MKS 653B - Chapter Three: Operation; Theory of Operation

Chapter Three: Operation Theor
y
of O
p
eration
19
Chapter Three: Operation
Theory of Operation
The 653 Exhaust Throttle Valve is one of three components in a closed loop, downstream
pressure control system. When coupled with a smart self tuning controller, such as the 651
controller, and a high accuracy Baratron

capacitance manometer, the 653 valve provides fast,
reproducible set point control. The Baratron senses the chamber pressure which is then
compared to the desired set point pressure in the pressure controller. The pressure controller
commands the valve to open or close, thereby adjusting the chamber pressure to the desired
process pressure set point.
Throttle valves, such as the 653 valve, provide:
•
Good control over a wide dynamic range
•
High conductance
•
Fast response
Using the Type 651, 1651, or 652 pressure controller in conjunction with the 653 valve has
another advantage. The flow rate of the 653 valve, like all throttle valves, is non-linear with
respect to position; that is, the percent change in flow rate ranges from very large values when
the valve is near the closed position, to zero when the valve is near the fully open position. Due
to this large change in transfer characteristic, gain and phase lead must be reset each time a valve
operates at a different position (to achieve optimum performance). The 651 and 652 self-tuning
pressure controllers alleviate this situation with the use of a special software algorithm designed
to compensate for the non-linearity in the valve.
Note
Revision A of the 652 controller
does not support
the 653 valve. Your
652 pressure controller must be at Revision B or later.