Improved accuracy mass flow meter / controller and method

Abstract

An exemplary optical measurement system includes a first light source emitting a first light beam, a first light sensor outputting a first measurement value based on detecting the first light beam, a second light source emitting a second light beam, a second light sensor outputting a second measurement value based on detecting the second light beam, the first measurement value and the second measurement value including a variable component, a third light sensor outputting a third measurement value based on detecting the second light beam or a third light beam, the third measurement value including a first steady-state component, and a compensation circuit controlling a first light output of the first light beam and a second light output of the second light beam by controlling current to the first light source and the second light source based on the third measurement value.

Description

Technical Field

[0001] [Related Applications] This application claims the benefit of U.S. Patent Application No. 16 / 906,222, filed Jun. 19, 2020, entitled "MASS FLOW METERS / CONTROLLERS AND METHODS HAVING IMPROVED ACCURACY". The entire disclosure of U.S. Patent Application No. 16 / 906,222 is hereby incorporated by reference in its entirety.

[0002] The present disclosure generally relates to mass flow measurement and control, and more particularly to mass flow meters / controllers and methods with improved accuracy.

Background Art

[0003] A Coriolis effect-based mass flow meter measures the mass flow rate of a medium by determining the phase difference between different portions of a flow tube through which the medium flows.

Summary of the Invention

[0004] A mass flow meter / controller with improved accuracy is substantially illustrated by at least one of the drawings, described in connection with at least one of the drawings, and more fully set forth in the claims.

Brief Description of the Drawings

[0005] [Figure 1] A schematic diagram of an exemplary mass flow meter / controller according to an aspect of the present disclosure. [Figure 2] A circuit diagram of an exemplary embodiment of the optical sensor, light source, and compensation circuit of FIG. 1. [Figure 3] A circuit diagram of another exemplary embodiment of the optical sensor and compensation circuit of FIG. 1, comprising a third optical sensor coupled to one of the light sources. [Figure 4] A circuit diagram of another exemplary embodiment of the optical sensor and compensation circuit of FIG. 1, comprising additional optical sensors coupled to each of the light sources. [Figure 5] This figure shows an example embodiment of a light source having a light sensor coupled to receive light output by the light source. [Figure 6] This flowchart illustrates an exemplary method by which the mass flowmeter / controller shown in Figures 1 to 4 can compensate for temperature changes and / or other influences on the light sensor and / or light source. [Modes for carrying out the invention]

[0006] The drawings are not necessarily to exact scale. Where appropriate, similar or identical reference numerals are used to refer to similar or identical components.

[0007] In flow meters that utilize the Coriolis effect, the temperature stability of the photosensor is a factor that affects measurement accuracy. Each photosensor, such as a photodiode or phototransistor, is accompanied by a light source, such as a light-emitting diode (LED). Both the LED and the photosensor have characteristics that are at least partially dependent on the ambient temperature. For example, the luminous intensity of an LED may change with temperature while being excited using the same excitation current.

[0008] Conventional techniques for temperature compensation when using LEDs and light sensors include operating the LED under a constant current, operating the LED under a constant temperature, biasing the LED using a temperature compensation circuit, and compensating the light sensor output for temperature. Furthermore, over long periods, light sensors tend to decrease in sensitivity, and LEDs tend to decrease in luminous intensity.

[0009] Constant temperature operation involves additional components such as heaters / coolers, power supplies, and control circuits. Such techniques are unacceptable in low-power devices, power-sensitive devices, and / or devices with space limitations. Conventional temperature compensation circuits require a temperature monitor and a processor to execute the compensation algorithm. Because luminosity is a nonlinear temperature function, conventional temperature compensation circuits do not adequately compensate for temperature changes.

[0010] The illustrated systems and methods disclosed isolate the light intensity of a light source from the temperature of the light source, providing a stable light source for measurement by a photosensor. In some examples, a Coriolis effect flowmeter includes a third photosensor in addition to two other photosensors used for phase / time difference measurement of the Coriolis effect flowmeter. The third photosensor does not engage with the vibrating tube. As a result, the output of the third photosensor is not modulated by the flow tube and is proportional only to the emitted brightness of the light beam.

[0011] In some disclosed systems and methods, the light source (LED) of a third photosensor is connected in series with the light sources of two other photosensors used to generate phase / time difference measurements. In the disclosed examples, the excitation currents of all photosensor light sources are identical and under closed-loop control. The excitation currents are controlled to stabilize the light intensity from the light sources regardless of temperature, aging, and / or any other disturbances in the circuit. All three sensors can be positioned close to each other so that the temperature difference between all photosensors is reduced or minimized.

[0012] In some cases, the stability of light intensity depends primarily on the stability of the reference signal and the overall control loop gain value. Changes in light intensity due to temperature fluctuations or edging of components are compensated for by the control loop. Since the LEDs of all three light sensors are connected in series, the light stabilization of the third sensor provides light stabilization for the other two light sensors.

[0013] In some disclosed examples, a second photosensor is added to receive light from one light source and provides a closed-loop control signal for stabilizing the light intensity of the light source. In such examples, the number of light sources can be reduced to two. In some examples, an additional photosensor is added to both light sources, and the outputs of the photosensors are averaged, combined, or otherwise filtered to provide feedback for brightness stabilization. The signal obtained by averaging the two outputs results in better compensation accuracy because the variations of both photosensors are included in the control loop.

[0014] By improving temperature stability, the disclosed system and method substantially improve the measurement characteristics of a flow meter due to the Coriolis effect, which is dependent on the stability and accuracy of the photosensor. By improving the temperature stability of the light source and photosensor, the disclosed system and method improve the overall precision of the flow meter.

[0015] As used herein, "substantially constant output" of a light source means an output having a degree of consistency greater than or equal to the degree of consistency of the reference signal used to control the output.

