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\documentclass{chowto}

\title{Monitoring SOS ``Utilities'' Systems}
\howtotype{user} % ``expert'', ``user'', ``reference''
%\experiment{Name of experiment} % Optional
\author{H. Fenker}
\category{sos} % Subject area of this document

%\maintainer{Name of person maintaining document} % Optional
\date{April 4, 2003} % Can use \today as the argument

\begin{document}
\providecommand{\degg}{\ensuremath{^{\circ}\ }}

\begin{abstract}
Herein is descirbed how to verify the status of the services
required by the detectors in the SOS:
high and low-voltage electrical supplies, gas, and environmental
conditions. Basically, these are the {\it utilities} that the
detectors need in order to function. They should be continuously
monitored or, at a minimum, manually checked at least one time
during each eight-hour shift while the detectors are to be 
kept ready for data. 

Note that users must also check the {\it quality} of the data
produced by the detectors. Maintenance of the {\it utilities}
described here is necessary but not sufficient
to maintain good detector performance.

\end{abstract}

\section{Room Temperature}

The ambient temperature inside the SOS shield house is indicated
by one of the two temperture gauges mounted on the wall of the 
Counting Room above the far left of the control console. The
reading is in degrees Fahrenheit, and should be no higher than
about $75\degg F$.

\section{Drift Chambers}

The SOS includes two identical drift chambers, each of which
contains six planes of sense wires. 

\subsection{High Voltage}

Each chamber requires two high voltage channels: the cathode plane or {\it foil} 
voltage, and the field-shaping wire or {\it potential} wire voltage. The 
nominal voltages are shown in \cite{howto:sos_nominal_settings}.
Check and modify the voltages using the High Voltage GUI
\cite{howto:caen_hv_gui}. Readback voltages should be within
about 20~V of the setpoint voltages. Normally the GUI
monitors the voltages and sounds an alarm if a channel is out of tolerance.
In this case, the user must simply verify that the alarm has
not been turned off. Typical currents in the wire chambers are less 
than 10~$\mu$A.


\subsection {Low Voltage}

The drift chamber preamplifiers, located on both sides, the 
bottom, and the top of
the chambers, require three supply voltages: +5V, -5V, and 
V$_{threshold}$. The $\pm 5V$ supplies are located in the SOS
electronics shed (downstream end of the shield house)
 and cannot be monitored remotely. (If one of them
dies or a fuse blows, the entire effected chamber will have
no hits.) The threshold-voltage supply, common to both chambers,
is located in rack
CH03B10 in the Counting house Electronics Room. The nominal
V$_{threshold}$ is noted in \cite{howto:sos_nominals}. 
It is only to be altered
by a staff expert, who will post the new nominal value at the
power supply if it differs from the value mentioned here.

These threshold voltages should be checked using {\bf only}
the digital voltmeter built in to the power supply. 

\subsection {Gas}

The drift chambers must be continuously flushed with fresh
operating gas. The gas is supplied from the gas shed. It is
composed of approximately 49.5\% argon, 49.5\% ethane, and
1\% {\it 2-propanol} (isopropyl alcohol). This mixture is automatically
controlled by the gas mixing system \cite{howto:drift_gas_system}.
Users must simply verify that the readings in the gas shed
are correct and that the gas supply does not run out. The
amount of argon left in a bottle can be determined from the
bottle pressure, while the ethane content may only be measured
by observing the drop in gross bottle weight. 

Nominal settings are given in \cite{howto:sos_nominal_settings}.

\section{Trigger Scintillators}

The trigger scintillators consist of two sets of crossed
scintillator paddles (S1X, S1Y) and (S2X, S2Y). Each paddle
has two phototubes (one at each end). The S1X, S1Y, and S2Y
planes have nine scintillator paddles each, while the S2X plane 
has sixteen paddles.

A hodoscope system expert will determine the appropriate high
voltage for each of the 86 phototubes during the commissioning
period of each experiment. Check the logbook for a record of what
the present values are -- they should also be saved by the HV GUI.
The settings listed in \cite{howto:sos_nominal_settings}
are typical values only. 

All of the SOS hodoscope tube bases have a load resistance of 
just over $1~M\Omega$
and should, therefore, draw in the neighborhood of 2.5~mA for a
supply voltage of 2500~V.

\section{Aerogel \v{C}erenkov Counter}

The aerogel \v{C}erenkov counter needs high voltage for each of
its phototubes. System experts will update the settings in the
HV GUI and make a log entry. High voltages are monitored by the
GUI, which sounds an alarm in case of error (if the GUI is running).
Typical voltage settings are given in \cite{howto:sos_nominal_settings}.

\section{Gas Cerenkov Counter}

The SOS Gas \v{C}erenkov needs high voltage for each of its
four photomultiplier tubes and the differential pressure relative to the
atmosphere must be kept small.  

\subsection{High Voltage}
The high voltages are controlled by the SOS
high voltage GUI, of course. The PMT bases for the gas \v{C}erenkov
use {\it positive} high voltage.  
They operate at about 2400 Volts.  Nominal voltages
are given in \cite{howto:sos_nominal_settings}. The bases are
loaded at about $1.4~M\Omega$ and, therefore, draw about 1.7~mA
at 2400~V.


\subsection{Pressure}
The tank is filled with freon maintained at atmospheric
pressure through a connection to a small flexible bladder located on
the floor of the SOS shield house. Care must be taken to prevent any
weight or other force being applied to this bladder (other than its
own weight), or kinking or otherwise blocking flow through the tube
connecting the bladder to the tank.
The differential pressure is measured by an Omega\texttrademark \ transducer and digital
readout. This readout is visible on one of the video links displayed in the
counting house. The tank will normally vary in pressure through $\pm 0.005~PSID$
as the atmospheric pressure changes. If the tank pressure is anywhere
below -0.020 PSID or above 0.020 PSID, notify one of the responsible
personnel.

\section{Lucite \v{C}erenkov Counter}

The only utility to be monitored for this detector is the high
voltage for each of its phototubes. If the detector is in use,
the HV GUI will have been set to proper operating voltages and
will provide an alarm should one of the voltages wander too far
away from the setpoint.

\section{Lead-glass Calorimeter}

The calorimeter consists of four layers of eleven glass blocks
each. Layers $A$ and $B$ have two phototubes per block. layers $C$ and
$D$ have one tube per block. The HV GUI will sound an alarm if
a channel's voltage differs significantly from the setpoint.
Typical voltages are shown in \cite{howto:sos_nominal_settings}.
The base resistances are $\approx 635 K\Omega $, drawing about
2.4~mA when provided 1500~V.

\section{Related {\it Howtos}}
\begin{itemize}
\item High Voltage GUI \cite{howto:CAEN_HV_operation}
\item SOS Nominal Settings \cite{howto:sos_nominal_settings}.
\item Signal and HV Cable Map \cite{howto:cable_map}
\item Drift Chamber Gas System \cite{howto:drift_gas_system}
\item SOS Nominal Settings \cite{howto:sos_nominals}
\end{itemize}

\end{document}

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