Patent Application
20070290382
Other objects and advantages of the invention may become apparent upon reading the following detailed description and upon reference to the accompanying drawings.
While the invention is subject to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and the accompanying detailed description. It should be understood, however, that the drawings and detailed description are not intended to limit the invention to the particular embodiments which are described. This disclosure is instead intended to cover all modifications, equivalents and alternatives falling within the scope of the present invention as defined by the appended claims.
One or more embodiments of the invention are described below. It should be noted that these and any other embodiments described below are exemplary and are intended to be illustrative of the invention rather than limiting.
As described herein, various embodiments of the invention comprise systems and methods for reducing temperature variations induced by flow control equipment in process fluids by separating heat-producing portions of the control equipment from portions of the equipment which handle or are in close proximity to a fluid flow path.
In one embodiment, a fluid handling device (e.g., a flow controller, pump or other fluid handling device) is designed for use in manufacturing processes in which temperature control of the process fluid being handled by the flow controller is critical. Consequently, it is desirable to move components of the fluid handling device that may affect or the temperature of the process fluid away from the fluid flow path and to thermally isolate these components. The fluid handling components in this embodiment are therefore contained in a first enclosure, while the heat-generating components are contained in a second enclosure. Although the various components are interconnected (e.g., by wires or pneumatic lines) to allow them to interact and function in the same way as components of conventional fluid handling devices, an air gap is maintained between the two enclosures to provide the needed thermal isolation.
In this embodiment, the fluid handling components are contained in a plastic enclosure which is sealed. Heat-generating components such as the control electronics of the system are contained in another enclosure. This enclosure, according to one embodiment, can be a fully metal enclosure or can be an enclosure with a metal inner housing and a plastic outer housing. The control electronics enclosure does not have any vents, but is instead sealed, as is desirable in many manufacturing environments. The enclosures are positioned with an air gap of approximately 1.25 inches between them. This gap is maintained by spacers that are positioned between the enclosures, and which connect the enclosures to each other. The spacers are tubes made of an insulating material such as polypropylene or other suitable material (e.g., Teflon or other material) to prevent conduction of heat through the spacers. The control lines which interconnect the heat generating components with the fluid handling components are run through one of the spacer tubes which is sealed at both ends to prevent convective transfer of heat between the enclosures.
For the sake explanation, embodiments of the present invention will be described in conjunction with a flow controller. Before describing the exemplary embodiments of the invention, it may be helpful to describe more conventional designs for flow controllers. Referring to
After fluid enters flow controller 100, it flows through a flow path that consists of an inlet conduit 171, flow control valve 110, intermediate conduit 172, restrictive flow element 130, and outlet conduit 173. Restrictive flow element 130 may be any type of element that causes a pressure drop in the fluid flow path corresponding to the rate at which the fluid is flowing through the path, such as an orifice plate, a small diameter tube, a constriction in the fluid flow path, or the like. The purpose of restrictive flow element 130 is simply to create a pressure drop which can be measured by pressure sensors 140 and 145. Because the characteristic flow rate of the fluid through restrictive flow element 130 as a function of this pressure drop is known, the measured pressure drop can be used to calculate the rate at which the fluid is flowing through the restrictive flow element, hence through the fluid flow path. Restrictive flow element 130 does not control the fluid flow rate, but simply provides a pressure drop across the element corresponding to the current flow rate. The flow rate of the fluid is adjusted by adjusting the setting of fluid flow control valve 110. Flow control valve 110 may be any suitable type of valve, such as a throttling valve, a poppet valve, a butterfly valve, or the like. Flow control valve 110 may be driven by any appropriate means, including, but not limited to, pneumatic actuators, stepper motors and the like. It should be noted that while in the embodiment of
As pointed out above, pressure sensors 140 and 145 are used to measure the pressure drop across restrictive flow element 130. Pressure sensors 140 and 145 may be any suitable type of sensors, including, for example, capacitance type sensors, piezoelectric sensors, transducer-type sensors, and the like. The portion of each sensor that is exposed to the process fluid should be inert with respect to the fluid. Pressure sensor 140 is positioned adjacent to and upstream from resistive flow element 130. Pressure sensor 145, the other hand, is positioned adjacent to, but downstream from restrictive flow element 130. Pressure sensors 140 and 145 do not, themselves, impede the flow of the fluid through flow controller 100, but simply measure the fluid pressure in the flow path immediately prior to and following restrictive flow element 130. Each of pressure sensors 140 and 145 generates a raw electrical signal corresponding to the sensed fluid pressure. Pressure sensor 140 provides its pressure measurement signal to control system 150 via sensor line (wire) 180, while pressure sensor 145 provides its pressure measurement to the control system via sensor line 185. Because control system 150 is positioned in close physical proximity to pressure sensors 140 and 145, it is not necessary to amplify the raw measurement signals from the pressure sensors before providing the signals to the control system.
