WO2001061284A1 - Method and apparatus for balancing resistance - Google Patents
Method and apparatus for balancing resistance Download PDFInfo
- Publication number
- WO2001061284A1 WO2001061284A1 PCT/US2001/004609 US0104609W WO0161284A1 WO 2001061284 A1 WO2001061284 A1 WO 2001061284A1 US 0104609 W US0104609 W US 0104609W WO 0161284 A1 WO0161284 A1 WO 0161284A1
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- Prior art keywords
- amplifier
- resistor
- electrically coupled
- input
- resistance
- Prior art date
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/76—Devices for measuring mass flow of a fluid or a fluent solid material
- G01F1/86—Indirect mass flowmeters, e.g. measuring volume flow and density, temperature or pressure
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
- G01F1/684—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow
- G01F1/6847—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow where sensing or heating elements are not disturbing the fluid flow, e.g. elements mounted outside the flow duct
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
- G01F1/696—Circuits therefor, e.g. constant-current flow meters
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
- G01F1/696—Circuits therefor, e.g. constant-current flow meters
- G01F1/698—Feedback or rebalancing circuits, e.g. self heated constant temperature flowmeters
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P5/00—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft
- G01P5/001—Full-field flow measurement, e.g. determining flow velocity and direction in a whole region at the same time, flow visualisation
Definitions
- the present invention is directed to resistance balancing, and more particularly to a mass flow sensor that is capable of detecting the mass flow rate of a fluid by balancing the resistance of upstream and downstream temperature sensors.
- Mass flow sensors are used in a wide variety of applications to measure the mass flow rate of a gas or other fluid.
- One application in which a mass flow sensor may be used is a mass flow controller.
- the mass flow rate of a fluid flowing in a main fluid flow path is regulated or controlled based upon a mass flow rate of a portion of the fluid that is diverted into a typically smaller conduit forming a part of the mass flow sensor. Assuming laminar flow in both the main flow path and the conduit of the sensor, the mass flow rate of the fluid flowing in the main flow path can be determined (and regulated or controlled) based upon the mass flow rate of the fluid flowing through the conduit of the sensor.
- a fluid flows in a sensor pipe or conduit in the direction of the arrow X.
- Heating resistors or "coils" Ri and R 2 having a large thermal coefficient of resistance are disposed about the sensor conduit on downstream and upstream portions of the sensor conduit, respectively, and are provided with a constant current I from a constant current source 901.
- voltages V and V 2 are developed across the coils.
- the difference between voltages Vi and V 2 (V ⁇ -V 2 ) is taken out of a differential amplifier 902, with the output of the amplifier 902 being proportional to the flow rate of the fluid through the sensor conduit.
- the circuit of Fig. 1 is configured so that the resistance value (and thus, the temperature) of coil Ri is equal to the resistance value (and temperature) of coil R . and the output of the amplifier 902 is zero.
- the resistance value (and thus, the temperature) of coil Ri is equal to the resistance value (and temperature) of coil R . and the output of the amplifier 902 is zero.
- heat that is generated by coil R 2 and imparted to the fluid is carried towards R
- the temperature of coil R decreases and that of coil Ri increases.
- voltage Vi increases with an increased rate of fluid flow and voltage V decreases, with the difference in voltage being proportional to the mass rate of flow of the fluid through the sensor conduit.
- An advantage of a constant current mass flow sensor is that it can operate over a wide range of temperatures, is relatively simple in construction, and is responsive to changes in the ambient temperature of the fluid entering the sensor conduit. In this regard, as the ambient temperature of the fluid entering the sensor conduit changes, so does the resistance of each of the coils R] and R 2 . However, it takes a relatively long time for the temperature (and thus, the resistance) of the coils Ri and R 2 to stabilize in response to a change in the rate of flow of the fluid.
- the other type of mass flow sensor that is frequently used is a constant temperature mass flow sensor, examples of which are illustrated in Figs. 2-4. As shown in the constant temperature mass flow sensor of Fig.
- heating resistors or "coils” R ⁇ a and Ri b are respectively disposed about the downstream and upstream portions of a sensor conduit through which a fluid flows in the direction of the arrow X.
- a and Ri b has a large thermal coefficient of resistance.
- the resistance (and thus the temperature) of each of the coils Ri a , Rib is fixed by separate and independent circuits to the same predetermined value that is governed by the value of resistors R 2a , R 3a , R ⁇ , and R 2 b, R 3b , R4 b , respectively.
- Control circuitry is provided to maintain each of the coils R ⁇ a , Ri b at the same predetermined value of resistance (and thus, temperature) independently of the rate of fluid flow through the sensor conduit.
- the circuit of Fig. 2 is configured so that the resistance (and temperature) of each of the downstream and upstream coils R) a and Ri b is set to the same predetermined value and the output of the circuit is zero.
- heat from the upstream coil Rib is carried towards R ⁇ a .
- less energy is required to maintain the downstream coil R ⁇ a at the fixed temperature than is required to maintain the upstream coil Ri b at that same fixed temperature.
