Remote Rotation

Cameras are installed to enable readout of the HMS spectrometer angle (using the plumb bob and the survey marks on the floor).

The wide-lens and zoom cameras located at the entrance and the exit of Hall C should be used to visually spot for obstructions before and during remote rotation.

Limit switches are installed at forward and backward angles which prevent HMS from rotating to angles more forward than 10.6 degrees and more backward than 85 degrees. To obtain more forward or more backward angles an access is needed, and rotation has to occur manually downstairs with spotters. Hard limit switches will be installed to prevent the spectrometer from rotating out of maximum allowed range.

In case the HMS spectrometer is rotated to more forward angles, pay special attention to possible interferences of HMS and SOS. Up to this moment the closest angle distance we have obtained between SOS and HMS is 28 degrees.

Remote rotation is accomplished via the PLC located in the Hall. It is currently installed in the HMS shield hut for protection from radiation. Commands can be issued to the PLC (Texas Instruments 5000), which executes these commands following algorithms stored in its memory. An EPICS screen is now used to talk to the PLC. The advantages of using the PLC are:

• No direct access by users to the algorithms, preventing unsafe rotation attempts (instead, the algorithms have to be loaded locally into the PLC).
• Rotation of both HMS and SOS by the same smart controller, enabling security checks of both angle decoders. This renders a better handle on the minimum allowed angle between the two spectrometers.
• Automatic slower rotation speeds (if desired) if close to desired angle when using proximity switches.

The PLC communicates directly with the control electronics of several limit switches, proximity switches, and decoders. Next to the limit switches also hard limit switches will be installed on the floor to mitigate failure of the PLC limit switches.