Centering Methods

Overview

Sample centring is now managed per sample, and can be edited in the Data collection table. 

Video guide to centring methods

Alignment perspective

The Sample Alignment perspective has been removed as part of these changes and the centring options moved to the OAV tab in all perspectives where appropriate. 

Data Collection OAV tab with centring options highlighted

 

Sample perspective

When manually loading a sample from the sample perspective, the sample will be loaded then loop centred. No further action will be performed unless requested. 

 

Data collection/Screening

When loading samples from the data collection perspective, whether from the data collection form/table or the screening tab, you now have a dropdown box that lists the type of centring to be used prior to data collection.

 

Data collection table

 

Data collection form

 

This dropdown gives the choice of several centring options:

  • Manual Loop will perform loop centring and then wait for any manual adjustments to be made before starting the data collection when you press Centring Complete.
     
  • Auto Loop will perform loop centring and then immediately start the data collection without pausing for manual adjustments.
     
  • Auto X-ray will perform loop centring followed by X-ray centring and then data collection.
     
  • None will do no centring and proceed with the data collection.
     

If you have already centred your sample then choose None to simply proceed with a single data collection/screening.

For queue mode you must select one of the Auto options, we recommend Auto X-ray which will take approximately [2 minutes + total exposure time] per sample. E.g. a queue with a 7s exposure time would take around 2min 7s in total for each sample (as measured from one robot load to next robot load).

Auto loop is only suitable for cases where the crystal size and shape match the loop.

 

Important:

 

You must make sure the appropriate sample centring mode is selected as part of your data collection form. The choice is literal and GDA will do exactly what you ask for.

If you have spent a lot of time and effort manually centring your sample then please double check that None is selected prior to collecting data. Otherwise your crystal will move.

Be careful when switching between screening and data collection tabs as the settings on the form are independent on each page.

 

 

Multisweep behaviour, including chi/phi changes

The move of centring mode from a global to a per sample basis has implications for data collections that involve multiple sweeps on the same sample, especially for collections involving chi/phi changes.

For multiple collections on the same sample that do not involve a chi/phi change, you should set the first sweep to include an automatic/manual centring step (if already centred choose None) and then use None for subsequent steps.

On I03 and I04, the Smargon goniometer is configured to allow changes of chi/phi without the need for recentring (see note regarding small crystals at bottom of page).

To take advantage of this, when setting up multiple chi/phi sweeps you only need to have a centring step for the first sweep (this can be manual or automatic). For every subsequent sweep, choose None and the Smargon will take care of the rest. An example is shown below:

Data Collection table

For small crystals (< 20µm), you may wish to retain diffraction based centring following each chi/phi change. To do this, simply make sure that Auto X-ray is the centring option for each sweep. X-ray centring works reliably for crystals down to 10 µm in size.

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