[0016] The illustrated optical measurement system disclosed comprises a first light source emitting a first light beam; a first photosensor outputting a first measurement value based on detection of the first light beam; a second light source emitting a second light beam; a second photosensor outputting a second measurement value based on detection of the second light beam, wherein the first and second measurement values ​​include a variable component; a third photosensor outputting a third measurement value based on detection of the second or third light beam, wherein the third measurement value includes a first steady-state component; and a compensation circuit that controls a first optical output of the first light beam and a second optical output of the second light beam by controlling one or more currents to the first and second light sources based on the first steady-state component of the third measurement value.

[0017] Some exemplary optical measurement systems further include a flow tube that guides a fluid from the inlet to the outlet of the flow tube, and an actuator that causes vibrations within the flow tube, wherein a first variable component of a first measurement is based on vibrations at a first location on the flow tube, and a second variable component of a second measurement is based on vibrations at a second location on the flow tube.

[0018] In some exemplary optical measurement systems, a first photosensor outputs a first measurement of a first location on a flow tube based on the detection of a first light beam, and a second photosensor outputs a second measurement of a second location on a flow tube based on the detection of a second light beam. Some exemplary optical measurement systems further include a control circuit that determines at least one of the mass flow rate through the flow tube or the density of the fluid in the flow tube based on the first and second measurements. In some exemplary optical measurement systems, the first location on the flow tube is positioned at least partially between a first light source and a first photosensor, and the second location on the flow tube is positioned at least partially between a second light source and a second photosensor.

[0019] Some exemplary optical measurement systems further include a fourth photosensor that outputs a fourth measurement value based on the detection of a first or fourth light beam, the fourth measurement value including a second steady-state component, and a compensation circuit that filters out the first and second steady-state components and includes a filter circuit that controls one or more currents to the first and second light sources based on the filtered first and second steady-state components.

[0020] In some exemplary optical measurement systems, a compensation circuit controls the first and second light sources to output a substantially constant output over a certain range of temperatures for the first and second light sources. In some exemplary optical measurement systems, the first light source includes a first light-emitting diode (LED), and the second light source includes a second LED. In some exemplary optical measurement systems, the first and second LEDs are connected in series and have the same excitation current, and the compensation circuit controls the excitation current.

[0021] In some exemplary optical measurement systems, the compensation circuit compares a third measurement value to a reference and controls one or more currents based on the comparison. In some exemplary optical measurement systems, the first optical sensor, the second optical sensor, and the third optical sensor are thermally coupled. Some exemplary optical measurement systems further include a third light source that emits a third light beam, and the third optical sensor outputs a third measurement value based on detection of the third light beam.

[0022] Another exemplary optical measurement system disclosed includes a first light source that emits a first light beam, a first optical sensor that outputs a first measurement value based on detection of the first light beam, a second light source that emits a second light beam, a second optical sensor that outputs a second measurement value based on detection of the second light beam, where the first measurement value and the second measurement value include a variable component, a third light source that emits a third light beam, a third optical sensor that outputs a third measurement value based on detection of the third light beam, where the third measurement value includes a first steady-state component, and a compensation circuit that controls the first light output of the first light beam and the second light output of the second light beam by controlling one or more currents to the first light source and the second light source based on the first steady-state component of the third measurement value.

[0023] In some exemplary optical measurement systems, the first light source includes a first light-emitting diode (LED), and the second light source includes a second LED. In some exemplary optical measurement systems, the first LED, the second LED, and the third LED are coupled in series and have the same excitation current, and the compensation circuit controls the excitation current. In some exemplary optical measurement systems, the compensation circuit compares a third measurement value to a reference and controls one or more currents based on the comparison.

[0024] Some exemplary optical measurement systems further include a flow tube that guides a fluid from an inlet of the flow tube to an outlet of the flow tube, and an actuator that causes vibrations within the flow tube. A first variable component of a first measurement value is based on vibrations at a first location on the flow tube, and a second variable component of a second measurement value is based on vibrations at a second location on the flow tube. In some exemplary optical measurement systems, a first optical sensor is configured to output a first measurement value of a first position at a first location on the flow tube based on detection of a first light beam, and a second optical sensor is configured to output a second measurement value of a second position at a second location on the flow tube based on detection of a second light beam. In some exemplary optical measurement systems, the first location on the flow tube is positioned at least partially between a first light source and the first optical sensor, and the second location on the flow tube is positioned at least partially between a second light source and the second optical sensor.

[0025] A method of performing an exemplary optical measurement disclosed includes emitting a first light beam via a first light source, performing a first measurement by detecting the first light beam via a first optical sensor, emitting a second light beam via a second light source, performing a second measurement by detecting the second light beam via a second optical sensor, wherein the first measurement value and the second measurement value include variable components, and performing a third measurement by detecting a second light beam or a third light beam via a third optical sensor, wherein the third measurement value includes a first steady-state component, and compensating a first light output of the first light beam and a second light output of the second light beam by controlling one or more currents to the first light source and the second light source based on the first steady-state component of the third measurement value.

[0026] Some exemplary methods include guiding a fluid from the inlet to the outlet of a flow tube, inducing vibrations within the flow tube, wherein a first variable component of a first measurement is based on vibrations at a first location on the flow tube, and a second variable component of a second measurement is based on vibrations at a second location on the flow tube, and determining at least one of the mass flow rate in the flow tube or the density of the fluid in the flow tube based on the first and second measurements.

[0027] In some exemplary methods, a first measurement indicates a first position of a first location on the flow tube based on the detection of a first light beam, and a second measurement indicates a second position of a second location on the flow tube based on the detection of a second light beam. In some examples, the first location on the flow tube is positioned at least partially between a first light source and a first photosensor, and the second location on the flow tube is positioned at least partially between a second light source and a second photosensor.