- the difference in energy required to maintain each of the coils R] a , Rib at the predetermined temperature is measured and is proportional to the mass flow rate of fluid flowing through the sensor conduit.
- the constant temperature mass flow sensor described with respect Fig. 2 is also relatively easy to construct.
- the circuit of Fig. 2 stabilizes more quickly in response to changes in the mass flow rate of the fluid entering the sensor conduit than the constant current mass flow sensor described with respect to Fig. 1.
- each of the coils ⁇ a and R] is set and maintained at a predetermined temperature independently of the ambient temperature of the fluid flowing into the sensor conduit, a problem arises when the ambient temperature of the fluid flowing into the sensor conduit increases.
- the circuit loses its ability to discern differences in the flow rate of the fluid, and when the ambient temperature of the fluid increases beyond this predetermined temperature, the sensor is rendered inoperable.
- the circuit of Fig. 3 provides a constant temperature mass flow sensor that is capable of responding to changes in the ambient temperature of a gas or fluid, at least to a certain degree.
- Ri b and R 2b are downstream and upstream temperature sensing coils with a large temperature coefficient of resistance.
- the circuit of Figure 3 maintains the temperature of the sensor coils Ri b , R 2b at a temperature that is above the ambient temperature of the fluid flowing into the sensor conduit.
- resistor R 3b must have the same value and the same (ideally large) thermal coefficient of resistance as resistor R4b
- resistor R 5b must have the same value and same (ideally zero) thermal coefficient of resistance as resistor R 6 b
- resistor R 7b must have the same value and same (ideally zero) thermal coefficient of resistance as resistor Rio b
- resistor R 9b must have the same value and same (ideally zero) thermal coefficient of resistance as resistor R 8 b
- amplifiers 91 1 and 912 must have the same operating and temperature characteristics.
- a problem with the circuit of Fig. 3 is that as the ambient temperature of the fluid flowing into the sensor conduit rises, the sensor becomes less accurate because the proportional difference between the temperature of the upstream and downstream coils relative to the temperature of the ambient fluid becomes smaller. Further, there is a problem due to drift in that the calibration of the sensor at one temperature does not necessarily allow its use at other ambient temperatures without some sort of compensation circuit.
- U.S. Patent No. 5,401,912 proposes a constant temperature rise (above ambient) mass flow sensor, an example of which is shown in Fig. 4.
- the circuit of Fig. 4 acts to maintain upstream and downstream sensor coils R 2 , Ri at a predetermined value above the ambient temperature of the fluid flowing into the sensor conduit.
- the circuit of Fig. 4 is identical to the circuit of Fig. 2, except that the fixed value resistors R 3a and R 3b of Fig. 2, which have an essentially zero thermal coefficient of resistance, are replaced with resistors R 5 and R 6 , respectively, having a large and specific valued thermal coefficient of resistance.
- a mass flow sensor as is shown in Fig. 4 is therefore termed a constant temperature difference (over ambient) or a constant temperature rise (over ambient) mass flow sensor.
- Each of the aforementioned constant temperature mass flow rate sensors utilizes separate and independent upstream and downstream circuits to set the temperature of the upstream and downstream coils to a particular value, or to a particular value over the ambient temperature of the fluid flowing into the sensor conduit.
- a disadvantage of each of these circuits is that they require a close matching of corresponding circuit elements (i.e., resistors, coils, and amplifiers) in the upstream and downstream circuits.
- a sensor includes a first resistor, a second resistor, a first circuit, and a second circuit.
- the first and second resistors each has a resistance that varies in response to a change in a physical property.
- the first circuit is electrically coupled to the first resistor and sets the resistance of the first resistor.
- the second circuit is electrically coupled to the second resistor and adjusts the resistance of the second resistor to equal the resistance of the first resistor.
- a processing circuit may be coupled to the first and second circuits to measure a difference in an amount of energy provided by the first and second circuits to the first and second resistors, respectively.
- a mass flow sensor is provided.
- the sensor includes a first heat sensitive coil, a second heat sensitive coil, a first circuit, a second circuit, and a processing circuit.
- the first and second heat sensitive coils are disposed at spaced apart positions about a conduit through which a fluid flows, and each has a resistance that varies with temperature.
- the first circuit is electrically coupled to the first heat sensitive coil and sets the resistance of the first heat sensitive coil to a value that corresponds to a predetermined temperature.
- the second circuit is electrically coupled to the second heat sensitive coil and adjusts an amount of current provided to the second heat sensitive coil so that the resistance of the second heat sensitive coil equals the resistance of the first heat sensitive coil.
- the processing circuit is coupled to the first and second circuits and measures a difference in an amount of energy provided by the first and second circuits to the first and second heat sensitive coils, respectively.
- a method of balancing a resistance of a first resistor and a resistance of a second resistor is provided.
