1 saw 1.1 \documentclass{chowto}
2
3 \title{Drift Chamber Gas System Operation}
4 \howtotype{expert} % ``expert'', ``user'', ``reference''
5 %\experiment{Name of experiment} % Optional
6 \author{H. Fenker}
7 \category{general} % Subject area of this document
8
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9 saw 1.5 \maintainer{H. Fenker} % Optional
10 \date{December 18, 2007} % Can use \today as the argument
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11 saw 1.1
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12 saw 1.5 %To attempt to make pretty-looking pdf files...(not standard howto)
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13 saw 1.1
14 \begin{document}
15 \providecommand{\degg}{\ensuremath{^{\circ}\ }}
16
17 \begin{abstract}
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18 saw 1.5 This document provides detailed setup information for the drift
19 chamber gas mixing system, as well as the correct procedure for
20 refilling the alcohol supply and changing gas bottles. This
21 information is intended for use by {\bf gas system experts only.} For
22 day-to-day shift worker instructions, refer to the corresponding {\it
23 user} howto document.
24
25 {\bf Please Note:} The Hall-C Drift Chamber Gas System was
26 significantly changed in early 2007. It is now a {\it pressure-driven
27 system} whereas it had been flow-controlled. Long-time Hall-C staff
28 and users will find that the system operates quite differently now.
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29 saw 1.1 \end{abstract}
30
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31 saw 1.5 %=====================================================================
32 %=====================================================================
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33 saw 1.1 \section{Overview}
34
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35 saw 1.5 The drift chamber gas is composed of 50\% Argon and 50\% Ethane (by
36 volume), bubbled through isopropanol maintained at a temperature such
37 that the gas mixture contains approximately 1\% alcohol vapor. The
38 mixing system that produces this gas is housed in the Hall-C gas shed
39 (Bldg. 96c). The bottles supplying the gas to the mixing system are
40 attached to two two-bottle manifolds outside the gas shed, within the
41 fenced-in gas bottle yard.
42
43 A single mixing system provides the gas for both the SOS and the HMS
44 detectors. Gas is delivered to the hall at a pressure of about 9 psi
45 (500~Torr) above atmospheric pressure. Each detector's flow is
46 controlled by its own individual needle-valve with flowmeter, located
47 in the appropriate shield house, near the detector. The job of the
48 mixing system is to simultaneously maintain the delivery pressure and
49 mixing ratio by providing whatever total flow rate of gas (between
50 zero and 5.28 standard liters per minute [SLM]) is demanded by the
51 detectors. This is accomplished by controlling two flow valves (argon
52 and ethane) so that they each flow the same volume of gas while
53 keeping the output pressure nearly constant. The mixing system flow
54 diagram is shown in Fig. \ref{fig:gas_mixer_diagram}.
55 %=====================================================================
56 saw 1.5 %=====================================================================
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57 saw 1.2 \section{Gas Interlock System}
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58 saw 1.5 The flow of gas from the supply bottles may be automatically shut off
59 by normally-closed solenoid valves installed in the primary argon and
60 ethane manifolds. Several conditions such as over-temperature, fan
61 failure, gas leak, and fire alarm must all be in the non-alarm state
62 before these valves will open. Alarm conditions are indicated on the
63 gas system alarm panel on the lower-left side of the center
64 counting-house console.
65
66 When any of the required conditions is not satisfied the sounder on
67 the panel in the counting room will make an annoying noise and both
68 solenoid valves will close. The audible alarm may be silenced by a
69 toggle switch on the panel. Be certain to return it to the ``on''
70 position as soon as the fault is cleared.
71
72 The most confusing, but most common alarm condition is ``Low
73 Pressure''. The solenoid valves will not remain open unless there is
74 already ample pressure on the output side of both valves. This
75 prevents, for example, the flow of pure ethane to the drift chambers
76 when the argon bottle is empty. The way to clear this condition is to
77 make sure there are no other faults and that both argon and ethane
78 manifolds are properly pressurized and fitted with non-empty bottles;
79 saw 1.5 then press and hold the ``override'' button on the alarm panel for
80 several minutes. This button forces the solenoid valves to open even
81 if there are fault conditions present. If all is well, gas will flow
82 through the valves and clear the ``low pressure'' condition so that
83 the button may be released.