[0028] Some exemplary methods include performing a fourth measurement by detecting a first or fourth light beam, the fourth measurement including a second steady-state component, and compensating for the first optical output of the first light beam and the second optical output of the second light beam includes filtering the first and second steady-state components and controlling one or more currents to the first and second light sources based on the filtered first and second steady-state components.

[0029] In some exemplary methods, compensating for the first optical output of a first optical beam and the second optical output of a second optical beam includes controlling the first and second light sources to output substantially constant outputs over a range of temperatures of the first and second light sources. In some exemplary methods, the first light source includes a first light-emitting diode (LED), the second light source includes a second LED, the first and second light-emitting diodes are connected in series and have the same excitation current, and compensating for the first optical output of the first optical beam and the second optical output of the second optical beam includes controlling the excitation current.

[0030] In some exemplary methods, compensating for the first optical output of the first optical beam and the second optical output of the second optical beam includes comparing a third measurement to a reference and controlling one or more currents based on the comparison. In some exemplary methods, the first, second, and third optical sensors are thermally coupled.

[0031] Figure 1 is a schematic diagram of an example mass flow meter / controller 100. By using the example mass flow meter / controller 100 in Figure 1, the mass flow rate and / or density of the fluid passing through a conduit connected in series with the mass flow meter / controller 100 can be measured, and / or the mass flow rate of the fluid passing through the conduit can be controlled by controlling a valve.

[0032] The exemplary mass flowmeter / controller 100 comprises a flow base 102, a flow tube 104, a fluid inlet 106, and a fluid outlet 108. The flow tube 104 guides the fluid from the fluid inlet 106 to the fluid outlet 108. To measure the mass flow rate and / or density of the fluid flowing through the flow tube 104, the exemplary mass flowmeter / controller 100 comprises a plurality of photosensors 110, 112 (also referred to herein as “photosensors”), a plurality of light sources 111, 113, an actuator (e.g., a permanent magnet 114 and a drive coil 116) that causes vibrations within the flow tube 104, and a control circuit 122. To reduce measurement errors, the exemplary mass flowmeter / controller 100 further comprises a temperature sensor 126.

[0033] The flow tube 104 is configured in a U-shape. The drive coil 116 generates an alternating magnetic field, which generates a driving force in the permanent magnet 114. The permanent magnet 114 is attached to the flow tube 104 and transmits the driving force to the flow tube 104, causing vibrations within the flow tube 104. The flow tube 104 vibrates at a certain frequency, and the control circuit unit 122 can control the drive coil 116 to approximate the vibration frequency to the natural frequency of the flow tube 104. As the medium (e.g., gas or liquid) inside the flow tube 104 moves, a Coriolis force is generated, causing a phase shift between a first location 118 upstream on the flow tube 104 and a second location 120 downstream on the flow tube 104. The optical sensors 110 and 112 measure the position of the flow tube 104 at the first location 118 and the second location 120, and output respective signals (e.g., measured values) that have the same frequency but a phase or time difference. The first location 118 on the flow tube 104 is positioned at least partially between the first light source 111 and the first light sensor 110, and the second location 120 on the flow tube 104 is positioned at least partially between the second light source 113 and the second light sensor 112.

[0034] The illustrated control circuit 122 determines the mass flow rate through the flow tube 104 and / or the density of the fluid in the flow tube 104 based on a first measurement from the optical sensor 110 and a second measurement from the optical sensor 112. In some examples, the control circuit 122 controls the mass flow rate through the flow tube 104 using a flow control valve 124. The control circuit 122 can control the flow control valve 124 based on a comparison of a desired flow rate with a measured flow rate and may include one or more control loops, such as a proportional-integral-derivative (PID) controller, and / or one or more filters.

[0035] The control circuit unit 122 illustrated in Figure 1 can be a general-purpose computer, laptop computer, tablet computer, mobile device, server, embedded device, and / or any other type of computing device.

[0036] The illustrated control circuit unit 122 in Figure 1 comprises a processor 132. The illustrated processor 132 can be any general-purpose central processing unit (CPU) from any manufacturer. In some other examples, the processor 132 may include one or more dedicated processing units, such as a graphics processing unit and / or a digital signal processor. The processor 132 executes machine-readable instructions 134. The machine-readable instructions 134 can be stored locally in the processor (e.g., in an internal cache), in random-access memory 136 (or other volatile memory), in read-only memory 138 (or other non-volatile memory, such as flash memory), and / or in a mass storage device 140. The illustrated mass storage device 140 can be a hard drive, a solid-state storage device, a hybrid drive, a RAID array, and / or any other mass data storage device.

[0037] Bus 142 enables communication between the processor 132, RAM 136, ROM 138, mass storage device 140, network interface 144, and / or input / output interface 146.

[0038] The illustrated network interface 144 includes hardware, firmware, and / or software for connecting the control circuit unit 122 to a communication network 148 such as the Internet. For example, the network interface 144 may include wireless and / or wired communication compliant with IEEE 802.X for transmitting and / or receiving communications.

[0039] The illustrated control circuit unit 122 can access the non-temporary machine-readable medium 152 via the I / O interface 146 and / or I / O device(s) 150. Examples of the machine-readable medium 152 in Figure 1 include optical discs (e.g., compact discs (CDs), digital versatile / video discs (DVDs), Blu-ray® discs, etc.), magnetic media (e.g., floppy disks), portable storage media (e.g., portable flash drives, Secure Digital (SD) cards, etc.), and / or any other type of removable and / or installable machine-readable medium.

[0040] To determine the mass flow rate, the example control circuit unit 122 may use the mass flow rate formula shown in Equation 1 below: MF = FCF * Δt (Equation 1)

[0041] In Equation 1, MF is the mass flow rate (e.g., kilograms / second (kg / s)), FCF is the flow rate calibration coefficient, which is a constant of a specific device (e.g., based on calibration), and Δt = θ / 2πF′, where θ is the phase difference between the output signals from the optical sensors 110 and 112, and F is the natural frequency of the flow tube 104.

