GENERAL DESCRIPTION
Page 2-8
IEEE-488 SYSTEM (OPTIONAL)
The IEEE-488 bus is also known as the “General Purpose Interface Bus” (or
GPIB). The purpose of the IEEE-488 bus is to transfer information between two
or more devices. A device may either be an instrument or a computer. Devices
may ‘Talk’ (send), ‘Listen’ (receive), or be idle on the bus. Only one device can be
‘addressed’ (allowed) to Talk on the bus at a time, while one or more devices may
Listen.
One device on the bus must be the System Controller. The Controller determines
which device will talk and which devices will listen. The Controller is usually a
computer containing a IEEE-488 interface card and application programs. The
IEEE-488 speci• cation allows the System Controller to pass its duties to another
device, making it the ‘Active Controller’.
There are two types of messages sent over the IEEE-488 bus: interface messages
and device dependent messages. Interface messages manage the IEEE-488
bus, using commands to clear the interface, address devices to talk or listen, and
so forth. Device dependent messages transfer commands speci• c to the device
controller.
The IEEE-488 bus interface is externally mounted on top of the unit using the
“hook and loop” (Velcro
®
) strips provided, or on a bench beside the unit. A 25
pin male serial cable has also been provided to connect the interface to the
communications port on the front of the unit.
LN2/CO2 BOOST COOLING SYSTEM (OPTIONAL)
In addition to the main refrigeration system, the chamber is equipped with an
optional connection port for supplying boost cooling from an external source of
cryogenic lique• ed gas (either carbon dioxide or liquid nitrogen). The boost cooling
gas is vented directly into the chamber by a controller under the
conditions of sustained cooling demand.
Speci• cs
The LN2 cylinder should be connected with a well insulated line that is at least
3/8”/9.5mm inside diameter. The line length should be 5FT/152cm or less. The LN2
tank should have a maximum supply pressure of 25 PSIG/172 kPa.
Mechanical cooling with LN2 boost: over the temperature range of the chamber,
the refrigeration system operates normally. When the LN2 switch is turn “on”,
the LN2 cooling valve will open when there has been a call for cooling from the
controller for more than 10 seconds. This will boost the cooling effect and reduce
the temperature in the chamber faster.
Gaseous Nitrogen/C02
vent must be ducted
out doors. To prevent
displacement of oxygen
around the unit. Asphyxia
can occur if this is not
installed properly.
WARNING
!
Wear appropriate PPE
when handl ing LN2
connection.
WARNING
!
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