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Monochromator blocked of miscalibrated

The monochromator blocks itself because of the collision of the internal mechanical arms if tuning to low photon energies, as described in Setting the photon energy. We remind you that photon energies below 40 eV must be set step-wisely. If you fail to do so, the collision switch activates and blocks further movement, in order to avoid the mechanical damage. You can see it in the Kleopatra software interface as the collision indicators. Users must contact the beamline scientist before proceeding!

As the movement is stopped very quickly, the reference points of the angular encoders might be lost. The references may be also gradually lost with time due to imperfect encoder reading, mechanical shocks and thermal effects, which results in incorrect photon energy scale. When the error is more than 0.5 % (i.e. 0.5 eV at 100 eV or few eV at >500 eV) we recommend to check the reference marks and then reset the encoders to 0.

Both procedures are done on the MSB-MONO computer in the Client software.

To unblock the monochromator

From the poinf of view of the software it behaves equally as if the Mirror (PM) Forward Limit Switch and the Grating (PG) Reverse Limit Switch were reached. The correct procedure is therefore to make one of the elements move towards the opposite limit switch, which increases the distance of the colliding parts, i.e.either
  • Mirror Axis - Find Index - Find Reverse Limit Switch - OK, or
  • Grating Axis - Find Index - Find Forward Limit Switch - OK.
Observe the movement of the chosen axis in the software and once the Collision indicator turns off interrupt the operation using the Stop button.

After this the reference marks must be checked.

To check the reference marks

  1. If the beam is available close the electropneumatical valve 9 in order to avoid saturating the mesh current amplifier by zero-order light intensities.
  2. Disconnect Kleopatra on the MSB-MASTER computer.
  3. In the Direct Axis Control window of the Client on the MSB-MONO computer Set the Mirror and Grating Axes to 100000 and  -100000 counts, respectively. Wait untils the positions are reached and the axes movement stopped.
  4. Set the Mirror and Grating axes to 25000 and  -25000 counts, respectively. Wait untils the positions are reached and the axes movement stopped.
  5. In the Mirror Axis-related part choose Find Index - Find Index - OK and wait. The Position, counts will move towards 0. When the reference mark is found the movement stops.
  6. The difference of the Position, counts from 0 indicates how much was the reference mark off. Write it down to the logbook. Differences below 10 counts are negligible.
  7. Reset the Position, counts to 0 by using Find Index - Reset - OK.
  8. (Optional: you can verify the reproducibility by repeating steps 3-7.)
  9. Repeat steps 5-8 for the Grating Axis.
  10. Connect Kleopatra on the MSB-MASTER computer, setEnergy to any value between 40 and 1000 eV and wait until reached. .
  11. Open the electropneumatical valve 9 if closed in step 1.
If the reference is off by more than 25000 counts or if there is a problem reading the reference marks the movement will take too long time (more than 1 minute) and fail to stop in step 5. In such case Stop the movement manually and consult the beamline scientist..


Last Updated on Wednesday, 20 May 2020 12:24