[0042] The example light sources 111 and 113 are configured to emit light beams 154 and 156, respectively, and the light sensors 110 and 112 output measurements based on their detection of the respective light beams 154 and 156. The vibration of the flow tube 104 modulates the light beams 154 and 156, causing modulation of the measurement signals output by the light sensors 110 and 112.

[0043] As described above, the light sensors 110 and 112 (for example, the LEDs (or multiple) and photodiodes (or multiple) of the light sensors 110 and 112) have characteristics that can change with temperature. The greater the fluctuation in the output signals from the light sensors 110 and 112 due to temperature changes, the greater the accuracy of measurement and / or control by the mass flow meter / controller 100 may be reduced. To stabilize the output over a range of temperatures, whether short-term or long-term, the exemplary mass flow meter / controller 100 includes a compensation circuit 158 ​​coupled to the light sensors 110 and 112. The compensation circuit 158 ​​controls the optical output of the light beams 154 and 156 by controlling one or more currents to the light sources 111 and 113 based on the steady-state component (or multiple) of one or more outputs of the light sensors 110 and 112.

[0044] The exemplary compensation circuit 158 ​​has the advantage of avoiding the use of the modulated output signals of the light sensors 110 and 112. Instead, the compensation circuit 158 ​​uses one or more signals that have a steady-state component indicating the optical output, but does not require filtering of the modulated signal, which may be imperfect and introduce noise into the compensation of the optical output. In some examples, the light sources 111 and 113 are coupled (e.g., coupled in series) and share an excitation current to reduce the number of variables between the light sources 111 and 113. Exemplary embodiments of the compensation circuit 158 ​​are disclosed below with reference to Figures 2 to 5.

[0045] Figure 2 is a circuit diagram of an example embodiment of the photosensors 110, 112, light sources 111, 113, and compensation circuit 158 ​​of Figure 1. In the example of Figure 2, the first photosensor 110 outputs a first measurement 202 based on the detection of a first light beam 154 modulated by a first location 118 of the flow tube 104. The second photosensor 112 outputs a second measurement 204 based on the detection of a second light beam 156 modulated by a second location 120 of the flow tube 104. The first measurement 202 and the second measurement 204 can be output to the control circuit unit 122 of Figure 1, which determines the mass flow rate through the flow tube 104 and / or the density of the fluid in the flow tube 104 based on the first measurement 202 and the second measurement 204.

[0046] The compensation circuit 158 ​​illustrated in Figure 2 includes a third light source 206 and a third light sensor 208 that provide outputs to compensate for variations in light sources 111, 113 and / or light sensors 110, 112 due to temperature, aging, and / or any other cause. Light sources 111 and 113 are connected in series, and both are connected in series with the third light source 206, and compensation for light sources 111 and 113 is provided by compensating for changes in the output of the third light source 206.

[0047] The photosensor 208 measures a third light beam 210 output by the light source 206, which is not modulated by the flow tube 104. As a result, the output of the photosensor 208 has a steady-state component and virtually no variable component. Instead, the steady-state component represents the steady-state output of the light source 206, which can be assumed to represent the light output of the light sources 111 and 113. In the example in Figure 2, the light sources 111, 113, and 206 share an excitation current (e.g., forward current). In some examples, the light sources 111, 113, and 206 can be arranged to limit (e.g., reduce, minimize) the temperature gradient between them by thermal coupling them.

[0048] The illustrated compensation circuit 158 ​​further comprises a comparator-amplifier 212 that compares the output of the light sensor 208 with a reference signal (e.g., a reference voltage 214) and outputs a compensation signal 216 to the LED control circuit 218. In the example in Figure 2, the compensation signal 216 is proportional to the difference between the output of the light sensor 208 and the reference voltage 214. The LED control circuit 218 controls the excitation current to the light sources 111, 113, and 206 based on the compensation signal 216. The stability of the optical outputs of the light beams 154, 156, and 210 depends on the stability of the reference voltage and the parameters of the comparator-amplifier 212, which can be configured as a PID controller and / or any other type of feedback loop.

[0049] Figure 3 is a circuit diagram of another exemplary embodiment of the light sensors 110, 112, light sources 111, 113, and compensation circuit 158 ​​of Figure 1. In the example of Figure 3, the compensation circuit 158 ​​includes a third light sensor 302 coupled to one of the light sources 111, 113. In the example of Figure 3, the light sensors 110, 112, and 302 are photodiodes.

[0050] In comparison with the example in Figure 2, the exemplary embodiment in Figure 3 reduces the number of light emitters by coupling the third photosensor 302 to the light source 113 (or light source 111) so that the light beam 304 emitted by the light source 113 and measured by the third photosensor 302 is not modulated by the flow measuring tube 104. For example, the third photosensor 302 can be directly coupled to the output of the light source 113, as shown in Figure 5 below. The output measurement of the photosensor 302 is provided to the comparator-amplifier 212, which provides a compensation signal 216 as described above with reference to Figure 2.

[0051] The LED light intensity stabilization in the examples of Figures 2 and 3 is based on the assumption that the light sensors 110, 112, 208 and / or 110, 112, 302 all have substantially identical temperature characteristics (e.g., identical within the limits of measurement accuracy considered acceptable for a given application). However, some variation exists in the characteristics of each component. Figure 4 is a schematic diagram of another exemplary embodiment of the light sensors 110, 112, light sources 111, 113, and compensation circuit 158 ​​of Figure 1, which can be used to further reduce measurement errors. In the exemplary embodiment of Figure 4, the compensation circuit 158 ​​includes additional light sensors 402, 404.

