Noise
9.3 Noise
Depending on the environment of the analyzer (ground, feedthrough connection
status, ... ), the handling during transport / installation (bake out, dust, ...) and the his-
tory of of operation (vacuum, gas load, total amount of accumulated charged particles,
etc.) some or all channels may show noise without any excitation. If the “Amplifier
Check” on page 80 shows that the amplifier is working correctly, the grounding of the
analyzer is ok; by following the advice given in sections 3.5 - “Single and Multichannel
Detector (SCD) / (MCD)” on page 25 and in section 9.1.1 - “Discriminator” on page 75 ,
the noisy channels can be suppressed. First, try to set the threshold of the noisy channel
to higher value (up to 10 mV). This will also shift the working point for the channeltron
(see “The Working Point of the CEM’s” on page 27). If this does not help, completely
suppress the channel. To continue to work with the analyzer (up to the replace of the
defective part) without the signal from the noisy channels:
● Suppress a noisy channel (section 9.3.1 )
● Switch off certain channels (section 9.3.2 )
9.3.1 Suppress a Noisy Channel
In some cases a channeltron becomes noisy (dust, contamination, overheated, etc.). To
avoid disturbing the acquisition of the other channeltrons, increase the threshold level
for this channel (Figure 26: Menu - “Analyzer Settings”, page 54). Note: You have to se-
lect the desired channel first before changing the value to 120mV (maximum) for ex-
ample.
To reset all channels to the same value select ’all’.
9.3.2 Switch off Certain Channels
To switch off certain channels, it is necessary to modify the registry entry for the
HSA3500Analyzer key. For a 150R5c type of analyzer the entry "CounterChannelMask"
is located at
"HKEY_LOCAL_MACHINE\SOFTWARE\Specs\Hsa3500Analyzer\Phoibos-Hsa3500\150 R5c"
The necessary type is “binary”. Create such a binary entry if it does not exist (Figure 36:
CounterChannelMask for MCD9, 1+2+8+9 off, page 78). Please also refer to the descrip-
tion about the registry entries in the SpecsLab2 manual.
The software masks not only the channels, but the detector shifts and channel gains
too. In the selection for the channels in the SpecsLab2 analyzer/settings menu the con-
secutive numbering of the remaining channels start with 1 and end with the number of
the available channels.
Note: After any hardware change (i.e. channel replacement), or any registry change (as
above), it is recommended to perform an MCD Calibration routine.
PHOIBOS 77
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