Automatic Pre-cooling System Overview for myself
6/21/2006  Tokoku






Objective
    (1)Save troubles and man-power.
    (2)The system is necessary for MOIRCS, COMICS, and CIAO.
       The pre-cooling pipe of COMICS and CIAO (the same system) are
       made of stainless steel with welding(=tough) and that of MOIRCS
       is made of copper with silver soldering(=fragile). 
       COMICS and CIAO don't mind a flow rate.
       COMICS takes 2 daytime operations, CIAO takes 1 daytime operation for
       pre-cooling. MOIRCS takes 7 daytime operations with serious care.
    (3)It is not clear whether this sytem will be allowed to run during night 
       time on safty grounds.

Current Status
    (1)Mechanical : Almost done. We want to add a vacuum system for LN2 pipe
                    for in case of high pressure inside.
    (2)Software   : Omata-san is improving it.

Current Control System
    Liquid flow rate control with adjustment OPEN/CLOSE of the pnumatic valve.
    Set point(flow rate) are determined by liquid flow rate and temprature.

Current Problems
    (1)No secure measure for power failure.
    (2)Need backup flow meter? (to where?)

When is a vacuum system necessary?
    (1)Avoid any damage from power failure.

    (2)After PV1 was closed, if a puressure of G1 is too high (>10^-1 Torr??)
    and
    (3)During night time or When both tanks run out.

    (4)How about using only relief valve?
       ---> Frost inside line.
            ---> Vacuuming during warm-up.

Issues about a vacuum system in a liquid nitrogen line.
    (1)The same line is used for liquid and high-vacuum.
       (1-1)Connectors are difference.
       (1-2)Gauges are difference.
    (2)
    (3)