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Once the patient temperature channel's accuracy has been temporarily
established, the CTU's temperature probe is connected to the Control
Module's Patient Temperature 1 input. The Control Module then circulates
water through the CTU at various temperatures. The patient temperature
channel can then be used to check and calibrate the accuracy of the
internal water temperature sensors and circuits.
The fluid path in the CTU is designed to allow a specific flow, which was
selected to provide this flow rate at a given pressure. Since the A
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Temperature Management System controls the inlet pressure at a
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constant value, a crosscheck of flow and pressure measurement accuracy
can be obtained. The flow rate and inlet pressure offset are checked, and
the inlet pressure offset is zeroed during the initial warm-up period.
The CTU contains heaters that can be used to raise the system water
temperature for troubleshooting. The test unit heaters are thermally and
electrically protected, and are only powered while pressing the Heater
Power Switch.
3.3 Controls
A rotary switch (S1), two slide switches (S2 and S3), and a heater
switch (S4) comprise the CTU controls. The Output Select Switch,
S1, is used to select the temperature simulator to be applied to the
patient temperature channel. Six switch positions represent specific
temperatures as follows:
•
Position A is "open" or "no connection"
•
Position B is approximately 10.8°C
•
Position C is approximately 25.5°C
•
Position D is approximately 34.5°C
•
Position E is approximately 40.0°C
•
Position F is a "shorted" connection.
The precise values of the simulators listed above are determined by
a factory calibration process and are listed on a calibration sticker on
the CTU.
The slide switch, S2, is used as follows:
•
Position A connects Patient Temperature Channel 1 to the rotary
switch and Patient Temperature Channel 2 to the Temperature
Out Channel.
•
Position B connects Patient Temperature Channel 1 to the CTU
temperature sensor and Patient Temperature Channel 2 to the
rotary switch.
•
Position C connects Patient Temperature Channel 1 to the
Temperature Out Channel.
The slide switch, S3, is used as follows:
•
Position A connects the internal thermistor in the water flow path to
the patient temperature circuit.
•
Position B connects a parallel resistance with the internal
thermistor, shifting the temperature up at the low water temperature
setting, allowing it to be read by the patient temperature circuit.
The heater power switch, S4, is a momentary, normally open switch that
applies AC power to the two 250W heaters when pressed and held in the
ON position. The AC power cable must be connected to the CTU and an
appropriate power receptacle to power the heaters.
3.4 Connections
A hydraulic connection and three electrical connections must be made
to the control module so that the unit will function correctly in conjunction
with the control module's software functions.
•
The hydraulic connection is a custom fitting which mates directly to
the control module. The seal must be tight with no leaks to ensure
a proper test.
•
The three electrical connections are labeled 'PT1', 'PT2', and 'TO'.
o
PT1 corresponds to the primary patient temperature
receptacle on the control module.
o
PT2 corresponds to the secondary patient temperature connector.
o
TO corresponds to the temperature out connector on the
control module.
•
TO has a different keying scheme from PT1 and PT2, and therefore
cannot be interchanged. However, care must be taken when
connecting PT1 and PT2 because they can be interchanged. If this
does occur, the control module will indicate an error on the user
interface display.
•
The PT1, PT2, and TO electrical cables do not supply a voltage or
current. They are passive connections with the voltage or current
being supplied by the control module.
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3.5 Understanding the Test and Calibration
Sequence
The Calibration Test Unit and the A
System Control Module work together to perform the tests and
calibration in a semi-automated sequence. This section gives a step by
step description of how this is accomplished. The calibration process
may be discontinued at any time by pressing the Cancel button. Power
must be cycled after a New Calibration process or Check Calibration
process has begun to resume normal operation.
3.5.1 Calibration Factor Longevity
In order to perform this process accurately, various parameters of
the Control Module must first be calibrated to be used in subsequent
measurements. It should be noted that this calibration is temporary and
it applies only during the Test and Calibration Sequence. This data is
saved only at completion of the New Calibration sequence.
3.5.2 Initiation
The Control Module will enter Test and Calibration Mode only if all of the
following are true:
•
Patient Temperature 1 is between 10°C and 12°C.
•
Patient Temperature 2 is less than 10°C.
•
The reservoir level is 4 or greater.
These unique conditions are required to ensure that the system is
connected to the CTU, not a patient. If one of the criteria above is not
met, the user is prompted to rectify it.
3.5.3 Pre-Warm and Flow Check
The system pre-warm and flow check begins when the Test and
Calibration Mode is initiated. This process starts with an automatic
10-minute pre-warm period. During this time, the unit runs in Manual
Mode with a 28°C water target temperature and a countdown timer
displays how many minutes remain in the pre-warm step. Approximately
55 seconds after initiating pre-warm, a bypass mode flow check is
also performed.
For successful completion of pre-warm to occur, the following criteria
must be met after 10 minutes:
•
The bypass mode flow check flow rate must be greater than the
non-bypass flow rate + 500ml/min.
•
The average flow rate must be within ±600ml/min. of the CTU
H value.
•
The inlet pressure average must be within 1.0 psi of –7.0 psi.
•
The bypass valve must be closed.
Once these conditions have been met, the system performs a purge
for approximately one minute to prepare for checking the inlet pressure
offset. The system performs an internal test of the patient temperature
channels when purging is complete. If successful completion of the pre-
warm / flow check does not occur within 12 minutes of its initiation,
a time-out error is indicated.
At this point, the inlet pressure offset is calculated after the pressure
stabilizes within 0.01 PSI. If the offset is greater than ±0.5 PSI, an error
message is displayed.
3.5.4 Patient Temperature Channel Checks
Operator assistance is needed to perform the Patient Temperature
1 (PT1) checks. The operator is prompted to change CTU Switch 1
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Temperature Management
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