[0052] The third photosensor 402 is coupled to the first light source 111 so that the light beam 406 emitted by the first light source 111 and measured by the third photosensor 402 is not modulated by the flow measurement tube 104. Similarly, the fourth photosensor 404 is coupled to the second light source 113 so that the light beam 408 emitted by the second light source 113 and measured by the fourth photosensor 404 is not modulated by the flow measurement tube 104.

[0053] The third photosensor 402 outputs a measured value (e.g., a first steady-state component) to the first comparator-amplifier 410, and the fourth photosensor 404 outputs a measured value (e.g., a second steady-state component) to the second comparator-amplifier 412. The reference voltage 214 is coupled to both comparator-amplifiers 410 and 412. The comparator-amplifier 410 outputs a compensation signal 414 proportional to the difference between the measured value from the third photosensor 402 (e.g., a first steady-state component) and the reference voltage 214. Similarly, the comparator-amplifier 412 outputs a compensation signal 416 proportional to the difference between the measured value from the fourth photosensor 404 (e.g., a second steady-state component) and the reference voltage 214. The compensation signals 414 and 416 are input to a filter circuit 418, which filters the compensation signals 414 and 416 and outputs a filtered compensation signal 420. In the example in Figure 4, the filter circuit 418 averages the compensation signals 414 and 416 to produce a filtered (e.g., averaged) compensation signal 420. However, other filtering functions can be used instead of averaging.

[0054] The filter circuit 418 outputs the filtered compensation signal 420 to the LED control circuit 218, which controls the excitation current to the light sources 111 and 113 (for example, light beams 406 and 408).

[0055] Figure 5 shows an exemplary embodiment of a light source 502 having a photosensor 504 coupled to receive unmodulated light output by the light source 502. The photosensor 504 is directly attached to the light source 502 to have a high degree of coupling between the light source 502 and the photosensor 504. In addition, the coupling of the photosensor 504 remains consistent, reducing or eliminating variations in the incident light emitted by the light source 502 onto the photosensor 504.

[0056] Figure 6 is a flowchart illustrating an exemplary method 600 that can be performed using the mass flowmeter / controller 100 and compensation circuit 158 ​​of Figures 1 to 4 to compensate for temperature changes and / or other effects on the photosensor and / or light source. The exemplary method 600 is described below with reference to the mass flowmeter / controller 100 of Figure 1 and the compensation circuit 158 ​​of Figure 3. However, method 600 can be performed using multiple photosensors and / or different compensation circuits, for example, other devices having the compensation circuits of Figures 2 and / or Figure 4.

[0057] In block 602, the LED control circuit 218 controls the excitation current to light sources 111 and 113 so that a first light beam 154 is emitted through the first light source 111 and a second light beam 156 is emitted through the second light source 113. In the example in Figure 3, light sources 111 and 113 are in series and have the same excitation current.

[0058] In block 604, the first optical sensor 110 performs a first measurement of the first optical beam 154. For example, the first optical beam 154 may be modulated by the flow tube 104, and the modulated optical beam is measured by the first optical sensor 110 and output to the control circuit unit 122 in Figure 1.

[0059] In block 606, the second optical sensor 112 performs a first measurement of the second optical beam 156. For example, the second optical beam 156 may be modulated by the flow tube 104, and the modulated optical beam is measured by the second optical sensor 112 and output to the control circuit unit 122.

[0060] In block 608, the third photosensor 302 performs a third measurement of the second light beam 156 (or the first light beam 154). In contrast to the measurement by the second photosensor 112, the measurement of the second light beam 156 by the third photosensor 302 is not modulated by the flow tube 104, and the third photosensor 302 outputs the measurement (e.g., steady-state component) to the comparator-amplifier 212.

[0061] In block 610, the control circuit 122 determines the mass flow rate and / or density measurements through the flow tube 104 based on the variable components of the first measurement from the first optical sensor 110 and the second measurement from the second optical sensor 112 (for example, via the processor 132). For example, the control circuit 122 can calculate the mass flow rate based on the phase difference between the first and second measurements, and / or calculate the fluid density based on the frequency of vibrations in the flow tube 104.

[0062] In block 612, the comparator-amplifier 212 compares the steady-state portion of the third measurement to a reference. For example, the comparator-amplifier 212 compares the measurement from the third photosensor 302 to a reference voltage 214 to generate a compensation signal 216. The illustrated compensation signal 216 is proportional to the difference between the steady-state portion of the measurement from the third photosensor 302 and the reference voltage 214.

[0063] In block 614, the LED control circuit 218 adjusts the excitation current based on a comparison (for example, based on the compensation signal 216).

[0064] In block 616, the control circuit 122 determines whether to control the flow rate. For example, a mass flow controller can be configured to control the flow rate, while a mass flow meter does not control the flow rate. If the flow rate is to be controlled (block 616), the control circuit 122 adjusts the flow control valve 124 based on the difference between the measured flow rate and the target flow rate.

[0065] After adjusting the flow control valve (block 618), or if the flow rate is not controlled (block 616), control returns to block 602 and measurement and / or control continues.

[0066] The method and system can be implemented in hardware, software, and / or a combination of hardware and software. The method and / or system can be implemented centrally in at least one computing system, or in a distributed manner in which different elements are distributed across several interconnected computing systems. Any type of computing system or other device adapted to perform the method described herein is suitable. A typical combination of hardware and software may include a general-purpose computing system, along with a program or other code that, when loaded and executed, controls the computing system to perform the method described herein. Another typical embodiment may include one or more application-specific integrated circuits or chips. Some embodiments may include non-temporary machine-readable (e.g., computer-readable) media (e.g., flash memory, optical disks, magnetic storage disks, etc.) that store one or more lines of machine-executable code, thereby causing a machine to perform a process such as that described herein. As used herein, the term “non-temporary machine-readable media” includes all types of machine-readable storage media and is defined as being free from propagated signals.

