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Series 830/840/860 Instruction Manual Chapter 3 Operation
IM-83/84/86-H 3-5
On-Off Control and Soft Start Option
On-off control is provided for all models equipped with an elec-
tromagnetic valve. This feature is available by connecting a man-
ual
on-off switch to the transducer connector as shown in Chapter 2.
Certain processes cannot tolerate the normally fast response of Si-
erra mass flow controllers. In these cases a “soft start” circuit
slows the mass flow controller’s valve response characteristics to
avoid any bursts of flow that could disrupt a delicate process or
perhaps stir up particulate.
The standard soft start time constant is 1.5 seconds, providing a 7.5
second response time to within 2 percent of final value. The time
constant is factory-set to fit your exact requirements.
Figure 3-1. Soft Start Response Times
The Model 860 provides valve on-off and soft start control with ei-
ther the manual hardware option, or with digital (software) control
via RS-485. For more information, refer to the Series 860 “Auto-
Net” Software Addendum.
Caution!
Do not use the manual
valve-off feature when
RS-485 is active.