- the resistance of the first and second resistors vary with temperature, and the method includes acts of setting the resistance of the first resistor to a first value and providing an amount of current to the second resistor so that the resistance of the second resistor matches the first value of the first resistor.
- a method of setting the resistance of a resistor includes acts of: (a) measuring an ambient temperature of a fluid flowing into a conduit about which the resistor is disposed, (b) incrementing the ambient temperature measured in act (a) by a predetermined amount to identify a temperature to which the resistor is to be set, (c) calculating a value of resistance corresponding the temperature identified in act (b), (d) determining a division ratio to be provided by a programmable voltage divider to force the resistance of the resistor to the value calculated in act (c), and (e) configuring the programmable voltage divider to provide the division ratio determined in act ( i).
- Fig. 1 is a constant current mass flow sensor according to the prior art
- Fig. 2 is a constant temperature mass flow sensor according to the prior art
- Fig. 3 is a constant temperature mass flow sensor that is capable of responding to changes in an ambient temperature of a fluid according to the prior art
- Fig. 4 is another constant temperature mass flow sensor that is capable of responding to changes in an ambient temperature of a fluid according to the prior art
- Fig. 5 is a constant temperature mass flow sensor according to one embodiment of the present invention
- Fig. 6 A is a constant temperature mass flow sensor according to another embodiment of the present invention
- Fig. 6B is a flowchart of a temperature setting routine that may be used with the constant temperature mass flow sensor of Fig. 6A;
- Fig. 7 is a constant temperature mass flow sensor according to yet another embodiment of the present invention.
- Fig. 8 is a constant temperature mass flow sensor according to yet another embodiment of the present invention.
- Fig. 9 is a constant temperature mass flow sensor according to yet another embodiment of the present invention. Detailed Description
- Figs. 5, 6A, and 7-9 illustrate a number of different mass flow sensors according to various embodiments of the present invention.
- the reference designator Ri represents the upstream coil
- reference designator R 2 represents the downstream coil.
- coils Ri and R 2 are disposed at spaced apart positions about a sensor conduit (not shown) through which a fluid flows.
- the term fluid includes any material or combination of materials in a solid, liquid, or gaseous state.
- Each of coils R) and R 2 has a large and substantially identical thermal coefficient of resistance, such that the resistance of each coil Rj, R 2 varies with temperature.
- mass flow sensors according to embodiments of the present invention do not use separate upstream and downstream circuits to independently set the temperature of the upstream and downstream coils to an identical value. Rather, embodiments of the present invention use a common circuit to set one of the upstream and downstream coils to a predetermined temperature or to a predetermined temperature above ambient, and then supply an amount of current to the other of the upstream and downstream coils to force the resistance, and thus, the temperature, of the upstream and downstream coils to be equal. As a result, embodiments of the present invention do not require the close matching of component values and characteristics that is required in the separate upstream and downstream circuits of Figs. 2-4.
- Fig. 5 illustrates a simplified schematic diagram of a mass flow sensor according to one embodiment of the present invention.
- the circuit of Fig. 5 performs two main functions: setting the temperature of the downstream coil R 2 to a predetermined temperature, or to a predetermined temperature above the ambient temperature of the fluid flowing into the sensor conduit, and forcing the resistance value (and thus the temperature) of the upstream coil R] to equal that of the downstream coil R 2 .
- the circuit of Fig. 5 makes the resistance of the upstream coil Ri equal to the resistance of the downstream coil R 2 , independently of the actual numeric value of resistance to which the downstream coil R 2 is set. It should be appreciated that the operation of the circuit of Fig.
- the temperature of upstream coil Ri is set to a predetermined temperature, or to a predetermined temperature above the ambient temperature of the fluid flowing into the sensor conduit, and the resistance value (and thus, the temperature) of the downstream coil R is forced to equal that of the upstream coil Rj
- the difference in the amount of energy supplied to the upstream and downstream coils is proportional to the mass flow rate of the fluid flowing through the sensor conduit.
- a high gain operational amplifier 51 current generated by a high gain operational amplifier 51 is provided to two different resistive branches of the circuit; a first resistive branch being formed by the series connection of R' and R", and a second resistive branch formed by the series connection of R'" and R .
- the output of the operational amplifier 51 is buffered by a transistor T 5 that is configured as an emitter- follower and connected to a supply voltage Vcc by a resistor R.
- the combination of transistor T 5 and resistor R operates as a buffer circuit 55.
- Other types of buffer circuits may also be used, as the present invention is not limited to any particular implementation of buffer circuit 55.
- a buffer circuit 55 is depicted in each of Figs. 5, 6A, and 7-9, the present invention is not so limited.
- One of the inputs of the operational amplifier 51 is connected between the series connection of R' and R" of the first resistive branch, and the other is connected between the series connection of R'" and R 2 of the second resistive branch.
- the non-inverting (+) input of operational amplifier 51 is connected to the midpoint of the first resistive branch
- the inverting (-) input of the operational amplifier 51 is connected to the midpoint of the second resistive branch.
