\documentclass{chowto}

\title{HMS Drift Chamber HV and Signal Connections}
\howtotype{reference} % ``expert'', ``user'', ``reference''
%\experiment{Name of experiment} % Optional
\author{H. Fenker}
\category{hms} % Subject area of this document

%\maintainer{Name of person maintaining document} % Optional
\date{June 23, 2004} % Can use \today as the argument

\begin{document}

\begin{abstract}
This documents the signal ribbon cable and high voltage cable
routing on the HMS drift chambers and the HMS drift chamber TDC's.
\end{abstract}


\section{Related {\it Howtos}} 
The following Hall-C {\it Howto} documents may be helpful.
%--DELETE THOSE  DOCUMENTS MENTIONED HERE WHICH ARE IRRELEVANT
User Level Documents-
    \par \indent \indent Monitoring HMS ``Utilities'' Systems \cite{howto:hms_detector_monitoring}
    \par \indent \indent Base Equipment Checklist \cite{howto:base_equip_checklist}
    \par \indent \indent High Voltage System Use and Reconfiguration \cite{howto:CAEN_HV_operation}
    \par \indent \indent Operating the HMS Shield House Door \cite{howto:open_hms_door}
    \par \indent \indent Operating the HMS Vacuum Window Shutter \cite{howto:open_hms_shutter}

Expert Level Documents-
    \par \indent \indent Starting Up and Shutting Down the HMS Detectors \cite{howto:turn_on_hms}
    \par \indent \indent Drift Chamber Gas System \cite{howto:drift_gas_system}
    \par \indent \indent Operating the Hall-C Flammable Gas Leak Detector System \cite{howto:flam_gas_sensors}

Reference Documents-
    \par \indent \indent HMS Nominal Settings: Voltages, Currents, Flows, etc. \cite{howto:hms_nominals}


\section{HV and Signal Cables on the Chambers}

The two HMS drift chambers are essentially identical. A number of preamplifier
cards read out the six planes of signal wires in each chamber. The
wire orientatation and layer order is shown in Fig. \ref{fig:HMS_DC_WIRES}.
 The preamps
are a mix of Nanometrics and LeCroy cards which function similarly. If
it is necessary to exchange preamps you do not need to be concerned about
which type of preamp you install. Ribbon cables run from the preamps
to the inputs of TDCs. The TDCs are in a FASTBUS crate inside the
HMS shield house.

\begin{figure}[hb]
\begin{centering}
\includegraphics[width=\textwidth]{hms_drift_map-HMS_DC_WIRES.eps}
\caption {HMS Drift Chamber Planes.The wire orientation, as viewed
by a particle coming from the target is on the left. On the right
is shown the order of the sense planes in each chamber box.
\label{fig:HMS_DC_WIRES}}
\end{centering}
\end{figure}

Threshold voltages for the preamp cards (actually they are
preamp / discriminator cards) are normally supplied from a
power supply in the counting room. Each chamber has its
own threshold supply. There are also threshold supplies
in two aluminum boxes on the frame underneath the HMS
detector stack. These supplies allow local control of the
threshold voltages and are only for use by experts when
debugging the drift chamber electronics. These boxes
have a local / remote switch that should remain in the
'remote' position under normal conditions.

Each signal plane is served by three independent high-voltage supplies.
They are called 'circle', 'square', and 'triangle'. Each sense wire
is located at the center of a rectangular cell with the sides and
corners of the cell defined by field or cathode wires held at one
of these potentials. Fig. \ref{fig:HMS_DC_CELLS}
 shows the arrangement of wires and voltages.
In addition, each drift chamber box has two 'guard' planes as the
most upstream and downstream layers. Thus there are 6*3 + 2 = 20
high-voltage channels for each drift chamber box.

\begin{figure}[hb]
\begin{centering}
\includegraphics{hms_drift_map-HMS_DC_CELLS.eps}
\caption {HMS Drift Chamber Cell Configuration. The electric field
within a drift cell is defined by the voltages on the 'CIRCLE', 'SQUARE',
and 'TRIANGLE' wires,  with the sense wire at ground.
\label{fig:HMS_DC_CELLS}}
\end{centering}
\end{figure}


As viewed from the target, the preamplifier cards are located along
the top and right sides of each box. The high-voltage connections
are on the lower left side and the left bottom side. Labels on
the chamber indicate the funtion of each connector. Some of the
labels are difficult to find or read, but at present they are the
only 'documentation' we have about which connections should go where.


\section{Preamp Low Voltage}

Preamplifier power and threshold are distributed over the chamber
via traces on the printed-circuit board into which the preamps
are plugged. The preamp power is supplied by two Acopian power
supplies (+5V and -5V) mounted in the rack under / behind the
detector stack. The LeCroy preamp cards have red and green LEDs
which can be used as a visual confirmation that the low-voltage
power is turned on. The $\pm 5V$ power is connected through
a distribution box near the Acopian supplies. This box contains
fuses for each power circuit. Spare fuses should be available in
the toolbox that resides in the shield house.



\section{TDC Signal Map}

The signals from the HMS drift chambers are carried over twisted-pair
ribbon cables to the inputs of the TDC's in the FASTBUS crate inside
the shield house. The signal wires going to each TDC channel are
as shown if Fig. \ref{fig:hms_drift_tdcs}. 


\begin{figure}[hb]
\begin{centering}
\htmlimage{scale=1.0}
\includegraphics[height=\textwidth, angle=90.0]{hms_drift_map-HMS_drift_map.eps}
\caption {HMS Drift Chamber TDC Channel Assignments.
\label{fig:hms_drift_tdcs}}
\end{centering}
\end{figure}



\clearpage
\end{document}

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