[0067] As used herein, the terms “circuit” and “circuit section” mean physical electronic components (i.e., hardware) and any software and / or firmware ("code") that can constitute the hardware, can be executed by the hardware, and / or can be otherwise associated with the hardware. As used herein, for example, a particular processor and memory may include a first “circuit” when executing one or more first lines of the code, and a second “circuit” when executing one or more second lines of the code. As used herein, “and / or” means any one or more items in the list linked by “and / or”. For example, “x and / or y” means any element of the set of three elements {(x), (y), (x,y)}. In other words, “x and / or y” means “one or both of x and y”. As another example, “x, y and / or z” means any element of the seven-element set {(x), (y), (z), (x,y), (x,z), (y,z), (x,y,z)}. In other words, “x, y and / or z” means “one or more of x, y and z.” As used herein, the term “exemplary” means to serve as an unrestricted example, case, or illustration. As used herein, the term “for example” begins a list of one or more unrestricted examples, cases, or illustrations. As used herein, whenever a circuit section includes the hardware and code (if any) necessary to perform a certain function, the circuit section is “operable” to perform that function, regardless of whether the performance of that function is disabled or not (e.g., by a user-configurable setting, factory trim, etc.).

[0068] The method and / or system can be implemented in hardware, software, or a combination of hardware and software. The method and / or system can be implemented centrally in at least one computing system, or in a distributed manner in which different elements are distributed across several interconnected computing systems. Any type of computing system or other device adapted to perform the method described herein is suitable. A typical combination of hardware and software may be a general-purpose computing system with a program or other code that, when loaded and executed, controls the computing system to perform the method described herein. Another typical embodiment may include an application-specific integrated circuit or chip. Some embodiments may include a non-temporary machine-readable (e.g., computer-readable) medium (e.g., flash drive, optical disk, magnetic storage disk, etc.) which stores one or more lines of machine-executable code, thereby causing a machine to perform a process such as that described herein.

