Aalborg DFM Digital - Manual (Page 33)

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CAUTION: TO PROTECT SERVICING PERSONNEL IT IS MANDATORY
THAT ANY INSTRUMENT BEING SERVICED IS COMPLETELY PURGED
AND NEUTRALIZED OF TOXIC, BACTERIOLOGICALLY INFECTED,
CORROSIVE OR RADIOACTIVE CONTENTS.
6.2 Flow Path Cleaning
Before attempting any disassembly of the unit for cleaning, try inspecting the flow
paths by looking into the inlet and outlet ends of the meter for any debris that may
be clogging the flow through the meter. Remove debris as necessary. If the flow
path is clogged, proceed with steps below.
Do not attempt to disassemble the sensor. If blockage of the sensor tube is not alle-
viated by flushing through with cleaning fluids, please return meter for servicing.
NOTE: DISASSEMBLY MAY COMPROMISE CURRENT CALIBRATION.
6.2.1 Restrictor Flow Element (RFE)
The Restrictor Flow Element (RFE) is a precision flow divider inside the transduc-
er, which splits the inlet gas flow by a preset amount to the sensor and main flow
paths. The particular RFE used in a given Mass Flow Meter depends on the gas and
flow range of the instrument.
6.2.2 DFM 26/27 models
Unscrew the inlet compression fitting of meter. Note that the Restrictor Flow
Element (RFE) is connected to the inlet fitting. Carefully disassemble the RFE from
the inlet connection. The 50 micron filter screen will now become visible. Push the
screen out through the inlet fitting. Clean or replace each of the removed parts as
necessary. If alcohol is used for cleaning, allow time for drying. Inspect the flow
path inside the transducer for any visible signs of contaminant. If necessary, flush
the flow path through with alcohol. Thoroughly dry the flow paths by flowing clean
dry gas through. Carefully re-install the RFE and inlet fitting, avoiding any twisting
and deforming the RFE. Be sure that no dust has collected on the O-ring seal.
NOTE: OVER TIGHTENING WILL DEFORM AND RENDER THE RFE
DEFECTIVE. IT IS ADVISABLE THAT AT LEAST ONE CALIBRATION
POINT BE CHECKED AFTER RE-INSTALLING THE INLET FITTING-
SEE SECTION (7.2.3).
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