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
9 %\maintainer{Name of person maintaining document} % Optional
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10 jones 1.3 \date{\today} % Can use \today as the argument
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11 saw 1.1
12
13 \begin{document}
14 \providecommand{\degg}{\ensuremath{^{\circ}\ }}
15
16 \begin{abstract}
17 This document provides detailed setup information for the drift chamber gas mixing
18 system, as well as the correct procedure for refilling the alcohol supply and changing
19 gas bottles. This information is intended for use by {\bf gas system experts only.}
20 For day-to-day shift worker instructions, refer to the corresponding {\it user} howto
21 document.
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22 jones 1.3
23 {\bf Please Note:} The Hall-C Drift Chamber Gas System was significantly changed in
24 early 2007. It is now a {\it pressure-driven system} whereas it had been
25 flow-controlled. Long-time Hall-C staff and users will find that the system
26 operates quite differently now.
27
28 {\bf Also Note:} During the 2007 running period, gas entering the hall is still
29 {\em flow controlled}, as it has been in the past. While the mixing system
30 produces pressurized gas, the flows to the HMS and SOS are at low pressure
31 and are controlled by needle valves in the gas shed. See the special note
32 in section \ref{sec:gas_flow_rates}.
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33 saw 1.1 \end{abstract}
34
35 \section{Overview}
36
37
38 The drift chamber gas is composed of 50\% Argon and 50\% Ethane (by volume),
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39 jones 1.3 bubbled through isopropanol maintained at a temperature such that the gas mixture contains
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40 saw 1.2 approximately 1\% alcohol vapor. The mixing system that produces this
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41 jones 1.4 gas is housed in the Hall-C gas shed (Bldg. 96c). The bottles supplying the gas to the mixing
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42 saw 1.1 system are attached to two two-bottle manifolds outside the gas shed, within
43 the fenced-in gas bottle yard.
44
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45 jones 1.3 A single mixing system provides the gas for both the SOS and the HMS as well
46 as auxiliary detectors such as the {\it Focal Plane Polarimeter} chambers. Gas
47 is delivered to the hall at a pressure of about 9 psi (500 Torr) above atmospheric
48 pressure. {\bf For 2007, see the note regarding the special interim installation
49 in section \ref{sec:gas_flow_rates}}. The flow to each detector is controlled by its own individual
50 needle-valve with flowmeter. The job of the mixing system is to simultaneously
51 maintain the delivery pressure and mixing ratio by providing whatever total
52 flow rate of gas (between zero and 5.28 slpm) is demanded by the detectors.
53 This is accomplished by controlling two flow valves (argon and ethane) so that
54 they each flow the same volume of gas while keeping the output pressure nearly
55 constant. The mixing system flow diagram is shown in Fig. \ref{fig:gas_mixer_diagram}.
56
57
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58 saw 1.2 \section{Gas Interlock System}
59 The flow of gas from the supply bottles may be automatically shut off by
60 normally-closed solenoid valves installed in the primary argon and ethane manifolds. Several
61 conditions such as overtemperature, fan failure, gas leak, and fire alarm must all
62 be in the non-alarm state before these valves will open. Alarm conditions are
63 indicated on the gas system alarm panel on the lower-left side of the
64 center counting-house console.
65
66 When any of the required conditions is not satisfied the sounder on the panel
67 will make an annoying noise and both solenoid valves will close. The audible
68 alarm may be silenced by a toggle switch on the panel. Be certain to return
69 it to the ``on'' position as soon as the fault is cleared.
70
71 The most confusing, but most common alarm condition is ``Low Pressure''.
72 The solenoid valves will not remain open unless there is already ample pressure
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73 jones 1.3 on the output side of both valves. This prevents, for example, the flow of
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74 saw 1.2 pure ethane to the drift chambers when the argon bottle is empty. The way
75 to clear this condition is to make sure there are no other faults and that
76 both argon and ethane manifolds are properly pressurized and fitted with
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77 jones 1.3 non-empty bottles; then press and hold the ``override'' button on the alarm panel
78 for several
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79 saw 1.2 seconds. This button forces the solenoid valves to open even if there are
80 fault conditions present. If all is well, gas will flow through the valves
81 and clear the ``low pressure'' condition so that the button many be released.
