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VELO Vacuum Expert Operations


Operating the VELO Vacuum system under neon atmosphere

  • The VELO is a vulnerable system when it is under neon atmosphere because the RF-boxes are fragile objects and temperature variations induce pressure variations that perhaps cannot be compensated for due to possible misconfigurations. The latter can be caused by power dips that bring the vacuum system in an undesired state. Therefore a number of precaustions have to be taken into account, like control scripts that continuously check the state of the vacuum system and send text messages if something is not as it should. Also the UPS-es have a mailing list of people that should be warned, however this often fails due to the fact that the router is then most of the time also down.
  • In the following DP or DP411 refers to the differential pressure between beam and detector volume, as measured with a baratron: DP = p_beam - p_det.
  • When cooling down one half from room temperature to +8 deg. C with the baseplate heating "ON", DP will increase with approximately 3 mbar. So for two halves the increase will amount to something like 6 mbar !! Evidently these values change when you want to cool to lower temperatures.
  • In the following the neon Gas Injection System is supposed to be non-active, although it might be on also, making operation of the VELO much more secure.
  • In the following a correct reading of the baratron DP is assumed. If not, consult an expert because it then has to be calibrated by means of a special procedure.
  • Continuous displaying of DP as a function of time can be achieved by starting from preferentially "vedcs02" under your own login the following shortcut: /group/online/ecs/Shortcuts315/VELO/VEDCSVMC/VEDCSVMC_UI_lbTrending. Then open "VEDCSVMC", open "Various", select "AP411andDP411", right-click, select "view" and left-click. If this doesn't work, then execute the actions decribed in the following point.
  • Make sure the WinCC-project "VEDCSVMC" is running under "velo_user" on "vedcs02". If not, start it via "XXXXXXXXXXXXX".
  • If "gedi" is not running, start it via logon to "vedcs02" and the command "WCCOAui -proj VEDCSVMC -m gedi" )
  • Start "Vision".
  • Select "Panels (*.pnl)" as "File type" at the bottom.
  • Select "/group/velo/pvss/fwComponents_VEDCSVMC/panels/" as "Project-directory" at the bottom.
  • Select "VeloVacuum_UI_Main.pnl" and click the "Open"-button.
  • Click on "Show Details/Hide Details" (left top) to get information of more/fewer vacuum meters.
  • Click on "Show Details" (left top) to get the actual reading of DP411 displayed.
Before starting the cooling you have to create good starting conditions
  • If -4.3 < DP < -3.5 mbar, you are lucky and can continue with "Cooling operating under neon". If not, you first have to create a good starting condition, i.e. a good differential pressure. This can be done in two completely different ways: by means of manual control of PV301, PV303, PV304 and PV305 on the screen of the vacuum PLC on platform C3 (never do this remotely, because if the Internet connection disappears when you just opened a valve you are in very deep trouble) or by moving the detector halves. To do the latter you have to perform the following actions on platform C3. Write down the positions of the detector halves, AP (the absolute pressure in the beam volume as measured with a baratron) and DP. Also when you are finished and please make an entry in the ELOG in which you document your actions together with the timestamps.
  • The actual value of DP can also be read off the Vacuum main page on the PLC-screen in rack C3B05.


  • bypass the vacuum interlock that prevents moving the detectors. So push the following marked buttons on the PLC screen. If you happen to be on a different page first press the "Home"-button (bottom-left) or "Vacuum scheme"-button to get there.


  • When pushing the "motion interlock" button, login as expert. Type loginname "vacuum". Password you evidently have to know yourself. Push the button again.



  • Push the "Go home" button
  • go to the "motion control" screen as shown on the second figure of this documentation. Login as motionoper, with the usual password and push the button again.
  • go to "MotionControl-2"
  • go to "MotionControl-3". Check that the PLC is not "hanging in a procedure". If so, one or more rectangular small blocks on the left of this page will be green and you have to push the button "Reset Procedures". Once all blocks are grey you can continue with the next step.
  • Go back to "MotionControl-2"
  • Pull out the red mushroom button on the motion system in motion rack C3B03 at 1m20 from the floor. Make sure the system doesn't start moving while doing so.
  • Now 2 of the 4 lights ("Vacuum" and "Stepper drive power relay") that are encircled in the following figure should be green, (the middle two being grey) indicating that you can move the VELO-detectors. Sorry no completely up2date screenshot available yet. Text is correct !!
  • Push the button "Reset Error Flags".


  • go to the main Motion Control screen. (see following figure). Beware of the fact that a higher value for X-LEFT or X-RIGHT corresponds to the left or right detector half being more to the outside !! Move alternatingly the VELO-halves outwards in steps of 0.5 or 1.0 mm. Always keep a spacing of at least 1.0 mm between the boxes, i.e., |XL + XR| >= 1.0 mm. (At AP=850 mbar moving one detector half 1 mm outwards corresponds to an decrease of DP of 0.6 mbar.) Wait after every step until the pressures, as represented by AP411 and DP411, are stabilized. To move a detector half, touch the corresponding setpoint, type a new value, type return, make sure you did the right thing, press the "MOVE HORIZONTALLY (X)" button and watch carefully what happens with: position, potmeter readings, DP411, PV301 ... 306 (which should stay closed, which means red).


  • When DP has reached a value between -4.3 and -3.5 mbar this part of your mission has been completed successfully. Now do the following:
  • Press the red mushroom button of the motion system in motion rack C3B03 (to inhibit movement of the detectors),
  • Remove the bypass of (in other words reactivate) "inhibit to motion".
  • Press the "logoff" button on the main panel.
  • From the neon point of view you can now start the warm cooling of the VELO with a setpoint of +8 deg. C.
  • Evidently all afore mentioned values change when you want to cool to lower temperatures.
-- EddyJans - 2015-04-17
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Topic revision: r5 - 2017-12-10 - KarolHENNESSY

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