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84 saw 1.2
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85 jones 1.3 \begin{figure}[hbt]
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86 saw 1.5 \psfig{figure=drift_gas_system-gasmixer2007.eps,width=\textwidth,bbllx=12,bblly=12,bburx=750,bbury=590}
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87 saw 1.1 \caption{Diagram of Hall~C Gas Mixing System\label{fig:gas_mixer_diagram}}
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88 jones 1.3 \vspace{0.5cm}
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89 saw 1.1 \end{figure}
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90 saw 1.5 %=====================================================================
91 %=====================================================================
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92 jones 1.3 \section{Operating the Mass Flow Controller.}
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93 saw 1.1
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94 jones 1.3 The gas flow is controlled by a MKS~647 controller and mass flow
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95 saw 1.5 control valves. Delivery pressure is sensed at the mixer output by a
96 {\it Baratron} pressure transducer. The 647 is menu driven from a
97 display on the front panel using a keypad with numeric and cursor
98 controls for input. It features a non-volatile memory so that most of
99 its settings are retained even if the unit is unpowered. The
100 pressure-regulation parameters do need to be reset if power is lost,
101 however, so the controller is powered through an uninterruptible power
102 supply (UPS).
103
104 The temperature of the control
105 system must be maintained within the
106 operating range of the MKS~647 (15\degg C - 40\degg C), the pressure
107 transducer (0\degg C - 50\degg C), and the mass-flow meters and valves
108 (0\degg C - 50\degg C). Therefore,
109 the heating and cooling systems in the gas shed must be maintained in
110 working order. The temperature is indicated by the
111 red LED display labeled \emph{Controller Temperature},
112 located in the right-hand rack of the gas shed.
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113 jones 1.3
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114 saw 1.5 %=====================================================================
115 %=====================================================================
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116 jones 1.3 \subsection{Settings for Normal Operation}
117
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118 saw 1.5 A summary of all of the settings required to make the controller
119 function properly is given in Table~\ref{tab:mixer_nominals}. The
120 table also shows which screen contains each parameter. Instructions
121 for setting parameters are given below. Detailed instructions for
122 configuring and operating the MKS~647 can be found in the
123 manufacturer's instruction manual\cite{647C_EN_0504A1}.
124
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125 jones 1.3 \begin{table}[hbt]
126 \begin{minipage}[h!]{\textwidth}
127 {\scriptsize
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128 saw 1.5 \begin{center}
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129 jones 1.3 \begin{tabular}{|l|c|l|}
130 \hline
131 Parameter & Set To & {\it Controller Screen}/Comments\\ \hline
132 \multicolumn{2}{|c|}{\bf Manual Valves } & Valves are labeled \\
133 Valves 1, 2, 4, 8 & OPEN & \\
134 Valves 3, 5, 6, 7 & CLOSED & \\ \hline
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135 saw 1.5 \multicolumn{2}{|c|}{\bf Pressure PID Loop Settings } & {\it Pressure Control} (Fig. \ref{fig:pressure_control}) \\
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136 jones 1.3 Pressure & 500 Torr & \\
137 PID Mode & AUTO & \\
138 PID GAIN & 4.0 & \\
139 PID INTEG & 10.0 & \\
140 PID LEAD & 0.000 & \\ \hline
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141 saw 1.5 \bf Mixture & 1 & {\it User} (Fig. \ref{fig:user_display})/ Lower-right corner\\ \hline
142 \multicolumn{2}{|c|}{\bf Gas Composition for Mixture 1} & {\it Gas Composition} (Fig. \ref{fig:gas_composition})\\
143 Channel 1 & 1.000 & (Argon) \\
144 Channel 2 & 1.000 & (Ethane) \\
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145 jones 1.3 Channel 3 & 0.000 & \\
146 Channel 4 & 0.000 & \\ \hline