- the non-inverting (+) input of operational amplifier 51 is connected to the midpoint of the second resistive branch, with the inverting (-) input of the operational amplifier 51 being connected to the midpoint of the first resistive branch.
- coil R ⁇ Connected to coil R are coil R ⁇ , an adjustable current source 52 that provides an adjustable current ⁇ I, and a high gain operational amplifier 53.
- the inverting (-) input of operational amplifier 53 is connected to coil R 2 , coil Ri, and the adjustable current source 52. Because the non-inverting (+) input of operational amplifier 53 is coupled to ground, the connection point between coil R 2 , coil Ri, and the adjustable current source 52 is also at ground potential (i.e., is a "virtual ground").
- a buffer circuit similar to buffer circuit 55 may be connected between the output of operational amplifier 53 and coil Ri, or alternatively, the operational amplifier 53 may include a buffered output stage.
- resistor R" includes a programmable resistor having a resistance value that is calculated to set the resistance, and thus, the temperature of coil R to a predetermined value above the ambient temperature of the fluid flowing into the sensor conduit.
- the temperature of coil R 2 is set approximately 30° to 100° C above the ambient temperature of the fluid flowing into the sensor conduit, although the present invention is not limited to a particular value.
- resistor R" includes a resistor having a high thermal coefficient of resistance, such that when the ambient temperature of the fluid flowing into the sensor conduit changes, the resistance, and thus the temperature, of coil R 2 changes in a proportional manner.
- resistors R', R", and R' could alternatively include a variable or temperature dependent resistor.
- the series combination of R' and R" may be replaced by a programmable voltage divider that includes a digital to analog converter to set the resistance of coil R 2 to the desired value.
- R. V,/I, (1)
- R 2 V 2 /I 2 (2)
- I1 ⁇ I + I2 (3).
- the output voltages V) and V 2 may be provided to other processing circuits (not shown) that calculate, monitor, display, or regulate the mass flow rate of the fluid, based upon the values of output voltages V] and V 2 .
- output voltages V] and V may be provided to the inputs of an amplifier, with the output of the amplifier and the output voltage V 2 being provided to a division circuit that forms the ratio (V]-V )/V 2 .
- these other processing circuits are well known and understood by those skilled in the art, the details of such processing circuits are omitted herein.
- the mass flow sensor of Fig. 5 does not require a close matching of circuit components.
- resistor R' is stable over temperature
- the actual resistance values of resistors R', R", and R'" are not critical.
- Fig. 6A illustrates a schematic diagram of a mass flow sensor according to another embodiment of the present invention.
- that portion of the circuit designated by reference numeral 62 corresponds to one exemplary implementation of adjustable current source 52 in Fig. 5.
- the remaining portion of the circuit bearing reference numeral 61 corresponds to the remainder of the circuit in Fig. 5.
- buffer 55 (which may include the emitter-follower circuit shown in Fig. 5) provides current generated by operational amplifier 51 to two resistive branches of the circuit; the first resistive branch including resistors R " and R", and the second resistive branch including resistor R" ' and coil R 2 .
- one of the inputs of high gain operational amplifier 51 is connected between the series connection of R' and R" of the first resistive branch, with the other being connected between the series connection of R'" and R 2 of the second resistive branch.
- coil R 2 Connected to coil R 2 are coil Ri and the inverting (-) input of high gain operational amplifier 53, with the non-inverting (+) input of operational amplifier 53 being coupled to ground.
- adjustable current source 52 includes a unity gain instrumentation amplifier 63, a Digital to Analog Converter (DAC) 64, a unity gain operational amplifier 66, an Analog to Digital Converter (A/D) 65, and a proportional/integral/ differential (PID) controller 69.
- DAC Digital to Analog Converter
- A/D Analog to Digital Converter
- PID proportional/integral/ differential
- Inverting (-) input of instrumentation amplifier 63 is connected to the inverting (-) input of operational amplifier 51 and voltage V 2 , and the non-inverting (+) input of instrumentation amplifier 63 is connected to the output of buffer 55.
- V Ref the output of instrumentation amplifier 63 that is provided as the reference voltage input to DAC 64 is given by the following equation:
- V ⁇ c the output voltage of a digital to analog converter is governed by the following relationship: where V ef is the voltage reference input provided to the DAC, X is a digital input word provided to the DAC, and 2" is the maximum permitted value of the input word X. Accordingly, in Fig. 6A the output voltage provided by DAC 64 is given by the following equation:
- V DA c [l2R"' * X]/2 n (7).
- a circuit for generating a binary word X, that when provided as an input to DAC 64, causes the output of DAC 64 to provide an appropriate amount of current ( ⁇ I) to coil Ri so that the resistance of coil Ri equals that of coil R 2.
- the non-inverting (+) input of operational amplifier 66 receives voltage V] and the inverting (-) input of operational amplifier 66 receives voltage V 2 .
- the voltage V 2 is also provided as a reference voltage to the reference voltage input of A/D 65.
- Operational amplifier 66 therefore provides an output that is equal to the difference of Vi and V 2 to the input of the A/D 65.
