Patent Application
20070071646
1. Technical Field
The present invention relates to analytical instruments, and more particularly, to a system and method for regulating temperature inside an instrument housing.
2. Description of Related Art
Analytical instruments are apparatuses used to analyze material samples. Examples of analytical instruments include microscopes and spectrometers. A spectrometer disperses particles or radiation according to some property (e.g. mass or energy) and measures the dispersion. In a mass spectrometer, ions from a sample are dispersed according to mass-to-charge (m/z) ratios. The amount of dispersion is measured to determine properties of the sample. For example, this measurement may be used to identify a compound in the sample according to the mass of one or more elements in the compound. This measurement may also be used to determine the isotopic composition of one or more elements in the compound.
Analytical instruments such as microscopes and mass spectrometers often have temperature sensitive components. For example, analytical instruments may include passive components (e.g. resistors, capacitors or inductors) that output a different value depending on the passive component's operating temperature. For example, a resistor outputs a different resistance (e.g. in ohms) depending on the resistor's operating temperature. In addition there are strain gauge effects and other well known electronic quirks which are typically ignored as insignificant relative to the overall system performance. For example, the IC lead to circuit board connection at every pin has a thermocouple effect of c.a. 10 microvolts per degree Celsius.
Analytical instruments may also include active components (e.g. diodes or transistors) that exhibit a number of changes as a function of temperature. For example, bulk resistance of silicon decreases as temperatures rises, as does the forward voltage of a bipolar junction. Leakage currents also typically increase with an increase in operating temperature.
These temperature dependent changes may significantly affect an analytical instrument's operation. For example, the instrument's operation may rely on a digital logic circuit output signal. A typical digital logic circuit produces an output signal in delayed response to an input signal (e.g. a clock signal). The delay between input and output signals is often dependent on the temperature of an integrated circuit (IC) implementing the circuit because the switching speeds of the gates forming the IC is temperature dependent. In electrical engineering, a temperature dependent change in the output of a circuit component (e.g. the change in this delay) is sometimes referred to as “thermal drift”.
The term “thermal drift” is also sometimes used to refer to temperature induced deformation of materials. The degree of deformation is dependent on a particular material's coefficient of thermal expansion. For example, in a microscope with an arm supporting high magnification optics above a sample, the size of the arm and coefficient of thermal expansion of materials (such as aluminum) composing the arm sometimes cause a misalignment between consecutive microscope images. The deformation which causes the misalignment is sometimes referred to as “thermal drift” as well.
Therefore, as used herein, the term “thermal drift” will refer generally to changes to a component's characteristics (e.g. value, output or physical form) which are a function of the component's temperature. Short term thermal drifts are reversible changes in which a component's characteristic returns to its previous value once the temperature reverts to a previous value, however, even reversible changes do not return to their accurate initial conditions due to hysteresis effects. Permanent thermal drifts are changes which are not reversible and often depend on the component's operating temperature and therefore, in the context of circuits, on the circuit's thermal design.
In certain instruments, such as high precision spectrometers and high magnification microscopes, even minor thermal drift can have a significant impact on the instrument's accuracy and performance. To reduce the effect of thermal drift on an instrument's accuracy and performance, conventional methods typically attempt to control a thermal environment surrounding the entire instrument. For example, conventional methods often place an instrument having temperature sensitive components in a room having a precisely controlled climate. Under this method, the entire room is maintained within a specific temperature range. Individuals using the instrument work inside this climate-controlled environment, and therefore under potentially uncomfortable conditions.
Other methods to reduce the effect of thermal drift use software to mathematically adjust results. The software is calibrated and/or trained using empirical data, a process which may be expensive and time-consuming depending on the instrument and the precision desired.
The present invention provides apparatus and methods for regulating temperature inside an instrument housing. One method transfers coolant from a cooler to a heat exchanger and draws air through the heat exchanger into a housing enclosing a temperature sensitive component of the instrument.
Particular implementations of the method can include one or more of the following features. The coolant can be used to influence the temperature of another component of the instrument before returning the coolant to the cooler. The drawn air can be used to maintain each of a plurality of compartments at different substantially constant temperatures. The rate at which coolant is transferred to the heat exchanger can be based on data from a temperature sensor inside the housing or on the ambient temperature outside the housing.