[0069] While the Method and / or System has been described with reference to certain specific embodiments, those skilled in the art will understand that various modifications and substitutions can be made without departing from the scope of the Method and / or System. In addition, many modifications can be made without departing from the scope of the Disclosure to adapt the teachings of the Disclosure to specific circumstances or materials. For example, the blocks and / or components of the disclosed examples can be combined, divided, rearranged, and / or otherwise modified. Thus, the Method and / or System is not limited to the specific embodiments disclosed, and is intended to include all embodiments that fall within the scope of the appended claims. Some aspects of the present invention are described below. [Aspect 1] In optical measurement systems, A first light source that emits a first light beam, A first light sensor that outputs a first measurement value based on the detection of the first light beam, A second light source that emits a second light beam, A second photosensor that outputs a second measurement value based on the detection of the second light beam, wherein the first measurement value and the second measurement value include a variable component, A third photosensor that outputs a third measurement value based on the detection of the second or third light beam, wherein the third measurement value includes a first steady-state component. An optical measurement system comprising: a compensation circuit that controls the first optical output of the first optical beam and the second optical output of the second optical beam by controlling one or more currents to the first light source and the second light source based on the first steady-state component of the third measured value. [Aspect 2] A flow pipe that guides the fluid from the inlet to the outlet of the flow pipe, The system further comprises an actuator that generates vibrations within the aforementioned flow pipe, The optical measurement system according to embodiment 1, wherein the first variable component of the first measurement is based on vibrations at a first location on the flow pipe, and the second variable component of the second measurement is based on vibrations at a second location on the flow pipe. [Aspect 3] The optical measurement system according to embodiment 2, wherein the first light sensor is configured to output a first measurement of a first position at the first location on the flow tube based on the detection of the first light beam, and the second light sensor outputs a second measurement of a second position at the second location on the flow tube based on the detection of the second light beam. [Aspect 4] The optical measurement system according to embodiment 2, further comprising a control circuit that determines at least one of the mass flow rate through the flow tube or the density of the fluid in the flow tube based on the first measurement value and the second measurement value. [Aspect 5] The optical measuring system according to embodiment 2, wherein the first location on the flow tube is positioned at least partially between the first light source and the first photosensor, and the second location on the flow tube is positioned at least partially between the second light source and the second photosensor. [Aspect 6] The optical measurement system according to embodiment 1, further comprising a fourth photosensor that outputs a fourth measurement value based on the detection of the first or fourth light beam, wherein the fourth measurement value includes a second steady-state component, and the compensation circuit includes a filter circuit that filters the first steady-state component and the second steady-state component, and controls the one or more currents to the first light source and the second light source based on the filtered first steady-state component and the second steady-state component. [Aspect 7] The optical measurement system according to embodiment 1, wherein the compensation circuit controls the first light source and the second light source to output a substantially constant output over a certain range of temperatures of the first light source and the second light source. [Aspect 8] The optical measurement system according to embodiment 1, wherein the first light source includes a first light-emitting diode (LED), and the second light source includes a second LED. [Aspect 9] The optical measurement system according to embodiment 8, wherein the first LED and the second LED are connected in series and have the same excitation current, and the compensation circuit controls the excitation current. [Aspect 10] The optical measurement system according to embodiment 1, wherein the compensation circuit compares the third measured value with a reference and controls the one or more currents based on the comparison. [Aspect 11] The optical measurement system according to embodiment 1, wherein the first optical sensor, the second optical sensor, and the third optical sensor are thermally coupled. [Aspect 12] The optical measurement system according to embodiment 1, further comprising a third light source that emits a third light beam, wherein the third light sensor outputs the third measurement value based on the detection of the third light beam. [Aspect 13] In optical measurement systems, A first light source that emits a first light beam, A first light sensor that outputs a first measurement value based on the detection of the first light beam, A second light source that emits a second light beam, A second photosensor that outputs a second measurement value based on the detection of the second light beam, wherein the first measurement value and the second measurement value include a variable component, A third light source that emits a third light beam, A third photosensor that outputs a third measurement value based on the detection of the third light beam, wherein the third measurement value includes a first steady-state component. An optical measurement system comprising: a compensation circuit that controls the first optical output of the first optical beam and the second optical output of the second optical beam by controlling one or more currents to the first light source and the second light source based on the first steady-state component of the third measured value. [Aspect 14] The optical measurement system according to embodiment 13, wherein the first light source includes a first light-emitting diode (LED) and the second light source includes a second LED. [Aspect 15] The optical measurement system according to embodiment 14, wherein the first LED, the second LED, and the third LED are connected in series and have the same excitation current, and the compensation circuit controls the excitation current. [Aspect 16] The optical measurement system according to embodiment 13, wherein the compensation circuit compares the third measured value with a reference and controls the one or more currents based on the comparison. [Aspect 17] A flow pipe that guides the fluid from the inlet to the outlet of the flow pipe, The system further comprises an actuator that generates vibrations within the aforementioned flow pipe, The optical measurement system according to embodiment 13, wherein the first variable component of the first measurement is based on vibrations at a first location on the flow pipe, and the second variable component of the second measurement is based on vibrations at a second location on the flow pipe. [Aspect 18] The optical measurement system according to embodiment 17, wherein the first light sensor outputs a first measurement value of the first position at the first location on the flow pipe based on the detection of the first light beam, and the second light sensor outputs a second measurement value of the second position at the second location on the flow pipe based on the detection of the second light beam. [Aspect 19] The optical measuring system according to embodiment 17, wherein the first location on the flow tube is positioned at least partially between the first light source and the first photosensor, and the second location on the flow tube is positioned at least partially between the second light source and the second photosensor. [Aspect 20] Emitting a first light beam through a first light source, The first measurement is performed by detecting the first light beam via the first light sensor, Emitting a second light beam through a second light source, A second measurement is performed by detecting the second light beam via a second optical sensor, wherein the first measurement and the second measurement include a variable component. A third measurement is performed by detecting the second or third light beam via a third optical sensor, wherein the third measurement includes a first steady-state component. A method for performing an optical measurement, comprising compensating for the first optical output of the first optical beam and the second optical output of the second optical beam by controlling one or more currents to the first light source and the second light source based on the first steady-state component of the third measured value. [Aspect 21] To guide the fluid from the inlet of the flow pipe to the outlet of the flow pipe, The method involves causing vibrations within the flow pipe, wherein the first variable component of the first measurement is based on vibrations at a first location on the flow pipe, and the second variable component of the second measurement is based on vibrations at a second location on the flow pipe. The method according to embodiment 20, further comprising determining at least one of the mass flow rate in the flow tube or the density of the fluid in the flow tube based on the first measurement and the second measurement. [Aspect 22] The method according to embodiment 21, wherein the first measurement indicates a first position of the first location on the flow tube based on the detection of the first light beam, and the second measurement indicates a second position of the second location on the flow tube based on the detection of the second light beam. [Aspect 23] The method according to embodiment 21, wherein the first location on the flow tube is at least partially positioned between the first light source and the first photosensor, and the second location on the flow tube is at least partially positioned between the second light source and the second photosensor. [Aspect 24] The method further includes performing a fourth measurement by detecting the first or fourth light beam, wherein the fourth measurement includes a second steady-state component, and the compensation for the first light output of the first light beam and the second light output of the second light beam is Filtering the first steady-state component and the second steady-state component, The method according to embodiment 20, further comprising controlling the one or more currents to the first light source and the second light source based on the filtered first steady-state component and the second steady-state component. [Pattern 25] The method according to embodiment 20, wherein the compensation of the first optical output of the first optical beam and the second optical output of the second optical beam is controlled to produce substantially constant output over a range of temperatures of the first and second light sources. [Aspect 26] The method according to embodiment 20, wherein the first light source includes a first light-emitting diode, the second light source includes a second light-emitting diode, the first light-emitting diode and the second light-emitting diode are coupled in series and have the same excitation current, and the compensation for the first optical output of the first light beam and the second optical output of the second light beam is controlled by controlling the excitation current. [Aspect 27] The method according to embodiment 20, wherein compensating the first optical output of the first optical beam and the second optical output of the second optical beam includes comparing the third measured value to a reference and controlling the one or more currents based on the comparison. [Aspect 28] The method according to embodiment 20, wherein the first photosensor, the second photosensor, and the third photosensor are thermally coupled.

Claims

1. In optical measurement systems, A first light source that emits a first light beam, A first photosensor that outputs a first measurement value including a first variable component based on the detection of the first light beam, A second light source that emits a second light beam, A second photosensor that outputs a second measurement value including a second variable component based on the detection of the second light beam, A third photosensor that outputs a third measurement value including a first steady-state component based on the detection of the second or third light beam, The system comprises a compensation circuit that controls the first optical output of the first optical beam and the second optical output of the second optical beam by controlling one or more currents to the first light source and the second light source based on the first steady-state component of the third measured value, The first optical sensor, the second optical sensor, and the third optical sensor are thermally coupled to form an optical measurement system.

2. A flow pipe that guides the fluid from the inlet to the outlet of the flow pipe, The system further comprises an actuator that generates vibrations within the aforementioned flow pipe, The optical measurement system according to claim 1, wherein the first variable component of the first measurement is based on vibrations at a first location on the flow pipe, and the second variable component of the second measurement is based on vibrations at a second location on the flow pipe.

3. The optical measurement system according to claim 2, wherein the first light sensor is configured to output a first measurement value of a first position at the first location on the flow tube based on the detection of the first light beam, and the second light sensor outputs a second measurement value of a second position at the second location on the flow tube based on the detection of the second light beam.

4. The optical measurement system according to claim 2, further comprising a control circuit that determines at least one of the mass flow rate through the flow tube or the density of the fluid in the flow tube based on the first measurement and the second measurement.

