Speaker
Description
Summary
In the ATLAS service caverns, the SCT power supply system comprises a total of 22 racks.
In addition to standard units such as the turbine, deflector and heat exchangers,
each rack contains two power pack shelves, one circuit breaker box (CBB), four fan trays
and four SCT power supply crates. Each power supply crate services up to 48 SCT modules.
It houses 12 LV cards of four channels each, 6 HV cards of 8 channels each, one SCT
Interlock Card (SIC), one Crate Controller card (CC), and one shorting card (for safety
reasons).
Each LV channel provides analogue and digital power to one module, as well
as two low current control lines, bias for two NTC thermistors
used to monitor the module temperature, and bias for the on-detector part of
the opto-electronic readout scheme. Sense wires are provided for all high
current lines. Each HV channel provides up to 500V bias to the silicon sensors
of one module. Both LV and HV supplies may be controlled, and monitored
parameters may be readout, by means of a parallel bus implemented on the crate
backplane.
Power input to the LV and HV cards is at 48V DC, supplied by four commercial
units housed in the power pack shelves. All units are connected to a common
bus, power being distributed to the crates through minature circuit breakers
housed in the CBB. Only three power packs are needed to power four fully loaded
crates: the fourth power pack provides redundancy. At each LV/HV card, an
oscillator block modulates the 48V DC input: each channel is isolated by means
of a transformer. Each group of four channels is associated with a hardware
interlock line, electrically isolated by means of opto couplers on the SIC
card, to provide a safety interlock which does not depend upon software.
The crate controller interfaces an ELMB card to the crate backplane
to provide a link between the power supply channels and CAN bus. Three
user defined sets of channel parameters, corresponding to
operational states of the detector, are stored in the ELMB's non-volatile
memory such that common operations may be performed with a minimum of
bus traffic.
The highest levels of the SCT Power Supply software take the form of a
Supervisory Control and Data Acquisition system, PVSS II. The
software is distributed between 9 PCs, 8 systems each being connected
to 11 PS crates over CAN bus.
The top layer solution for the overall control of ATLAS takes the form
of a Finite State Machine (FSM) written in SMI++. Accordingly an FSM
has been built following the operational model of the SCT power supplies,
with channels grouped together according to the physical
cooling structures of the detector. The physical routing of the SCT
power cables dictates that, in many cases, the PS channels servicing
the modules of a single cooling structure are distributed amongst
several PS crates. This has added greatly to the complexity of the
control software.
