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Operation and Performance
PLM Series Operation Manual rev 1.1.9
Figure 5-3: VHF Protection Attack Time Variations
The VHF protection circuit is NOT a limiter and does not alter the PLM’s frequency response. It is imple-
mented solely to detect continuous VHF content. HF content of normal music or speech signals at peak
levels will be passed in full.
Operation of the VHF protection circuits is indicated by one (or more) of the output channel LEDs (in the
right-hand soft function buttons) showing steady red. The adjacent fault message will show VHF FAULT. It is
also reported as a fault via the control network.
5.3.11 Short Circuit Protection
A low impedance or short circuit at the power output terminals is detected when the output current is high
(Current Peak Limiter is active) and, simultaneously, the peak output voltage is below a predetermined
threshold (42 V with the PLM 10000Q, for example). When this situation occurs, the output stage is muted
to protect it from damage. Operation of the short circuit protection system is indicated by an output channel
LED (in the right-hand soft function buttons) showing steady red. The adjacent fault message will show
SHORT CIRCUIT. It is also reported as a fault via the control network to the Lake Controller software. The
presence of a short circuit (or low impedance) is re-tested every six seconds, and the output remains muted
until the fault clears.
5.4 Power Supply
The R.SMPS (Regulated Switch Mode Power Supply) is designed to keep supply voltage rails at optimum
levels even when the mains voltage drops. Mains voltages can drop as much as 20% below nominal before
there is any effect on rail voltages. Thus the R.SMPS can deliver full rail voltage to the output stage at all
times, allowing the PLM to exhibit consistent transient response and a clean LF response.
The PLM 20000Q is also equipped with a universal power supply with power factor correction (PFC). The
device can take any mains voltage from 70 to 265 volts allowing it to function worldwide in many different
congurations. The PFC reduces current peaks on the lines and reduces the requirements placed on the
mains distribution system. The PLM 20000Q has an unparalleled power factor extremely close to one.
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