5. The optical measurement system according to claim 2, wherein the first location on the flow tube is positioned at least partially between the first light source and the first photosensor, and the second location on the flow tube is positioned at least partially between the second light source and the second photosensor.

6. The optical measurement system according to claim 1, further comprising a fourth photosensor that outputs a fourth measurement value based on the detection of the first or fourth light beam, wherein the fourth measurement value includes a second steady-state component, and the compensation circuit includes a filter circuit that filters the first steady-state component and the second steady-state component, and controls the one or more currents to the first light source and the second light source based on the filtered first steady-state component and the second steady-state component.

7. The optical measurement system according to claim 1, wherein the compensation circuit controls the first light source and the second light source to output a substantially constant output over a certain range of temperatures of the first light source and the second light source.

8. The optical measurement system according to claim 1, wherein the first light source includes a first light-emitting diode (LED), and the second light source includes a second LED.

9. The optical measurement system according to claim 8, wherein the first LED and the second LED are connected in series and have the same excitation current, and the compensation circuit controls the excitation current.

10. The optical measurement system according to claim 1, wherein the compensation circuit compares the third measured value with a reference and controls the one or more currents based on the comparison.

11. The optical measurement system according to claim 1, further comprising a third light source that emits a third light beam, wherein the third light sensor outputs the third measurement value based on the detection of the third light beam.

12. In optical measurement systems, A first light source that emits a first light beam, A first photosensor that outputs a first measurement value including a first variable component based on the detection of the first light beam, A second light source that emits a second light beam, A second photosensor that outputs a second measurement value including a second variable component based on the detection of the second light beam, A third light source that emits a third light beam, A third photosensor that outputs a third measurement value including a first steady-state component based on the detection of the third light beam, The system comprises a compensation circuit that controls the first optical output of the first optical beam and the second optical output of the second optical beam by controlling one or more currents to the first light source and the second light source based on the first steady-state component of the third measured value, The first optical sensor, the second optical sensor, and the third optical sensor are thermally coupled to form an optical measurement system.

13. The optical measurement system according to claim 12, wherein the first light source includes a first light-emitting diode (LED), and the second light source includes a second LED.

14. The optical measurement system according to claim 13, wherein the first LED, the second LED, and the third LED are connected in series and have the same excitation current, and the compensation circuit controls the excitation current.

15. The optical measurement system according to claim 12, wherein the compensation circuit compares the third measured value with a reference and controls one or more currents based on the comparison.

16. A flow pipe that guides the fluid from the inlet to the outlet of the flow pipe, The system further comprises an actuator that generates vibrations within the aforementioned flow pipe, The optical measurement system according to claim 12, wherein the first variable component of the first measurement is based on vibrations at a first location on the flow pipe, and the second variable component of the second measurement is based on vibrations at a second location on the flow pipe.

17. The optical measurement system according to claim 16, wherein the first light sensor outputs a first measurement value of a first position at a first location on the flow pipe based on the detection of the first light beam, and the second light sensor outputs a second measurement value of a second position at a second location on the flow pipe based on the detection of the second light beam.

18. The optical measurement system according to claim 16, wherein the first location on the flow tube is positioned at least partially between the first light source and the first photosensor, and the second location on the flow tube is positioned at least partially between the second light source and the second photosensor.

19. Emitting a first light beam through a first light source, By detecting the first light beam via the first light sensor, a first measurement value including a first variable component is obtained. Emitting a second light beam through a second light source, By detecting the second light beam via the second optical sensor, a second measurement value including a second variable component is obtained. By detecting the second or third light beam via a third optical sensor, a third measurement value including a first steady-state component is obtained. This includes compensating for the first optical output of the first optical beam and the second optical output of the second optical beam by controlling one or more currents to the first light source and the second light source based on the first steady-state component of the third measured value, A method for performing optical measurements, wherein the first optical sensor, the second optical sensor, and the third optical sensor are thermally coupled.

20. To guide the fluid from the inlet of the flow pipe to the outlet of the flow pipe, The method involves causing vibrations within the flow pipe, wherein the first variable component of the first measurement is based on vibrations at a first location on the flow pipe, and the second variable component of the second measurement is based on vibrations at a second location on the flow pipe. The method according to claim 19, further comprising determining at least one of the mass flow rate in the flow tube or the density of the fluid in the flow tube based on the first measurement and the second measurement.

21. The method according to claim 20, wherein the first measurement indicates a first position of the first location on the flow tube based on the detection of the first light beam, and the second measurement indicates a second position of the second location on the flow tube based on the detection of the second light beam.

22. The method according to claim 20, wherein the first location on the flow tube is at least partially positioned between the first light source and the first photosensor, and the second location on the flow tube is at least partially positioned between the second light source and the second photosensor.

23. The method further includes obtaining a fourth measurement by detecting the first or fourth light beam, the fourth measurement including a second steady-state component, and compensating the first light output of the first light beam and the second light output of the second light beam. Filtering the first steady-state component and the second steady-state component, The method according to claim 19, further comprising controlling the one or more currents to the first light source and the second light source based on the filtered first steady-state component and the second steady-state component.

24. The method according to claim 19, wherein compensating the first optical output of the first optical beam and the second optical output of the second optical beam includes controlling the first light source and the second light source to output a substantially constant output over a range of temperatures of the first and second light sources.

25. The method according to claim 19, wherein the first light source includes a first light-emitting diode, the second light source includes a second light-emitting diode, the first light-emitting diode and the second light-emitting diode are coupled in series and have the same excitation current, and the compensation for the first optical output of the first light beam and the second optical output of the second light beam includes controlling the excitation current.

26. The method according to claim 19, wherein compensating the first optical output of the first optical beam and the second optical output of the second optical beam comprises comparing the third measured value to a reference and controlling the one or more currents based on the comparison.

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