Dwyer GFC - Manual (Page 16)

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Alternatively, a variable 0 to 5VDC or 4 to 20 mA analog signal may be applied
directly to the SETPOINT and COMMON connections of the GFC transducer (see
Figure 2-a). Be sure to apply the appropriate signal for the designated jumper set-
tings.
5.5 Valve OFF Control (Open Collector NPN Compatible)
It may be necessary or desirable to set the flow and maintain that setting while
being able to turn the flow control valve off and on again. Closing of the valve
(without changing the setpoint adjustment) can be accomplished by connecting
pin 12 of the 15-pin "D" connector to COMMON (or power ground). When pin 12
is connected to COMMON, the solenoid valve is not powered and therefore will
remain normally closed regardless of the setpoint. The Motorized valve will be
given the command to close indicated by a green light on top of the unit).
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.