Patent Description:
This disclosure relates generally to mass flow measurement and control and, more particularly, to mass flow meters/controllers and methods having improved accuracy.

Coriolis effect-based mass flow meters measure mass flow of media by determining a phase difference between different portions of a flow tube through which the media flows.

<CIT> discloses mass flow meters/controllers according to the prior art.

Mass flow meters/controllers having improved accuracy, substantially as illustrated by and described in connection with at least one of the figures, as set forth more completely in the claims.

The accuracy of mass flow measurement is dependent on the quality of the signals output by the optical sensors. In conventional optical sensors for Coriolis mass flow meters, a separate light source (e.g., a channel) provides a light beam for measurement by the respective optical sensor. Optical sensors in the conventional arrangement output signals include a DC bias signal and an AC signal due to flow tube modulation. In convention mass flow meters having multiple optical channels, in which each optical channel includes a light source, a light source control circuit, and an optical sensor, each component of a given channel also generates a noise, which affects the total optical channel output signal. For example, each optical channel optical channel may include a photo sensor noise signal due to the light source control circuit, a photo sensor noise signal due to the light source, and a AC noise signal due to the photo sensor.

Because the noise sources mentioned above are random noise with no correlation between them, these noise signals cannot be compensated and adversely impact flow meter accuracy in conventional flow meters. Therefore, for conventional mass flow meters, having two separate channels, there are at least six independent variables contributing some noise to total phase shift value.

Disclosed example mass flow meters/controllers reduce the number of independent noise sources in the mass flow measurements, thereby increasing the accuracy. In some disclosed examples, one or more beam splitters split a single source of light for use by multiple channels, and direct the resulting light beams to traverse different locations on the flow tube for measurement of the phase difference between the locations.

Mass flow meters/controller according to the invention include: a flow tube configured to direct a fluid from an inlet of the flow tube to an outlet of the flow tube; an actuator configured to cause a vibration in the flow tube; a light source configured to emit light; at least one beam splitter configured to split the light emitted by the light source into a first light beam and a second light beam; a first optical sensor configured to output first measurements of a first position of a first location on the flow tube based on detecting the first light beam; a second optical sensor configured to output second measurements of a second position of a second location on the flow tube based on detecting the second light beam; and control circuitry configured to determine at least one of a mass flow rate through the flow tube or a density of the fluid in the flow tube based on the first measurements and the second measurements.

According to the invention, the at least one beam splitter is configured to direct the first light beam and the second light beam in opposite directions, and the first optical sensor and the second optical sensor are positioned on opposite sides of the at least one beam splitter to receive the first light beam and the second light beam, respectively, from the at least one beam splitter. In some examples, the at least one beam splitter includes: a first mirror arranged at substantially a <NUM> degree angle to the light source to reflect a first portion of the light from the light source to form the first light beam; and a second mirror arranged to reflect a second portion of light from the light source that passes through the first mirror back toward the first mirror. The first mirror is configured to reflect the second portion of the light from the second mirror to form the second light beam.

In some example mass flow meters/controllers, the at least one beam splitter further includes a third mirror configured to reflect the first light beam from the first mirror to the first optical sensor, and a fourth mirror configured to reflect the second light beam from the first mirror to the second optical sensor. Some example mass flow meters/controllers further include a printed circuit board, in which the first optical sensor and the second optical sensor are mounted to the printed circuit board. In some example mass flow meters/controllers, the printed circuit board is configured to thermally couple the first optical sensor and the second optical sensor. In some example mass flow meters/controllers, the light source is mounted to the printed circuit board and is thermally coupled to the first optical sensor and the second optical sensor.

In some example mass flow meters/controllers, the first location of the flow tube, the second location of the flow tube, and a portion of the flow tube between the first location and the second location are oriented on a two-dimensional plane, and the actuator is configured to cause the vibration in the flow tube in a direction along the two-dimensional plane. In some example mass flow meters/controllers, the first location of the flow tube, the second location of the flow tube, and a portion of the flow tube between the first location and the second location are oriented on a two-dimensional plane, and the actuator is configured to cause the vibration in the flow tube in a direction transverse to the two-dimensional plane.