82
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83 jones 1.3 \begin{figure}[hbt]
84 \psfig{figure=gasmixer2007.eps,width=6in,bbllx=12,bblly=12,bburx=750,bbury=590}
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85 saw 1.1 \caption{Diagram of Hall~C Gas Mixing System\label{fig:gas_mixer_diagram}}
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86 jones 1.3 \vspace{0.5cm}
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87 saw 1.1 \end{figure}
88
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89 jones 1.3 \section{Operating the Mass Flow Controller.}
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90 saw 1.1
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91 jones 1.3 The gas flow is controlled by a MKS~647 controller and mass flow
92 control valves. Delivery pressure is sensed at the mixer output
93 by a {\it Baratron} pressure transducer.
94 The 647 is menu driven from a display on the front panel using
95 a keypad with numeric and cursor controls for input. It features a non-volatile memory
96 so that most of its settings are retained even if the unit is unpowered.
97 Unfortunately, the pressure-regulation parameters do need to be reset
98 if power is lost, however, so the controller is powered through an
99 uninterruptable power supply (UPS).
100
101 \subsection{Settings for Normal Operation}
102
103 A summary of all of the settings required to make the controller function
104 properly is given in Table~\ref{tab:mixer_nominals}. The table also shows
105 which screen contains each parameter. Instructions for setting parameters
106 is given below. Detailed instructions for configuring and operating the
107 MKS~647 can be found in the manufacturer's instruction manual, a copy of
108 which is posted at $http://hallcweb.jlab.org/document/vendor\_manuals/$.
109 \begin{table}[hbt]
110 \begin{minipage}[h!]{\textwidth}
111 \centering
112 jones 1.3 %\vspace*{-8.4 cm}
113 %\hspace{-1.0cm}
114 {\scriptsize
115 \begin{tabular}{|l|c|l|}
116 \hline
117 Parameter & Set To & {\it Controller Screen}/Comments\\ \hline
118 \multicolumn{2}{|c|}{\bf Manual Valves } & Valves are labeled \\
119 Valves 1, 2, 4, 8 & OPEN & \\
120 Valves 3, 5, 6, 7 & CLOSED & \\ \hline
121 \multicolumn{2}{|c|}{\bf Pressure PID Loop Settings } & {\it Pressure Control} \\
122 Pressure & 500 Torr & \\
123 PID Mode & AUTO & \\
124 PID GAIN & 4.0 & \\
125 PID INTEG & 10.0 & \\
126 PID LEAD & 0.000 & \\ \hline
127 \bf Mixture & 1 & {\it User}/ Lower-right corner of screen \\ \hline
128 \multicolumn{2}{|c|}{\bf Gas Composition for Mixture 1} & {\it Gas Composition} \\
129 Channel 1 & 1.000 & \\
130 Channel 2 & 1.000 & \\
131 Channel 3 & 0.000 & \\
132 Channel 4 & 0.000 & \\ \hline
133 jones 1.3 \multicolumn{2}{|c|}{\bf MFC Valve Size / Gas} & {\it Extended Display} \\
134 Channel 1 & 2.0 slpm / Ar & provides 2.78 slpm Argon\\
135 Channel 2 & 5.0 slpm / C$_2$H$_6$ & provides 2.50 slpm Ethane\\
136 Channel 3 & \it unused& \\
137 Channel 4 & \it unused& \\ \hline
138 \multicolumn{2}{|c|}{\bf Channels ON/OFF Settings} & {\it Extended Display} \\
139 Channel 1 & ON & Press ``ON 1'' (\em Argon) \\
140 Channel 2 & ON & Press ``ON 2'' (\em Ethane) \\
141 Channel 3 & OFF & Press ``OFF 3'' (\em not in use) \\
142 Channel 4 & OFF & Press ``OFF 4'' (\em not in use) \\ \hline
143 \multicolumn{2}{|c|}{\bf Pressure Transducer} & {\it Pressure Setup} \\
144 Type & STD & \\
145 Full Scale & 1000 Torr& \\ \hline
146 \multicolumn{2}{|c|}{\bf MFC Valve Controls } & {\it Instrument Setup} \\
147 Channel 1 & PID & \\
148 Channel 2 & SLAVE / 1& \\
149 Channel 3 & INDEP & \\
150 Channel 4 & INDEP & \\ \hline
151 \bf Alcohol Temp. & $2^\circ $ C & Electronic Temperature \\
152 & & Control Box \\ \hline
153 \hline
154 jones 1.3 \end{tabular}
155 }%end of \small
156 \end{minipage}
157 \caption{Normal Valve and Parameter Settings for the Gas Mixing System.
