Aalborg DFC Digital - Manual (Page 14)

5. OPERATING INSTRUCTIONS
5.1 Preparation and Warm Up
It is assumed that the Mass Flow Controller or Controller has been correctly
installed and thoroughly leak tested as described in section (2). Make sure the
flow source is OFF. Power up the transducer using your own power supply (or
switch the POWER switch to the ON position at the front panel of your SDPROC
Command Module). Allow the Mass Flow Meter or Controller to warm-up for a
minimum of 15 minutes.
During initial powering of the DFC transducer, the flow output signal will be indi-
cating a higher than usual output. This is indication that the DFC transducer has
not yet attained it's minimum operating temperature. This condition will automat-
ically cancel within a few minutes and the transducer should eventually zero.
5.2 Flow Signal Output Readings
The flow signal output can be viewed on the panel meter, digital multimeter, or
other display device used as shown in figure b-1.
When using the accessory SDPROC Command Module the flow rate will appear
on the display at the front panel. The observed reading is a 0 to 100% indication
(direct engineering units are optional). [If using a multichannel readout, be sure
that the CHANNEL selector switch is set to the correct channel.]
Analog output flow signals of 0 to 5 VDC or optional 4 to 20 mA are attained at
the appropriate pins the 25-pin "D" connector (see Figure b-2) on the side of the
DFC transducer. The output flow signal is also available at the DATA connector on
the rear panel of the SDPROC Command Module.
Meter signal output is linearly proportional to the mass molecular flow rate of the
gas being metered. The full scale range and gas for which your meter has been
calibrated are shown on the flow transducer's front label.
For information on the RS485 or optional RS232 interfaces please contact your
distributor or Aalborg
7.
5.3 Swamping Condition
If a flow of more than 10% above the maximum flow rate of the Mass Flow
Controller is taking place, a condition known as "swamping" may occur. Readings
of a "swamped" meter cannot be assumed to be either accurate or linear. Flow
must be restored to below 110% of maximum meter range. Once flow rates are
lowered to within calibrated range, the swamping condition will end. Operation of
the meter above 110% of maximum calibrated flow may increase recovery time.
11
Caution: If the valve is left in the AUTO (control) or OPEN mode for an
extended period of time, it may become warm or even hot to the touch.
Use care in avoiding direct contact with the valve during operation. ƽ