The invention further includes a system that can perform such a method. Particular implementations of the system can include one or more of the following features. The instrument can include an analytical instrument such as mass spectrometer. The housing can comprise a plurality of compartments, each compartment maintained at a different substantially constant temperature. The instrument can include a temperature sensor inside the housing to measure the temperature of the air drawn over the temperature sensitive component. The instrument may comprise a dew point sensor.
The invention can be implemented to realize one or more of the following advantages. The thermal drift of temperature sensitive components can be reduced, thus reducing the effects of thermal drift on an instrument's accuracy and performance. The need for other methods such as software to mathematically compensate for the effects of thermal drift can be reduced or eliminated, these other methods typically being expensive and time-consuming, and dependent on the precision desired.
Other aspects of the invention will be apparent from the accompanying figures and the detailed description which follow.
A system and method for regulating temperature inside an instrument housing is disclosed. Coolant is transferred to a heat exchanger disposed adjacent to an opening in the housing. Using the coolant, the heat exchanger regulates the temperature of air drawn through the heat exchanger and into the housing.
By regulating the temperature of air drawn into the housing, the operating temperatures of temperature sensitive components inside the housing are also regulated. This regulation can reduce thermal drift and increase the instrument's accuracy and performance. In certain embodiments of the invention, the operating temperature of other components in the instrument are also regulated by transferring coolant used by the heat exchanger to other structures and/or components of the instrument.
The following provides variations and examples of various aspects of embodiments of the invention. It will be appreciated that the following variations and examples are not intended to be exhaustive or to limit the invention to the precise forms disclosed. These variations and examples are to provide further understanding of embodiments of the present invention.
In one embodiment, analytical instrument 102 is a mass spectrometer. The mass spectrometer may be, for example, a quadrupole mass spectrometer (e.g. shown in
The temperature sensitive component 112 may be one or a combination of an integrated circuit (IC), a digital-to-analog converter (DAC) subsystem, an operational amplifier, a gain setting resistor, a radio frequency (RF) detection diode, a trace on a circuit board, a tank circuit or a coil assembly, for example. In certain embodiments, the temperature sensitive component 112 is part of a control system, e.g. a circuit controlling the analytical instrument, as will be described in further detail below.
In
Openings 114 and 116 allow air to flow through housing 110. An air flow path in accordance with one embodiment of this invention is described in further detail in relation to
In certain embodiments, housing 110 is composed of a thermally conducive material, e.g. aluminum or copper, to help dissipate thermal energy away from the instrument. In certain embodiments, housing 110 is composed of electrically conductive material, e.g. aluminum or copper, to act as an electrical ground for a circuit (e.g. in a control system) disposed inside the housing. In certain embodiments, housing 110 is composed of corrosion resistant material, e.g. titanium.
In certain embodiments, to protect against corrosion, housing 110 and heat exchanger 120 are composed of similar material. For example, in one embodiment, housing 110 and heat exchanger 120 are both composed of aluminum. When the housing and heat exchanger are composed of the same material, physical contact between the housing and the heat exchanger does not expose either to galvanic corrosion.
The amount of physical contact between the heat exchanger 120 and the housing 110 depends on the dimensions of the heat exchanger 120 relative to the opening 114 in the housing 110. If the dimensions of the opening are small relative to the dimensions of the heat exchanger, more of the heat exchanger's surface may be in physical contact with the housing. Dimensions and shapes of the opening and the heat exchanger vary depending on the embodiment of the invention. In one embodiment, the opening is circular and the heat exchanger has a circular cross-section that fits into or over the opening. In another embodiment, the opening is rectangular and the heat exchanger has rectangular cross-section that fits into or over the opening. In one embodiment, the rectangular opening is approximately 6 to 7 inches by 9 to 10 inches and a portion of the heat exchanger slides into the opening, extending approximately 2 inches deep into the housing.
Heat exchanger 120 is disposed adjacent to the opening 114 such that air outside the housing flows into the housing through the heat exchanger. In
Cooler 130 pumps coolant to and through heat exchanger 120 to allow the heat exchanger 120 to regulate the temperature of air drawn into the housing (e.g. air 122B) and over a temperature sensitive component 112. Typically, the coolant acts as a heat sink, absorbing thermal energy from air that flows through the heat exchanger 120 into the housing 110. In certain instances, to maintain the air inside the housing at a stable temperature, the coolant may also act as a heat source, adding thermal energy to the air that flows through the heat exchanger and into the housing.
