Fluid handling – Line condition change responsive valves – Pilot or servo controlled
Reexamination Certificate
2000-04-24
2001-11-13
Michalsky, Gerald A. (Department: 3753)
Fluid handling
Line condition change responsive valves
Pilot or servo controlled
C137S487500
Reexamination Certificate
active
06314992
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a flow rate control apparatus adaptable for a variety of fluids, such as gases, for use in the manufacture of such products as semiconductors, chemicals, and precision machine parts. More specifically, the present invention relates to a fluid-switchable flow rate control system that permits high-precision control of the flow rates of a variety of fluids with the use of a single orifice over specific ranges of flow rate. The orifice mounted in the present fluid-switchable flow rate control system is replaceable, so that the type of fluid and the flow rate range can be widely varied.
2. Description of the Prior Art
Mass flow rate controllers have been widely used in fluid supply systems for such manufacturing facilities as for semiconductors and chemical products.
FIG. 7
shows an example of a high-purity moisture generator for use in semiconductor manufacturing facilities. Three kinds of gases—H
2
gas, O
2
gas and N
2
gas—are introduced into a reactor RR through valves V
1
to V
3
, with the flow rates regulated by mass flow rate controllers MFC
1
to MFC
3
. That is, first, valve V
3
is opened with valves V
1
and V
2
kept closed, and the reactor RR is purged with N
2
gas. Then, valve V
3
is closed and valves V
1
and V
2
are opened to feed H
2
gas and O
2
gas to the reactor RR at specific flow rates. In the reactor RR, H
2
gas and O
2
gas are allowed to react into H
2
O with platinum serving as catalyst without combustion. The high-purity water vapor thus produced is supplied to production facilities (not shown).
Mass flow rate controllers each have undergone linear correction and adjustment for a specific gas and flow range, and cannot be used for gases other than that for which the mass flow rate controllers are adjusted. Therefore, the mass flow rate controllers MFC
1
to MFC
3
are installed for H
2
gas, O
2
gas and N
2
gas respectively, that is, one particular mass flow rate controller for one particular gas as shown in FIG.
7
. Another problem is that even with the same gas, the mass flow rate controller itself will have to be replaced when the flow range, that is, the full scale flow rate is to be changed.
For a gas supply system as shown in
FIG. 7
, replacement is stocked for mass flow rate controllers MFC
1
to MFC
3
. Those mass flow rate controllers themselves are expensive and so are their replacement parts. That boosts equipment costs and running costs.
Linearity correction and adjustment takes a long time. If the linearity correction and adjustment is effected for a new gas each time types of gases and flow ranges are changed instead of replacing the mass flow rate controller, the production plant has to be temporarily shut down. For this reason, it is necessary to have spare mass flow rate controllers in stock at all times.
SUMMARY OF THE INVENTION
The fluid-switchable flow rate control system according to the present invention addresses those problems with the mass flow rate controller. The present invention provides a flow rate control system which controls the flow rate of fluid with the pressure P
1
on the upstream side of the orifice held about twice or more higher than the downstream pressure P
2
, the fluid-switchable flow rate control system comprising an orifice member replaceable with another to provide a suitable orifice diameter according to the kind of fluid and the flow rate range, a control valve provided on the upstream thereof, a pressure detector provided between the control valve and the orifice member, and a flow rate calculation circuit where from the pressure P
1
detected by the pressure detector, the flow rate Qc is calculated with the equation Qc=KP
1
(K:constant), a flow rate-setting circuit for outputting flow rate setting signal Qe, a flow rate conversion circuit for converting the calculated flow rate signal Qc into calculated switch-over flow rate signal Qf to change the full scale flow rate and a calculation control circuit to output the difference between that calculated switch-over flow rate signal Qf and the flow rate setting signal Qe as control signal Qy to the drive for the control valve, thereby opening or closing the control valve to bring the control signal Qy to zero, thus controlling the flow rate on the downstream side of the orifice member.
The invention provides a flow rate control system as described above wherein the flow rate conversion circuit is configured so that the calculated flow rate Qc is multiplied by conversion rate k into the calculated switch-over flow rate signal (Qf(Qf=kQc).
The invention also provides a flow rate control system wherein the flow rate conversion circuit regulates the amplification rate of an output amplifier of the pressure detector.
The present invention provides a flow rate control syustem as defined above wherein the flow rate conversion circuit is a DIP switch or dual in-line switch.
The invention provides a fluid-switchable flow rate control system which controls the flow rate of fluid with the pressure P
1
on the upstream side of the orifice held about twice or more higher than the downstream pressure P
2
, the fluid-switchable flow rate control system comprising an orifice member replaceable with another to provide a suitable orifice diameter according to the kind of fluid and the flow rate range, a control valve provided on the upstream thereof, a pressure detector provided between the control valve and the orifice member, and a flow rate calculation circuit where from the pressure P
1
detected by the pressure detector, the flow rate Qc is calculated with the equation Qc=KP
1
(K=constant), a flow rate-setting circuit for outputting flow rate setting signal Qe, a flow rate conversion circuit for converting the flow rate setting signal Qe into flow rate specifying signal Qs to change the full scale flow rate and a calculation control circuit to output the difference between the flow rate specifying signal Qs and the calculated flow rate Qc as control signal Qy to the drive for the control valve, thereby opening or closing the control valve to bring the control signal Qy to zero, thus controlling the flow rate on the downstream side of the orifice member.
The invention provides a flow rate control system as wherein the flow rate conversion circuit is so configured that the flow rate setting signal Qe is multiplied by the flow rate conversion rate k into the flow specifying rate signal Qs (Qs=kQc).
REFERENCES:
patent: 6178995 (2001-01-01), Ohmi et al.
Hirose Jun
Kagatsume Satoshi
Nishino Kouji
Ohmi Tadahiro
Fujikin Incorporated
Griffin & Szipl, P.C.
Michalsky Gerald A.
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