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44 of 66 Maintenance and Troubleshooting - 3654 Portable H2/N2 Analyzer
Operator Manual
ORBISPHERE
6.2.3 Mounting Dual Membranes
In order to prevent unwanted stretching of the membrane on a hydrogen sensor it is
recommended to simultaneously mount a support membrane beneath the primary
membrane.
The primary membrane, or top membrane, determines the rate at which the H
2
gas
enters the measurement chamber of the sensor. The secondary membrane, or support
membrane on the bottom, is extremely permeable and is installed to stabilize the position
of the primary membrane.
Two primary membrane types are used for H
2
measurement depending on the type of
application:
• 29561A - used for waste gas, off gas and dH
2
in a boiling water reactor
• 2952A - used for dH
2
in reactor cooling systems of a pressurized water reactor.
The support or secondary membrane for all H
2
measurement applications is the 29562A.
As two membranes will be mounted together, the mounting ring used must be part
number 29229 which is designed for a thickness of 50 microns or more. Mounting ring
part number 29228 is designed for a single membrane and should not be used for
mounting dual membranes.
6.3 Membrane Replacement
Note:
After replacing a membrane, the sensor must always be re-calibrated. Allow the sensor
to settle for 30 minutes in measurement phase to allow measurements to stabilize,
before performing the sensor calibration.
6.3.1 Removing the Membrane
It is recommended to leave the sensor in place in the instrument when changing the
membrane. It is not necessary to remove it.
To remove the membrane, follow the steps below:
First remove the flow chamber from the sensor by turning the flow chamber locking pin
(see position in Fig 1-1 on page 9) counter-clockwise and gently lifting the flow chamber
off the sensor.
CAUTION:
A thermistor at the top of the sensor (illustrated
right) is used to measure the sample temperature.
Do not bend or damage this component by trying to
twist the flow chamber off the sensor.