Meeting with POMO

Date: Sep 22, 2014 (Mon)
Time: 10 am (7:00am PDT departure from Cahill)
Location: Palomar conference room and P48 ... TBC


Attending at from POMO: Dan McKenna, John Henning, Bruce Baker, Kevin Rykoski, Drew Roderick, Carl Dunscombe
Attending from Campus: Richard Dekany, Roger Smith, Paul Gardner, Justin Belicki


  • Intro to ZTF - Rich Dekany (45 minutes)
  • Telescope Requirements - Roger Smith (30 minutes)
  • Open Discussion on how requirements translate to the physical work on the telescope (1-2 hours)
  • Lunch (continued discussion during lunch)
  • Resources/Scheduling/Management Structure (1 hr)


  • We hope to be ready to take advantage rainy winter period, especially for tasks which require interruption to observing.
  • Many tasks can proceed with daytime work which we would like to start well before commissioning.
  • There is much to do so it is important to start soon, in order to complete the telescope and down upgrades well before the commissioning period for the many tasks where this is possible.

Measurements to be made -- first priority


  • Roger+Justin+Richard Walters will measure the image motion in response to forces that simulate shutter motion profile(s), with differing amplitudes, to validate shutter requirements as well as measure telescope resonance frequencies.
  • Linear Motor delivery has been promised for Monday Sep 29. Paul is racing to get adapter bracket made by about then. Justin has written the control program fore the motor profile but has yet to test it (Wed Sep 24). David Hale has developed the special CCD exposure scheme wherein charge is shifted vertically during exposure. Richard Walters plans to test it tonight (Sep 24) then practice analyzing the data.
  • Will need to remove top end counterweights to compensate for mass of the direct drive linear motor and support frame to be used in this test. Approximately 25 kg .


  • Display telemetry on web page (in manner similar to detector temperature and heater power). A button to download the current log file would be useful.
  • Link from ZTF Twiki.
  • Description of sensor types and locations on Twiki.

HUMIDITY IN TUBE -- Log humidity and/or dew point inside tube vs dry air flow rate.

  • Record humidity and temperatures inside and outside tube. This is currently recorded but only displayed at the observers console in the 200".
  • Examine logs to see how quickly humidity and temperature inside the tube responds to outside of tube (correcting for temperature change).
  • Reinstate flow form original dry air system in place of the LN2 boil-off flow currently used. Report how much the flow rate can be increased.
  • Monitor change in humidity when a) hatch is opened for 2 minutes with no-one entering tube; b) humans enter tube for a period 2 minutes, this being an allowance for installing a cover over the ZTF window; c) repeat with humans wearing suitable Tyvek overalls with hood. (Clean room garb).


  • Dan will select a differential pressure sensor for wind and install. Roger will send wind speed calculation to Dan.
  • Will direct shaft encoders in future TCS allow some compensation for wind buffeting? This would need some analysis. Note we have this on Dec axis.
  • Let's look at image quality as a function of wind speed when new sensors are in place and when we understand resent frequencies of telescope.
  • Note that new imaging mode for looking at image motion may tell us about wind buffeting using existing wind speed data ... Can we record it in headers?


  • Roger (and Richard Walters) test whether dust on corrector can be measured by direct illumination of corrector when looking at sky (e.g. with flat field LEDs).


  • Once tests of Archon CCD Controller reliability have been completed in the lab, let's run in dome to determine if there is noise pickup in our passband when telescope or dome move since reading out during these moves is a requirement.


  • Place accelerometers on dome to monitor acceleration and vibration as diagnostic of dome bogey and friction roller conduction. (Wireless communication).
  • Monitor motor torque (when new drive system installed).
  • Conduct thermal imaging of dome bogies as part of periodic (annual?) maintenance.

Other near term actions

  • Rich will update MTBF budget to include allowances based on projected downtime for each cause.
  • Pointing requirements are very loose for ZTF: Roger will add these to IRD.
  • Roger to add field rotation to IRD: control with polar axis (mis)alignment or hexapod.

Upgrades required to meet ZTF performance requirements

  • Paul to calculate mass distribution and start on new counterweights.
  • Install dry air system with higher flow rate (?)
  • Dome drive upgrade (speed controlled motor; new software; present encoder). Possibly dual drive rollers and motors. [Start this upgrade soon after P200 Aluminizing]
  • Dec axis gear box change to provide higher torque (at cost of top speed)
  • Add trim plate, new shutter, new forward baffle.

Thermal Concerns

  • Cool air falling from the window may degrade image quality significantly. How to predict? How to mitigate?
  • Radiative cooling of corrector to sky will create a similar downward convection problem inside the top of the tube. What does temperature sensor on present corrector tell us. Fortunately this problem is less severe since the trim plate will act as a radiation shield.

Deferred maintenance

  • Windscreen: may order new blinds and possibly better encoders. POMO will test to decide what is needed. Currently bang-bang may needs speed controlled motor and better encoder. Rich, proposes delaying work on this until tests indicate that its needed: motor torque, differential wind pressure, telescope shake tests.
  • PTF cold head replacement.
  • Paul to select suitable low outgassing black paint for tube interior.
  • Re-Aluminize after work in tube is completed and before main survey.
  • Pre-emptive Dec bearing replacement ? How can we assess state of present bearing? How hard to change?

Upgrades to minimize future downtime and/or improve reliability

  • TCS upgrade to Henning's universal TCS after 60" retrofit. Can use existing motor and encoders. CPU and software to be replaced. Maybe some amplifiers too. New system may offer some performance improvement such as soft-start acceleration profiles, and software will be easier to modify.
  • UPS: Dan argues for coolers to be on UPS.
  • Dan to investigate power requirements: does AC power to dome need to be increased. With the possible exception of air dryer power needs should be similar to PTF.
  • Lightning protection: move weather station out of TCS and connect wirelessly. Check grounding of dome rail since a strike to the dome will come through dome wheels.
  • Slip rings: what to do here? Adopt wireless communications to systems on dome (which will need control upgrades as a result). This will reduce the number of slip rings to 3 or 4 (power only). The 9(?) on the interior can be ganged while the hidden rings on the back side can be abandoned.

Possible Additional Spares ?

  • Dome truck
  • TCS computer
  • TCS motor drivers (amplifiers)
  • ZTF server

-- RogerSmith - 25 Sep 2014

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