- a more detailed implementation of a circuit for providing the difference between Vi and V 2 is illustrated in Fig. 6A by reference designator 66'.
- the A/D 65 generates a binary number X representing the ratio of V]-V 2 to V 2 , which, when provided to the input of DAC 64 after some additional processing, generates an appropriate amount of current ⁇ I to coil R] so that the resistance of coil R) equals that of coil R 2 .
- the circuit of Fig. 6A will tend to be unstable.
- the output X provided by the A/D 65 will cause the resistance of coil R ⁇ to diverge from that of R 2.
- the output (shown as X' in Fig. 6A) from A/D 65 may be input to a proportional/ integral/differential (PID) controller 69, with the output of the PID controller 69 being provided to the input X of DAC 64.
- PID proportional/ integral/differential
- the output X' of A/D 65 is provided to the feedback input of PID controller 69, with the output of the PID controller 69 being connected to the setpoint input of the PID controller 69.
- PID controller 69 As the use and construction of a PID controller and similar types of control circuits are well known to those skilled in the art, further discussion of the PID controller 69 is omitted herein. It should be appreciated that because the circuit of Fig. 6A forces the ratio of ⁇ I/I to be equal to the difference of V] and V 2 divided by V 2 , the circuit of Fig. 6A allows one to detect drift in the mass flow sensor.
- the quantity (Vi- V 2 )/V 2 changes proportionally, irrespective of the flow rate and ambient temperature of the fluid flowing into the sensor conduit. If at a time T ⁇ , a change in ⁇ I results in a particular value of change in the quantity (V ⁇ -V 2 )/V 2 , and at a later time T 2 , that same change in ⁇ I results in a different value of change in the quantity (V ⁇ -V 2 )/V 2 , it may be determined that the mass flow sensor has drifted. This is significant because in a typical mass flow sensor, it is nearly impossible to determine the difference between drift in the sensor and a change in the detected amount of flow.
- a number of corrective actions may be taken. For example, upon the detection of drift in the sensor, an alert condition may be set to notify personnel that the sensor has drifted. The sensor may then be returned to the manufacturer for re-calibration. Alternatively, upon the detection of drift in the sensor, a correction factor may be supplied to compensate for the drift.
- FIG. 6B A flowchart of an exemplary temperature setting routine that may be used with the constant temperature mass flow sensor of Fig. 6A is now described with respect to Fig. 6B.
- mass flow sensors frequently form but a portion of a mass flow controller.
- Other portions of the mass flower controller typically include one or more valves, a main flow path, and a processor (e.g., a CPU) that monitors and regulates the valves to control the amount of fluid flowing through the main flow path, according to the mass flow rate determined by the mass flow sensor.
- a processor e.g., a CPU
- a temperature setting routine may be implemented in software that executes on a processor of a mass flow controller to set the value of resistance of one of the upstream Ri and downstream R? coils of the sensor.
- the resistance balancing sensor circuits described with respect to Figs. 5 and 6A may be used to equalize the resistance of the other one of the upstream R ⁇ and downstream R 2 coils of the sensor.
- the mass flow rate of the fluid flowing in the conduit of the sensor By then detecting the difference in the amount of energy supplied to each of the upstream Ri and downstream R coils when their resistance is equal, the mass flow rate of the fluid flowing in the conduit of the sensor, and thus, the mass flow- rate of the fluid flowing in the main flow path may be determined.
- the temperature setting routine described below need not be implemented in software, but may alternatively be implemented by a dedicated state machine or other control logic.
- tne temperature setting routine of Fig. 6B may be modified to set the temperature o one of the upstream Ri and downstream R 2 coils to a predetermined temperature, rather than to a predetermined temperature above the ambient temperature of the fluid entering the sensor conduit.
- the temperature setting routine measures the ambient temperature of the fluid entering into the sensor conduit. This step may be performed, for example, by monitoring a thermometer (not shown) that is in thermal contact with the fluid entering into the sensor conduit, by monitoring a thermometer that is in thermal contact with the main fluid path, etc.
- the routine proceeds to step 611, wherein the routine determines a temperature to which one of the upstream Rj or downstream R 2 coils is set. For example, in the embodiment of Fig.
- the temperature to which the downstream coil R 2 is set may be based upon the following relationship:
- T TAmbient + TRise, (12), where T Amb i ent is the ambient temperature measured in step 601, and TRj se is a fixed value, such as 30° to 100°C. In general the value of T R j se should be at least several tens of degrees higher than the ambient temperature of the fluid entering into the sensor conduit, but not so high that it would create a problem with highly reactive fluids.
- step 621 the routine determines the appropriate value of resistance to which the downstream coil R 2 should be set based on the temperature of the coil (e.g., R ) determined in step 611.
- R the temperature of the coil
- step 621 the routine proceeds to step 631, wherein a division ratio that is to be set by the ratio of R'VR' is determined.