158 \label{tab:mixer_nominals}}
159 \end{table}
160
161
162
163 \subsection{General}
164
165 If the controller screen is dark, press {\bf ESC} to awaken the display.
166 Many screens merely provide a menu of other screens you may access:
167 simply press the item number you desire. To go up one level in
168 the menu hierarchy, press {\bf ESC}.
169
170 In general, to change a parameter displayed on the controller
171 screen use the {\bf left/right} arrow keys to move the cursor to the item you
172 wish to change. Then either use the number keys to enter the
173 value desired for that item (numeric parameter) or use the
174 {\bf ENTER} or {\bf up/down} keys to cycle a parameter through
175 jones 1.3 its available settings (configuration parameter). Numeric parameters
176 may be incrementally modified by using the {\bf up/down} arrow keys. To make
177 certain that a new parameter becomes active, move the cursor
178 off of the parameter after you have entered the new value.
179
180 \begin{center}
181 \begin{figure}[hbt]
182 \begin{minipage}{2.7in}
183 \psfig{figure=main_menu.eps,width=2.6in,height=1.8in}
184 \caption{MKS 647 Main Menu\label{fig:main_menu}}
185 \end{minipage}
186 \begin{minipage}{2.7in}
187 \psfig{figure=user_display.eps,width=2.6in,height=1.8in}
188 \caption{MKS 647 User Display\label{fig:user_display}}
189 \end{minipage}
190 \end{figure}
191 \end{center}
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192 saw 1.1
193
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194 jones 1.3 The initial menu
195 upon startup is the {\bf Main Menu}. For normal operation use the
196 {\bf User Display} menu (Main Menu item \#1). It shows the amount of
197 each gas currently flowing, the total gas flow, and the current delivery
198 pressure. This display also shows which of several possible pre-defined
199 gas mixtures is selected. For normal operation, we use only mixture {\bf \#1},
200 (number shown on the lower-right of the display). Only on this screen
201 can this parameter be changed.
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202 saw 1.1
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203 jones 1.3 The {\bf Extended Display} menu (Main Menu item \#2) shows actual
204 flow, flow set point, units, valve full scale range, gas calibration
205 factor, whether that channel is enabled, and whether each channel is
206 operating in master, slave, PID, or independent mode. This display is most
207 useful to a system expert wishing to verify the system parameter settings.
208 Most parameters cannot be modified from this screen, however.
209
210
211 Delivery pressure setpoint and pressure {\bf PID} control parameters
212 may be configured from the {\bf Pressure Control} screen.
213
214 \begin{center}
215 \begin{figure}[hbt]
216 \begin{minipage}{2.7in}
217 \psfig{figure=extended_display.eps,width=2.6in,height=1.8in}
218 \caption{Extended Display Screen\label{fig:extended_display}}
219 \end{minipage}
220 \begin{minipage}{2.7in}
221 \psfig{figure=pressure_control.eps,width=2.6in,height=1.8in}
222 \caption{Pressure Control Screen\label{fig:pressure_control}}
223 \end{minipage}
224 jones 1.3 \end{figure}
225 \end{center}
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226 saw 1.1
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227 jones 1.3 \subsection{Gas Flow Rates}
228 \label{sec:gas_flow_rates}
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229 saw 1.1
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230 jones 1.3 The flow rates are adjusted automatically by the controller in order
231 to maintain a constant delivery pressure at the output. Only the flow
232 {\em ratios} should be set by the operator. We use a 1:1 ratio, set
233 on the {\bf Gas Composition} screen (Fig.~\ref{fig:gas_composition}),
234 as indicated in Table~\ref{tab:mixer_nominals}.
