Description of Problematic Channels

General description of the plots

The channels are shown for the eta-phi range they cover and the different colors correspond to different layers in the detector, as explained in the legends. For the FCAL, the geometry is non projective and therefore only the center of the corresponding readout cells is indicated in the plots.

High Voltage Status

Shown are all readout channels for which a HV correction factor of >1.01 is applied to compensate for reduced signal height due to reduced high voltage for the corresponding channel. The correction factors are obtained from a cool/DCS database. They are based on the actual settings of the HV channels belonging to the corresponding readout channel on the date indicated on the plot. For nominal HV settings, the correction factor is 1. Values above 1 are applied in cases where at least one of the corresponding HV channels is operated at reduced voltage. The exact calculation of the correction factor depends on the HV setting and on the geometry of the cell and is based on testbeam results. For the EM calorimeters, only the presampler and accordion regions are distinguished in the plots. (Any HV problem in the accordion always affects all 3 accordion layers.) For the HEC and FCAL, all 4 layers are distinguished in the plots.

Dead Channels inside the detector

Shown are all channels that can not be read out from the detector and where the problem is expected to be located inside the detector. These channels are expected to be permanently lost.

Dead Readout Channels

Shown are all channels for which the electronics readout is currently not functioning. This can be due to malfunctioning low-voltage power supplies (LVPS), malfunctioning frontend readout boards (FEBs) or problems with the frontend-to-backend cabling. These problems are expected to be fixed during the next long shutdown phase. Non functioning FEBs or LVPS are visible as larger continuous areas in the plots.

Dead Calibration

Shown are readout channels for which the electronics calibration system is not functioning, but the physics pulses are expected not to be affected. This can be caused by damaged calibration lines or resistors, for which a repair is not possible. It can also be caused by a malfunctioning calibration board, in which case a repair is foreseen during the next long shutdown phase. The calibration constants for dead calibration channels are obtained from the average of all phi neighbors at the same eta position. In this case, the error on the reconstructed pulse height is dominated by the spread of the preamplifier gains, which is about +-2%.

Bad Calibration

Shown are readout channels for which a distortion is visible in the calibration signal that is expected to affect both calibration and physics pulses. No further corrections are applied. In addition some peculiar calibration problems are included in this category.

High Noise Channels

Channels are shown for which the RMS of the pedestal readout value, as obtained from dedicated runs with random triggers, is far outside the distribution of the RMS values for all other channels at the same eta position. A cut of 10 times the RMS of the corresponding RMS distribution is applied. High Noise Channels are expected to be above trigger threshold and are therefore to be disabled from the L1Calo trigger by closing the corresponding shaper switch on the FEB. Note that additional intermittently noisy channels are observed in physics running, which are in general not visible in the short dedicated pedestal runs. They are not included in the plots.

Low Noise Channels

Same definition as high noise channels (see above), except the cut is between 5 and 10 RMS. Low noise channels are expected to have only minor impact on the performance and are kept track of mainly to watch the stability and correlate with other problems.

Major updates:
-- DominikDannheim - 07 Oct 2008

%RESPONSIBLE% DominikDannheim
%REVIEW% Never reviewed

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Topic revision: r3 - 2008-10-23 - StephenHaywood
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