- the division ratio may be set by adjusting the resistance of one or more variable resistors, by using a programmable voltage divider circuit that includes a Digital to Analog Converter (DAC). or in other ways known to those skilled in the art.
- DAC Digital to Analog Converter
- the series combination of R' and R' ' may be replaced by a DAC (not shown) having a voltage reference input that receives the output of buffer circuit 55, an output that is coupled to the non-inverting (+) input of operational amplifier 51 , and an input that receives an appropriately valued input word X to provide the desired division ratio.
- a DAC not shown
- step 641 After determining the division ratio that is needed to set the resistance value of coil R 2 to the determined value, the routine proceeds to step 641, wherein the value of the ratio R'VR' determined at step 631 is set, and the routine terminates.
- Fig. 7 illustrates a mass flow sensor according to another embodiment of the present invention.
- the mass flow sensor of Fig. 7 does not use a computational circuit to set the amount of current ⁇ I that is provided by the adjustable current source (e.g., adjustable current source 62 in Fig. 6A). Instead, the circuit of Fig. 7 balances currents in various resistive branches of the circuit to maintain the upstream coil Ri and the downstream coil R at the same resistance value. In a manner similar to that described with respect to Figs.
- a large gain operational amplifier 71 having a non-inverting (+) input that is connected to the inverting (-) input of operational amplifier 51 , and an inverting (-) input that is fed back from the output of the operational amplifier 71.
- the operational amplifier 71 acts as a buffer to mirror the voltage V 2 and provide this voltage to R 2 '.
- R 2 ' and Ri ' Connected to the midpoint of a third resistive branch formed by R 2 ' and Ri ' is a high gain operational amplifier 72.
- the inverting (-) input of operational amplifier 72 is connected to the midpoint of the third resistive branch, with the non-inverting (+) input of operational amplifier 72 being coupled to ground.
- the output of operational amplifier 72 is fed back through R ⁇ ' and is also connected to coil Ri .
- a fourth resistive branch is formed by the series connection of R 2 and R ⁇ .
- Operational amplifier 72 acts to force the voltage at the midpoint of the third resistive branch formed by R 2 ' and Ri' to be equal to that at the midpoint of the fourth resistive branch formed by R 2 and Ri, with the result that the same proportional currents flow in R 2 ' and R and in Ri ' and Ri .
- the ratio of R 2 7R,' R 2 /R ⁇ .
- the remaining portion of the circuit of Fig. 7 designated by reference numeral 75 functions as an adjustable current source to provide an amount of current ⁇ I to the upstream coil Ri so that the resistance of coil Ri is equal to that of coil R .
- resistor R is connected between the inverting (-) input and the output of operational amplifier 53
- resistor R 3 ' is connected between the output of operational amplifier 53 and the midpoint of the third resistive branch formed by R 2 ' and Ri'
- the non-inverting (+) input of operational amplifier 53 is coupled to ground.
- high gain operational amplifier 71 may be replaced by a unity gain buffer.
- high gain operational amplifier 71 could be eliminated and resistor R 2 ' connected directly to the inverting (-) input of operational amplifier 51 , such that the ratio of R7R' ' is equal to R" ' divided by the parallel combination of R 2 and R 2 '.
- resistor R 2 ' connected directly to the inverting (-) input of operational amplifier 51 , such that the ratio of R7R' ' is equal to R" ' divided by the parallel combination of R 2 and R 2 '.
- those connections that are shown as being coupled directly to ground may alternatively be coupled to ground through one or more resistors.
- operational amplifiers 72 and 53 function to maintain the midpoints of the third and fourth resistive branches at a particular level
- other circuit topologies may be used to achieve a similar result.
- this input may instead be connected to the midpoint of the fourth resistive branch formed by coils R 2 and Ri, or alternatively, the non-inverting (+) input of operational amplifier 53 may instead be connected to the midpoint of the third resistive branch formed by resistors R ' and Ri'.
- the mass flow sensor of Fig. 7 is a constant temperature mass flow sensor, rather than a constant temperature rise (above ambient) sensor like that of Fig. 6A.
- the circuit of Fig. 7 does not require any digital to analog converters or analog to digital converters.
- the circuit of Fig. 7 may be modified to provide a constant temperature rise (above ambient) sensor, in a manner analogous to that of Fig. 6A.
- digital to analog converters may be used to set the ratio of R'7R' and the ratio of R 3 /R 3 ' to a desired value.
- one or more resistors e.g., R' "
- R' " having a high thermal coefficient of resistance may be used to automatically compensate for changes in the ambient temperature of the fluid flowing into the sensor conduit.
- Fig. 8 illustrates a mass flow sensor according to another embodiment of the present invention.
- the mass flow sensor of Fig. 8 is similar in operation to the mass flow sensor previously described with respect to Fig. 7.
- large gain operational amplifier 71 has been replaced by a unity gain buffer 71 ' connected between the midpoint of the second resistive branch that includes R'" and R 2 , the inverting (-) input of operational amplifier 51, and resistor R 2 '.