235
236 The average total flow should equal the sum of the flows to all of the detectors in the
237 shield house. (Note that the ball-type flowmeters in the shield house are
238 calibrated for nitrogen. The approximate multiplier to convert these
239 readings for 50/50 Argon-Ethane is 0.9 .)
240
241 System configuration parameters specifying the full-scale flow
242 capacity (for nitrogen) of each valve, the types of gases actually
243 flowing through each valve, and the mode of control for the valves
244 are set in the screens pictured in Figs.~\ref{fig:range_selection},
245 \ref{fig:gas_selection}, and \ref{fig:mode_selection}. These
246 figures show the nominal settings for the Hall-C system.
247
248 \begin{center}
249 \begin{figure}[hbt]
250 \begin{minipage}{2.7in}
251 jones 1.3 \psfig{figure=gas_composition.eps,width=2.6in,height=1.8in}
252 \caption{Gas Composition Screen\label{fig:gas_composition}}
253 \end{minipage}
254 \begin{minipage}{2.7in}
255 \psfig{figure=range_selection.eps,width=2.6in,height=1.8in}
256 \caption{Range Selection Screen\label{fig:range_selection}}
257 \end{minipage}
258 \end{figure}
259 \begin{figure}[hbt]
260 \begin{minipage}{2.7in}
261 \psfig{figure=gas_selection.eps,width=2.6in,height=1.8in}
262 \caption{Gas Selection Screen\label{fig:gas_selection}}
263 \end{minipage}
264 \begin{minipage}{2.7in}
265 \psfig{figure=mode_selection.eps,width=2.6in,height=1.8in}
266 \caption{Mode Selection Screen\label{fig:mode_selection}}
267 \end{minipage}
268 \end{figure}
269 \end{center}
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270 saw 1.1
271
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272 jones 1.3 {\bf SPECIAL NOTE REGARDING THE 2007 RUNNING PERIOD:}
273 During the 2007 running period the total flows to each of the
274 {\em Shield Houses (HMS and SOS)} are set by needle valve~/~ball flowmeter
275 units located in the gas shed. This interim installation makes gas
276 delivery to the shield houses very similar to what the old mixing
277 system provided. The old total flows were 0.6~slpm to the HMS and
278 0.3~slpm to the SOS. Thus the needle valves in the gas shed should
279 be set to obtain ball flowmeter readings of
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280 saw 1.1 \begin{itemize}
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281 jones 1.3 \item SOS: (300 / 0.9) = 333~sccm
282 \item HMS: (600 / 0.9) = 666~sccm
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283 saw 1.1 \end{itemize}
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284 jones 1.3 when the mixer delivery pressure is stabilized at its nominal setting.
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285 saw 1.1
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286 jones 1.3 \subsection{To set the Delivery Pressure:}
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287 saw 1.1
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288 jones 1.3 Navigate to the {\bf Pressure Control} menu. The pressure setpoint
289 (in Torr) is indicated at the bottom-center of the screen. This
290 value should be se to 500.0. Note that the system can not respond
291 instantly to a change in requested gas pressure: it has no way
292 to release excess pressure and must wait for the detector systems
293 to consume it; it cannot build up pressure any faster than the
294 flow-control valves can supply it. It may take thirty minutes or
295 so for the pressure regulation system to stabilize at a new
296 setpoint or stabilize in response to a change in total gas
297 consumption. However, you should be able to observe a change in
298 the gas flow within a few seconds (possibly up to a minute)
299 after a setpoint change.
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300 saw 1.1
301 \subsection{To turn gas flow on or off:}
302
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303 jones 1.3 The gas flow can be turned on or off while in any menu.
304 In the Extended Display menu the bottom line displays ``ON''
305 or ``OFF'', by channel, to show which mass flow valves are enabled.
306 ``ON" must be displayed in the bottom row of the
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307 saw 1.1 Extended Display menu for gas to be flowing in a particular channel.
308
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309 jones 1.3 Turning the gas on or off is done in two steps which can be done in
310 either order.
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311 saw 1.1 Each channel must be enabled by pressing ``ON" and then
312 that channel number. The command input must be enabled by pressing ``ON"
313 and then ``ALL" from the keypad. This allows a single channel or all of the
314 enabled channels to be turned on or off at once. Both steps must be
315 performed initially, but thereafter only one of the steps need be performed
316 to cycle the gas flow on or off.
