POINTING LIMITS

The new TCSGalil software protects against slewing too far over. The ntcs program on flwo60 adds another protection to prevent slewing to the hardware limits.

As a first line of defense, the telescope will not move if you have requested a move beyond the limits. On the TCSGalil monitor, under Operating Mode, "OUT OF RANGE" will appear in red.

• Broadly, the software limits are: |HA| <= 4.8 hours, DEC >= -39 degrees. There are additional restrictions from interlock (see below) and HA limits and from a trip wire, depending on which direction the telescope is pointing.
  

• The new encoders (DEC, HA) impose limits of ZD 71, 50 at AZ 180, 10, and ZD 60 (HA=4), 71 (HA=5) at AZ 90, 270, respectively, and ZD 74 (HA=5) at AZ 278. If the telescope attempts a move (slew or track) past these limits, the motors stop. If you slew to or beyond one of these limits, you will usually be able to use the handpaddle to move in the opposite direction of the slew. If you are too far beyond the limits, you need to use the jumper labeled DIR to move away from the limit (see below for the jumper procedure). On the TCSGalil monitor, under Operating Mode, "BEYOND LIMIT" will appear in red.
  
• The trip wire is mounted on the E side of the pier. If the telescope touches the wire, the motors stop. Then, you need to switch the jumper labeled C2 with the MDC connector labeled C2 to move away from the limit (see below for the jumper procedure). On the TCSGalil monitor, under Operating Mode, "TRIP WIRE" will appear in red.


• An interlock device mounted on the NW corner of the OSS establishes a horizon limit at all azimuths of ZD 72 deg. The limits are tighter in the direction of the ladder to the mezzanine, to avoid a collision with it. When you slew or track past interlock limits, the motors will stop. Then, you must use the jumper labeled INTERLOCK (see below for the jumper procedure). On the TCSGalil monitor, under Operating Mode, "INTERLOCK" will appear in red.
  
• If you have reached a limit, perhaps by moving there with the handpaddle, or perhaps because the telescope simply tracked into the W limit, the motors shut off. To restart, first and most important, find out what you did wrong and correct that. It could be that you have reset the coordinates incorrectly, and then tried to slew to what would have been a reasonable place, but which was rendered impossible to achieve by the zero-point mistake. Once you know what you did wrong, go out to the telescope and determine whether a move in RA or in DEC is needed. You will also need to use the jumpers ONE AT A TIME according to which limit was violated (see below for the jumper procedure).
  

• The plot here shows the old limits in a visually effective way (thanks to Warren Brown). A hardcopy is posted in the 1.5m control room. The new limits are fairly close to the old ones, and they are still being adjusted.
  

• When pointing to the far North-East with FAST, the back end of FAST is very near the storage location of the TRES front end. The TRES front end must always be placed as far into the SE corner of the dome as possible. When pointing to the East, the telescope becomes partially vignetted by the dome at ZD > 46 deg. The current HA limit actually allows the telescope to slew below 46 deg. We will have a better HA limit as soon as DFM provides a part for the HA encoder.
  

• The procedure to move off a limit is to be used only if you have been trained, or by requesting guidance from staff before attempting it.

• There are 3 jumpers as described above, in a plastic bag on top of the MDC rack. To swap in any jumper, you must first exit TCSGalil, power off the MDC, and switch the cable in back of the MDC with the jumper. Then, power on the MDC, restart TCSGalil, and use a handpaddle to move away from the limit. Once the display no longer shows "OVER LIMIT" you must exit TCSGalil, power off the MDC, switch the cable and the jumper, power on the MDC, and restart TCSGalil. Make sure to return the jumper to the bag.