ALES, Richard, A. (32010 Sedgefield Oval, Solon, OH, 44139, US)
1. Solenoid control circuit, comprising: a solenoid coil; an input that is connectable to a voltage source and couples a first voltage to said coil; a boost circuit that produces a second voltage that is coupled to said coil and is sufficient to energize the solenoid; said first voltage being sufficient to hold the solenoid in an energized state after said second voltage is removed.
2. The circuit of claim 1 wherein said boost circuit comprises a voltage multiplier circuit connected to said input, said multiplier circuit producing said second voltage that is higher than said first voltage.
3. The circuit of claim 2 wherein said boost circuit is selected from one or more of the following: capacitor charge pump, Dickson charge pump, voltage multiplier, DC to DC converter.
4. The circuit of claim 1 comprising a logic circuit that controls application of said second voltage to said coil for a time period sufficient to energize the solenoid and then removes said second voltage.
5. The circuit of claim 4 wherein said logic circuit comprises a switch that controls energizing the solenoid by closing a circuit between said coil and said voltages.
6. The circuit of claim 5 wherein said solenoid is deenergized when said switch is open.
7. System for controlling fluid flow, comprising: one or more solenoid valves, each solenoid valve controlling flow of a process fluid to a process;
a solenoid valve actuation circuit that applies a pull-in voltage to energize said solenoid valve and a hold-in voltage sufficient to maintain said solenoid valve in an energized state, said hold-in voltage being less than said pull-in voltage.
8. The system of claim 7 wherein said actuation circuit comprises a boost circuit that has an input coupled to said hold-in voltage and produces said pull-in voltage at its output.
9. The system of claim 8 wherein said boost circuit is selected from one or more of the following: capacitor charge pump, Dickson charge pump, voltage multiplier, DC to DC converter.
10. The system of claim 8 wherein said actuation circuit comprises a logic circuit that controls when said pull-in voltage is coupled to said solenoid valve.
11. The system of claim 10 wherein said logic circuit removes said pull-in voltage from said solenoid valve after said solenoid valve is energized, said hold-in voltage maintaining said solenoid valve in an energized state after said pull-in voltage is removed.
12. The system of claim 11 wherein said logic circuit disconnects said hold-in voltage from said solenoid valve to deenergize said solenoid valve.
13. The system of claim 7 comprising at least two solenoid valves, said actuation circuit separately controlling operation of each of said solenoid valves.
14. The system of claim 13 comprising a process control valve for each said solenoid valve, each solenoid valve controlling actuation of its respective process control valve, each process control valve controlling flow of a process fluid.
15. The system of claim 14 wherein each process control valve comprises a stream selector valve.
16. The system of claim 14 wherein each process control valve is a pneumatically actuated valve and its associated solenoid valve comprises a pilot valve that controls actuation air to said process valve.
17. A method for controlling a solenoid comprising: boosting a first voltage to a higher second voltage; applying said second voltage for a time period sufficient to energize the solenoid; reducing the applied voltage from said second voltage to said first voltage wherein said first voltage is sufficient to maintain the solenoid in an energized state.
18. The method of claim 17 comprising removing said first voltage to deenergize the solenoid.
19. The method of claim 17 comprising controlling flow of pressurized air in response to operation of the solenoid.
20. The method of claim 19 comprising controlling flow of a process fluid in response to said pressurized air flow.
21. The circuit of claim 1 comprising two or more solenoids, each solenoid being operable individually in response to said first and second voltages.
SOLENOID CONTROL CIRCUIT
 This application claims the benefit of pending United States provisional application serial number 60/829,747 filed on October 17, 2006 for SOLENOID CONTROL CIRCUIT, the entire disclosure of which is fully incorporated herein by reference.
 Numerous industries and technologies utilize process fluids, including biopharmaceutical, petrochemical, semiconductor and so on. The process fluids may at times need to be sampled and analyzed, or the flow of such fluids may need to be controlled as part of a process. Many different types of flow control devices have been developed to control the flow of process fluids. One such device is generally known as a stream selector which may include one or more valves that control flow. Some stream selectors are pneumatically actuated, meaning that pressurized air moves a piston that opens and closes the various valves.
