Aalborg DFC Digital - Manual (Page 18)

Inspect the flow path inside the transducer for any visible signs of contaminants.
If necessary, flush the flow path through with alcohol. Thoroughly dry the flow
paths by flowing clean dry gas through.
Re-install the inlet parts and filter screen. Be sure that no dust has collected on
the O-ring seal.
It is advisable that at least one calibration point be checked after re installing the
inlet fitting - see section (7).
6.2.4 Valve Maintenance (DFC)
The solenoid valve consists of 316 and 416 stainless steel, and VITON
7 (or
optional EPR or KALREZ
7) O-rings and seals. No regular maintenance is required
except for periodic cleaning.
Various corrosive gases may demand more frequent replacement of VITON
7
O- rings and seals inside the valve. Be sure to use an elastomer material, appro-
priate for your specific gas application. Contact your distributor or Aalborg
7 for
optional sealing materials available.
Set the DFC into PURGE mode, and attempt to flush through with a clean, fil-
tered, and neutral gas such as nitrogen. [Another option for fully opening the valve
is to remove the plastic cap on top of the valve, and turn the set screw counter-
clockwise until it stops. Set valve for the closed position. Apply an inlet pressure
of 5 psig and atmospheric pressure at the outlet. If a small flow occurs, turn the
set screw on top of the solenoid valve clockwise until the flow through the DFC
just stops.
7. CALIBRATION PROCEDURES
7.1 Flow Calibration
Aalborg
7 Instruments' Flow Calibration Laboratory offers professional calibration
support for Mass Flow Meters and Controllers, using precision calibrators under
strictly controlled conditions. NIST traceable calibrations are available.
Calibrations can also be performed at customers' site using available standards.
Factory calibrations are performed using NIST traceable precision volumetric cal-
ibrators incorporating liquid sealed frictionless actuators.
Generally, calibrations are performed using dry nitrogen gas. The calibration can
then be corrected to the appropriate gas desired based on relative correction [K]
factors shown in the gas factor table see Appendix 2. A reference gas, other than
nitrogen, may be used to closer approximate the flow characteristics of certain
gases. This practice is recommended when a reference gas is found with ther-
modynamic properties similar to the actual gas under consideration. The appro-
15
Note: Removal of the factory installed calibration seals and/or any
adjustments made to the meter, as described in this section, will void
any calibration warranty applicable. ƽ