In certain embodiments, the coolant flow rate is a function of the volume of air being drawn into the housing, the temperature of the air outside the housing (e.g. air 122A), and/or a temperature desired for the air inside the housing (e.g. air 122B). For example, in one embodiment, the coolant flow rate is proportional to the volume of air being drawn into the housing (ratecoolant flow ∝ volume air drawn into housing). In certain embodiments, air is drawn into the housing using fans disposed inside the housing (e.g. in
In certain embodiments, the coolant flow rate is proportional to a difference between the temperature of the air outside the housing and a temperature desired for the air inside the housing (ratecoolant flow ∝ temperatureair outside housing—desired temperatureair inside housing). In other words, the coolant flow rate is greater when the difference is greater. Accordingly, the coolant flow rate may vary depending on the location of the instrument.
In certain embodiments, a temperature sensor 121 coupled to the heat exchanger provides data used to adjust the coolant flow rate. When the sensor is mounted outside the housing, data from the sensor may be used to adjust the coolant flow rate based on the temperature of air outside the housing. When the sensor is mounted inside the housing, data from the sensor may be used to adjust the coolant flow rate based on the temperature of air inside the housing. In the latter scenario, the sensor provides feedback data to allow the system 100 to determine when the temperature inside the housing reaches a desired temperature. Based on the feedback data, the system 100 may automatically increase or decrease the rate at which coolant is transferred to the heat exchanger, thereby allowing the heat exchanger to maintain the air inside the housing at a specific substantially constant temperature independent of temperatures outside the housing.
In one embodiment, the instrument is placed outdoors such that the air temperature outside the instrument's housing fluctuates with varying sunlight. A temperature sensor provides data to allow the system to adjust the coolant flow rate to maintain the air inside the housing at a substantially constant temperature independent of the air temperature outside the housing. During the daytime, the flow rate may be higher than at night, for example. In addition to the flow rate, in embodiments in which the heat exchanger substantially alters the air's temperature as it flows through the heat exchanger and into the housing, other variables such as the temperature of the coolant and/or the air flow rate may also be adjusted.
In certain embodiments, the heat exchanger alters the air's temperature only slightly to account for the minor fluctuations in ambient air temperature. These slight alterations still allow the heat exchanger to maintain the air temperature inside the housing stable, however. In such embodiments, the air temperature inside the housing is dependent on the ambient air temperature. For example, in one embodiment, the instrument is placed in a room with an ambient temperature of around 20° C.±2° C. The heat exchanger uses the coolant to maintain the air inside the instrument's housing at a stable 20° C. When the same instrument is moved to another room with an ambient temperature of around 15° C.±2° C., the heat exchanger again uses the coolant to maintain the air inside the instrument's housing stable, but this time at 15° C. rather than 20° C. Accordingly, the heat exchanger may maintain the air inside the housing at a temperature which is either dependent on or independent of the air outside the housing.
The coolant may be any liquid that can absorb thermal energy. For example, in certain embodiments, the coolant includes methanol, ethylene glycol, propylene glycol, water or nitrogen. In one embodiment, the coolant is a combination of propylene glycol and water, a 50/50 percentage mixture. In another embodiment, the coolant is a combination of ethylene glycol, water and a bitter-tasting agent (e.g. denatonium benzoate).
In
Cooler 130 pumps coolant through channels 132A-B. In one embodiment, cooler 130 is an immersion cooler, e.g. a Neslab cooler from Thermo Electron Corporation. Cooler 130 maintains the coolant at a certain temperature, e.g. 23° C. In one embodiment, cooler 130 is coupled to a dew point sensor 134. Data from dew point sensor 134 is used to determine the temperature at which to maintain the coolant in the cooler 130. By adjusting the coolant temperature based on data from the dew point sensor 134, the system 100 can prevent the heat exchanger 120 from cooling the air drawn into the housing to a temperature that would lead to condensation inside the housing. In one embodiment, dew point sensor 134 is coupled to a drip tray to collect condensation that may form near the system, e.g. near the cooler or near the heat exchanger.
