Current Peak Limiter, (Cpl); Protection, Faults And Warnings; Introduction; Safe Operating Area Detector (Soad) - Lab.gruppen C Series C 16 4 Operation Manual

7 OPERATION AND PERFORMANCE
delivering excessively high continuous power to the
speaker or overheating of the output channel through
high current draw. For example, with a very "hot"
continuous output signal, the temperature could rise
to a critical level and activate Temp warning or even
Temp Mute. Lowering the VPL setting normally will
solve this situation.
If the Current Peak Limiter is active or indicates low
impedance, lowering the VPL setting can rectify this
situation as well.
7.4.6 Constant Voltage 70 V and 100 V systems
setup and operation
When using C Series amplifiers to drive constant
voltage (high-impedance) speaker systems at 70 V
or 100 V , you can in most cases simply connect
rms
the speakers to the amplifier output terminals, select
the correct VPL setting, and place the amplifier in
service.
7.4.7 Output Current Peak Limiter (CPL)
The Current Peak Limiter (CPL) ensures that the
amplifier will not be damaged by trying to deliver
current to the outputs exceeding the physical limits
of the transistors. The CPL keeps the amplifier within
the Safe Operating Area. The CPL is non-adjustable
and has different limit values depending on model
type. The maximum output current values for the
four C Series models are:
• C 68:4, 24.5 A rms per channel
• C 48:4, 17.5 A rms per channel
• C 28:4, A rms per channel
• C 16:4, 8.5 A rms per channel
CPL activity is indicated by illumination of an orange
LED for each channel on the front-panel. Warnings
also are shown in the DeviceControl software's
GUI.
A steadily illuminated orange CPL LED indicates a
short circuit situation (or very low impedance). The
output will mute for 6 seconds before measuring
the output impedance again. This will continue until
the short circuit is fixed, at which time the output
will automatically un-mute. An input signal must be
present to allow detection of short circuit or low-
impedance conditions.
18 C Series C 68:4, C 48:4, C 28:4 and C 16:4 Operation Manual
If the CPL LED is steadily illuminated orange
while the output is muted and the -4 dB
signal LED is NOT on, then the amplifier
output is detecting a short circuit or low
impedance condition. The problem can be solved by
checking input and output cables and examining the
state of the loudspeaker load. If there is no short
circuit present, then the condition may be rectified
by lowering the VPL or input levels.
If the CPL and -4 dB indicators are lit simultaneously,
then the amplifier is delivering excessive current and
is being forced into a current limiting state (output
muted).
rms
7.5 Protection, faults and
warnings

7.5.1 Introduction

The C Series amplifiers incorporate a sophisticated
and comprehensive set of protection features. Faults
and warnings are indicated on the front-panel and
reported via the NomadLink network for indication
on the DeviceControl GUI.

7.5.2 Safe Operating Area detector (SOAd)

The Safe Operating Area Detector (SOAD) compares
output voltage against output current to ensure that
the output transistors are working inside their safe
operating area.
The SOAD provides fault monitoring and input to
the Current Peak Limiter (CPL). The SOAD has no
dedicated indicator, and its operation is revealed only
in conjunction with features such as the CPL.
7.5.3 Very high frequency protection
All C Series amplifiers include protection circuits
that detect continuous Very High Frequency (VHF)
content in the input signals. The detection begins at
approximately 10 kHz and moves upwards to include
ultrasonic signals If VHF signals are detected, the
output will mute for 6 seconds before re-measuring.
Once no continuing VHF signal is detected, the output
un-mutes and returns to normal operation.
This feature recognizes that continuous full-scale VHF
signals do not appear in "natural" sources such as
music. Any such signals can therefore be considered
as a fault when present. VHF protection is essential
for avoiding damage to high frequency drivers.
The VHF protection operational area is dependent
on output power level and frequency. The illustration
below shows a decreasing threshold on the output
power level, starting at approximately 10 kHz and
rising with a -6 dB slope. This defines the VHF protec-
tion area. When continuous output power above
the threshold line is detected the VHF protection
becomes active.
Output Max. Peak
output power
power
VHF protection
operation area
- 6 dB slope
Max. Continous
output power
20 Hz 10 kHz 20 kHz 30 kHz
Slow
Attack time
VHF protection
Fast
20 Hz 10 kHz 20 kHz 30 kHz
The Attack time for the VHF protection is increa-
singly shorter at higher frequencies. For example, an
ultrasonic continuous signal will cause the outputs to
mute rapidly, where it will take several milliseconds
for a 10 kHz continuous signal to trigger the output
mute. This is shown in the illustration above.
The VHF protection is NOT a limiter and does not
alter the amplifier's frequency response. It is imple-
mented solely to detect continuous VHF content. The
amplifier will always pass VHF peaks at full power,
with no effect on musical "transients".
The VHF protection is indicated by a yellow LED
on the amplifier front-panel, with output muting for
6 seconds when in action. It is reported as a fault
via the NomadLink network on the DeviceControl
GUI.
If you bench test the amplifier using a
continuous, full scale sine-wave input above
10 kHz, the VHF protection will activate and
C Series C 68:4, C 48:4, C 28:4 and C 16:4 Operation Manual 19
OPERATION AND PERFORMANCE 7
prevent measurement of full peak output power.
(Output will be muted long before maximum output
power is attained.) To measure the true peak output
power, use a burst signal.

7.5.4 dC protection

DC protection is implemented on each output
to prevent damage to connected loudspeakers.
DC present at the output will trigger muting and
illuminate the fault LED indicator. Any DC present
at the output indicates a hardware malfunction that
requires servicing of the amplifier.

7.5.5 high-impedance warning (open load)

A high-impedance (open load) condition is indicated
when an input signal above approximately -29dB
is detected and no functioning loudspeakers are
connected to the amplifier. The fault in indicated by
a red Sig/Hi-imp LED. The indicator is green when
a valid load is present under the same input signal
conditions
Since the High-impedance detection
initially triggers only when the input signal
rises above -29dB, it might cause the
indicator to first turn green, and then red,
even in situations where no speaker is connected.
7.5.6 Low-impedance protection
(short circuit)
A low-impedance or short circuit fault is detected
when current draw is high (Current Peak Limiter
active) and when, simultaneously, output signal
is low (-4 dB LED does not illuminate). When this
occurs, the amplifier protects the output stage
from damage by muting the output signal and
bypassing the circuits. Indication of this fault is a
constant orange illumination of the Current Peak
Limiter (CPL) LED on the front-panel. The protection
will sequence at 6 second intervals to re-measure
conditions. If the low-impedance fault is no longer
detected, the amplifier will un-mute.
If the CPL turns constant orange, the output
is muted, and the -4dB signal LED is ON,
then the amplifier has gone into maximum
current protection. This situation is caused
by an excessive input signal and is not due to a short
circuit. Turn down the input signal to avoid or
remedy this situation.