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147 saw 1.5 \multicolumn{2}{|c|}{\bf MFC Valve Size } & {\it Range Selection} (Fig. \ref{fig:range_selection}) \\
148 \multicolumn{2}{|c|}{\bf / Gas} & {\it Gas Selection} (Fig. \ref{fig:gas_selection}) \\
149 Channel 1 & 2.0 SLM / Ar & provides 2.78 SLM Argon\\
150 Channel 2 & 5.0 SLM / C$_2$H$_6$ & provides 2.50 SLM Ethane\\
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151 jones 1.3 Channel 3 & \it unused& \\
152 Channel 4 & \it unused& \\ \hline
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153 saw 1.5 \multicolumn{2}{|c|}{\bf Channels ON/OFF Settings} & {\it Extended Display} (Fig. \ref{fig:extended_display}) \\
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154 jones 1.3 Channel 1 & ON & Press ``ON 1'' (\em Argon) \\
155 Channel 2 & ON & Press ``ON 2'' (\em Ethane) \\
156 Channel 3 & OFF & Press ``OFF 3'' (\em not in use) \\
157 Channel 4 & OFF & Press ``OFF 4'' (\em not in use) \\ \hline
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158 saw 1.5 \multicolumn{2}{|c|}{\bf Pressure Transducer} & {\it Pressure Setup} \\
159 Controller & STD & \\
160 Range F.S. & 1000 Torr& \\ \hline
161 \multicolumn{2}{|c|}{\bf MFC Valve Controls } & {\it Mode Selection} (Fig. \ref{fig:mode_selection}) \\
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162 jones 1.3 Channel 1 & PID & \\
163 Channel 2 & SLAVE / 1& \\
164 Channel 3 & INDEP & \\
165 Channel 4 & INDEP & \\ \hline
166 \bf Alcohol Temp. & $2^\circ $ C & Electronic Temperature \\
167 & & Control Box \\ \hline
168 \hline
169 \end{tabular}
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170 saw 1.5 \end{center}
171 }%end of \scriptsize
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172 jones 1.3 \end{minipage}
173 \caption{Normal Valve and Parameter Settings for the Gas Mixing System.
174 \label{tab:mixer_nominals}}
175 \end{table}
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176 saw 1.5 %=====================================================================
177 \subsection{General Operation of the Mass Flow Controller}
178 If the controller screen is dark, press {\bf ESC} to awaken the
179 display. Many screens merely provide a menu of other screens you may
180 access: simply press the item number you desire. To go up one level in
181 the menu hierarchy, press {\bf ESC}. The \emph{Menu Tree} for the 647C
182 controller is shown in Fig. \ref{fig:command_tree}.
183
184 In general, to change a parameter displayed on the controller screen
185 use the {\bf left/right} arrow keys to move the cursor to the item you
186 wish to change. Then either use the number keys to enter the value
187 desired for that item (numeric parameter) or use the {\bf ENTER} or
188 {\bf up/down} keys to cycle a parameter through its available settings
189 (configuration parameter). Numeric parameters may be incrementally
190 modified by using the {\bf up/down} arrow keys. To make certain that a
191 new parameter becomes active, move the cursor off of the parameter
192 after you have entered the new value.
193
194 The initial menu upon startup is the {\bf Main Menu}
195 (Fig.~\ref{fig:main_menu}). For normal operation use the {\bf User
196 Display} menu (Fig.~\ref{fig:user_display}). It shows the amount of
197 saw 1.5 each gas currently flowing, the total gas flow, and the current
198 delivery pressure. This display also shows which of several possible
199 pre-defined gas mixtures is selected. These mixtures are configured
200 on the {\bf Gas Composition} screen, Fig. \ref{fig:gas_composition}.
201 For normal operation, we use
202 only mixture {\bf \#1}, (number shown on the lower-right of the
203 display). {\bf Only on this screen can this parameter be changed.}
204 Mixture {\bf \#2} is usually configured to provide 100\% argon for
205 purging flammable gas out of the chambers.
206
207 The {\bf Extended Display} menu (Fig.~\ref{fig:extended_display})
208 shows actual flow, flow set point, units, valve full-scale range, gas
209 calibration factor, whether that channel is enabled, and whether each
210 channel is operating in master, slave, PID, or independent mode. This
211 display is most useful to a system expert wishing to verify the system
212 parameter settings. Most parameters cannot be modified from this
213 screen, however.
214
215 Delivery pressure set-point and pressure \emph{PID-loop} control parameters
216 may be configured from the {\bf Pressure Control} screen
217 (Fig.~\ref{fig:pressure_control}).