In some example mass flow meters/controllers, the at least one beam splitter comprises at least one of a cube beam splitter, a plate beam splitter, a pellicle beam splitter, a Wollaston prism, a diffractive beam splitter, an actuated beam splitter, or a fused fiber beam splitter. In some example mass flow meters/controllers, the actuator includes a driving coil configured to actuate the flow tube via a magnet attached to the flow tube. Some example mass flow meters/controllers further include a flow control valve configured to control a flow of the fluid through the flow tube, in which the control circuitry is configured to control the flow control valve based on the determined mass flow rate.

Methods according to the invention involve: directing a fluid from an inlet of a flow tube to an outlet of the flow tube; causing a vibration in the flow tube via an actuator; emitting light from a light source; splitting, via at least one beam splitter, the light emitted by the light source into a first light beam and a second light beam; outputting, via a first optical sensor, first measurements of a first position of a first location on the flow tube based on detecting the first light beam; outputting, via a second optical sensor, second measurements of a second position of a second location on the flow tube based on detecting the second light beam; and determining, via control circuitry, at least one of a mass flow rate through the flow tube or a density of the fluid in the flow tube based on the first measurements and the second measurements.

According to the invention, splitting the light via the at least one beam splitter involves:
reflecting a first portion of the light from the light source, via a first mirror arranged at substantially a <NUM> degree angle to the light source, to form the first light beam; reflecting a second portion of light from the light source that passes through the first mirror back toward the first mirror via a second mirror; and reflecting the second portion of the light from the light source via the first mirror to form the second light beam.

Methods according to the invention further involve directing the first light beam and the second light beam in opposite directions. Some example methods further involve reflecting the first light beam via the first mirror to the first optical sensor via a second mirror and reflecting the second light beam reflected via the first mirror to the second optical sensor. Some example methods further involve thermally coupling the first optical sensor and the second optical sensor. Some example methods further involve thermally coupling the light source to the first optical sensor and the second optical sensor.

In some examples, splitting the light involves splitting the light using at least one of a cube beam splitter, a plate beam splitter, a pellicle beam splitter, a Wollaston prism, a diffractive beam splitter, an actuated beam splitter, or a fused fiber beam splitter. In some example methods, causing the vibration in the flow tube comprises actuating the flow tube via a magnet and a driving coil.

<FIG> is a schematic diagram of an example mass flow meter/controller <NUM>. The example mass flow meter/controller <NUM> of <FIG> may be used to measure mass flow and/or density of a fluid through a conduit connected in line with the mass flow meter/controller <NUM>, and/or to control mass flow of a fluid through the conduit by controlling a valve.

The example mass flow meter/controller <NUM> includes a flow-through base <NUM>, a flow tube <NUM>, a fluid inlet <NUM>, and a fluid outlet <NUM>. The flow tube <NUM> directs a fluid from the fluid inlet <NUM> of the flow tube <NUM> to the fluid outlet <NUM> of the flow tube <NUM>. To measure mass flow and/or density of the fluid flowing through the flow tube <NUM>, the example mass flow meter/controller <NUM> includes multiple optical sensors <NUM>, <NUM> (also referred to herein as "photo sensors"), an actuator to cause vibration in the flow tube <NUM> (e.g., a permanent magnet <NUM> and a driving coil <NUM>), and control circuitry <NUM>. To reduce measurement error, the example mass flow meter/controller <NUM> further includes a temperature sensor <NUM>.

The flow tube <NUM> is configured in a U-shape. The driving coil <NUM> generates an alternating magnetic field, which creates a driving force on the permanent magnet <NUM>, which is attached to the flow tube <NUM> and transfers the driving force to the flow tube <NUM> to result in a vibration in the flow tube <NUM>. The flow tube <NUM> vibrates at a frequency, and the control circuitry <NUM> may control the driving coil <NUM> to cause the vibration frequency to approximate the natural oscillation frequency of the flow tube <NUM>. Moving media (e.g., gas or liquid) inside the flow tube <NUM> creates a Coriolis force, which causes a phase shift between a first location <NUM> on the flow tube <NUM> that is upstream of the actuator and a second location <NUM> on the flow tube <NUM> that is downstream of the actuator. The optical sensors <NUM>, <NUM> measure the positions of the flow tube <NUM> at the first and second locations <NUM>, <NUM> and output respective signals (e.g., measurements) having the same frequency, but having a phase or time difference.