Control system 150 calculates a pressure drop across restrictive flow element 130 based upon the signals received from pressure sensors 140 and 145. The pressure drop may be calculated by control system 150 in a variety of ways. As noted above, the signals received from pressure sensors 140 and 145 are raw signals, so control system 150 may convert each raw signal into a pressure measurement and then subtract the pressure corresponding to the signal of pressure sensor 145 from the pressure corresponding to the signal of pressure sensor 140 to determine the pressure drop. Alternatively, control system 150 may simply take the difference between the raw signals received from pressure sensors 140 and 145 and determine the pressure drop across restrictive flow element 130 from this difference. Other alternatives may also be possible.
After control system 150 has determined the pressure drop across restrictive flow element 130, this pressure drop is compared to a target value. The target value is a desired pressure drop that corresponds to a desired flow rate through flow controller 100. If the sensed pressure drop is less than the target value, the fluid flow rate through flow controller 100 is too low, so the flow rate should be increased. If, on the other hand, the sensed pressure drop is greater than the target value, the flow rate through the flow controller is too high, so the flow rate should be decreased. Control system 150 may employ proportional-integral (PI,) proportional-integral-derivative (PID,) or any other suitable control scheme. Control system 150 increases or decreases the flow rate of the fluid through flow controller 100 by sending appropriate signals to control valve actuator 120. Upon receiving these control signals from control system 150, actuator 120 takes appropriate action to adjust flow control valve 110. For example, if actuator 120 uses a stepper motor to adjust to the flow control valve, the actuator will move the mechanical linkage between itself and the flow control valve by an appropriate number of steps.
Referring to
Referring to
The components of fluid flow controller 100 which actually handle the fluid (i.e., flow control valve 110, restrictive flow element 130, pressure sensors 140, 145) do not generate a significant amount of heat which can be transferred to the fluid. Control system 150, on the other hand, consumes electrical power as it processes the pressure sensor data, determines whether the fluid flow rate is too high or too low, ends generates control signals to drive the flow control valve (via the control valve actuator.) As a result, control system 150 dissipates energy, heating its environment, including other components in flow controller 100. The heating of these components can affect the control of the process fluid in several ways. For example, the heat transferred to the components may then be transferred to the fluid itself. The heating of the fluid can cause the viscosity of the fluid to change. This is detrimental to flow control because flow controllers are often calibrated for a particular viscosity fluid. If the fluid heats and changes viscosity, the calibration curves used by the flow controller to correlate a pressure drop to flow rate may not longer be accurate. Additionally, heating of components can be detrimental as it may cause the components to behave differently than they would in the absence of this heating (e.g., heating of a temperature sensitive pressure sensor can cause the readings of the pressure sensor to drift.)
The present systems and methods therefore isolate at least some of the heat-generating components of the flow controller from the fluid handling components are in order to prevent the generated heat from adversely affecting the operation of the flow controller or from being conveyed to the process fluid itself. The isolation of these components is illustrated in
Referring to
As depicted in the figure, the fluid handling portion of flow controller 200 is housed within a first enclosure 260, while the control portion of the components are housed in a second enclosure 265. As pointed out above, the fluid handling portion of the flow controller includes components that do not generate a significant amount of heat. Consequently, they do not significantly alter the temperature of the process fluid when the fluid flows through or near these components. Some of the control components of this system, however, such as control system 250 do generate a significant amount of heat which could be transferred to the process fluid if not for the separation of these components from the fluid handling components. Thus, the present system isolates the fluid handling portion of the flow controller from the heat generated by some of the components without causing the problems posed by remote location of the control components (e.g., the need to amplify sensor signals in the fluid handling enclosure.) It should be noted that control valve actuator 220 is depicted in
As shown in
Referring to
In this embodiment, enclosure 260 is made of plastic. The plastic serves to provide some insulation between the fluid handling components in the sealed enclosure and the environment external to the enclosure. Enclosure 265, on the other hand, can be fully metal or can include, for example, a metal inner housing to house the electronics and a plastic outer housing that is exposed to the process environment. According to another embodiment, an all plastic enclosure can be used that is preferably coated to prevent RF transfer with an EMI coating or other coating. Because of the environments in which the flow controller is typically used, it is desirable for all of the components of the flow controller to be in sealed enclosures. Since the enclosures need to be sealed for some applications, enclosure 265, which contains the heat generating components, cannot be vented to allow cooling air flow through the enclosure. The metal construction of enclosure 265 (or the inner portion of enclosure 265) allows heat to be dissipated through the walls of the enclosure.
