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nitrogen is delivered to the cargo area of the container.
In turn, Oxygen and other trace gases are discharged
through the front of the unit, behind the CA controller,
located near the membrane air filter assembly. The rate
of gas separation is determined by the flow of air through
the membrane. The flow rate through the membrane is
determined by the Nitrogen Purity Valve (NPV). When
de--energized, the NPV allows a nearly pure stream of
nitrogen to pass into the container, used to decrease the
amount of oxygen. To decrease the amount of CO
the container the NPV is energized. When energized,
the NPV introduces a higher flow rate of less pure
nitrogen that purges the excess CO
demand for the O
level to increase, the Controller will
2
energize the oxygen solenoid valve (OSV) to allow the
filtered, pressurized air to flow directly into the container,
bypassing the nitrogen membrane separator.
The CA Controller monitors the amount of oxygen and
carbon dioxide in the container by using oxygen and
carbon dioxide sensors. In conjunction, the CA
Controller uses four electrically actuated solenoid
valves that are selectively actuated to provide the
desired gas sample flow to these sensors. These four
solenoid valves are combined in a manifold block.
The air calibration solenoid valve (ASV) delivers a
sample of heated ambient air to the sensors from the
same line that supplies air to the nitrogen membrane
separator and is used to calibrate the O
The nitrogen solenoid valve (NSV) delivers a sample of
the nitrogen being supplied to the container from the
nitrogen membrane separator to the sensors.
The gas calibration solenoid valve (GSV) delivers a
sample of gas from an external calibration bottle. This
bottle contains a calibration gas made up of 5% carbon
dioxide and 95% nitrogen, is connected temporarily to a
fitting located on the outside of the container (see
Figure 56, page 89), which is used to zero calibrate the
O
sensor, and check the CO
2
flows must be within the range of 0.5 to 1.0 lpm)
(approximately 1-2 cuft/hr), an external flow meter must
be used. Do not exceed five psig input pressure.
The sample air solenoid valve (SAV) delivers a sample
of the atmosphere inside the container , which is used to
monitor current concentrations of O
container.
All of the outputs from the oxygen and carbon dioxide
sensors are delivered to the CA Controller to monitor the
operation and performance of the CA system.
In some cases, a higher level of carbon dioxide is
required to transport some commodities. A physically
separate carbon dioxide supply must be provided by the
user. Connection ports are located in two different
areas: on the outside of the container (see Figure 56,
page 89), and on the inside of the container (see
Figure 57, page 90). The user must initiate CO
point; the CA Controller will then actuate the solenoid
valve (CSV) when required.
9.2 CA PRE-TRIP DIAGNOSTICS
Pre-trip Diagnostics is an independent mode which will
suspend the normal Control Mode activities when
initiated by the user. With pre-trip diagnostics, either all
the pre-trip tests can be executed in a defined sequence
(Auto Mode), or one of the pre-trip tests can be selected
to be executed (Manual Mode), based on the sequence
of key selections made.
in
2
When there is a
2.
sensor span.
2
sensor. Calibration gas
2
and CO
within the
2
2
set
2
a. Starting and Terminating Pre-Trip
Pre-trip is initiated by pressing the PRE-TRIP key. This
places the user into a test selection menu. If no selection
is made, pre-trip will terminate automatically. While
tests are being executed, the user can terminate the
pre-trip mode by holding the PRE-TRIP key. The system
will then resume normal operation. If the user decides to
terminate a test but remain at the test selection menu,
the user may press the UP ARROW key. When this is
done all machinery outputs will be de-energized and the
test selection menu will be displayed.
The pre-trip diagnostics may also be initiated via remote
communication, but when initiated will always attempt to
execute the entire battery of tests (auto mode).
b. Temperature Controller Approval of Controlled
Atmosphere Pre-Trip request
The CA Controller will make a request for CA Pre-Trip
from the Temperature (refrigeration) Controller. The
Temperature Controller will approve the request, except
when the Temperature Controller is in Pre-Trip itself or
CA is in standby mode.
In response to the CA Pre-Trip request, the
Temperature Controller will have the following
response:
Exit defrost and lock-out defrost until
S
Controlled Atmosphere Pre-Trip is complete.
Lock-out Temperature Controller Pre-Trip.
S
Alternate the message P-CA on the display
S
with the set point until CA Pre-Trip is
complete.
Force the high speed evaporator fans ON.
S
Disable Dehumidification.
S
When CA Pre-Trip requests are not approved, while the
Temperature Controller is in Pre-Trip or CA is in standby
mode, the display wll read "PPPP PPPP". This will
continue until the user presses the PRE-TRIP key or the
UP ARROW key for more than three seconds. When the
Temperature Control exits from pre-trip and CA is not in
standby mode, CA pre-trip request will be approved.
Upon CA being taken out of standby mode, CA pre-trip
will re-start the test that was aborted.
CA will request a Pre-trip to continue from the
Temperature
Controller
completion of CA pre-trip.
c. Test Codes
A detailed description of the pre-trip test codes are listed
in Table 25, page 109.
9.2.1 Pre-Trip
In this mode, the system will automatically test system
components
using
comparison logic, and will provide a "PASS" or "FAIL"
display to indicate the results of each test.
If the user depresses the PRE-TRIP key, the unit gives
access to a pre-trip selection menu. The contents of the
menu is as follows:
PRE-TRIP SELECTION MENU
Auto, P1, P2, P3, P4, P5, P6, rSLts
If the pre-trip was last executed manually since power
up, the last menu selection will appear on the left
107
every
minute
until
internal
measurements
the
and
T-305
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Troubleshooting
