Aalborg AFC - Manual (Page 15)

It is recommended that a potentiometer between 5K to 100K ohm and capable of
at least 10-turns or more for adjustment be used. Use the control potentiometer
to command the percentage of flow desired.
Alternatively, a variable 0 to 5VDC analog signal may be applied directly to the
SET POINT and COMMON connections of the AFC transducer (see Figure 2-1).
5.5 TTL, Valve OFF Control (AFC)
It may, at times, be desirable to set the flow and maintain that setting while being
able to turn the flow control valve off and on again. This can be accomplished by
applying a (TTL compatible) high and low signal of +5 VDC and 0 VDC to pin 8,
on the 15-pin "D" connector. When 0 VDC (LOW) signal is applied, the solenoid
valve is not powered and therefore will remain normally closed. Conversely, a +5
VDC (HIGH) signal applied will allow the solenoid valve to remain active. The
solenoid valve will remain active when the VALVE OFF pin remains "floating".
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 AFC transduc-
er. Toggling the switch on and off will allow for activating and deactivating the sole-
noid valve.
5.6 Valve Test/Purge (AFC)
At times, it may be necessary to purge the flow system with a neutralizing gas
such as pure dry nitrogen. The AFC transducer is capable of a full open condition
for the solenoid valve, regardless of set point conditions. For AFC's utilizing
+15VDC valve configuration, connecting the TEST pin 12 on 15-pin "D" connec-
tors) to ground will fully open the valve. For AFC's with a +30VDC valve configu-
ration, connecting the TEST pin to +15VDC will fully open the valve.
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