In the embodiment of
The ion source 204 ionizes a sample material under analysis (sometimes referred to as the analyte). In certain embodiments, the ion source is an atmospheric pressure chemical ionization (APCI) source or a heated electrospray ionization (ESI) source. In other embodiments, the ion source is an atmospheric pressure photo-ionization (APPI) source, an atmospheric pressure photo-chemical-ionization (APPCI) source, a matrix assisted laser desorption ionization (MALDI) source, an atmospheric pressure MALDI (AP-MALDI) source, an electron impact ionization (EI) source, a chemical ionization (CI) source, an electron capture ionization source, or a fast bombardment source or a secondary ions (SIMS) source. The ions from the ion source 204 are transported (e.g. by magnetic or electric fields) to the mass analyzer 206.
Mass analyzer 206 is coupled to ion source 204 and uses an electric or magnetic field to deflect the ions from the ion source 204. In a quadrupole mass spectrometer, the mass analyzer 206 includes a quadrupole (or “quad”) which consists of four parallel rods. In a triple quadrupole (or “triple quad”) mass spectrometer, three quadrupoles are used, such as Q1, Q2 and Q3 shown in
Ion detector 208 is coupled to the mass analyzer 206 and detects ions exiting the mass analyzer 204. The ions detected produce a spectrum. Knowing properties of the mass spectrometer (e.g. the length of the mass analyzer and/or the strength of the magnetic or electric field used to accelerate the ions), the spectrum may be analyzed to determine numbers of ions at certain mass-to-charge ratios.
The mass spectrometer 202 of
Temperature sensitive component 112 may include, for example, an integrated circuit (IC), a digital-to-analog converter (DAC) subsystem, an operational amplifier, a gain setting resistor, a radio frequency (RF) detection diode, a trace, or a tank circuit mounted on the PCB. In other embodiments, temperature sensitive component 112 is inside PCB 210, e.g. a trace the inside the PCB.
In certain embodiments, temperature sensitive component 112 includes components coupled to the PCB but not mounted on or in the PCB. For example, in one embodiment, temperature sensitive component 112 may be or include coil assembly 216, which acts as a tank circuit for the control system. In
Therefore, as can be understood from
The embodiment shown in
Air filter 222 is disposed adjacent to the heat exchanger 120. Similar to heat exchanger 120, air filter 222 may be disposed inside or outside the housing. In the embodiment shown in
In other embodiments, the air filter is disposed outside the housing 110 while the heat exchanger 120 is disposed inside the housing 110, as shown in
Like heat exchanger 120, air filter 222 may be a variety of dimensions and shapes. For example, air filter 222 may be a round panel air filter with a radius that allows the filter to cover a circular opening. Air filter 222 may also be a rectangular panel air filter with a width and height that allows the filter to cover a rectangular opening.
In certain embodiments, after the coolant is used to maintain the drawn air at a substantially constant temperature, thereby minimizing thermal drift experienced by temperature sensitive components inside the housing, the coolant may be used for other purposes, e.g. to dissipate heat from a vacuum pump or a radio frequency (RF) generator.
For example, the channel 226 may be part of a “water jacket” surrounding the vacuum pump. A water jacket is a liquid-filled (e.g. water-filled) void surrounding a device. Water jackets typically are metal (e.g. copper) sheaths having intake and outlet vents to allow liquids to be pumped through the void.
In certain embodiments, channel 226 is part of a water jacket surrounding a radio frequency (RF) generator or amplifier. In those embodiments, the coolant is used to dissipate heat originating from the RF generator or amplifier. The coolant may also be used to maintain the RF generator or amplifier relatively isothermal.
In
Therefore, as can be understood from
These other structures or components may be disposed inside or outside the instrument housing. For example, the coolant may regulate the thermal temperature of heating sources associated with ion source 204 which is disposed outside the housing 110 in
In certain embodiments, the other structure or component to be regulated is or includes a radio frequency (RF) amplifier, a vacuum pump, a flange disposed between an ion source and a mass analyzer, a quadrupole, or a flight tube. For example, in one embodiment, the coolant is used to cool a radio frequency (RF) amplifier. By cooling an RF amplifier using coolant rather than a fan, mechanical noise and vibrations in the system, which often lead to undesirable microphonics, is reduced. Microphonics is a phenomenon in which certain components in electronic devices transform mechanical vibrations into an undesired electrical signal (noise). Therefore, by using the coolant to cool the RF amplifiers, microphonics may be reduced and the instrument's performance improved.
