Aalborg AFC - Manual (Page 16)

6. MAINTENANCE
6.1 Introduction
It is important that the Mass Flow Meter/Controller is used with clean, filtered
gases only. Liquids may not be metered. Since the RTD sensor consists, in part,
of a small capillary stainless steel tube, it is prone to occlusion due to impedi-
ments or gas crystallization. Other flow passages are also easily obstructed.
Therefore, great care must be exercised to avoid the introduction of any potential
flow impediment. To protect the instrument a 50 micron (AFM 26/ AFC 26) or 60
micron (AFM 36/46, AFC 36/46) filter is built into the inlet of the flow transducer.
The filter screen and the flow paths may require occasional cleaning as described
below. There is no other recommended maintenance required. It is good practice,
however, to keep the meter away from vibration, hot or corrosive environments
and excessive RF or magnetic interference.
If periodic calibrations are required they should be performed by qualified per-
sonnel and calibrating instruments, as described in section 7. It is recommended
that units are returned to Aalborg
7 for repair service and calibration.
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 not unclogged, then proceed with steps below.
Do not attempt to disassemble the sensor. If blockage of the sensor tube is not
alleviated by flushing through with cleaning fluids, please return meter to Aalborg
for servicing.
6.2.1 Restrictor Flow Element (RFE)
The Restrictor Flow Element (RFE) is a precision flow divider inside the trans-
ducer, 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/Controller
depends on the gas and flow range of the instrument.
6.2.2 AFM 26 and AFC 26 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
ƽ
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