A summary of the procedure required to move the spectrometers is given below. Here an overview of the process is given. Although spectrometer rotation is automated (i.e. computer controlled), the operator is required to be present in the Hall to identify and correct potential problems that may appear during the course of the operation.
Prior to operating the spectrometer positioning system, an inspection of the floor plates for fallen objects in the path of the wheels must be done. Visually check also both sides of the spectrometer for potential interfering pipes, cables or temporary stairs in the path of the spectrometer. No person should be in the spectrometer while it moves. After the visual inspection is completed, you can login into the Hall-A controls account and activate the spectrometer motion screen.
The screen for the hadron spectrometer is shown in figure 2.1. The electron spectrometer screen is similar. Towards the left side of the screen there is a row of 'check' buttons lebeled 'PSM ENABLE' (Power Supply Module), 'DM ENABLE' (Drive Module), 'BRAKE ENABLE' and, 'CLAMP RELEASE'. The 'PSM ENABLE' button activates the power supply modules. The 'DM ENABLE' button activates the servo-amplifiers. The 'BRAKE ENABLE' button releases all brakes. The 'CLAMP RELEASE' allows the commanded spectrometer rotation (see below) to be passed to the servo-amplifiers so that spectrometer motion starts. The hardware interlock system treats these buttons in a herarchy. The 'PSM ENABLE' button is the highest in the herarchy and the 'CLAMP RELEASE' the lowest. Pressing a button will activate its corresponding function ONLY if functions higher in the herarchy have been activated and no faults have been detected. Release the 'CLAMP RELEASE' button for an inmediate stop the spectrometer while its moving. Towards the right hand side of the screen, there are tree status bits labeled 'PSM OK', 'DM OK' and, 'BRAKE OK'. These bits will read 'NO' when there is no power, the function has not been activated or if there is a hardware failure. If things are working properly and the given function is active, the corresponding status bit will read 'YES'.
The entry field labeled 'VELOCITY SET' is used to set the servomotors speed. The value ranges from -1000 to +1000 RPM (revolutions per minute) corresponding to 2 per minute of spectrometer rotation. Negative values correspond to clockwise rotation of the spectrometer as viewed from above (i.e. the roof of the hall). Positive to counter-clockwise rotations. The field lebeled 'DIRECTION' towards the right hand side of the screen presents the direction of motion. Moving,for example, the electron spectrometer clockwise makes the scattering angle smaller while in the case of the hadron spectrometer, it will make the scattering angle larger.
Two rows of numbers are used for information and troubleshooting. One row reads 'MVO Ix', 'MVO My' and 'MVO Oy' where 'x' ranges from 1 to 2 and 'y' ranges from 1 to 4. 'MVO' stands for Motor Velocity Output, the 'I' represents the inner (front of the cradle, closest to the target) row of servomotors, 'M' referres to the middle row of servomotors (back of the cradle) and, 'O' represents the row of servomotors at the detector shield house gantry legs. Looking at the spectrometer from the target, servomotor 1 of each row is the one located at the most right hand side. The values shown by these fields should be similar, in magnitude, to the value entered in the 'VELOCITY SET' field. Another row of numbers is labeled 'MCO Ix', 'MCO My' and 'MCO Oy'. 'MCO' stands for Motor Current Output. The remaining part of the field labels follow the same notation as in the case of the 'MVO' fields. Typical values for the hadron spectrometer and a 'VELOCITY SET' field of 1000 RPM are 2 Amps in the inner servomotors and 3 Amps for the middle and outer servomotors. The electron arm values are typically 1 Amp higher. At the top of the spectrometer control screen there is a button labeled 'graph'. Pressing it opens a window where the various 'MVO' and 'MCO' quantities can be selected for plotting while the spectrometer operates.
The screen has three fields labeled 'INNER MASTER', 'MIDDLE MASTER' and, 'OUTER MASTER'. The servomotors of each row of wheels (inner, middle and outer) operate in a master-follower mode: one of the servomotors (the master) operates in speed regulation mode while the remaining servomotors (followers) operate in torque mode (they just follow the current ouput of the master). The default is servomotor 1 of each row to be the master. As mentioned previously, the spectrometer wheels are mounted in groups of 4 in a structure called a bogie with one of the wheels in the group powered by a servomotor. While each bogie has some compliance for floor irregularities, the individual wheels of each bogie do not. Consequently, it is possible for the propeled wheel of a given bogie to either substantially loose friction force with the floor or to become totally detached from the floor. The three fields allow to change the master function allocation for each servomotor row. The 'INNER MASTER' field has two possible values only: 1 and 2 while the other two servomotor rows can take the values of 1, 2, 3 or, 4. These values can only be changed when the the power supply modules are enabled ('PSM ENABLE' button depress and status bit 'PSM OK' reads 'YES') and everything else is disabled.