| ||
|
|
|
| ||
 |
| A photo of a Peripheral Crate. |
 |
| An isometric view of a Peripheral Crate. |
 |
Endcap Muon chambers (EMU) provide the CMS experiment with muon sensitivity in the pseudorapidity range from 0.9 to 2.4. These detectors consist of four stations on each side of the interaction point, labeled (ME+1, ME+2, ME+3, ME+4, and ME-1, ME-2, ME-3, ME-4). The endcap muon system consists of 540 Cathode Strip Chambers (CSCs), which are gas-filled volumes that detect the 2-D positions of passing muons by collecting charge from ionized gas on orthogonal wires and cathode strips.
Peripheral Crates (PCs: I will not use the acronym) are electronics boxes in the experiment hall, roughly a meter on each side, containing 21 VERSA Module Eurocard (VME) modules. The VME modules read data from the CSCs and perform one step in the trigger chain, to decide if a given event contains high-pT muons and should be recorded for offline analysis. Analog charge measurements and digital track segments are passed from electronics mounted on the CSCs into the VME boards through the peripheral crate backplane, merging data from 9 CSC chambers (1 sector) in each peripheral crate. If the resulting pattern matches a template, the data continue to a sector processor in the control room. The sector processor merges all 6 sectors, and sends the event to the global level 1 trigger if the hit pattern resembles a high-pT muon.
This webpage documents the electronics which control and regulate low-voltage power supplied to the on-board CSC electronics and the peripheral crates, though in more detail for the peripheral crates.
Low voltage for 9 CSC chambers is supplied by a junction box in the experiment hall. Each CSC has a Low Voltage Distribution Board (LVDB), which is controlled by a Low Voltage Monitoring Board (LVMB). The LVDB is controlled through the data acquisition system (DAQ), and can be switched on and off remotely. The LVMB monitors both currents and voltages, and communicates with the control room by a simple serial protocol.
Low voltage for a peripheral crate is regulated by a Crate Regulator Board (CRB), controlled by a Peripheral Crate Mezzanine Board (PCMB), and recieves commands from an Embedded Local Monitoring Board (ELMB), sent to the system from the control room by an Ethernet wire running the CANbus protocol. (The RJ-45 Ethernet connector is actually on the PCMB.) These are three cards, each mounted on the last in a mezzanine configuration:
To switch a signal processing board on or off, we can send a command to the ELMB over CANbus, the ELMB informs the PCMB, and the PCMB switches the power on or off in the CRB. To measure the voltage applied on a given processing board, we can send a command to the ELMB which measures the voltage using on-board ADCs (analog-to-digital), returning the value over CANbus. These are the two primary functions we forsee. (We cannot remotely measure currents in the peripheral crates.)
Low voltage for the CSCs and peripheral crates is supplied by a MARATON power supply, which provides two lines to the CSC's junction box: 6 V DC and 7 V DC, and two lines to the peripheral crates: 4.5 V DC at 40 A and 6.5 V DC at 10 A. In the peripheral crates, the CRB (rated for 80 A and 25 A, respectively) divides the former voltage to 1.5 V and 3.3 V and the latter to 5 V for the VME modules.
We communicate with the ELMB board through the CANbus, a 100-meter Ethernet wire transmitting CAN packets rather than TCP/IP. Commands are expressed in a high-level CANopen protocol (written in C/C++) and transmitted from a Kvaser PCIcan card installed in a workstation in the control room. This workstation is also running an OLE Process Control (OPC) server and the Detector Control System (DCS), which is locally-developed software that links the OPC server with the CMS conditions database, and hence controls power for the peripheral crates within the standard CMS software environment and CERN's ProzessVisualisierungs und Steuerungs System (PVSS) framework. The full path for a voltage monitoring or switching command to take is the following:
See a full graphical layout below.
I visited Sasha at CERN in November--December 2006 to learn more
about the low voltage system. To record what I learned and organize
photographs and movies, I wrote the above blog.
To help diagnose problems with the EMU low voltage system, we
developed a ROOT-based GUI which organizes logfile data into
interactive plots. We envision low voltage experts using this tool
occasionally to look for trips, determine the extent of those trips,
and correlate variables in search of a pattern.
Click on the link above to download it, get installation
instructions and a full screen-by-screen tutorial.
To keep track of what has been ordered and what has been recieved.
Low Voltage Monitoring Program
Equipment List
| For questions about these pages, e-mail | Jim Pivarski |
| Also involved: | Alexander Golyash |
| Alexei Safonov |