Vector 750 Watt Power Inverter User Manual download pdf (Page 21)

IV. CLOSED LOOP CONTROL

In “Leaks: the Good, the Bad and the Ugly” we saw

how closed loop control is applied in a mass flow

controller with the control input being supplied by the

flow sensor with a solenoid proportioning valve as the

variable flow control element. The same approach can

be applied on a larger scale to a vacuum system. Figure

4 on the next page represents an extension to the

previous example with closed loop pressure control.

This particular configuration is referred to as upstream

pressure control. This is because we are driving a valve

that is upstream of the chamber.

Proportioning valves are an important element in

vacuum systems. Figure 5 depicts the general

configuration of a solenoid proportioning valve.

This type of valve uses the magnetic field

developed by a solenoid to move a magnetic armature

the Bell Jar, Vol. 10, No. 3/4, Summer/Fall 2001

Figure 4 -

Figure 2 - Ace Glass 8741 Vacuum Regulator. “Increased sensitivity

and versatility over other models, mercury requirement is reduced to

20-30cc. A control point within 1mm Hg can be fine-tuned by adjusting

the height of the pump-out tubulation. The Cartesian driver float drops

away from pump-out orifice on an increas- ing system pressure and

reseals it when the reference pressure set within large bulb is

reattained. Reference pressure is easily set. The spherical joint allows

the attitude of the orifice to be adjusted to accomodate a small

continuous leak without hunting of the float.” $430.12 in 2007.

Vacuum Chamber

Pressure

Gauge

Leak

Valve

Throttle Valve

To Pump

Gas

Supply

Figure 3 - Manual Pressure Control Elements

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Vector 750 Watt Power Inverter User Manual Page 21