4. Charts
The charts for the Hall A
cryotarget are still based on Fraser Duncan's Tcl/Tk charting scripts.
4.1 Starting the
Charts
The main chart menu can be launched from the pull down menu located in
the upper right corner of the main control screen. It is labelled
Charts & Alarms. The chart menu is shown below, and has
several preselected combinations which can be accessed under the Chart
menu. The most common charts are grouped under the menu item
Loop Charts . These are probably the only charts that the target
operator needs.
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4.2 Configuring Loop vs Gas Panel
The first entry, Configure
Loop vs Gaspanel, can be used to specify
which gas panel (hydrogen, deuterium, or helium) is connected to which
target loop (1, 2, or 3). This configuration is always made by the
JLab Target Group, so the Hall A operator should not alter this screen unless
specified to do so.
Once configured, the chart maker will automatically generate the proper
groups of charts for each loop (e.g. as indicated above, the deuterium pressures
will be charted alongside the LOOP2 temperatures).
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4.2 Saving Chart Options
Once the charts have
been configured by the user (usually only the y-axes need to be set), he
or she should use the Charts menu to Save Strip Chart Options.
This will launch the FIle Dialog Box shown directly below. Type
a new (or old) name into the lower text enty box and click OK. To
load an alternative set of options, choose Load Strip Chart Options
from the main chart menu.
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5. Alarms
5.1 Starting the Alarm Handler
Like the Charts, the Alarm
Handler for the Hall A cryotarget is still based
on Fraser Duncan's Tcl/Tk code and can be launched from the pull-down
menu located in the upper right corner of the main control
screen. After this choice is made, a new Xterm window and the
two Tcl/Tk windows shown below should appear.
The File Dialog Window
allows you to select the proper alarm file to be used by the alarm handler.
The file that is normally used during data-taking is
atarg.alh. Choose this file (or another) and press "OK".
After the file is read into the alarm handler the dialog box will
disappear and the alarm handler is enabled.
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5.2 Acknowledging Alarms
After the alarm handler
has been enabled, the above window labelled tgtalh, should
have a single button whose color indicates the alarm status of the target:
- yellow=MINOR
- red=MAJOR
- white=INVALID
- other color=NO ALARM
By clicking on this button,
a window showing the "alarm tree" for the Hall
A target appears. If you click on the name of a component in this window,
(e.g. temperatures2) the tree opens to display
the various alarm records in that group. An Epics record (e.g. a
temperature sensor) that has exceeded a certain prescribed limit will produce
an alarm. The records that alarmed will have a colored box to their
sides. The alarm handler captures both transient alarms in addition
to continuing alarms. A bell will sound until the alarm is acknowledged.
To acknowledge an alarm, click on the colored alarm box on the left
panel.
If an alarm persists,
it may be necessary to adjust its limits. Consult Target On-Call before
adjusting any alarm limits.
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5.3 Saving and Loading Alarm Set Points
Once the alarm limits
have been properly set, they should be saved as a file with an "
alh" extension. Under the Options menu on the atarg
Alarm Tree, choose Save Alarm Set Points in order to create
or update the alh file
on the local computer. Next, choose Save Current Set Points to
Boot File. This will copy the
alh file to the IOC boot directory and ensures that the new alarm
settings will remain the same following a reboot of the IOC. Contact
Target On-Call if the new alarms limit are not automatically loaded into
the control computer following an IOC reboot.
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6. Target Motion
The target is positioned
vertically in the path of the electron beam by three servo motors, each
connected to its own motion controller called a BDS. Two of the BDS
units are configured as "Slaves" and are controlled by the third, the "Master".
The target operator communicates with the Master BDS through the IOC
in order to move the target. The position is determined by an encoder
attached to the Master's servo motor. The various target positions (Loop1
top cell, Loop1 bottom cell, Carbon target, etc) are stored as 15 encoder
values on the control computer (IOC).
Target Motion is controlled by the operator through the Lifter
GUI shown below. The 15 encoder values can
be viewed by clicking on BDS positions at the top of this GUI.
On the left of the Lifter GUI are a column of buttons for selecting
amongst the available scattering targets (4 cm H2, 15 cm D2, Carbon, etc).