218 saw 1.5 %
219 \begin{figure}[tb]
220 \begin{center}
221 \framebox{
222 \begin{minipage}{.65\textwidth}
223 \footnotesize
224 \begin{itemize}
225 \item MAIN MENU (Fig. \ref{fig:main_menu})
226 \begin{enumerate}
227 \item [1] USER DISPLAY (Fig.\ref{fig:user_display})
228 \item [2] EXTENDED DISPLAY (Fig.~\ref{fig:extended_display})
229 \item [3] PRESSURE CONTROL (Fig.~\ref{fig:pressure_control})
230 \item [4] DIAGNOSTICS
231 \begin{enumerate}
232 \item [4.1] ERROR LISTING
233 \item [4.2] SIGNALS
234 \end{enumerate}
235 \item [5] INSTRUMENT SETUP
236 \begin{enumerate}
237 \item [5.1] RANGE SELECTION (Fig.~\ref{fig:range_selection})
238 \item [5.2] GAS SELECTION (Fig.~\ref{fig:gas_selection})
239 saw 1.5 \item [5.3] MODE SELECTION (Fig.~\ref{fig:mode_selection})
240 \item [5.4] ZERO ADJUST
241 \item [5.5] TRIP LIMITS
242 \item [5.6] GAS COMPOSITION (Fig.~\ref{fig:gas_composition})
243 \end{enumerate}
244 \item [6] SYSTEM SETUP
245 \item [7] PRESSURE SETUP
246 \item [ ]
247 \item [9] INFORMATION
248 \item [0] POWER OFF
249 \end{enumerate}
250 \end{itemize}
251 \end{minipage}
252 } %%end of \framebox{
253 \caption{Command Tree for the MKS-647C Control Panel}
254 \label{fig:command_tree}
255 \end{center}
256 \end{figure}
257 %
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258 jones 1.3 \begin{center}
259 \begin{figure}[hbt]
260 \begin{minipage}{2.7in}
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261 saw 1.5 \psfig{figure=drift_gas_system-main_menu.eps,width=2.6in,height=1.8in}
262 \caption{MKS~647 Main Menu\label{fig:main_menu}}
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263 jones 1.3 \end{minipage}
264 \begin{minipage}{2.7in}
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265 saw 1.5 \psfig{figure=drift_gas_system-user_display.eps,width=2.6in,height=1.8in}
266 \caption{MKS~647 User Display\label{fig:user_display}}
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267 jones 1.3 \end{minipage}
268 \end{figure}
269 \end{center}
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270 saw 1.5 %
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271 jones 1.3 \begin{center}
272 \begin{figure}[hbt]
273 \begin{minipage}{2.7in}
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274 saw 1.5 \psfig{figure=drift_gas_system-extended_display.eps,width=2.6in,height=1.8in}
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275 jones 1.3 \caption{Extended Display Screen\label{fig:extended_display}}
276 \end{minipage}
277 \begin{minipage}{2.7in}
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278 saw 1.5 \psfig{figure=drift_gas_system-pressure_control.eps,width=2.6in,height=1.8in}
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279 jones 1.3 \caption{Pressure Control Screen\label{fig:pressure_control}}
280 \end{minipage}
281 \end{figure}
282 \end{center}
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283 saw 1.5 %=====================================================================
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284 jones 1.3 \subsection{Gas Flow Rates}
285 \label{sec:gas_flow_rates}
286 The flow rates are adjusted automatically by the controller in order
287 to maintain a constant delivery pressure at the output. Only the flow
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288 saw 1.5 {\em ratios} should be set by the operator. We use a 1:1 ratio, set on
289 the {\bf Gas Composition} screen (Fig.~\ref{fig:gas_composition}), as
290 indicated in Table~\ref{tab:mixer_nominals}.
291
292 The average total flow should equal the sum of the flows to all of the
293 detectors in the shield house. (Note that the ball-type flowmeters in
294 the shield house are calibrated for nitrogen. The approximate
295 multiplier to convert these readings for 50/50 Argon-Ethane is 0.9 .)
