Aalborg GFC - Manual (Page 16)

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12
,
Conversely, when the connection is left open or pin [12] remains unconnected the
valve remains active. The valve will remain active when the VALVE OFF pin
remains “floating”. This feature is compatible with open collector NPN transistor
switches, as found in DC output ports of programmable controllers and similar
devices.
The simplest means for utilizing the VALVE OFF control feature, is to connect a
toggle switch between the COMMON and VALVE OFF pins of the GFC transduc-
er. Toggling the switch on and off will allow for activating and deactivating the sole-
noid valve.
5.6 Valve Test/Purge
At times, it may be necessary to purge the flow system with a neutralizing gas
such as pure dry nitrogen. The GFC transducer is capable of a full open condition
for the valve, regardless of setpoint conditions. Connecting the OPEN (PURGE)
pin (pin 4 on 15-pin “D” connector) to ground will fully open the valve.
The Motorized Valve: Connect pins [3] and [4] to OPEN the motorized control
valve. A red light on top of the valve will indicate an OPEN valve, normal for flow
conditions.
NOTE: The motorized control valve stays OPEN even if power is
no longer applied. To CLOSE the Motorized Control Valve, connect pins
[3] and [12].
6. MAINTENANCE
6.1 Introduction
It is important that the Mass Flow Controller/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 (GFC17) or 60
micron(GFC37/47) 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, how-
ever, 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 recommend-
ed that units are returned to Aalborg
7 for repair service and calibration.
CAUTION: TO PROTECT SERVICING PERSONNEL IT IS MANDATO-
RY THAT ANY INSTRUMENT BEING SERVICED IS COMPLETELY
PURGED AND NEUTRALIZED OF TOXIC, BACTERIOLOGICALLY
INFECTED, CORROSIVE OR RADIOACTIVE CONTENTS.