 Solenoid actuated valves are also well known and commonly used throughout many industries. Typical solenoid valves include a solenoid energized plunger that moves in response to voltage applied across the solenoid coil. Often times, the plunger is spring biased so that a higher voltage is used to pull-in or actuate the valve and a lower voltage is used to hold-in or maintain the valve actuated. A common technique is to ballast a higher input voltage to a lower voltage to reduce coil heating. This approach, however, is not conducive to an intrinsically safe design.
BRIEF DESCRIPTION OF THE DRAWINGS
 Fig. 1 is a functional block diagram of a system for controlling fluid flow, incorporating various inventive aspects of this disclosure;
 Fig. 2 is an exemplary functional block diagram of a solenoid actuation circuit for a single solenoid;
 Fig. 3 is an exemplary timing diagram for the circuit of Fig. 2; and
 Fig. 4 is another exemplary functional block diagram of a solenoid actuation circuit for multiple solenoids.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
 The disclosure is directed to systems for controlling fluid flow, and also methods and apparatus for controlling operation of a solenoid or solenoid actuated valve. Such solenoid and solenoid valve aspects may be used, for example, in the described system for controlling fluid flow. Although various inventive aspects of the present disclosure are described in terms of the exemplary embodiments utilizing stream selector valves, solenoid pilot valves and exemplary related circuits, such descriptions are intended to be exemplary and not limiting. Inventive aspects relating to solenoid and solenoid valve control may find application anywhere a solenoid or solenoid actuated valve is used. The inventive aspects as to fluid flow control, solenoid control and solenoid valve control may also find application in different flow control systems that utilize flow control devices other than stream selectors or pneumatically actuated valves.
 While various inventive aspects, concepts and features of the inventions may be described and illustrated herein as embodied in combination in the exemplary embodiments, these various aspects, concepts and features may be used in many alternative embodiments, either individually or in various combinations and sub-combinations thereof. Unless expressly excluded herein all such combinations and sub-combinations are intended to be within the scope of the present inventions. Still further, while various alternative embodiments as to the various aspects, concepts and features of the inventions— such as alternative materials, structures,
configurations, methods, circuits, devices and components, software, hardware, control logic, alternatives as to form, fit and function, and so on—may be described herein, such descriptions are not intended to be a complete or exhaustive list of available alternative embodiments, whether presently known or later developed. Those skilled in the art may readily adopt one or more of the inventive aspects, concepts or features into additional embodiments and uses within the scope of the present inventions even if such embodiments are not expressly disclosed herein. Additionally, even though some features, concepts or aspects of the inventions may be described herein as being a preferred arrangement or method, such description is not intended to suggest that such feature is required or necessary unless expressly so stated. Still further, exemplary or representative values and ranges may be included to assist in understanding the present disclosure, however, such values and ranges are not to be construed in a limiting sense and are intended to be critical values or ranges only if so expressly stated. Moreover, while various aspects, features and concepts may be expressly identified herein as being inventive or forming part of an invention, such identification is not intended to be exclusive, but rather there may be inventive aspects, concepts and features that are fully described herein without being expressly identified as such or as part of a specific invention, the inventions instead being set forth in the appended claims. Descriptions of exemplary methods or processes are not limited to inclusion of all steps as being required in all cases, nor is the order that the steps are presented to be construed as required or necessary unless expressly so stated.
 With reference to Fig. 1, a system for controlling fluid flow is generally indicated by the numeral 10. The system 10 may be used, for example, to control the flow of a process media or fluid F, and may, for example, be used to control N process streams where N>1. A typical application of the system 10 may be in the instrumentation field, for example, sampling and analyzing various process fluids F N used in or by a process P. For example, one type of process may be chromatography or chemical liquid, gas and/or vapor. Many other examples will be readily apparent to those skilled in the art.
 Process fluid flow may be controlled by a process valve 12. Typically a separate process valve (12 I -12 N ) is used for each process fluid, process or sampling/analyzer. An example of a process valve 12 is a SSV Series stream selector, model SS-SSV- V-X-F2 available
from Swagelok Company, Cleveland, Ohio. Many other types of process valves may be used to control flow of the process fluid. In the exemplary embodiments of this disclosure the process valve(s) 12 is pneumatically actuated.
