A/D_FWD_PWR
2
Forward Factor = 5kW / 806
2
= 0.007697 (rounded up)
The A/D FWD PWR reading must be squared to make the voltage from the coupler
linearly track the transmitter power output (Power is the square of the voltage).
The Forward Factor is now used for all forward power level settings. For example,
to set the Low power control to 2.5kW you press the lower button. This gradually
lowers the transmitter power output by reducing the DAC_APC_REF and therefore
the APC_REF voltage and transmitter power. This in turn lowers forward power
sample and the A/D_FWD_PWR number which can be calculated at 2.5kW as:
A/D FWD PWR = SQRT(FWD PWR / Forward Factor)
A/D FWD PWR = SQRT(2.5kW / 0.007697) = 570
At an A/D FWD PWR reading of 570 the front panel Forward Power meter will
read 2.5kW.