PROCEDURE FOR MEASURING THE POSITIONS OF THE BUILDING-ANTENNA LIMIT SWITCHES 4 Oct 01 Version In order to check the positions where the building-antenna limit switches trip, the switches must be defeated. Therefore, locate the sign that indicates that the switches are defeated so that no one forgets to re-enable the switches. (It is usually kept in the pocket of the left hand Krupp rack door.) There are six limit switches, 3 for each direction of travel. They should trip within a quarter of a degree of their nominal positions 1.0, 1.5, and 2 degrees. The last switch should be no closer than 0.1 degree from the second one, and must trip last. If the limit switches trip at the wrong angle, they should be adjusted. The first two limits are proximity switches attached to the bottom left of the antenna fork and tripped by sheet metal attached to the building wall. There are four of these switches, two for each direction. The final limit is implemented by two yellow proximity switches, one for each direction, located above the false ceiling at the wall behind the Krupp rack. They are mounted on either side of the hole in the wall that provides access to the telescope fork. The angle where the switches trip is influenced by how much the building has drifted off-center. The building "walks" off center depending upon the azimuth. So we first measure the trip points of the first limit switchs in each direction at 5 different azimuths 90 degrees apart to find the worst azimuth. In the past, the worst case has been 320 degrees, so we choose 50, 140, 230, 320, and 410 degrees. 1) Move the antenna & building to one of the above azimuths. 2) Turn off the building drive by pressing "Azimuth System Shutdown". (Or if the system is powered off, power up the "grey box", press "Reset", but don't push "Start".) 3) Set the Krupp azimuth rate to 5% (0,50 on the potentiometer). 4) Select CW with the toggle switch and move the antenna CW (by holding down the Rate button) until the difference angle light comes on. Locate the BLDG-ANT value on the lower left of the color monitor and record the building azimuth and the average BLDG-ANT value. 5) Select the CCW direction and hold down both the Rate button and the lighted Bypass CCW button. When the Bypass light goes off, it can be released, but hold the Rate button down until the Difference Angle light is lit again. Record the azimuth and the average BLDG-ANT value. 6) Select the CW direction and center the antenna with the Rate and Bypass buttons. Press Start on the building drive and repeat the above for the other four azimuths. Pick the azimuth where the switches tripped farthest from the nominal positions and move the antenna to that azimuth. Press Stop on the building drive and find the trip points of the other switches: 7) Move CW until the difference angle light is lit again. Record the average BLDG-ANT value. This limit switch must now be defeated. The first two limits in each direction are defeated by jumpering the top left terminal to the bottom left terminal of the corresponding switch block inside the right hand side of the Krupp rack at about knee level. The switch blocks are labeled -K102, -K104, -K106, and -K108. The jumpering is usually done with a 3-inch wire. You can press the wire braid into a hole so as to contact the recessed screw of the terminal in it. There should be enough friction to hold the jumper in place. There are usually a couple of jumper wires kept in a pocket on the inside of the left Krupp rack door. When the limit(s) are defeated, the difference angle light on the front panel will go out, and so will the "Delta Angle" LED inside the Krupp rack. (It is the 11th from the bottom in the column labeled A16.) 8) Post the "limit-switch-defeated" sign on the Krupp rack, and jumper the switch block -K102. The "Bypass CCW Ang" light will remain on. 9) Continue to move the antenna CW until the difference angle light comes on again. Record the average BLDG-ANT value. 10) Jumper the switch block -K106. The difference angle light will go off. 11) Continue to move the antenna CW until last switch is encountered. This will turn off the building control panel ("grey box"). You will see "Master Control Relay" lighted on the Krupp rack when this happens. Record the average BLDG-ANT value. 12) Open the building control panel door and hold down the button that defeats the interlock. It is the orange button pointing up, on a relay box with orange tape on it, attached to the rear wall of the building control panel. 13) While still holding the button, re-enable the building drive by pressing "Azimuth System Reset", but DO NOT press "Start". 14) While still holding the button, at the Krupp rack, drive the antenna CCW until the "Bypass CCW angle" light goes out. (This obviously requires two people!) 15) Release the override button. (You may need to press "Azimuth System Reset" again if the override relay "bounces", but DO NOT press "Start".) Remove the two jumpers from the Krupp rack that were installed in steps 7) and 10). 16) Move the antenna CCW until the difference angle light comes on and record the average BLDG-ANT value. 17) Jumper the Krupp switch block -K104. The "Bypass CW Ang" light will remain on. 18) Continue to move the antenna CCW until the difference angle light comes on again. Record the average BLDG-ANT value. 19) Jumper the switch block -K108. The difference angle light will go off. 20) Continue to move the antenna CCW until last switch is encountered, the drives shut off and "Master Control Relay" lights. Note the antenna azimuth on the color monitor. 21) Again hold down the orange button inside the building control panel that defeats the last interlock. 22) While holding the button, re-enable the building drive by pressing "Azimuth System Reset", but DO NOT press "Start". 23) While still holding the button, at the Krupp rack, drive the antenna CW until the "Bypass CW angle" light goes out. 24) Release the override button. Remove the two jumpers from the Krupp rack that were installed in steps 17) and 19). If any switch positions need adjustment, make the adjustments and record the new trip points. 25) Remove the "limit-switch-defeated" sign. Enable the VAX azimuth control so that the antenna drives back to the original azimuth. Press "Start" on the building control panel. 26) Record the BLDG-ANT positions and corresponding switch numbers as well as the building azimuths in the Site Supervisor or FoT report. Note the difference between 50 and 410 azimuth. If they disagree by more than 0.3 degree, the buliding has "walked" more than about a half an inch and a new wheel alignment may be required.