 Pressurized air +PA is provided to each of the process valves 12 by a respective control device 14. In the exemplary embodiment, each control device 14 may be realized in the form of a solenoid actuated valve 16, such as a pilot valve model EI-2M-15.5 available from Clippard Instrument Laboratory Inc.. For separate individual control of each process valve 12 N there may be provided a respective pilot valve 16 N - Alternatively, a single pilot valve may be used to control one or more or all of the process valves when simultaneous operation may be desired. The solenoid valves 16 provide pressurized air since the process valves are pneumatic, but other solenoid actuated valves may be used as needed based on the type of process valve used. Whenever it is desired to actuate a process valve 12, the corresponding pilot valve 16 is opened to supply pressurized air to the process valve.
 Control of the pilot valve 16 N ~ and thus control of the process valves 12 N and process fluid F N flow as well ~ is carried out by a solenoid actuation or control circuit 18. The actuation circuit 18 controls which solenoid valves 16 N are actuated and when, in response to a command signal 20. The command signal 20 may be any signal that is recognized by the actuation circuit 18 to open and close the various solenoid valves 12 N and 16 N - Thus, the command signal 20 is provided by a controller (not shown) that determines when the various valves 16 N are to be actuated as part of the overall process P. The command signal 20 may be coupled to the actuation circuit 18 by any convenient means such as a network bus, wireless, fiber optic and so on. The command signal 20 may also be an operator controlled or manually actuated control signal.
 Fig. 2 illustrates an exemplary functional block diagram of the solenoid actuation or control circuit 18. Fig. 3 is an exemplary timing diagram for the circuit of Fig. 2. Although Fig. 2 illustrates a control circuit for a single solenoid, in an alternative embodiment the control function may be implemented for two or more solenoids as illustrated in Fig. 4.
 With reference to Figs. 2 and 3, the circuit 18 includes a boost circuit 22, a logic circuit 24 and a solenoid circuit 26. Physically these circuits may all be contained on a common circuit board but they need not be so arranged. The circuit functions may also be combined in different ways with different circuits. In one embodiment, the control circuit 18 may be as simple as a supply voltage, a circuit to increase for a short time period the supply voltage to a coil that is sufficient to pull-in the solenoid, and then returning the voltage to a hold-in voltage which may be the supply voltage. Moreover, the solenoid circuit 26 is illustrated in schematic form to include the solenoid coil Ci though in practice the coil Ci may physically be part of another component such as the solenoid valve 16 of Fig. 1. A typical solenoid includes a coil and a plunger, but for purposes of the electrical circuit only the coil is represented.
 In the exemplary embodiment of Figs. 2 and 3, an input 28 receives a voltage
VCC. This voltage typically will be but need not be a digital signal and in the exemplary embodiment may be about +9.5 VDC. This voltage is selected based on overall circuit parameters and a minimum hold-in voltage across the coil Ci needed to keep the solenoid energized after is has pulled-in. This generally minimized voltage level significantly reduces power consumption when the solenoid is energized, and also reduces voltage to the circuit 18 to meet intrinsic safety (IS) requirements for those applications where IS is either mandated or desirable.
 The voltage VCC is coupled to the high side of the solenoid coil Ci through a blocking diode 30. The voltage VCC also is input to the boost circuit 22. The boost circuit 22 may be realized in many different forms and configurations as will be readily apparent to those skilled in the art. The function of the boost circuit is to provide at its output 32 an increased voltage VPULL-IN that is sufficient to ensure that the solenoid coil Ci will develop enough magnetic flux to energize or pull-in the solenoid. Thus, the output 32 of the boost circuit 22 is coupled to the high side of the solenoid coil Ci (noting that the low side of the coil typically is at ground). The blocking diode 30 isolates the boost circuit output from the VCC input.
 The boost circuit 22 may be realized using any well known circuit design, such as for example, a capacitor charge pump, Dickson charge pump, voltage doubler, or boost switch
mode DC to DC converter to name a few examples, or a custom circuit may be used. The boost circuit output 32 may simply be a multiple of the input voltage VCC but need not be.
 The logic circuit 24 may be used to control timing of the solenoid actuation by controlling the timing of when the pull-in voltage and hold-in voltage are applied across the solenoid coil Ci. The logic circuit 24 may be realized in many different ways including digital logic, part of a controller, analog circuits and so on. The function of the logic circuit 24 is such that when a command signal 20 input is received ~ indicating that the solenoid valve 14 is to open and thus activate the process valve 12, the logic circuit produces a first or ENABLE output 34 to the boost circuit 22. This enable signal causes the boost circuit to charge up. When the ENABLE signal 34 is removed, the output 32 is an open circuit or high impedance so as to not load the input VCC.