Clicking one of these buttons sends the "MOVE" command to the Master
BDS along with that target's encoder value.
The current position of the target is
indicated in three ways on the GUI:
- by the
Beam arrow in the center of the GUI
- by a GREEN
LED beside the aformentioned column of buttons
- by the actual encoder
reading beneath the drawing of the target stack
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To change to a new position:
- Select the proper target
from the list on the left of the Lifter GUI and click that button.
- A new window should
appear with a single MOVE TARGET button will appear. Clicking this
button will begin target motion.
- Once you have clicked
the MOVE TARGET button, be sure to close this window.
- When the target is moving,
a YELLOW LED beside the button should illuminate, and you should see the
Current Position
changing every 5 seconds.
- When the target has reached
its new location, the YELLOW LED will turn GREEN
Page Target On-Call in case
of any target motion difficulties!
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6.2 Killing Target Motion (Emergency Stop)
If you need to suddenly stop the target, hit the KILL MOTION
button. To resume motion, press Clear Select Record and then
click the desired target button.
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6.3 The GO HOME routine
Whenever power to a BDS motion controller is interrupted, it loses
it current encoder value. A pre-programmed motion routine called "HOME"
is used to recover the encoder position in the following way. If the
GO Home option is chosen from the column of target positions, the
lifter moves the target upward until it contacts the "Home Switch", mounted
on the outside of the scattering chamber. The lifter will reverse its
motion for a couple of centimeters, and then move upwards to the home switch
once more, very slowly this time. When "home" is contacted a second
time, the Lifter stops, and a value of -46952 (this value may change) is
loaded into its encoder. Each of the 15 encoder positions stored on the IOC
are relative to the "Home" position and were determined prior to the experiment
by the JLab Alignment Group.
Never run the Go Home routine unless instructed to do so by Target
On-Call or another Target Expert!
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6.4 Lifter Status Lights
The Lifter reports the
status BDS motion controller by means of the following indicators located
at the bottom left corner of the GUI.
- Power Fail - Alert.
Power to the BDS has been interrupted. See
GO HOME above.
- Busy - Normal.
Indicates that the BDS is processing a command.
- Brake - Normal.
Indicates that motion has stopped and the brakes have been applied.
Breaks should not be on if Lifter is still moving.
- Status - Normal.
Confirms that motion is enabled. Should not be on if Error
is on.
- Hardware Limit
- Error. Indicates that the lifter has hit either
an upper or lower hardware limit switch mounted outside the scattering chamber.
Page Target On-Call.
- 1st Up Limit -
Error. Lifter has hit an inner upper limit. Page Target
On-Call.
- 1st Down Limit
- Error. Lifter has hit an inner lower limit. Page Target
On-Call.
- Home - Alert.
Lifter has reached HOME switch.
- Fault - Error.
Internal hardware error. Contact Target On-Call.
- Error - Error.
Software error. Contact Target On-Call.
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6.5
Miscellaneous Comands
- Set Position -
launches a new window that allows the user to move to an arbitrary encoder
value.
- MIN/MAX Position
- minimum and maximum software positions for Set Position
- Lifter Speed -
determines how fast the lifter moves. Usually set at 200. DO
NOT CHANGE.
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7. High Power Heaters
7.1
Operation Modes
The high power heaters
(HPH) are used to regulate the target loop temperatures and are located
inside each of the three heat exchangers. The control GUI for each heater
(Loop 1, 2, or 3) can be launched either from the
main control GUI, or from the bottom of the given LOOP GUI. The
heaters have three operation modes:
- Off - no power
is sent to the heater. The heater must be ON for any other operation
mode to function.
- MAN - the operator
manually selects the power (in Watts) for the high power heater;
- PID - the control
computer (IOC) adjusts the heater power in order to maintain a specific
target temperature
There is a new feature to
the heaters, namely "Beam Compensation".
You can read about it below.
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7.2
Turning the Heaters On and Off
To turn the heater on,
click
the red ON button in the upper left corner of the Heater GUI.
"Heater On" should appear in RED. The actual heater output will
depend on whether it is in PID or Manual mode, described below.