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296 jones 1.3
297 System configuration parameters specifying the full-scale flow
298 capacity (for nitrogen) of each valve, the types of gases actually
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299 saw 1.5 flowing through each valve, and the mode of control for the valves are
300 set in the screens pictured in Figs.~\ref{fig:range_selection},
301 \ref{fig:gas_selection}, and \ref{fig:mode_selection}. These figures
302 show the nominal settings for the Hall-C system.
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303 jones 1.3
304 \begin{center}
305 \begin{figure}[hbt]
306 \begin{minipage}{2.7in}
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307 saw 1.5 \psfig{figure=drift_gas_system-gas_composition.eps,width=2.6in,height=1.8in}
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308 jones 1.3 \caption{Gas Composition Screen\label{fig:gas_composition}}
309 \end{minipage}
310 \begin{minipage}{2.7in}
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311 saw 1.5 \psfig{figure=drift_gas_system-range_selection.eps,width=2.6in,height=1.8in}
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312 jones 1.3 \caption{Range Selection Screen\label{fig:range_selection}}
313 \end{minipage}
314 \end{figure}
315 \begin{figure}[hbt]
316 \begin{minipage}{2.7in}
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317 saw 1.5 \psfig{figure=drift_gas_system-gas_selection.eps,width=2.6in,height=1.8in}
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318 jones 1.3 \caption{Gas Selection Screen\label{fig:gas_selection}}
319 \end{minipage}
320 \begin{minipage}{2.7in}
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321 saw 1.5 \psfig{figure=drift_gas_system-mode_selection.eps,width=2.6in,height=1.8in}
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322 jones 1.3 \caption{Mode Selection Screen\label{fig:mode_selection}}
323 \end{minipage}
324 \end{figure}
325 \end{center}
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326 saw 1.1
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327 saw 1.5 %=====================================================================
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328 jones 1.3 \subsection{To set the Delivery Pressure:}
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329 saw 1.1
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330 saw 1.5 Navigate to the {\bf Pressure Control} menu. The pressure set-point (in
331 Torr) is indicated at the bottom-center of the screen. This value
332 should be se to 500.0. Note that the system can not respond instantly
333 to a change in requested gas pressure: it has no way to release excess
334 pressure and must wait for the detector systems to consume it
335 \footnote{An \emph{over-pressure relief valve} releases gas through a
336 small oil bubbler in the gas shed if the pressure exceeds about
337 600~Torr.}; it cannot build up pressure any faster than the
338 flow-control valves can supply it. It may take thirty minutes or so
339 for the pressure regulation system to stabilize at a new set-point or
340 stabilize in response to a change in total gas consumption. However,
341 you should be able to observe a change in the gas flow within a few
342 seconds (possibly up to a minute) after a set-point change.
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343 saw 1.1
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344 saw 1.5 %=====================================================================
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345 saw 1.1 \subsection{To turn gas flow on or off:}
346
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347 saw 1.5 The gas flow can be turned on or off while in any menu. In the
348 Extended Display menu the bottom line displays ``ON'' or ``OFF'', by
349 channel, to show which mass flow valves are enabled. ``ON" must be
350 displayed in the bottom row of the Extended Display menu for gas to be
351 flowing in a particular channel.
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352 saw 1.1
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353 saw 1.5 For gas to flow, two conditions must be met:
354 \begin{enumerate}
355 \item Each channel (1 and 2) must be enabled by pressing ``ON" and then
356 the desired channel number.
357 \item The entire system must be enabled by pressing
358 ``ON" and then ``ALL" from the keypad.
359 \end{enumerate}
360 Thus, each valve can be controlled individually using ``ON/OFF~-~\emph{Channel Number}'',
361 or all flow can be controlled using ``ON/OFF~-~ALL''. If the system
362 is enabled, the status line at the bottom of every screen will
363 indicate ``FLOW ON GAS ON''. {\bf Note:} because Valve-2 (ethane) is
364 normally slaved to Valve-1 (argon), when Valve-1 is disabled there will
365 be no flow through Valve-2.