The example control circuitry <NUM> determines a mass flow rate through the flow tube <NUM> and/or a density of the fluid in the flow tube <NUM> based on first measurements from the optical sensor <NUM> and second measurements from the optical sensor <NUM>. In some examples, the control circuitry <NUM> controls a mass flow rate through the flow tube <NUM> using a flow control valve <NUM>. The control circuitry <NUM> may control the flow control valve <NUM> based on a comparison of a desired flow rate and the measured flow rate, and may include one or more control loops and/or filters such as a proportional-integral-derivative (PID) controller.

The example control circuitry <NUM> of <FIG> may be a general-purpose computer, a laptop computer, a tablet computer, a mobile device, a server, an embedded device, and/or any other type of computing device.

The example control circuitry <NUM> of <FIG> includes a processor <NUM>. The example processor <NUM> may be any general purpose central processing unit (CPU) from any manufacturer. In some other examples, the processor <NUM> may include one or more specialized processing units, such as graphic processing units and/or digital signal processors. The processor <NUM> executes machine readable instructions <NUM> that may be stored locally at the processor (e.g., in an included cache), in a random access memory <NUM> (or other volatile memory), in a read only memory <NUM> (or other non-volatile memory such as FLASH memory), and/or in a mass storage device <NUM>. The example mass storage device <NUM> may be a hard drive, a solid state storage drive, a hybrid drive, a RAID array, and/or any other mass data storage device.

A bus <NUM> enables communications between the processor <NUM>, the RAM <NUM>, the ROM <NUM>, the mass storage device <NUM>, a network interface <NUM>, and/or an input/output interface <NUM>.

The example network interface <NUM> includes hardware, firmware, and/or software to connect the control circuitry <NUM> to a communications network <NUM> such as the Internet. For example, the network interface <NUM> may include IEEE <NUM>. X-compliant wireless and/or wired communications hardware for transmitting and/or receiving communications.

The example control circuitry <NUM> may access a non-transitory machine readable medium <NUM> via the I/O interface <NUM> and/or the I/O device(s) <NUM>. Examples of the machine readable medium <NUM> of <FIG> 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 installed machine readable media.

To determine the mass flow rate, the example control circuitry <NUM> may use the mass flow equation shown in Equation <NUM> below: <MAT>.

In Equation <NUM>, MF is the mass flow (e.g., kilograms/second (kg/s), FCF is the flow calibration factor, which is a constant for a specific device (e.g., based on a calibration), and Δt = <MAT>, in which Θ is the phase difference between the output signals from the optical sensors <NUM>, <NUM>, and F is the natural oscillation frequency of the flow tube <NUM>.

<FIG> is a schematic diagram of an example implementation of the mass flow meter/controller <NUM> of <FIG>, in which a single light source <NUM> (e.g., an LED) provides multiple light beams <NUM>, <NUM> for detection by the optical sensors <NUM>, <NUM>. The light source <NUM> is controlled by a light source controller <NUM>. By reducing the number of light sources to one, the example of <FIG> reduces the number of independent noise or error sources in the measurement and increases the accuracy of the mass flow and/or density measurement(s). The optical sensors <NUM>, <NUM> output the resulting signals to respective amplifiers <NUM>, <NUM>, which may be implemented in the control circuitry <NUM> of <FIG>.

To direct multiple light beams <NUM>, <NUM> from the same light source <NUM> to two different optical sensors <NUM>, <NUM> such that the optical sensors <NUM>, <NUM> are capable of measuring the vibration of the flow tube <NUM> via the light beams <NUM>, <NUM>, the light source <NUM> may be configured to emit light in multiple directions. Additionally or alternatively, as discussed in more detail below, the mass flow meter/controller may include one or more beam splitters and/or the optical sensors <NUM>, <NUM> may be configured to output measurements of the positions of the first and second locations <NUM>, <NUM> on the flow tube <NUM> based on detecting multiple light beams generated using the single light source <NUM>.

<FIG> is a schematic diagram of an implementation according to the invention of the mass flow meter/controller <NUM> of <FIG>, including a beam splitter <NUM> to split light <NUM> output by a single light source <NUM> into multiple light beams <NUM>, <NUM> for detection by the optical sensors <NUM>, <NUM>.