- the nverting (-) input of operational amplifier 51 is connected directly to resistor R 2 ', rather tha 1 being connected thereto via operational amplifier 71 as in Fig. 7.
- Unity gain buffer 71 ' mir ors voltage V 2 and provides this voltage to the third resistive branch formed by the se ⁇ e connection of R 2 ' and Rj'.
- the current through R 2 ' and R 2 and the current J rough Ri ' and Ri are equal with the result that the ratio of R 2 '/R ⁇ ' is equal to R 2 /R,.
- the circuit of Fig. 8 operates to provide an amount of current ⁇ I to the upstream coil Ri so that the resistance of coil Ri is equal to that of coil R 2 .
- a close matching of components is not required.
- the circuit of Fig. 8 may be modified in a number of ways, without departing from the basic operation of the circuit.
- the non- inverting (+) input of operational amplifier 72 may be connected to the midpoint of the fourth resistive branch formed by coils R 2 and R
- the circuit of Fig. 8 may be modified to provide a constant temperature rise (over ambient) mass flow sensor, rather than a constant temperature mass flow sensor.
- the series combination of resistors R' and R" may be replaced with a digital to analog converter having a reference voltage input that receives the output of operational amplifier 51 , an output that is coupled to the non-inverting (+) input of operational amplifier 51 , and an input that receives an appropriately valued input word to set the value of coil R 2 to the desired value.
- another digital to analog converter may be used to adjust the ratio of R 3 /R ' to equal the value of R 2 /R 2 '(or alternatively, so that the ratio of ⁇ I/ ⁇ F is equal to that of I 2 /I 2 ').
- This may be performed by adding a digital to analog converter between the output of operational amplifier 53 and resistor R 3 having a reference voltage input that receives the output of operational amplifier 53, an output that is coupled to resistor R 3 , and an input that receives an appropriately valued input word to set the value of coil R 3 to the desired value.
- Fig. 9 illustrates a mass flow sensor according to another embodiment of the present invention.
- the mass flow sensor of Fig. 9 is similar in operation to the mass flow sensor previously described with respect to Fig. 8. However, the configuration of operational amplifiers 53 and 72 in Fig. 9 is essentially the reverse of that in Fig. 8.
- the inverting (-) input of operational amplifier 72 is connected to the midpoint of the third resistive branch formed by R 2 ' and R] ', with the non-inverting (-) input of operational amplifier 72 being coupled to ground.
- the circuit of Fig. 9 illustrates a mass flow sensor according to another embodiment of the present invention.
- the mass flow sensor of Fig. 9 is similar in operation to the mass flow sensor previously described with respect to Fig. 8. However, the configuration of operational amplifiers 53 and 72 in Fig. 9 is essentially the reverse of that in Fig. 8.
- the inverting (-) input of operational amplifier 72 is connected to the midpoint of the third resistive branch formed by R 2 ' and R] '
- the output of operational amplifier 72 is coupled through resistor R 3 ' to the midpoint of the fourth resistive branch formed by coil Ri and coil R , and is fed back to the inverting (-) input of operational amplifier 72 through resistor R 3 .
- the inverting (-) input of operational amplifier 53 is again connected to the midpoint of the fourth resistive branch formed by coil Ri and coil R 2 , with the non-inverting (+) input of operational amplifier being coupled to ground.
- resistor R 3 ' may again be a variable resistor that can be set to a value that eliminates gain/temperature coefficients and provides a constant gain despite changes in the ambient temperature of the fluid flowing into the sensor conduit.
- the circuit of Fig. 9 operates to provide an amount of current ⁇ I to the upstream coil Rj so that the resistance of coil Ri is equal to that of coil R .
- the circuit of Fig. 9 may also be modified in a number of ways, while preserving the basic operation of the circuit.
- the non- inverting (+) input of operational amplifier 72 may be connected to the midpoint of the fourth resistive branch formed by coils R 2 and Ri, rather than being coupled to ground, or alternatively, the non-inverting (+) input of operational amplifier 53 may be connected to the midpoint of the third resistive branch formed by resistors R 2 " and R ⁇ rather than being coupled to ground.
- the circuit of Fig. 9 may be modified to use digital to analog converters that can adjust and/or set the values of R 2 and R 3 to a desired value.
- each of the mass flow sensors of Figs. 5, 6A, and 7-9 may benefit from the use of one or more stabilizing circuits that improve the transient response of sensor without overshoot or ringing.
- stabilizing circuits that are well known in the art and which may be used in conjunction with the mass flow sensors described with respect to Figs 5, 6 A, and 7-9, a detailed description such circuits is omitted herein.
- embodiments of the present invention have been described with respect to a mass flow sensor that is particularly well suited for semiconductor manufacturing processes, it should be appreciated that embodiments of the present invention may be used in other applications and processes.
- embodiments of the present invention may be used in automotive applications to measure the amount of a fluid such as gasoline, or diesel fuel, or air that is delivered to a combustion chamber.
