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Once the impedance reading has registered, click in the Properties window by the
Impedance Alarm Value for this channel. A "Set" button will appear. Pressing
this will capture the impedance displayed on the main panel, and the amplifier
will learn this as its valid load reference. You can press this as often as you want
to capture the value required.
The last step in this procedure is to enter a percentage deviation value allowable
from this reference. Note the following points when considering the deviation
value.
1) The allowable range is 0 – 100%. This means that if the reference is, for
example 8 ohms and the deviation is 25%, the load will be flagged as OK
as long as it stays with the range of 8 ohms, +25%, so 6 – 10 ohms.
2) It is recommended that load monitoring is performed using a steady state
stimulus – so a sine test tone or pink noise. For the reasons outlined in
the overview section, attempting to measure impedance accurately with a
music signal will result in erratic performance.
3) For non-continuous monitoring with test tones or pink noise, if these are
performed in the absence of any normal program material (music or voice
announcements) the deviation can be set to a relatively low number (30 –
40%) as the test conditions can be accurately repeated.
4) For continuous monitoring, with HF (>17k) tones at low levels, if the
system checks cannot be performed in the absence of program material,
set the deviation to a much higher value (60 – 80%). This will allow for
program material to affect the measured impedance without causing
warnings to be triggered.
5) To DISABLE impedance measurements for any channel, once a value has
been set, just enter a value of 0 for the window value.
Amplifier Operator's Manual
Click the "Value" property
and press "Set" to learn the
impedance displayed on the
Status Display.
Page 47
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