Garnet MULTIRACK 688-D, Manual

Page: 5 / 14

Page 5 688 Manual
Rack Controller Operation
The rack controller connects to the module via fiber optic cable
and goes to permit only if the light pulse is present. The fiber cable
is used to provide electrical isolation between the SeeLeveL and
the intrinsically safe wiring of the loading rack. The controller will
only accept light pulses from a 688M module; it cannot be fooled
by ambient light or the output from a sender bar. The controller
operates entirely from rack power; it contains no batteries, and
will function only when connected to an optic or thermistor rack.
If the truck has two trailers, then one controller is required per
trailer, since the fiber optic cable cannot be connected between
trailers. The single controller has one fiber input, and it is used
for single compartment applications. The dual controller has two
fiber inputs, and it is used for two compartment applications, and
both fiber inputs must receive light pulses for the controller to
permit.
The controller can operate either an optic (five wire) or a thermistor
(two wire) loading rack. If the application has two trailers, then
the optic portions of the two controllers are series wired just like
optic probes. The controller has two thermistor leads to simulate
two thermistor probes, and will operate with either one or both
of the thermistor leads connected. For two trailer applications,
each of the thermistor leads from the rack socket is connected to
its own controller. The controller simulates a two wire thermistor
regardless of product temperature; the third temperature
compensation (rack green) lead is not used.
The controller is mounted in a round Betts junction box with a
snap lid, providing excellent sealing against weather conditions, as
well as visibility of the diagnostic LEDs. The cover of the controller
is illustrated on the front page.
The OPTIC diagnostic LED indicates proper connection to the optic
rack, it will illuminate whenever the ground and red power wires
are connected, regardless of whether the controller is in permit
or not. The OPTIC LED does not indicate whether the yellow or
orange pulse leads are connected.
The THERM A and THERM B diagnostic LEDs indicate proper
connection to the thermistor rack, regardless of whether the
controller is in permit or not. If only one of the thermistor leads is
used, then only its corresponding LED will illuminate.