Lab.gruppen PLM 20K44 Operation Manual page 22

5. Operation and performance
Limiter (ATL) is engaged, reducing power output to avoid amp channel protection (muting). Limiting is removed
when temperature falls below the warning threshold.
5.3.8.3. Power Supply / DSP
A power supply (PSU) or DSP temperature warning or fault is indicated by flashing Frame LEDs.
• A warning is indicated by flashing yellow LEDs
• Power supply Temperature Limit (PTL) is indicated by flashing yellow LED
• A fault is indicated with flashing red LEDs
When the power supply reaches the temperature warning threshold, the Power supply Temperature Limiter (PTL)
is engaged. Total amplifier output power is reduced to avoid power supply fault protection (muting of all channels).
Limiting is removed when the temperature falls below the warning threshold.
5.3.9. DC Protection
DC protection is implemented on each power output to prevent damage to connected loudspeakers or any PLM+
components. DC present at the output will cause the unit's power output module breaker to blow, causing a
permanent hardware fault that prevents signal throughput. In this instance the channel's LED will illuminate red and
a service channel fault will be visible on the display and registered in the Lake Controller and CAFÉ status views on the
PLM 12K44 and PLM 20K44. For the PLM 5K44, there is no fault displayed in this instance, but no signal will be
present on the output. For all models, the device will need to be sent in for service.
NOTE: A blown breaker in the power output module is not a user serviceable fault
condition and the unit should be returned for repair.
5.3.10. VHF Protection
The PLM+ includes protection circuits that detect Very High Frequency (VHF) content in the output signal.
The detection is amplitude–, frequency– and time–dependent. If continuous VHF signals are detected above the
threshold for more than the attack time, the output will (for 20K44 and 12K44 only) attenuate the signal until it is
below the VHF threshold. When this is done, a VHF Warning is displayed. If the signal is above the VHF threshold
and the maximum of -12 dB of gain reduction is not enough to take the signal below the VHF threshold, the signal
will go into mute after 15 seconds and a VHF Fault is displayed. VHF Fault will release the mute again after
approximately 6 seconds. For a 5K44, the VHF threshold will directly go to VHF Fault and mute the signal for
approximately 6 seconds before release and test again. When continuous VHF signal stops, the amplifier returns to
normal operation.
This protection system recognizes only continuous VHF signals at high levels that will not appear in speech or
music. Any such content can therefore be considered as a fault condition. VHF protection is essential to avoid
damage to HF drivers. VHF protection is dependent on a combination of output power level and frequency.
Figure 11.4 shows a decreasing power threshold, from approximately 10 kHz upwards, which illustrates increasing
sensitivity of the protection system with frequency. When continuous output power above the threshold line is
detected, VHF protection becomes active.
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PLM+ SERIES Operation Manual rev 3.0.1