366
367 %=====================================================================
368 %=====================================================================
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369 saw 1.1 \section{To Change a Gas Bottle}
370
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371 saw 1.2 The argon and ethane supply bottles should be replaced by new (full)
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372 saw 1.5 bottles when the bottle content drops below about 10\% of its
373 capacity. For argon, the bottle content is directly indicated by the
374 bottle pressure: a new bottle usually contains 2000 to
375 3000~psig. Argon bottles should be changed whenever the bottle
376 pressure is found to be below about 200~psig.
377
378 Ethane bottles, on the
379 other hand, contain liquefied ethane. Thus the bottle pressure is just
380 the vapor pressure of ethane at whatever the current temperature
381 happens to be. At 70\degg F this is about 544~psig. The pressure gauge
382 will not tell you how much ethane is left in the bottle until it reads
383 zero! Instead, we measure the ethane content by observing the weight
384 of the bottle and comparing it to the weight when the bottle was
385 full. A standard B-size cylinder contains about 32~pounds of ethane.
386 The ethane cylinders on the manifold sit on scales which have been
387 pre-set to indicate the net weight of ethane in the bottle.
388 Numbers in the green portion of the dial indicate ethane remaining.
389 If the indicator points to the red portion of the dial, the bottle
390 is empty.
391
392 Handling and connecting bottles of compressed gas require special
393 saw 1.5 knowledge. The high pressure gas stored in the cylinders (bottles)
394 constitutes significant stored energy. Mishandling of a gas bottle can
395 pose a lethal hazard! Refer to the JLab ESH\&Q Manual\cite{bi:jlabehs}
396 for safe handling practices. If you do not already know how to safely
397 manipulate compressed gas hardware, have a knowledgeable person train
398 you.
399
400 After attaching a new gas bottle to the supply manifold, check the
401 connection for leaks using \emph{Snoop} or a similar leak detector.
402
403 %=====================================================================
404 %=====================================================================
405 \section{The Alcohol Bubbler}
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406 saw 1.1
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407 jones 1.3 To reduce the rate of aging of the wire chambers, the operating gas
408 contains a small quantity of alcohol vapor. The vapor is added by
409 bubbling the argon/ethane mixture through liquid alcohol. The
410 temperature of the alcohol controls the alcohol vapor pressure, which
411 determines the amount of vapor added to the gas. The alcohol content
412 also affects the electron drift velocity in the wire chambers, so it
413 must be held approximately constant.
414
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415 saw 1.5 Gas is bubbled through the liquid alcohol inside the glass
416 dome vessel in the refrigerator. The dome is covered by a
417 perforated steel cylinder as a precaution against breakage. The
418 alcohol level is controlled by a float valve inside the metal cold
419 reservoir, which is also inside the refrigerator. As long as there is
420 alcohol in the warm reservoir (sitting on top of the refrigerator),
421 the liquid levels inside the refrigerator will remain constant. A
422 drain valve (\#7) inside the refrigerator is available for emptying
423 all liquid from the system. It is for use by experts only and should
424 remain closed during normal operation.
425
426 {\bf The reservoir should be refilled before it becomes empty to
427 maintain a head of liquid over the float valve. This will prevent air
428 from entering the system.}
429 %=====================================================================
430 \subsection{To by-pass the alcohol system}
431
432 Open valve {\bf 3}, then promptly close valves {\bf 1 \& 2}, in that order!
433
434 \noindent To restore flow through the bubbler, open valves {\bf 1 \& 2} then
435 close valve {\bf 3}.
436 saw 1.5
437 %=====================================================================
438 \subsection {Alcohol Temperature Control}
439
440 To keep the alcohol temperature (and thus the vapor pressure) constant,
441 the alcohol bubbler is housed in a refrigerator which is controlled by
442 an electronic temperature regulator having 1~C\degg sensitivity. The
443 controller is located on a shelf in the right-hand rack of the gas mixing
444 system. Normally, the actual temperature in the refrigerator is
445 indicated on the front panel of the controller. The controller should
446 be set to maintain a temperature of 2\degg C.