To turn the heater off, click the Off button. This will
immediately set the power to zero, regardless of the other operation modes.
"Heater Off" should
appear in RED.
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7.3 Setting a manual heater power
Assuming that the heater is Off:
- Verify that the desired
power setting does not exceed the Maximum Heater Power
- Enter the desired power
(in Watts) into the Manual Power Setting box;
- Click the MAN
button under Operation Mode;
- Click the red On
button under Operations Mode, "Heater On" should appear in red;
- Verify the desired power
appears in the Heater Readback LEDs;
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7.4 Putting the Heaters in PID mode
During normal operations, the heater powers are determined by the IOC
using a feedback (PID) loop to maintain a constant target temperature. The
temperature is measured by one of several thermometers in the target loop,
and the selection of which thermometer to use cannot be changed by the operator.
Each PID loop has several parameters which can be viewed/changed by pressing
the PID Parameters button on the Heater GUI. The
PID_settings window shown below ought to appear. The setting
have the following meaning and should not be changed without the authorization
of Target On-Call or another target expert.
- Set Pt - the temperature
set point that the feedback loop attempts to maintain (usually 19.00 for
H2, and 22.00 for D2);
- Cur. Temp - the
actual temperature of the target;
- PID Output - the power
setting that the PID loop is sending to the HPH. The power deposited
by the beam may or may not be subtracted from this value (see
Compensating for the Beam Current below).
- Prop - proportional
gain of feedback loop (usually 600);
- Integ - integral
gain of the feedback loop(usually 40) ;
- Deriv - derivative
gain of the feedback loop (usually 0);
- Scan -
scan time (in sec) of feedback (i.e. how often the heater adjusts itself)
(usually 1);
- MIN - minimum
PID power setting (usually 0);
- MAX - maximum
PID power setting (usually 500);
- dMIN - the minimum
change in heater power that the PID loop will allow in one Scan period (usually
0);
- dMAX - the maximum
change that the PID loop will allow in one Scan period (usually 50);
Assuming that the heater is
Off, follow the steps below to place a heater in PID mode:
- Verify that the desired
Set Pt. is loaded into the PID loop. If not, click the
PID_Settings button and change the Set Pt. there.
- Verify that Maximum
Heater Setting is correct
- Press the PID
button under Operation Mode, "PID Mode" should appear in red
- Press the On button
under Operation Mode, "Heater On" should appear in red
- If the heater does not
regulate the temperature properly, click the PID_Settings button
and verify that the PID settings are correct
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7.5 Compensating
for the Beam Current
Sizeable fluctuations
have been observed in the target temperature whenever the electron beam
is unstable. The beam can deposit several hundred watts on a target, and
the PID simply can't respond quickly enough if the beam current changes
suddenly. To combat this problem, we have implemented a new term in
the HPH control algorithm called "Beam Compensation".
When ENABLED, the target computer (IOC) measures the beam current on
the target loop using IBCxxxxCRCUR2 - this is Accelerator's "official
Hall B beam current monitor". The IOC converts this current to a power
(in Watts) deposited on the target via
Pbeam = I*Length*Density*dE/dX
Values for Length, Density, and energy loss (dE/dx) are
specific to each of the six target cells and can be adjusted by clicking
on the Cell Properties button on the
Heater GUI.
This value is automatically subtracted from the power that the PID loop
calculates. The result is then sent to the HPH. For example,
imagine that the electron beam current is zero, and that the PID loop has
empirically determined that 500 W is necessary to maintain a target temperature
of 19.00 K. The heater output will of course be 500 W. If the
electron beam current suddenly increases and deposits 300 W on the target,
the heater output power will automatically drop to 200 W (500-300). The
total heat load on the loop will still be the necessary 500 W (300
from the beam, 200 from the HPH) so there should be little or no change
in the target temperature. Since there is no temperature change, the
PID will continue to calculate 500 W, and the heater will remain at 200
W (500-300). If the beam current again drops to zero, the heater output
will automatically jump back to 500 W (500-0) and again, there should be
little or no temperature fluctuation. Ideally, the PID loop should
only respond to changes in coolant flow, fan circulation speed, etc.
