MKS 1579A, Instruction Manual

Page: 37 / 87

1579A/579A Chapter 5: Operation (Analog Units)
37
Override the Control Valve
The valve override feature enables the control valve to be fully opened (purged) or closed
independent of the set point command signal:
To open the valve, apply a TTL low to pin 4 or connect pin 4 to pin 5 (analog ground).
To close the valve, apply a TTL low to pin 3 or connect pin 3 to pin 5 (analog ground).
Priority of Commands
The 1579 flow controller executes commands based on a hierarchical command structure. The
highest priority command is Valve Open, followed by Valve Close, and finally the 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.