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LV Workshop 08 Jun 10
Introduction & Welcome
S. Lusin
S. Lusin, LV Workshop, CERN 08 Jun 10
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Objectives of LV Workshop …
Identify issues affecting:
• CMS readiness for data-taking
• CMS data quality
Address manpower issues:
• Do we have enough expert manpower to diagnose problems in the
LV and HV systems?
• Do we have enough expert manpower to deal with the repair
situations that may arise?
Identify systems specific to certain subdetectors that require
specialized knowledge and skills
S. Lusin, LV Workshop, CERN 08 Jun 10
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Common Issues …
Will ask of all subdetectors:
• Who’s in charge of:
• Low voltage?
• High voltage systems?
• Mainframes? CANBus?
• Who will fix things?
• How many of these people are away from CERN?
• How do you fix bad modules? (LV, HV, others?)
• Through CERN POOL? Private arrangements? Remote institution?
• How do you keep records?
• Do you know what the problems have been?
• What hardware interlocks do you use? Who understands them?
S. Lusin, LV Workshop, CERN 08 Jun 10
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CAEN Subsystems …
Power cabling:
• Do you monitor state of PP75 connectors? How?
• Have you changed to flexible cable interconnects?
• Have you installed connector retaining brackets?
Service power:
• Have you installed inline fuses between MAO outputs and service
power inputs?
• Do you want to?
Operation:
• Have you observed any strange behavior on outputs as a result of
interruptions of primary power or service power?
S. Lusin, LV Workshop, CERN 08 Jun 10
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Wiener Subsystems …
OPFCs:
• Have you observed any further issues with OPFCS?
• Internal contact heating?
• Power switch / circuit breaker failure?
• What has operating history of OPFC DCS readout been?
Maratons:
• Cooling:
• Have there been any water-leak issues? Cooling system issues?
• What are consequences of loss of water circulation?
• Do you have any means of monitoring water flow rate?
S. Lusin, LV Workshop, CERN 08 Jun 10
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ST Microelectronics Systems …
The LHC 4913 linear voltage regulator chip from ST Microelectronics
is used extensively throughout CMS. This device is one of the few
radiation-tolerant voltage regulators available, but has certain
special requirements that have to be taken into account in the
design of the subdetector LV system:
• Active high inhibit: if we want the regulator to come up in the
inhibited state on power-up, we need to have an alternate source of
power present at the time of LV turn-on.
• Slew-rate limitations: if the slew rate of the input voltage is below a
critical value, the regulator can go into a state of shunting large
currents to ground. This in turn, can load the source in such a way to
keep the input voltage hovering in a metastable state, and the
regulator will “hang” at an intermediate voltage.
As a result, subdetectors that use an LHC4913 regulator in their
front end must include a special design to accommodate the two
features above.
• By itself, this is not a problem. The problem is that there are few
people who understand the workings of this supplementary system.
• All users of LHC 4913 regulator chips are asked to identify who
understands the system that accomodates it
S. Lusin, LV Workshop, CERN 08 Jun 10
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