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No apparent signal coming from a detector (but control voltage apparently operational).
Probable cause: data acquisition system issue
o Disconnect the detection system from the data acquisition unit and carry out an
independent test of the data acquisition system (according to the manufacturer’s
instructions) to ensure that it is responding correctly. If all is well, proceed with the tests
below.
Probable cause: connectivity and measurement issues.
o The signal connections may be intermittent. Try moving the cables, especially close to
the end connections or near any location where the cables may have been sharply bent.
If this restores the signal, then the cable(s) should be replaced. If you are using other
cables and BNC T-pieces to monitor the signals, then try replacing these as well.
o With the system turned off, remove the signal cable from the problem detector and
inspect it for damage. Using a multi-meter set for resistance or continuity measurement
check the resistance between the outer shell of the SMA connector and the outer shell
of the BNC connector – the reading should be less than 0.5 Ohms. Make a similar
measurement between the central contacts of the SMA and BNC connectors – again the
result should be less than 0.5 Ohms. Finally, check that there is NO connection (infinite
resistance) between the central pin and the outer body of each connector. If any of
these requirements is not met, replace the cable.
o If the cable passes inspection, re-connect it to the detector module and ensure that the
SMA connector is screwed fully home (hand-tight). Connect the far end of the cable to
an oscilloscope input directly.
o Set the oscilloscope as follows: the input must be DC coupled, with a sensitivity of 0.1 V
per division, and any probe setting should be 1:1 gain. Set the triggering mode to AUTO
and the trigger source to the input channel to which the cable has been connected.
o Turn on the controller, turn both high-voltage controls to minimum and set the master
safety switch to “enable”. The oscilloscope should be showing a very small noise level
(a few mV peak-to-peak). Gradually increase the high-voltage control corresponding to
the detector under test until a voltage of about -200V to -250V is attained. At this point
shining a dim torch towards the sample area or turning on dim room lights should
produce a visible change in the background signal level of the oscilloscope. If room
lights are on, then the oscilloscope should show a significant 100Hz or 120 Hz
oscillating signal on top of an offset. If the expected response is not seen then turn the
system off and contact Scientifica for assistance.
Excessive noise and offset during imaging at low detector gain (voltages between 0V and -700
V)
Probable cause: stray light or detector noise.
o If the images appear to have a high background level or if they are very noisy even if the
detector(s) are operating at low to medium voltage , then the system may be suffering
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