How To Override the Valve (MFC only)
Chapter Four: Operation
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How To Override the Valve (MFC only)
The valve override feature enables the control valve to be fully opened (purged) or closed
independent of the set point command signal. Refer to Table 8, page 34, or Table 7, page 33, for
the appropriate pin locations.
If the 1179 flow controller is equipped with a 15-pin Type “D” connector:
To open the valve, apply a TTL low to pin 4 or connect pin 4 to signal ground (pin 12).
To close the valve, apply a TTL low to pin 3 or connect pin 3 to signal ground (pin 12).
If the 1179 flow controller is equipped with a 9-pin Type “D” connector:
To open the valve, apply a +5 Volt signal to pin 1.
To close the valve, apply ground to pin 1.
Note
To control with a TTL signal, use a tri-stated device.
If the 1179 flow controller is equipped with an Edge Card connector:
To open the valve, apply a TTL low to pin D or connect pin D to signal ground (pin 10).
To close the valve, apply a TTL low to pin L or connect pin L to signal ground (pin 10).
Priority of the Commands
The 1179 flow controller executes commands based on a hierarchical command structure. The
highest priority command is Valve Open, followed by Valve Close, and Set Point Control.
Therefore, if the flow controller is operating under Set Point Control, you can send a Valve Open
command to force the valve to the full open position.
Note
When both the Valve Close and Valve Open pins are pulled down, the
Valve Open command takes precedence and the valve is moved to the
open position.
