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Loading etalons

Etalons can be loaded into positions 1, 2, 4 or 5 of the etalon wheel. Positions 3 and 6 are intended as clear positions, and have no cabling for etalons. Note that each position in the etalon wheel which has cabling for an etalon must always contain either a real or dummy etalon, properly cabled up. Otherwise loose cables can be snagged when the wheel is moved.

In order to access a particular position in the etalon wheel, it is necessary to move it into the light-table, by moving the opposite position into the beam.

Etalons are loaded into the etalon wheel through the access hatch for the pupil-plane filter wheel, which is located in the top of the TAURUS--2 light-table. In order to cable up the etalon it will also be necessary to open the access hatch for the etalon wheel, which is located in the bottom of the TAURUS--2 light-table. Both hatches are opened using a special two-pronged tool, which is usually attached to the side of the instrument with a piece of string.

In order to access the etalon wheel from the top of the light-table, it is necessary to move the pupil-plane filter wheel so that the large hole in this wheel is located in the light table position. Do this by putting position 5 of the pupil plane filter wheel into the beam.

When changing an etalon it is convenient to disengage the detent pins for the etalon and pupil plane filter wheels, so that they are not clamped. This will make accessing the etalon in order to connect wiring more straightforward. To do this, the parameters used when requesting the wheels to move should be negative. For example, in order to change the etalon in position 1 of the etalon wheel, issue the following commands from the instrument control computer:

The procedure to change the etalon is as follows:

1. Disconnect the cabling to the etalon currently in the wheel. Access to the connectors is rather cramped. The simplest approach is first to disconnect the piezo drives (multiway connector with locking screw), accessing the connector block from underneath. Then disconnect the temperature sensor and bridge drive from above. Finally disconnect the 3 bridge receivers. Put the cables to one side.
2. Use an Allen key to unscrew the three bolts attaching the etalon to the etalon wheel. Don't unscrew the kinematic mounts by mistake !
3. Attach the etalon handling tool to the etalon in the wheel. To do this, locate the two screw threads at the bottom of the tool in the corresponding holes in the etalon flange, then tighten the black knobs on the top of the tool.
4. Lift the etalon out of the etalon wheel, and through the access hatch in the top of the light table. Detach the handling tool.
5. If the etalon removed is a real rather than a dummy one, attach its protective covers and put it away.
6. Attach the handling tool to the etalon to be used.
7. Lower the etalon through the access hatch in the top of the light table, into the etalon wheel. The etalon should locate in the kinematic mounts on the wheel. Detach the handling tool.
8. Fix the etalon to the wheel using the three Allen screws.
9. Cable the etalon up. The simplest approach is first to connect the 3 bridge receivers. Make sure these are connected the right way around; note that the Z bridge receiver is between the other two. Then connect the temperature sensor and bridge drive from above. Finally connect the piezo drives (multiway connector with locking screw), accessing the connector block from underneath. Take care when doing this, since it is easy to misalign and bend the connection pins if the connector is carelessly inserted.