A large part of the front-end electronics will be located in crates, except specialized electronics required to be mounted inside the detector itself. In many cases the main requirements to these crates are of mechanical nature ( size of boards, number of boards in crate, place for connectors, etc.) and the supply of electrical power and its related cooling.
For front-end electronics and trigger modules it is often required to use large module sizes to obtain the required integration level of the system and also minimize the number of links between modules. To integrate the electronics of many detector channels on one module it is often required to interface a large number of signals to the board. 9U modules have traditionally been used for this ( 9U VME) and this form factor still seems to be the most appropriate for the future LHC experiments.
With the current changes in the technology of integrated circuits it will often be required to use several different supply voltages on front-end modules (+/- 12 for special analog, 5 v for old digital, 3.3/2.5/1.8 volt for modern digital IC's). Standardized crates do not have all these voltages available to cover all kinds of applications. Typical +/- 12 v , 5 v and optionally 3.3 volts are available in standardized crates. Lower supply voltages for IC's implemented in sub-micron technologies must be generated with local DC-DC power converters.
The operation of power supplies in the crates must be verified to be compatible with the environment in which they have to operate. The stray field from the main magnet of LHCb will in certain locations of the cavern have significant effects on transformers, fans and inductors used in normal commercial power supplies. The radiation environment may also provoke early and frequent power supply failures. Certain power supply failures provoked by radiation have been seen to result in the output voltage increasing above nominal levels, which can have catastrophic effects on the electronic modules powered from this source.
Crates to be used in limited radiation and magnetic fields must use special qualified power supplies. Such power supplies can be purchased via the CERN ESS group as part of a special frame contract with Wiener.
The high complexity and the large number of electronic modules in the front-end system requires a careful evaluation of its cooling requirements. Normal forced air 9 U crates can accept up to ~100 watts per module. The large number of front-end crates will require the use of water cooled racks or crates (water cooled racks largely preferred because of maintenance reasons and the advantage of using standard crates). The magnetic stray field from the LHCb magnet must be confirmed to be compatible to the correct function of the electrical fans used for the forced air cooling of the modules. Limited power density crates they can be used without fans relying on the airflow from the rack turbines that exist in a magnetic field tolerant version.
The Experiment Control System must be capable of controlling and monitoring the state of all crates. Power supplies must be under the control (on/off) of the ECS and their status must be continuously monitored ( fail/no fail, output voltages, currents, etc). The correct cooling of the crate must be carefully monitored via temperature sensors in critical places and fan failures must be detected. An undetected failure state in a crate may in a worst case scenario result in the complete destruction of all its electronics ( over-voltage, overheating ) and potentially cause a fire.
A dedicated 9U crate with a simple power supply backplane has been made for the use with the TELL1 module. This crate can also be ordered via the CERN ESS group.
This page was last modified by JC on 10 May, 2006 . This page has been accessed number of times.