The example beam splitter <NUM> of <FIG> includes a first mirror <NUM> oriented at a <NUM> degree angle to the light <NUM> from the light source <NUM>. The first mirror <NUM> reflects a first portion of the light <NUM> from the light source <NUM> to form the first light beam <NUM>, and directs the first light beam <NUM> toward the first optical sensor <NUM>. The first location <NUM> on the flow tube <NUM> is positioned between the first mirror <NUM> and the optical sensor <NUM>, such that the first location <NUM> of the flow tube <NUM> occludes a portion of the first light beam <NUM> based on the vibration of the flow tube <NUM>.

The beam splitter <NUM> includes a second mirror <NUM> that reflects a second portion <NUM> of the light <NUM> from the light source <NUM> that passes through the first mirror <NUM> back toward the first mirror <NUM>. The first mirror <NUM> reflects the second portion <NUM> of the light from the second mirror <NUM> to form the second light beam <NUM>, and directs the second light beam <NUM> toward the second optical sensor <NUM>. The second location <NUM> on the flow tube <NUM> is positioned between the first mirror <NUM> and the optical sensor <NUM>, such that the second location <NUM> of the flow tube <NUM> occludes a portion of the second light beam <NUM> based on the vibration of the flow tube <NUM>.

The beam splitter (e.g., mirrors <NUM>, <NUM>) are configured to direct the first light beam <NUM> and the second light beam <NUM> in opposite directions, and the first optical sensor <NUM> and the second optical sensor <NUM> are positioned on opposite sides of the beam splitter to receive the first light beam <NUM> and the second light beam <NUM>, respectively, from the at least one beam splitter (e.g., from mirrors <NUM>, <NUM>).

In contrast to the conventional Coriolis mass flow meters discussed above, the example flow meter of <FIG> has a reduced phase noise. Because only one light source <NUM> is used for both channels (e.g., both optical sensors <NUM>, <NUM>) the noise contributions to each channel from the light source <NUM> and the light source controller <NUM> are not independent, because the noise contributions are generated by the same components (e.g., the light source <NUM> and the light source controller <NUM>) for both channels, and can be compensated by the control circuitry <NUM>. As a result, the disclosed example mass flow meter of <FIG> reduces the number of noise contributors from six to two and improves the measurement accuracy of the example mass flow meter over the conventional mass flow meters.

<FIG> is a schematic diagram of another implementation according to the invention of the mass flow meter/controller <NUM> of <FIG>, including one or more beam splitters (e.g., mirrors <NUM>, <NUM>) to split light <NUM> output by a single light source <NUM> into multiple light beams <NUM>, <NUM> for detection by multiple optical sensors <NUM>, <NUM>.

In the example of <FIG>, the optical sensors <NUM>, <NUM> are thermally coupled to each other via a printed circuit board <NUM>. That is, the optical sensors <NUM>, <NUM> are coupled to the same printed circuit board <NUM>, and the printed circuit board <NUM> further includes a path of thermally conductive material <NUM> (e.g., a strip of copper, aluminum, etc.) coupling the optical sensors <NUM>, <NUM>. Because the optical sensors <NUM>, <NUM> have some parameters dependent on temperature, temperature differences between the optical sensors <NUM>, <NUM> may create a difference in output signal and additional phase error. The example printed circuit board <NUM> reduces temperature-dependent phase errors in the optical sensors <NUM>, <NUM> by closely locating the optical sensors <NUM>, <NUM>, and thereby reducing or substantially eliminating temperature gradients between the optical sensors <NUM>, <NUM>.

Instead of being mounted on opposite sides of the flow tube <NUM> from the mirror <NUM>, the example optical sensors <NUM>, <NUM> are mounted on the circuit board <NUM>. A third mirror <NUM> is configured at a <NUM> degree angle to the first light beam 308a to reflect the first light beam 308a from the first mirror <NUM> to the first optical sensor <NUM>. A fourth mirror <NUM> is configured at a <NUM> degree angle to the second light beam 310a to reflect the second light beam 310a from the first mirror <NUM> to the second optical sensor <NUM>. Both mirrors <NUM>, <NUM> reflect almost all incident light (e.g., the first and second light beams 308a, 308b, 310a, 310b) <NUM> degrees, and direct the light beams 308a, 308b, 310a, 310b toward the optical sensors <NUM>, <NUM> such that the light beams 308b, 310b incident on the optical sensors <NUM>, <NUM> are traveling in the same direction (e.g., <NUM> degrees relative to the emitted light <NUM> generated by the light source <NUM>).