To enable this term to the heater controls, press the Enabled button
at the bottom left corner of the Heater GUI.
Click Off if you wish to disable this feature.
A separate value for
Pbeam is calculate for each of the 3 target loops.
The control computer monitors the position of the target and using
the settings loaded in Cell Properties can automatically determine
the proper values to use for Length, Density, and dE/dx. When
a loop is no longer in the beam path, its Length is automatically
set to zero. This forces the corresponding value of Pbeam
to zero so that this loop's heater is no longer affected by the beam
current.
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8. Fan Controls
Fans (or "pumps")
located inside the three heat exchangers are used to circulate the target
fluid (LH2, LD2 or Helium) from the target cells through the heat exchangers
where the fluid is cooled by cold, high pressure helium from the End Station
Refrigerator (ESR). The control settings for the fans can be adjusted
from the GUI below, which can be launched either from the
main control GUI or from one of the 3 LOOP GUIs. The
rotational speed of the fan blades are measured by tachometers attached directly
to the blades. The speed is set by specifying a "Percent Frequency"
to the Fan Controllers, with 25% corresponding to about 60 Hz.
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8.1 Turning the Fans On
or Off
To turn a Fan off:
- Press the Off
button under POWER. The "Fan Stopping" lamp should illuminate.
- Wait 5 seconds and then
press the Update button. The "Fan Stopped" lamp should illuminate.
To turn a Fan on:
- Verify that the desired
percent frequency is correct under
FAN SETTINGS
- Press the On button
under POWER.
- Wait 5 seconds and then
press the Update button. The "Fan Running" lamp should illuminate.
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8.2 Changing the Fan Speed
Assuming that the fan
is already running, change the fan speed using the following steps:
- enter the desired
percent frequency under FAN SETTINGS. The desired
setting should be displayed to the right of the input box.
- Verify that the tachometer
readback is closed to the desired value.
NOTE: I don't know why
the percent frequency readback is sometimes 2% low. The important
quantity is the tachometer reading listed in the READBACK
box. You should see it change as you adjust the fan frequency.
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8.2
Adjusting Other Fan Settings
Additional settings for the Fan Controller can be accessed by pressing
the INPUT WINDOW button. These settings should never be changed
without authorization from Target On-Call or another Target Expert.
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9. JT Valve Controls
Three Joule-Thompson (JT)
valves are used to control the flow of coolant from ESR through the three
cryotarget heat exchangers. There is a fourth JT valve, the "Precool
JT", that is only used during the initial cooling of the cryotarget and
remains closed thereafter. Likewise a relay-controlled ball valve
called the "Warm Return Valve" is only used during the initial cooldown
is should be closed otherwise. The controls for the JT valves can be launched
from several places:
- the main ATARG
GUI
- from a button at the
bottom of each LOOP GUI
- from the blue "JT" valve
icon near the top of each LOOP GUI
- from the CRYOSTAT
GUI
Regardless of where it is
launched from, the control GUI for a JT valve looks like
this . The readback is in units of percent open, with 100% meaning
fully open.
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9.1 Adjusting JT valve
positions
There are two way to set the position of a JT valve.
- Specify the amount that
you the want the valve to move (say 10%) in the STEP Size entry
box. Then press either the Step Open or Step Close.
- Specify the new position
that you wish for the valve using the entry box to the left of the GOTO
button, then press the GOTO button.
The calibrations are not perfect,
so you may need to hit the GOTO button a few times to get it exactly
right.
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10. Rebooting the IOC
Under normal conditions the Target IOC should not require rebooting.
Compared to the Tcl/Tk controls, the MEDM control screens present
a much smaller load to the IOC's CPU. The load on the IOC can be monitored
from the the main control menu. Under normal circumstances, the
IOC %CPU Free number should be 50-70%.
During an experiment it has been observed that intense radiation can
cause the IOC to reboot itself or "freeze" (require rebooting externally).
You can tell that the IOC is frozen when the MEDM screens go "white".
The reboot procedure requires about 5 minutes, so please be patient.
