Author: Nick Beser Date: 970215 Revision: #0 970215 Key Words: instrumentation, operations
Herbert Johnson suggested that we summarize some of the hardware problems that we have run into with TASS #5. The following is not a complete list (that means I drew it from my memory):
Our mount is about 14 feet above the observing room on the roof of Building 40 (JHU/APL Complex in Laurel, MD). The facilities engineers specified 1/2 inch tubing to go from the water tank to the roof, hook into the camera and then 1/2 inch pipe coming down from the roof. We noticed that the water flow was not very large due to the decrease in diameter at the camera. This was fixed by threading a 1/4 inch tube through the 1/2 tube up to the camera.
Water pump (submersible sump pump) was heating the water to about 95 degrees F, and needed to be primed before it would work. Solution: A motorized external pump (rotory design) was substituted). The water flow is about 1 Gal per minute. Water temperature is slightly below room temperature. A mix of environmentally safe antifreeze was added to the water to keep the water from freezing in the event of a power failure.
The housing was initially pointed to -10 degrees declination. This was later adjusted to 0 degrees.
The camera was mounted too far forward in the box, so that the focus adjustment had no room for the telephoto lens to come out farther. The camera was slid back slightly. Note that we have optical windows in our system that keeps the lens from moving too far out.
Remote control of the doors seemed to effect the control hardware of the camera (ie The data collection could not happen when the doors were being opened). Solution was to take dark current files, and then shut software off, and open the doors. There seems to be some electrical noise in the system (we have solved that by procedure rather than design). The door control is also being modified so that the html home page control of the telescope will control the powering on of the TEC and opening/closing the doors.
This last one was wierd. We share the roof with some radar dishes. The people doing some installation up there tied a crane to the railing (same one where the telescope was mounted on). The wind (blowing the crain) was causing visible motion effects on the data. Solution (the crane tie down has been moved)
Twice our data collection has gone over to pre-dawn hours (about 5-6am.) The data files indicate that the ambient light levels are too high to continue recording stars. At the end of the run, the sensors completely saturate including the dark current pixels on each line, and the temperature gauges indicated a sudden shift in temperature. The program eventually shuts down when it indicates a temperature of 135 C. The temperature does not really happen, it seems to be a controller failure brought on by the saturated system. (NOTE: At no time has our camer viewed the sun).
Alignment and Focus of the camera reminds me of the problems I had converging a color monitor (ie. I can never get a color monitor converged). We have seen the following problems:
Alignment setting is not smooth, ie. it sticks and then overshoots the setting. (Need coarse and fine adjustment) I know it has silicon greese. I know it also sticks and then shoots past the setting.
VCO setting seems unstable. A camera that seems to be completely aligned, in focus suddenly exhibits the symptoms of VCO setting errors. We currently have CCD2 higher by 1 degree than CCD1 and CCD0. CCD2 and CCD0 both need alignment adjustment. It is also possible that the VCO may not be correct for these two camera, however, it seems correct for camera CCD1. We are still investigating this problem.
We are still slightly out of focus. (Focus is very close on CCD1, and can be improved on CCD0 and CCD2)
Saturated pixels on one camera become visible on the other cameras. We have seen examples (Mars images) that have the specular pattern repeated on the other cameras. This is a design issue, and there is nothing we can do about it.
Our primary problem right now is that the weather in Baltimore has been very cloudy since Feb 9 (the last observation session). We have worked up a way of turning on the TEC power remotely (so that we can have it on 1 hour before we start observing). We also can open the doors remotely (we need to wire that in). This is being done by X-10 remote control devices under control of a unix workstation. I also have a RPC program that may run under windows 95, and can be used to cause the TASS data collection machine to start collecting data remotely by rebooting itself in MSDOS mode, running tm3get11 and then when it ends, come up in Windows mode with a FTP server operating. We really would like to get our hands on a linux version of TM3GET11. We also are investigating workarounds (There is a patch just announce for the linux kernal that will enable real time control interrupts.)
More after Marty and Bernie have a chance to look at this.