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Advantech AMT SSPB-Ci60 Installation And Operating Manual
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SSPB-Ci608.4 AUTOMATIC LEVEL CONTROL (ALC)The unit has Automatic Level Control feature (ALC) that will keep the output level at a previouslyset value. Normally the unit should work with 10 dB less gain (set by operator) than the maximumgain, in ALC mode and at an output power 3 to 15 dB back-off from P1dB. The 10 dB less gain setis necessary as a reserve, in order to allow the ALC system to ensure a constant output power incase the input power dropped.The output power is monitored via an output power detector that sends to the Monitor & ControlBoard an analogue voltage signal proportional with the actual output power. This signal isconverted into a digital value and stored in a calibration table putting in correspondence digitalvalues with actual output power levels. After a certain output power is set (by setting a certain gainlevel to the unit) the M&C is able to maintain this set output power level by increasing ordecreasing the attenuation command signal that is sent to the attenuator for gain control. An ALCcontrol loop is so created ensuring the maintaining of the output power at the set level when theinput power varies.The ALC command may be followed by a value of the needed output power level and in this casethe target power will be set to that value. If the ALC command is not followed by any value, thecurrent value of the output power level will be considered as target value.Note that if the ALC feature is ON, the gain control is not available for the operator.The ALC “high” alarm is issued when the input power is too high and the attenuation reached themaximum allowable value (the attenuator cannot ensure enough attenuation of the input power).The ALC “low” alarm is issued when the input power is too low and the attenuation reached theminimum allowable value (even with 0 dB attenuation, at maximum gain set, the input power levelis too low for maintaining the target output level).MONITORANDCONTROLGAIN CONTROLUp-CONVERTEROUTPUTPOWERDETECTOR30 dBAMPLIFIERALC LOOP30 |
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