In the example of <FIG>, the direction of vibration of the flow tube <NUM> is a different direction than the example of <FIG>. The first location <NUM> on the flow tube <NUM>, the second location <NUM> on the flow tube <NUM>, and a portion of the flow tube <NUM> between the first location <NUM> and the second location <NUM> (e.g., the U-shaped portion of the flow tube <NUM>) are oriented on a two-dimensional plane <NUM> as illustrated in <FIG>. In the example of <FIG>, the direction of vibration of the flow tube <NUM> is transverse to the plane <NUM>, while the direction of vibration in the examples of <FIG>, <FIG> and <FIG> are within the plane <NUM>. The actuator (e.g., the driving coil <NUM> and/or the magnet <NUM>) are configured to obtain the direction of vibration based on the arrangement of the optical sensors <NUM>, <NUM> and the light beams <NUM>, <NUM> relative to the flow tube <NUM>.

In the example of <FIG>, the light source <NUM> and/or the light source controller <NUM> are coupled to a second printed circuit board <NUM> that is separate from the printed circuit board <NUM>. In the example of <FIG>, the optical sensors <NUM>, <NUM> may be physically separated from the light source <NUM> and the light source controller <NUM>. A temperature difference may occur between the optical sensors <NUM>, <NUM> and the light source <NUM> and the light source controller <NUM> due to the physical separation, which can result in a difference in output signal, additional phase error, and a loss in measurement accuracy. <FIG> is a schematic diagram of an example implementation of the mass flow meter/controller <NUM> of <FIG>, including one or more beam splitters (e.g., the mirrors <NUM>, <NUM>) to split the light <NUM> output by the single light source <NUM> into multiple light beams <NUM>, <NUM> for detection by multiple optical sensors <NUM>, <NUM>. In the example of <FIG>, the optical sensors <NUM>, <NUM>, the light source <NUM>, and the light source controller <NUM> are thermally coupled to each other via a printed circuit board <NUM>.

Because the optical sensors <NUM>, <NUM>, the light source <NUM>, and the light source controller <NUM> have some parameters dependent on temperature, temperature differences between the optical sensors <NUM>, <NUM> may create a difference in output signal and additional phase error. The example printed circuit board <NUM> includes a path of thermally conductive material <NUM> (e.g., a strip of copper, aluminum, etc.) coupling the optical sensors <NUM>, <NUM>, the light source <NUM>, and the light source controller <NUM>. The example arrangement of the optical sensors <NUM>, <NUM>, the light source <NUM>, and the light source controller <NUM> in <FIG> reduces temperature-dependent phase errors in the optical sensors <NUM>, <NUM>, the light source <NUM>, and the light source controller <NUM> by closely locating the components and thereby reducing or substantially eliminating temperature gradients between the components.

To enable the single light source <NUM> to provide the light beams <NUM>, <NUM> to the optical sensors <NUM>, <NUM> located on the same printed circuit board <NUM>, in a way that causes the light beams 308a, 308b, 310a, 310b to traverse the flow tube <NUM>, the example of <FIG> includes a third mirror <NUM> and a fourth mirror <NUM>. The third mirror <NUM> is configured at a <NUM> degree angle to the first light beam 308a to reflect the first light beam 308a from the first mirror <NUM> to the first optical sensor <NUM>. The fourth mirror <NUM> is configured at a <NUM> degree angle to the second light beam 310a to reflect the second light beam 310a from the first mirror <NUM> to the second optical sensor <NUM>. Both mirrors <NUM>, <NUM> reflect almost all incident light (e.g., the first and second beams 308a, 310a) <NUM> degrees, and direct the light beams 308b, 310b toward the optical sensors <NUM>, <NUM> such that the light beams 308b, 310b incident on the optical sensors <NUM>, <NUM> are traveling in the opposite direction (e.g., <NUM> degrees relative to the emitted light <NUM> generated by the light source <NUM>).

Due to the different locations of the optical sensors <NUM>, <NUM> relative to the flow tube <NUM> (compared to the example of <FIG>), the mirror <NUM> is oriented at a <NUM> degree angle compared to the orientation of the mirror <NUM> of <FIG>, and the mirror <NUM> is oriented at a <NUM> degree angle compared to the orientation of the mirror <NUM>.

