Operating the VELO Motion System while being under vacuum

Make sure the PVSS-project "VEDCS_VacMot" is running under "velo_user" on "vedcs02w". If not, start it. If "gedi" is not running yet, start it. Then start via "Vision" the panel G:\velo\pvss\VELO_VacuumMotion\panels\VeloMotionUI_Main.pnl

You should see the following panel:


A number of conditions has to be satisfied before one is able and allowed to move the VELO-detectors.

  • the red emergency mushroom button of the stepping motors in rack C3B03 on platform C3 has to be pulled to the out-position,
  • all 3 coordinates of the system have to be in the mode "Referenced", as depicted in the panel above by the green status field with the text "Referenced" in the left bottom. If not the system first has to be referenced, but since this is a non-standard procedure an expert should be contacted first,
  • the motion-PLC has to be in mode "remote" (whether this is the case or not can be seen in the expert panel, see below),
  • there should be no interlock from the vacuum system (whether this is the case or not can be seen in the expert panel, see below),
  • LHC should be in the state "Movable devices Allowed", otherwise the beam will get dumped when moving away from the "out"-position.

The detectors should be in the out-position, i.e. XA > 28.0 & XC < -28.0 mm, to permit injection of beams into LHC. This is repesented by the status field "Injection" on the right.

The "Emergency STOP" button on the right, really does what its label suggests: when clicked the power to the stepping motors gets cut abruptly, which is not advantageous for the mechanics of the system. Therefore the use of this button should be limited to real emergency cases.

Moving XA and XC can be done simultaneously. Changing the Y-coordinate is a single action. The allowed regions are indicated in the figure above, but can be summarized as follows:

  • 29.0 > XA > -5.0 mm and -5.0 > XC > -29.0 mm, evidently without mutual overlap.
  • 4.8 > Y > -4.8 mm for (|XA| & |XC|) < 15.0 mm. For (|XA| & |XC|) > 15.0 mm holds: 1.0 > Y > -1.0 mm.

To change the X-position(s) do the following:

  • type the wanted XA and/or XC position in the corresponding field
  • click on "GoTo X"
  • XA and/or XC will start moving if the specified values are within the allowed range
To change the Y-position do the following:
  • type the wanted Y-position in the corresponding field
  • click on "GoTo Y"
  • Y will start moving if the specified value is within the allowed range

However, the VELO closing procedure, which requires a password at each step, has to be followed till further notice.

Detailed information about the state of the motion system can be obtained by clicking the button "Expert Panel" on the bottom left. A panel like the one shown below will pop up.


Below a short explanation of the most important parameters and status bits is given:

  • "Resolver": the readings of the 3 resolvers (XA, XC and Y)
  • "Stepper": the readings of the 3 stepper motors (XA, XC and Y)
  • "Potmeter": the readings of the 3, 3 and 4 potmeters of XA, XC and Y
  • "start Ref.Proc": a button to initiate the referencing procedure. Take care: this should only (!!) be done if the system has come into an unreferenced state. First find out why this happened and only press this button after consulting an expert, because the detectors will move to the outside until they hit their reference switch. For XA (XC) this is located at 29.8 (-29.8) mm . The one for Y is at +4.9 mm. But in order to be able to reference Y, first XA (XC) is moved to the position 15 (-15) mm.
  • "General RESET": a button to send a reset command to the motion PLC and accompanying equipment like Atmel processors
  • "WantedPos": the by the user given next destination for XA, XC and Y
  • "ResolPos": the present value of the resolver of XA, XC and Y
  • "SteppPos": the present value of the stepper motor of XA, XC and Y
  • All the bits with the word "Error" identify a specific error condition
  • "Potm.Av_Resol_Diff": if a bit is set it means that for that axis there is a too large difference between the reading of the resolver and the average value of the potmeters.
  • "Referencing": if a bit is set it means this axis is presently being referenced
  • "IsReferenced": if a bit is set it means this axis has been referenced
  • "Moving": if a bit is set it means this axis is presently moving
  • "CtrlMode or Local/PVSS": if this bit is set it means the PLC is in Local/PVSS mode. This mode can only be changed on the PLC-screen on platform C3, an action that is password protected.
  • "ExpertMode_On": if this bit is set someone is working in expert mode at the PLC-screen on platform C3
  • "VacOK_MoveAllowed": if this bit is set it means the vacuum conditions are such that moving the detectors is allowed
  • "Vent_Allowed": if this bit is set it means the detectors are in a position, i.e. XA=2, XC=-2 and Y=0, which allows the LHCb beam pipe and VELO to be vented or evacuated.
  • "InjectionAllowed": if this bit is set it means the detectors are in a position that permits injection of beam in LHC, i.e. XA>28 and XC<-28 mm.
  • "AllReferenced": if this bit is set it means all three axis are referenced. This is a minimal condition to change either of the 3 coordinates.
  • "UPS_Active: if this bit is set it means the UPS of the motion system is active. If the power gets cut by whatever reason, both halves will be moved to the out-position, thus again permitting the injection of beam into LHC.
  • "OverallERROR": this is the OR of all the error conditions and as such prevents the change of the position of the detectors.

In all cases, a green background means that the current state is correct for giving motion commands. Light green and red fields correspond to datapoint elements which have to be false to be 'OK', dark green and orange correspond to datapoints which have to be true to be 'OK'.

The actual readings and a lot more can be seen at the various Motion pages on the PLC-screen in rack C3B05 on platform C3. However, access to these pages is password protected.

-- EddyJans - 31 Jul 2008

Topic attachments
I AttachmentSorted ascending History Action Size Date Who Comment
JPEGjpg ExpertPanel.jpg r1 manage 126.8 K 2008-08-05 - 15:21 EddyJans  
Bitmapbmp MonitorStatusPVSS2.bmp r1 manage 2303.1 K 2008-08-05 - 15:20 EddyJans  
JPEGjpg MonitorStatusPVSS2.jpg r1 manage 94.7 K 2008-08-05 - 15:22 EddyJans  
JPEGjpg pvss.motionscreen.jpg r1 manage 102.6 K 2008-07-31 - 15:23 EddyJans  

This topic: LHCb > WebHome > LHCbVELO > VELOOperatingManuals > Motion
Topic revision: r5 - 2008-08-22 - IvanMous
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