317
318 To turn gas off in a single channel press ``OFF" and then the
319 desired channel. If you want to close all the valves simultaneously, press
320 the ``OFF" key and then the ``ALL/0" key. To turn gas back on you must
321 reverse whichever sequence you used to stop the gas flow. For example if
322 you turned the gas off by pressing ``OFF" and then the channel number, it
323 must be turned back on by pressing ``on" and then the channel number. If
324 you turn off all the channels by pressing ``OFF" , ``ALL" you must turn it
325 back on by pressing ``ON" , ``ALL."
326
327 \section{To Change a Gas Bottle}
328
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329 saw 1.2 The argon and ethane supply bottles should be replaced by new (full)
330 bottles when the bottle content drops below about 10\% of its capacity.
331 For argon, the bottle content is directly indicated by the bottle
332 pressure: a new bottle usually contains 2000 to 3000~psig. Argon bottles
333 should be changed whenever the bottle pressure is found to be below
334 about 200~psig. Ethane bottles, on the other hand, contain liquified
335 ethane. Thus the bottle pressure is just the vapor pressure of ethane
336 at whatever the current temperature happens to be. At 70\degg F this is
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337 jones 1.3 about 544~psig. The pressure gauge
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338 saw 1.2 will not tell you how much ethane is left in the bottle until it
339 reads zero! Instead, we measure the ethane content by observing the
340 weight of the bottle and comparing it to the weight when the bottle
341 was full. A standard B-size cylinder contains about 32~pounds of ethane.
342 Thus, when the bottle weight is about 30~pounds less than its full weight,
343 the bottle should be replaced. Recent (as of April 2003) experience
344 indicates that full bottles weigh $165\pm 1 lbs.$
345
346 Handling and connecting bottles of compressed gas require special knowledge.
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347 saw 1.1 The high pressure gas stored in the cylinders (bottles) constitutes significant
348 stored energy. Mishandling of a gas bottle can pose a lethal hazard! Refer to
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349 saw 1.2 the JLab EH\&S Manual\cite{bi:jlabehs} for safe handling practices. If you do not already know
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350 saw 1.1 how to safely manipulate compressed gas hardware, have a knowledgeable
351 person train you.
352
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353 saw 1.2 \section{To by-pass the alcohol system}
354
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355 jones 1.3 Open valve {\bf 3}, then close valves {\bf 1 \& 2}, in that order!
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356 saw 1.1
357
358 \section{The Alcohol Bubblers}
359
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360 jones 1.3 To reduce the rate of aging of the wire chambers, the operating gas
361 contains a small quantity of alcohol vapor. The vapor is added by
362 bubbling the argon/ethane mixture through liquid alcohol. The
363 temperature of the alcohol controls the alcohol vapor pressure, which
364 determines the amount of vapor added to the gas. The alcohol content
365 also affects the electron drift velocity in the wire chambers, so it
366 must be held approximately constant.
367
368 Gas is bubbled through the liquid alcohol inside the glass dome-covered
369 vessel in the refrigerator. The dome is covered by a steel cylinder
370 as a precaution against breakage. If you lift the cylinder you can
371 see the alcohol and gas bubbles inside the dome. The alcohol level
372 is controlled by a float valve inside the metal cold reservoir, which
373 is also inside the refrigerator. As long as there is alcohol in the
374 warm reservoir (sitting on top of the refrigerator), the liquid levels
375 inside the refrigerator will remain constant. A drain valve (\#7) inside
376 the refrigerator is available for emptying all liquid from the system.
377 It is for use by experts only and should remain closed during normal
378 operation.
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379 saw 1.1
380 \subsection{To refill the alcohol bubblers:}
381
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382 jones 1.3 {\bf The reservoir should be refilled
383 before it becomes empty to maintain a head of liquid over the float valve.
384 This will prevent air from entering the system.}
385
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386 saw 1.1
387 \subsection{Step-by-Step Instructions for Refilling the SOS Alcohol Bubbler}
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388 jones 1.3 {\em These steps must be individually completed in the order listed!}\\
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389 saw 1.1 Refer to Fig.~\ref{fig:gas_mixer_diagram}.
