14
4
Operation
4.1
Front Panel Controls
The front panel controls are grouped together in logically related blocks.
POWER
The main ON/OFF switch. A green lamp illuminates whenever the instrument is switched
on.
ADJUST
The red RAISE and LOWER buttons provide the main means of adjusting any parameter.
In ILM their main use is for adjusting the display reading during the configuration and
calibration process. They have no effect on their own but are always used in conjunction
with one of the other buttons. Whenever a parameter is being adjusted, its current value
is shown on the display. Setting a value involves pressing RAISE or LOWER until the
required value is shown.
Operation of the RAISE and LOWER controls has been designed to allow large changes to
be made relatively quickly whilst at the same time enabling any value to be set exactly.
Pressing RAISE or LOWER briefly will cause the value to change by one unit. If the button
is held in, the last figure will start to change at about 5 units per second. After 2 seconds,
an approximately 10-fold increase in rate will occur, followed after another 2 seconds by
a further rate increase and so on. Altogether there are 4 different rates. Whenever RAISE
or LOWER is released, the next lower speed will be selected. This allows the user to
"home-in" on the required value in a logical way.
A secondary use of RAISE and LOWER is in conjunction with SILENCE, to enter the TEST &
CONFIGURATION mode, as described below.
STATUS
Certain functions of ILM, such as Alarm and Magnet Shut-Down in the event of low
cryogen levels, are common to all channels. ALARM and SHUT DOWN lamps in the
STATUS box allow the operation of these functions to be observed. In particular these
conditions remain latched, so that once an alarm or shut down is initiated, it will remain
in force, even if the cryogen level is restored. A SILENCE button is provided to clear the
alarm and shut down conditions. If the low level causing the condition has been cleared,
pressing the SILENCE button will silence the alarm and reset the lamps. If the low level is
still present, pressing SILENCE will stop the alarm sounding and release Relay 4.
However the ALARM and/or SHUT DOWN lamps will remain lit, and any of Relays 1 to 3
which are active will remain so. If the alarm has been silenced in this way, it indicates to
ILM that the operator is aware of the problem. The ALARM lamp will therefore
automatically cancel when the low level condition is removed. The SHUT DOWN
condition will not cancel until the SILENCE button is pressed,
after
the low level
condition has been cleared. The reason for this is that once a run down has been
initiated, it is not advisable to terminate this at some arbitrary magnet current without
operator intervention.