447
448 %=====================================================================
449 \pagebreak[4]
450 \subsection{Step-by-Step Instructions for Refilling the Alcohol Bubbler}
451 {\em These 13 steps must be individually completed in the order listed!}
452 Refer to Fig.~\ref{fig:gas_mixer_diagram}.\\
453
454 \begin{minipage}{\textwidth}
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455 saw 1.1 \begin{enumerate}
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456 saw 1.5 \footnotesize{
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457 jones 1.3 \item{Remove the three screws securing the cover on the alcohol fill-tank
458 (the top-most metal tank at the rear of the mixer rack. Carefully remove the lid
459 without allowing dust or dirt to fall into the tank.}
460 \item{Fill this tank to about 75\% full from a bottle of 2-propanol.}
461 \item{Replace the lid and retaining screws.}
462 \item{Remove the small brass cap which seals the port on the lid.}
463 \item{Isolate the warm reservoir by {\bf closing valves 4 and 8.}}
464 \item{Release pressure in the warm reservoir by {\bf slowly opening valve 6 fully.}}
465 \item{{\bf Open valve 5 fully} to begin the flow of alcohol from the fill-tank to the warm reservoir.}
466 \item{{\bf Monitor the level} of alcohol in the warm reservoir sight-tube.}
467 \item{When the level is 2~cm from the top of the sight-tube, {\bf close valve 5.}}
468 \item{Replace the brass cap on the lid of the fill-tank.}
469 \item{{\bf Close valve 6, {\it then} slowly open valve 4.}}
470 \item{{\bf Open valve 8.}}
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471 saw 1.5 \item{Record what you did in both the gas logbook and the electronic logbook.}
472 } %end of scriptsize
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473 saw 1.1 \end{enumerate}
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474 saw 1.5 \end{minipage}
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475 saw 1.1
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476 saw 1.5 %=====================================================================
477 %=====================================================================
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478 saw 1.1 \section{Gas Filters Maintenance}
479
480 There are gas filters on the argon and ethane supply lines just inside
481 the gas shed. These filters should be replaced on a regular schedule.
482 See Bill Vulcan for details.
483
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484 saw 1.5 %=====================================================================
485 %=====================================================================
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486 saw 1.1 \section{Secure Pressure Regulators}
487
488 The gas mixing system is protected from failure or mis-setting of the
489 primary pressure regulators (the ones mounted on the manifolds on the
490 exterior of the gas shed -- near the bottles) by {\it hidden} regulators
491 mounted just inside the gas shed. It is these regulators which actually
492 set the maximum supply pressure to the mixing valves. These regulators
493 should {\em never} be adjusted by other than a gas system expert! The
494 nominal secondary pressure supplied by both the argon and ethane
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495 jones 1.3 secure regulators is 30 psig.
496
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497 saw 1.5 %=====================================================================
498 %=====================================================================
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499 jones 1.3 \section{Ethane Flow Restrictor}
500
501 A calibrated flow-restricting orifice is installed at the outlet of
502 the main ethane high-pressure manifold outside the gas shed. This
503 orifice passively limits the flow rate of ethane into the gas shed
504 even if there is a catastrophic failure of the flow and pressure-controlling
505 devices inside the shed. It is model {\tt IC-DM4-9-SS} manufactured by
506 {\em O'Keefe Controls Co.}, Trumbull, CT, USA. While it may look like
507 simply a stainless-steel union fitting, it is in fact a precision part,
508 and a necessary component of the gas safety system. It limits the flow
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509 saw 1.5 of ethane to less than 26.5 SLM, which is a little
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510 jones 1.3 less than ten times the maximum capacity of the flow-control system.
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511 saw 1.1
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512 saw 1.5 %=====================================================================
513 %=====================================================================
514
515 \raggedright %this fixes formatting of bibliography, too.
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516 saw 1.1
517 \section{Related {\it Howtos}}
518 \begin{itemize}
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519 jones 1.3 \item MKS~647 Mass Flow Controller Manual \cite{647C_EN_0504A1}
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520 saw 1.1 \item Base Equipment Shift Checklist Items \cite{howto:base_equip_checklist}
521 \end{itemize}
522
523 \end{document}
524
525 % Revision history:
526 % 1st draft by Howard Fenker 27FEB03 -- taken from existing ops manual.
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527 jones 1.3 % Rev. 1.1 - added notes on bottle changing, ethane bottle pressure.
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528 saw 1.6 % $Log: drift_gas_system.tex,v $
529 % Revision 1.5 2008/01/02 16:46:03 saw
530 % Latest update
531 %
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