In addition to using to the coolant to regulate the temperature of these other structures or components, fans may route the temperature regulated air inside the housing to various compartments enclosing these other structures or components. For example, a fan may be used to draw the air in the housing into a compartment (e.g. compartment 224 in
In
The thermal environment surrounding a vacuum housing (not shown) containing Q1, Q2 and Q3 may be regulated by drawing the air inside the housing into the compartment before expelling the air back out of the housing. In certain embodiments, the temperature of compartment 224 may differ from the temperature of the compartment enclosing temperature sensitive component 112. In other words, in certain embodiments, the instrument housing may include a plurality of compartments and each of the plurality of compartments may be maintained at a different, yet substantially constant, temperature.
For example, one compartment may be maintained at 10° C. while another compartment may be maintained at 25° C. The temperature of each of these compartments may be maintained using air drawn through heat exchanger 120 into housing 110, the coolant, or a combination thereof.
As can be understood from the discussion above, in certain embodiments, coolant and/or air drawn into an instrument housing may be used to regulate the temperature of more than one component and/or more than one compartment in an analytical instrument. One such embodiment is shown in
In one embodiment, data from one or more of these sensors 314A-E are used to adjust the speed of fans 312A and 312B to alter the air flow rate into the housing 110, and thereby regulate the temperature of air inside the housing. In other embodiments, data from one or more of these sensors 314A-E are used to adjust the coolant flow rate or coolant temperature to regulate the temperature of air inside the housing.
In one embodiment, the data is transmitted to a control system inside the housing, e.g. a processor mounted on the printed circuit board 210. In other embodiments, the data is transmitted to a control system outside the housing, e.g. a processor inside or coupled to the cooler.
In
Ion transit time through the flight tube 306 is dependent on the length of the flight tube. Changes in the thermal environment surrounding the flight tube may cause the length of the tube to change as the tube's material expands and contracts in response to changes in temperature. As can be seen from
At 404, air is drawn through the heat exchanger into a housing enclosing a temperature sensitive component (e.g. an IC). As previously discussed, this air may be drawn into the housing by a fan, such as squirrel cage fans mounted inside the housing. The air may also flow through a plurality of compartments. An air flow path in accordance with one embodiment of this invention is illustrated in
In the embodiment shown of
At 508, the coolant flows to a vacuum pump before returning to the cooler. In one embodiment, the coolant flows to the vacuum pump by flowing into a water jacket surrounding the pump, as previously described. In the embodiment shown in
At 604, the air (at ambient temperature) flows through a heat exchanger. Using coolant from a cooler, the heat exchanger regulates the temperature of the air drawn into the housing such that the air is at a controlled temperature. In one embodiment, the heat exchanger cools the air as it passes through the exchanger so that the temperature of the air inside the housing is lower than the temperature of the air outside the housing. In another embodiment, the heat exchanger may heat the air as it passes through the exchanger in order to maintain the temperature of the air inside the housing at a substantially constant temperature as the ambient air fluctuates around a certain temperature.
At 606, the air flows from the heat exchanger through an air filter. As previously discussed, in certain embodiments, the air may flow through the air filter before flowing through the heat exchanger. At 608, the air flows from the air filter into a first compartment and over a temperature sensitive component (e.g. temperature sensitive component 112). In one embodiment, the first compartment does not enclose the temperature sensitive component. Rather, the first compartment is an air intake region with an opening to another compartment enclosing the temperature sensitive component (e.g. in
In the embodiment of
Thus, a system and method for regulating temperature inside an instrument housing is disclosed. In the above detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that these specific details need not be used to practice the present invention. In other circumstances, well-known structures, materials, or processes have not been shown or described in detail in order not to unnecessarily obscure the present invention.
Although the present invention is described herein with reference to a specific preferred embodiment, many modifications and variations therein will readily occur to those with ordinary skill in the art. Accordingly, all such variations and modifications are included within the intended scope of the present invention as defined by the following claims.
Furthermore, the use of the phrase “one embodiment” throughout does not necessarily mean the same embodiment. Although these particular embodiments of the invention have been described, the invention should not be limited to these particular embodiments. Accordingly, the specification and drawings are to be regarded in an illustrative sense rather than a restrictive sense.
