Contents; Dc Protection; Vhf Protection - Lab.gruppen PLM Series Operation Manual

message TEMP FLT:PsU. In either case, a report is
also sent via the control network to the DLC PLM
Edition software.
However, before the monitored components reach
their maximum permitted temperature, a warning is
given by the appropriate LEDs (as above) first turning
yellow and an adjacent warning message TEMP
WARN:CH being displayed. Again, a corresponding
message is sent via the network to the DLC PLM
Edition software.
If an output channel temperature fault condition
arises, the output of the channel causing the condition
will be muted. Temperature checking will continue
thereafter at 0.5 second intervals, with the output
remaining muted until the fault condition clears.

7.3.7 DC Protection

DC protection is implemented on each output to
prevent damage to connected loudspeakers or any
PLM components. DC present at the output will
cause the PLM's fuse to blow
This only applies to 230 V versions as no
fuse is fitted to 115 V models). This is not
a user-servicable fault condition and the
unit should be returned for repair.

7.3.8 VHF Protection

The PLM includes protection circuits that detect Very
High Frequency (VHF) content in the input signal. The
detection is frequency-conscious, and is from 10 kHz
upwards. If VHF signals are detected above the allowed
threshold, the output will mute for approximately 6
seconds before a further measurement is taken.
Once no continuous VHF signal is detected, the
output unmutes and the amplifier returns to normal
operation.
This protection system recognizes that continuous
VHF signals at high levels do 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. The graph
below 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
OPERATION AND PERFORMANCE 7
threshold line is detected, VHF protection becomes
active.
VHF protection is dependent on a combination of
output power level and frequency. Figure 7-2 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.
Figure 7-2
The attack time of the VHF protection circuitry also
changes with frequency, becoming shorter at higher
frequencies. This is shown in figure 7-3.
Figure 7-3
The VHF protection circuit is NOT a limiter and
does not alter the PLM's frequency response. It
is implemented 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 buttons) showing steady red. The
adjacent fault message will show VHF FAULT. It is
also reported as a fault via the control network.
PLM Series Operation Manual 21