Tech Meet 11

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Tech Meet 11

Technical Meeting #11: Testing

09:30 Mon 25 Oct, Ryle.

This meeting is intended as an initial brainstorm on how we will perform the component and integrated tests in the PDR phase.


Some thoughts to kick off the discussion:

  • What mean T and delta-T values should we test at?
  • How to control test environment? Duration of test?
  • Test at Cavendish or COAST?
  • How to remove effects of instability in other components besides the one being measured (e.g. differential measurement) ?
  • How to measure movement of mount versus movement of optic in mount?
  • How to record and analyse test data?


  • The mean temperature at which testing is conducted is not important.
  • The Delta-T should be at least 5C but more if greater measurable response is required.
  • We think that we do not need to create a large test environment - it is too difficult to control optical bench performance.
  • Most tests should be differential where possible to remove effects of test apparatus and environment.
  • We are initially concerned about movement of the optical component compared to the mount, which we expect to be symmetric and not undergo any distortion due to temperature change. So differential tests could be made of tilt of optic with respect to mount. This may require a reflective surface to be attached to the mount somehow.
  • Measurement equipment should be remote from the test subject where possible to limit the effects of temperature differentials on the test apparatus.
  • Most tests should be conducted here in the lab but we could use COAST for some tests, particularly a system level test using a pin-hole at one end of the tables and the base-plate, optics and camera arrangement at the other end.
  • Plan to use as much DL software as feasible for logging test data - particularly if an interferometric test is used.

Test methods mentioned:

  • Capacitive sensing of displacement of dichroic with respect to stable reference
    • Stable reference has to be close to dichroic mount and probably cannot be kept sufficiently stable when heat applied to mount.
    • Very high resolution.
    • Expensive to purchase.
    • Might be OK if sensors are part of mount and measurement is differential.
  • Set up an interferometer to measure to measure displacement at either edge of dichroic.
    • We have the equipment (we can divert beam from HP laser without disturbing test track)
    • Gives high resolution
    • Measurement gear is at distance from subject
    • Is turbulence around warm subject likely to be a problem?
  • We have money for a dual measurement SpotON detector and so we could bounce laser beams off dichroic and mount and use a large lever arm.
    • Not too expensive to purchase
    • Might be able to use shear camera instead
    • Need to get good reflection from mount

New Tasks

  • EBS - investigate use of metrology system
  • DMAW - investigate interferometric arrangement
  • XS - investigate capacitive systems a bit further
  • MF - see DFB about cheap capacitive sensing (post meeting discussion)
  • CAH - check out holographic interferometry (post meeting discussion)
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