- embodiments of the present invention are not limited to mass flow sensors, as the present invention may be used in other sensor and detection circuits.
- embodiments of the present invention may be readily adapted for use in a hot-wire anemometer or any other applications in which variations in the resistance of a leg of a resistive bridge circuit is indicative of a change in a property that varies with resistance.
Abstract
Description
Claims
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2001560630A JP2003523507A (en) | 2000-02-14 | 2001-02-14 | Method and apparatus for balancing resistance |
EP01910613A EP1257790A1 (en) | 2000-02-14 | 2001-02-14 | Method and apparatus for balancing resistance |
AU2001238204A AU2001238204A1 (en) | 2000-02-14 | 2001-02-14 | Method and apparatus for balancing resistance |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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US18230600P | 2000-02-14 | 2000-02-14 | |
US60/182,306 | 2000-02-14 |
Publications (1)
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WO2001061284A1 true WO2001061284A1 (en) | 2001-08-23 |
Family
ID=22667893
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US2001/004609 WO2001061284A1 (en) | 2000-02-14 | 2001-02-14 | Method and apparatus for balancing resistance |
Country Status (7)
Country | Link |
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US (1) | US6539792B2 (en) |
EP (1) | EP1257790A1 (en) |
JP (1) | JP2003523507A (en) |
KR (1) | KR100808727B1 (en) |
AU (1) | AU2001238204A1 (en) |
TW (1) | TW514720B (en) |
WO (1) | WO2001061284A1 (en) |
Cited By (2)
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---|---|---|---|---|
WO2004010091A1 (en) * | 2002-07-19 | 2004-01-29 | Celerity Group Inc. | Variable resistance sensor with common reference leg |
WO2005071367A1 (en) * | 2004-01-08 | 2005-08-04 | Analog Devices, Inc. | Anemometer circuit |
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US6627465B2 (en) * | 2001-08-30 | 2003-09-30 | Micron Technology, Inc. | System and method for detecting flow in a mass flow controller |
US7762958B1 (en) * | 2001-12-19 | 2010-07-27 | Abbott Cardiovascular Systems Inc. | Method and apparatus for determining injection depth and tissue type |
US20070084280A1 (en) * | 2005-08-26 | 2007-04-19 | Gill Rajinder S | Semi-constant temperature excitation method for fluid flow sensors |
JP4467603B2 (en) * | 2007-05-29 | 2010-05-26 | 日立オートモティブシステムズ株式会社 | Gas flow meter and internal combustion engine control system |
US8564274B2 (en) * | 2009-01-24 | 2013-10-22 | Micron Technology, Inc. | Reference voltage generation for single-ended communication channels |
GB2553681B (en) | 2015-01-07 | 2019-06-26 | Homeserve Plc | Flow detection device |
US10151772B2 (en) | 2015-01-23 | 2018-12-11 | Embry-Riddle Aeronautical Univeristy, Inc. | Hot wire anemometer |
GB201501935D0 (en) | 2015-02-05 | 2015-03-25 | Tooms Moore Consulting Ltd And Trow Consulting Ltd | Water flow analysis |
USD800591S1 (en) | 2016-03-31 | 2017-10-24 | Homeserve Plc | Flowmeter |
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2001
- 2001-02-14 US US09/783,439 patent/US6539792B2/en not_active Expired - Fee Related
- 2001-02-14 TW TW090103216A patent/TW514720B/en not_active IP Right Cessation
- 2001-02-14 KR KR1020027010507A patent/KR100808727B1/en not_active IP Right Cessation
- 2001-02-14 EP EP01910613A patent/EP1257790A1/en not_active Withdrawn
- 2001-02-14 AU AU2001238204A patent/AU2001238204A1/en not_active Abandoned
- 2001-02-14 WO PCT/US2001/004609 patent/WO2001061284A1/en active Application Filing
- 2001-02-14 JP JP2001560630A patent/JP2003523507A/en not_active Withdrawn
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Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
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WO2004010091A1 (en) * | 2002-07-19 | 2004-01-29 | Celerity Group Inc. | Variable resistance sensor with common reference leg |
US6845659B2 (en) | 2002-07-19 | 2005-01-25 | Celerity Group, Inc. | Variable resistance sensor with common reference leg |
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WO2005071367A1 (en) * | 2004-01-08 | 2005-08-04 | Analog Devices, Inc. | Anemometer circuit |
US7140263B2 (en) | 2004-01-08 | 2006-11-28 | Analog Devices, Inc. | Anemometer circuit |
Also Published As
Publication number | Publication date |
---|---|
US6539792B2 (en) | 2003-04-01 |
JP2003523507A (en) | 2003-08-05 |
KR100808727B1 (en) | 2008-02-29 |
AU2001238204A1 (en) | 2001-08-27 |
KR20020075417A (en) | 2002-10-04 |
EP1257790A1 (en) | 2002-11-20 |
TW514720B (en) | 2002-12-21 |
US20010052261A1 (en) | 2001-12-20 |
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