390 \begin{enumerate}
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391 jones 1.3 \item{Remove the three screws securing the cover on the alcohol fill-tank
392 (the top-most metal tank at the rear of the mixer rack. Carefully remove the lid
393 without allowing dust or dirt to fall into the tank.}
394 \item{Fill this tank to about 75\% full from a bottle of 2-propanol.}
395 \item{Replace the lid and retaining screws.}
396 \item{Remove the small brass cap which seals the port on the lid.}
397 \item{Isolate the warm reservoir by {\bf closing valves 4 and 8.}}
398 \item{Release pressure in the warm reservoir by {\bf slowly opening valve 6 fully.}}
399 \item{{\bf Open valve 5 fully} to begin the flow of alcohol from the fill-tank to the warm reservoir.}
400 \item{{\bf Monitor the level} of alcohol in the warm reservoir sight-tube.}
401 \item{When the level is 2~cm from the top of the sight-tube, {\bf close valve 5.}}
402 \item{Replace the brass cap on the lid of the fill-tank.}
403 \item{{\bf Close valve 6, {\it then} slowly open valve 4.}}
404 \item{{\bf Open valve 8.}}
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405 saw 1.1 \item{Record what you did in both the gas logbook and the electronic logbook.}
406 \end{enumerate}
407
408
409 \subsection {Alcohol Temperature Control}
410
411 To keep the alcohol temperature (and thus the vapor pressure) constant,
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412 jones 1.3 the alcohol bubbler is housed in a refrigerator which is controlled by
413 an electronic temperature regulator having 1~C\degg sensitivity. The
414 controller is located on a shelf in the rack of the gas mixing
415 system. Normally, the actual temperature in the refrigerator is
416 indicated on the front panel of the controller. The controller should
417 be set to maintain a temperature of 2\degg C.
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418 saw 1.1
419 \section{Gas Filters Maintenance}
420
421 There are gas filters on the argon and ethane supply lines just inside
422 the gas shed. These filters should be replaced on a regular schedule.
423 See Bill Vulcan for details.
424
425 \section{Secure Pressure Regulators}
426
427 The gas mixing system is protected from failure or mis-setting of the
428 primary pressure regulators (the ones mounted on the manifolds on the
429 exterior of the gas shed -- near the bottles) by {\it hidden} regulators
430 mounted just inside the gas shed. It is these regulators which actually
431 set the maximum supply pressure to the mixing valves. These regulators
432 should {\em never} be adjusted by other than a gas system expert! The
433 nominal secondary pressure supplied by both the argon and ethane
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434 jones 1.3 secure regulators is 30 psig.
435
436 \section{Ethane Flow Restrictor}
437
438 A calibrated flow-restricting orifice is installed at the outlet of
439 the main ethane high-pressure manifold outside the gas shed. This
440 orifice passively limits the flow rate of ethane into the gas shed
441 even if there is a catastrophic failure of the flow and pressure-controlling
442 devices inside the shed. It is model {\tt IC-DM4-9-SS} manufactured by
443 {\em O'Keefe Controls Co.}, Trumbull, CT, USA. While it may look like
444 simply a stainless-steel union fitting, it is in fact a precision part,
445 and a necessary component of the gas safety system. It limits the flow
446 of ethane to less than 26.5 standard liters per minute, which is a little
447 less than ten times the maximum capacity of the flow-control system.
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448 saw 1.1
449
450 \section{Related {\it Howtos}}
451 \begin{itemize}
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452 jones 1.3 \item MKS~647 Mass Flow Controller Manual \cite{647C_EN_0504A1}
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453 saw 1.1 \item Flammable Gas Detector System \cite{howto:flam_gas_detector}
454 \item Gas System Interlock Panel \cite{howto:gas_interlock_panel}
455 \item Base Equipment Shift Checklist Items \cite{howto:base_equip_checklist}
456 \end{itemize}
457
458 \end{document}
459
460 % Revision history:
461 % 1st draft by Howard Fenker 27FEB03 -- taken from existing ops manual.
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462 jones 1.3 % Rev. 1.1 - added notes on bottle changing, ethane bottle pressure.
463 % $Log$
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