Spacers 295 between the enclosures consist of polypropylene or other material tubes. The polypropylene serves as an insulator, so that heat is not conducted from enclosure 265, through the spacers to enclosure 260. (It should be noted that the additional insulating material may also be used between the enclosures to augment the thermal isolation of the air gap.) In this embodiment, the spacers are approximately 1.25 inches long to maintain a corresponding air gap between the enclosures. Empirical testing with different sizes of air gaps indicated that, when using flow controller enclosures as described above, 1.25 inches is a sufficient air gap to prevent any significant heating of the fluid handling enclosure resulting from heating in the enclosure containing the heat generating components at start-up of the controller. (The temperature in the upper enclosure increased by approximately 30 degrees Fahrenheit during start-up.) By comparison, an air gap of 0.75 inches resulted in the temperature in the fluid handling enclosure increasing by about 1 degree Fahrenheit during start-up. It should be noted, of course, that the optimal size of the air gap may depend upon a number of factors, such as the amount of heat generated in the control system enclosure, the insulating properties of the spacers, the amount of airflow through the air gap, and so on.
In this embodiment, a conduit 292 is placed between upper enclosure 265 and lower enclosure 260, and interconnects between components in the two enclosures are routed through the conduit. Conduit 292 is a polypropylene or other material tube similar to spacers 295. Each end of conduit 292 is connected to one of the enclosures at an opening through which the interconnects extend. Conduit 292 is sealed at each end (around the interconnects) so that each enclosure remains sealed. It should be noted that there are no openings in enclosures 260 or 265 where spacers 295 are connected to the enclosures.
It should be noted that the particular structures described above are exemplary. While the various embodiments of the invention are distinctive in their isolation of heat generating components of the flow controller from the fluid handling components, the particular components and structures employed in the different embodiments may vary. For example, alternative embodiments may employ fluid flow measurement mechanisms other than that described above, in which pressure sensors are positioned upstream and downstream from a restrictive flow element to measure a pressure drop across the element so that a corresponding flow rate can be determined. Any suitable means can be used to measure fluid flow parameters, compute flow rates, generate control signals, and so on.
It should be noted that various components of the foregoing embodiments have not been described in detail because these components are of essentially the same type and configuration as used in prior art systems. For example, the construction and configuration of flow control valves are also well known. Similarly, the general structure, configuration and operation of control systems for flow control valves are known. Despite the use of these known components, the particular arrangement of the components, as described above and claimed below, is believed to be distinctive of the prior art.
Those of skill in the art will understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and the like that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. The information and signals may be communicated between components of the disclosed systems using any suitable transport media, including wires, metallic traces, vias, optical fibers, and the like.
Those of skill will further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, software (including firmware,) or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Those of skill in the art may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
The various illustrative logical blocks, modules, and circuits described in connection with the electronic circuits disclosed herein may be implemented or performed with application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), general purpose processors, digital signal processors (DSPs) or other logic devices, discrete gates or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be any conventional processor, controller, microcontroller, state machine or the like. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.
The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in software (program instructions) executed by a processor, or in a combination of the two. Software may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. Such a storage medium containing program instructions that embody one of the present methods is itself an alternative embodiment of the invention. One exemplary storage medium may be coupled to a processor, such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside, for example, in an ASIC. The ASIC may reside in a user terminal.
It should be further noted that embodiments of the present invention can be applied to other types of fluid handling devices, such as dispense pumps. In this example, the electronics for driving the pump(s) can be separated from the fluid handling portions of the pump by an air gap. Again, the electronics can be housed in a metal or metal and plastic enclosure spaced from the pump body through which fluid flows. The electronics can be connected to components of the pump via conduits as described above. The enclosure that encloses the fluid handling components can be the pump body itself.
The benefits and advantages which may be provided by the present invention have been described above with regard to specific embodiments. These benefits and advantages, and any elements or limitations that may cause them to occur or to become more pronounced are not to be construed as critical, required, or essential features of any or all of the claims. As used herein, the terms “comprises,” “comprising,” or any other variations thereof, are intended to be interpreted as non-exclusively including the elements or limitations which follow those terms. Accordingly, a system, method, or other embodiment that comprises a set of elements is not limited to only those elements, and may include other elements not expressly listed or inherent to the claimed embodiment.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein and recited within the following claims.