If the IOC never comes back to life, contact Target On-Call and follow
the procedures outlined in What to do whlle the IOC Reboots.
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10.1 How to Reboot
the Target IOC
If you need to reboot the Target IOC (from the counting house), follow
these steps:
- walk into the middle
room and press the green button labeled "Reset IOC". This button is
located under the auxilliary heaters.
- After about 5 minutes
the MEDM screens should return to life. If the MEDM screens remain
"white" after 5 minutes, try restarting the screens -- first find the primary
MEDM window and press the X button in it upper right corner. Then follow
the steps in Starting the GUI.
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10.2 What to do while the IOC Reboots
During the reboot procedure the operator's primary concern is the temperature
of the 3 Loops. While the IOC reboots, the High Power Heaters will
continue to provide exactly the same amount of power as just before the
reboot (e.g. if the PID was providing 310 W just before the reboot, the
heater will stay at exactly 310 W during most of the reboot). There
is a period of a few seconds when this power will drop to zero. During
this time the operator may need to use the Auxiliary heaters to maintain
the loop temperatures.
Following a reboot the High Power Heaters should return to exactly the
same state they were before the reboot (PID, MAN or OFF). Since it
is initialized with zero watts following a reboot, the PID loop will require
a few seconds before it can successfully regulate the temperature at the
set point.
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10.3 What To
Do If the IOC Does Not Reboot
This is an indication
of a serious problem. Contact Target-On Call immediately and use
the Auxiliary heaters
to maintain the loop temperatures.
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10.4 Use of the Auxiliary Heaters
The auxiliary power supplies for
the high power heaters are mounted in a rack in the middle room of the counting
house. During an "extended" IOC reboot, these supplies for (at least)
the deuterium loop should be turned on by pressing the on/off switch on the
left hand side of the box. The power output to the heater is then controlled
by individually setting the voltage and current outputs with two knobs located
on the front of the supply (voltage=left knob, current=right
knob).
When the auxiliary power set by the operator exceeds that of the primary
supply in the hall, the heater inside the loop will begin to draw current
from the auxlliary supply. This will be evident when the voltage and
current readbacks both begin to display non-zero numbers. If the auxiliary
supply isn't putting out enough power to maintain the desired temperature,
it may have reached either a voltage or current limit. These limits
are indicated by the illumination of two lights on the front of the power
supply, close to the knobs. Simply increase the voltage or current
output by turning the knobs until you have passed the limit.
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11. Troubleshooting (under construction)
11.1 When I launch the GUI with the
tgtgui command, the screens appear, but all the readback are white.
There are two possiblities.
Either the IOC is dead and needs rebooting (try pinging it from an
Xterminal -- ping iocha13
), Or there is a network problem - contact MCC?
11.2 I receive an error message when I type
tgtgui.
Make sure that your current working directory is
/home/atarg/gui/MEDM. If not, change to that directory.
Type
source setup. Then try
tgtgui again.
11.3 All the signals from ESR are white
Two possibilities: The GUI was not launched with the proper EPICS variables.
Try quiting MEDM. Type
source setup in the original
Xterminal. Try tgtgui again.
Or, there is a problem with the IOC that provides the ESR signals. Contact
MCC.
11.4 The charts/alarms won't start
Tcl/Tk *&#$*#@!! Contact either Kathy McCormick or Chris Keith.
- The Strip Charts are
launched by a script called
/home/atarg/gui/MEDM/start_charts . All the files for the
charts are in
/home/atarg/gui/MEDM/tclcharts/
-
The alarm handler is launched by a script called
/home/atarg/gui/MEDM/start_alarms. All the files for the
charts are in
/home/atarg/gui/MEDM/tclalh/
11.5 The percent frequency input box for the fans say "0",
but the tachometer indicates that the fan is turning.
The value in the input box automatically returns to zero after a new
setting is entered. The frequency readback is displayed to the right
of the input box.
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11.6 I don't see a Beam arrow on the Lifter GUI.
This indicates that the target stack is not at one of the
predetermined target positions. Click BDS positions button at
the top of the Lifter GUI and compare the current encoder value to
the values listed on the BDS positions Next contact Target On-Call
and ask for instructions. page.