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Subsections
If construction work occurs in Hall C, the wearing of a hard hat is obligatory.
Since Hall C is not normally in a ``construction'' state, signs will be posted
at the entrance to the hall when a hard hat is mandatory.
If one must work in the immediate vicinity of the Hall C crane
when it is in use, a hard hat is also required.
The carriages are the support structures of the spectrometers.
First and foremost as it is a multileveled structure it is important to keep in
mind that people may be working above you. This means that the wearing of
hard hats in Hall C is strongly advised.
Taller individuals should be mindful when using the flight of steps leading
towards the higher levels due to the limited head room at some points.
Safety railings have been installed everywhere along the carriage perimeters.
Be aware that some of these may be removed during the experimental data taking
to enable spectrometer rotation and will need to be installed (or you need to
wear a safety harness) before accessing these areas.
The pivot area is the platform giving access to the Hall C scattering chambers.
The Hall C pivot area is to a large extent part of the SOS carriage, and as such
access to this pivot area requires also installment of the safety railings
or the wearing of a safety harness. Furthermore, if the scattering chamber is
pumped down ear plugs will need to be worn when working closer than 3ft. from
the vacuum windows. This is also true if you need to work within 3ft. from
the HMS and/or SOS spectrometer vacuum windows if those spectrometers are
under vacuum.
In case a polarized target is used, special safety
measures are taken to be allowed access to the pivot area.
It cannot be overemphasized that one of the most significant hazards
in hall C is a simple fall. Even standard access routes such as
stairs or ladders can lead to serious injury if proper care is not
taken. The risk is multiplied if the individual is carrying a load
of equipment such as oscilloscopes.
Another fall hazard exists in the form of non-standard access routes.
Generally speaking, these are to be avoided. An egregious example
might be climbing a rickety chair on the HMS platform to access the
pivot area. However, use of a non-stndard access route such as a
well-secured ladder may occassionally be necessary.
Certain areas on the pivot and the HMS carriage will have the
handrails removed during experiment operations. When acess to these
areas is required, use fall protection as mandated by the EHS manual.
The obvious problem with spectrometer rotation is that one rotates a
many-ton object which will crush whatever is in its way.
Rotation of the spectrometer
is accomplished by using the two motors on the carriage itself (the motors on
the shield house bogies are not used in the present rotation system).
These AC motors are controlled by synchronous pulse width modulated
drives which are mounted near the bottom of the shield house steps.
The spectrometer motors may only be controlled by trained personnel.
At least two people are required for manual spectrometer rotation, one to
run the motors and at least one spotter. Prior to rotating the spectrometer
a visual inspection of the area should be made to insure that there
is nothing in the spectrometer's path or on the rails.
The spotter should pay special attention to the cables which run from the
spectrometer to the target motor controller to make sure that
nothing is hung up or stretching.
After the possible angle range of both HMS and SOS have been verified by the
Hall C engineering staff, limit switches will be installed at forward and
backward angles.
Remote spectrometer rotation occurs by PLC computer. Commands can be
issued to this PLC (Texas Instruments 5000), which executes these commands
following algorithms stored in its memory. The verified minimal angle between
the HMS and SOS spectrometers has been loaded into this PLC.
The PLC is situated at the first
level of the HMS carriage, opposite to the magnet power supplies.
The CPU of this PLC is located in the HMS Detector hut.
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 in between both spectrometers.
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 are installed on the floor, in the event of failure
of the PLC limit switches.
The HMS and SOS slit ladders each consist of three heavy densimet blocks,
two collimators and one sieve slit. The total weight for each slit
ladder amounts to 350 Lbs (160 kg) and can easily cause serious damage to
body parts.
Install a metal support under the slit ladder when you work with your
hands under it. The remote control systems are equipped with
a brake cable to prevent the slit ladders from sliding down in case of a
power failure, but this must not be relied upon for personnel safety.
The shield house interior access is covered by a two piece door. The two
halves counterweight against each other, opening vertically. The bottom
door (30 tons) is 5 tons heavier than the top door. Thus, the door will want
to open naturally if unconstrained. The door control system is used to keep
the doors closed.
The valves in the control system are set by a PLC that resides in a box
mounted beneath the stairs at the rear of the spectrometer.
The user operates the door electronically via a control box
mounted along the walkway near the door (or from the panel beneath the stairs).
The main hazards are associated with differential motion of the two hydraulic
cylinders enabling the door motion. This can bend or destroy these hydraulic
cylinders causing major down time. Alternatively, one has to be careful with
body parts in between the two door parts when closing the door.
- With the loss of electrical power all valves close automatically. This
will stop all movement of the door. The fluid in the cylinders may slowly leak
past the seals causing the door to open.
- Hydraulic pressure indicators in the system will stop
the system if loss of pressure is detected.
- The solenoid valves have lifetimes of many thousands of cycles.
If a valve fails, the two pressure indicators will start to differ, soon
resulting in a too large difference between the two decoders (one for each
side of the door), causing the motion mechanism to stop.
- In the unlikely event of a cylinder failure, the door will slip slightly
to one side in the track and any motion will stop.
- The hydraulic pump has two motors that are independently switched.
Either will provide adequate power to operate the SOS door hydraulics.
The motion of the door is monitored by the control system. Linear
displacement encoders on each cylinder provide analog signals to the controls.
The two cylinders must move at the same rate or the control system will
stop the door progress. The doors will stop if the difference between the
cylinders becomes more than 0.020". The control system will attempt to
level the door and continue. Massive skewing of the door will cause the
door to wedge in the track.
- A section of handrail is attached to the downstream end of the
flip-down section of walkway. It is advised to stay behind this
handrail until the doors open completely and the flip-down walkway
can be rotated over the lower door.
Next: Hazardous and Toxic Materials
Up: Description of Hall C
Previous: Vacuum and Pressure Hazards
Hall-C Staff
2008-01-17