 The ENABLE signal 34 is applied for a suitable time period to allow the boost circuit to charge. After an appropriate delay, the logic circuit produces and output H or HOLD signal 36 which actuates a control switch 38. The control switch 38 is in series between the high side of the coil Ci and a common node 40 for the pull-in voltage VPULL-IN and the blocking diode 30. The control switch 38 may be any suitable switch such as an FET, relay and so on.
 When the control switch 38 is closed, the higher voltage VPULL-IN is applied across the coil Ci to energize the solenoid. The ENABLE signal is then removed, which causes the boost circuit output 32 to drop out. This causes the voltage across the coil to drop to about VCC or the hold-in voltage. The solenoid can be deenergized by removing the signal HOLD which opens the switch 38 to isolate the coil Ci from the node 40. A flyback diode 42 may be provided to suppress any transient spikes when the control switch 38 is opened. The HOLD signal may be removed, for example, when the command input 20 is removed.
 Fig. 3 is an exemplary timing diagram for the circuit of Fig. 2. At time TO the
COMMAND signal enables the boost circuit 22 to charge up to voltage VPULL-IN that is at least sufficient to energize and pull-in the solenoid. At time Tl the HOLD signal 36 closes the control switch 38 and the solenoid is energized. The ENABLE signal 34 goes low after pull-in so that the voltage across the coil Ci drops to about VCC or the hold-in voltage needed to keep the
solenoid energized. At time T2 the COMMAND signal goes low causing the HOLD signal to go low and opening the control switch 38 which deenergizes the solenoid. The duration of the time periods Tl and T2 will vary depending on the components used and overall system design. The boost circuit 22 thus functions to provide an on demand pulse for solenoid actuation that avoids the need to supply or store a high voltage to the circuit. This is more conducive to an overall intrinsically safe design and also has a default voltage of 0 volts.
 Fig. 4 illustrates a control circuit 50 that may be used for controlling multiple solenoids. The basic circuit is similar to Fig. 2 except that there are N solenoids with a corresponding N solenoid circuits 52 N - In this embodiment a single boost circuit 54 may be used to provide the pull-in voltage needed by the solenoids. The input voltage VCC may also be used by all the solenoids.
 In the embodiment of Fig. 4, individual and separate control of each solenoid is effected by using multiple input COMMAND signals 56 N and multiple output HOLD signals 58 N . Because the pull-in voltage 60 is shared by more than one solenoid, each solenoid circuit 52 N includes a second control switch 62. This switch responds to an additional output from the logic circuit 64 which is identified as the PULL-IN signal 66. The second control switch 62 is used to isolate the non-selected solenoids when the boost circuit output is used to energize one or more of the solenoids. For example, if solenoid circuit 1 is to be energized, a command signal CMDl is received and the ENABLE signal EN 68 causes the boost circuit 54 to charge up. After an appropriate delay, the PULL-IN signal Pl goes high and the HOLD signal Hl goes high, thus energizing the solenoid associated with solenoid circuit 1 (52i). The ENABLE signal 68 may still be a pulse that goes low after the solenoid is pulled in. Alternatively, the signal 68 may be a steady output voltage since the solenoid circuits 52 N include the second control switch 62. The solenoids are deenergized by removing the COMMAND signal to cause the HOLD signal to go low and open the first switch Sl.
 Note that the embodiment in Fig. 4 may be modified to control two or more solenoids to pull-in at the same time, either by receiving simultaneous COMMAND signals or by sharing common PULL-IN and HOLD signals.
 Reference may be made to the above incorporated provisional application for an exemplary embodiment of a boost circuit and related circuits of the embodiment of Figs. 1-4, however, as noted, the inventive aspects of the solenoid control functions may be carried out with any of a wide variety of circuits and techniques that take a first voltage, boost or increase the first voltage to a second voltage for a period of time that is sufficient to pull-in a solenoid, and then reduce to the first voltage that is sufficient to hold in the solenoid.
 The inventions have been described with reference to the preferred embodiment.
Modifications and alterations will occur to others upon a reading and understanding of this specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.