While the examples of <FIG> include an example implementation of a beam splitter, any type of beam splitter may be used. Example beam splitters that may be used include a cube beam splitter, a plate beam splitter, a pellicle beam splitter, a Wollaston prism, a diffractive beam splitter, an actuated beam splitter, or a fused fiber beam splitter.

<FIG> is a flowchart representative of an example method <NUM> that may be performed by the mass flow meter/controller <NUM> of <FIG> to measure mass flow and/or fluid density, and/or to control mass flow. The example method <NUM> will be described with reference to the example mass flow meter/controller <NUM> of <FIG> and <FIG>. However, the method <NUM> may be performed using any of the disclosed example mass flow meters/controllers.

At block <NUM>, the flow tube <NUM> directions a fluid from the inlet of the flow tube <NUM> to the outlet of the flow tube <NUM>. At block <NUM>, the actuator induces a vibration in the flow tube <NUM>.

At block <NUM>, the control circuitry <NUM> controls the light source <NUM> to emit light <NUM> by controlling the light source controller <NUM>. For example, the control circuitry <NUM> may enable the light source controller <NUM> to enable the light source <NUM>. At block <NUM>, one or more beam splitters (e.g., the mirrors <NUM>, <NUM>) split the light <NUM> emitted by the light source <NUM> into a first light beam <NUM> and a second light beam <NUM>.

At block <NUM>, the first optical sensor <NUM> measures a first position of the first location <NUM> on the flow tube <NUM> based on detecting the first light beam <NUM> or 308b, and outputs the first measurements (e.g., after amplification by the amplifier <NUM>). At block <NUM>, the second optical sensor <NUM> measures a second position of the second location <NUM> on the flow tube <NUM> based on detecting the second light beam <NUM> or 310b, and outputs the second measurements (e.g., after amplification by the amplifier <NUM>). The first and second measurements may be signals representative of the respective magnitudes of the first and second light beams <NUM>, 308b, <NUM>, 310b received by the optical sensors <NUM>, <NUM>. The magnitudes of the signals may change based on the occlusion of the light beams <NUM>, 308b, <NUM>, 310b by the flow tube <NUM>, which changes as a result of the vibration of the flow tube <NUM>.

At block <NUM>, the control circuitry <NUM> determines the mass flow rate through the flow tube <NUM> (e.g., based on a phase difference between the first measurements and the second measurements) and/or determines a density of the fluid within the flow tube <NUM> (e.g., based on the vibration frequency of the flow tube <NUM>).

At block <NUM>, the control circuitry <NUM> determines whether the flow rate is to be controlled. For example, a mass flow controller may be configured to control the flow rate, while a mass flow meter omits controlling the flow rate. If the flow rate is to be controlled (block <NUM>), the control circuitry <NUM> adjusts the flow control valve <NUM> based on the difference between the measured flow rate and a target flow rate.

After adjusting the flow control valve (block <NUM>), or if the flow control rate is not being controlled (block <NUM>), control returns to block <NUM> to continue measurement and/or control.

Another typical implementation may comprise one or more application specific integrated circuit or chip. Some implementations may comprise a non-transitory machine-readable (e.g., computer readable) medium (e.g., FLASH memory, optical disk, magnetic storage disk, or the like) having stored thereon one or more lines of code executable by a machine, thereby causing the machine to perform processes as described herein.

While the present method and/or system has been described with reference to certain implementations, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present method and/or system. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from its scope. For example, blocks and/or components of disclosed examples may be combined, divided, re-arranged, and/or otherwise modified. Therefore, it is intended that the present method and/or system not be limited to the particular implementations disclosed, but that the present method and/or system will include all implementations falling within the scope of the appended claims.

The present methods and/or systems may be realized in hardware, software, or a combination of hardware and software. A typical combination of hardware and software may be a general-purpose computing system with a program or other code that, when being loaded and executed, controls the computing system such that it carries out the methods described herein.

Claim 1:
A mass flow meter/controller (<NUM>), comprising:
a flow tube (<NUM>) configured to direct a fluid from an inlet of the flow tube to an outlet of the flow tube;
an actuator configured to cause a vibration in the flow tube;
a light source (<NUM>) configured to emit light;
at least one beam splitter configured to split the light emitted by the light source (<NUM>) into a first light beam (<NUM>) and a second light beam (<NUM>);
a first optical sensor (<NUM>) configured to output first measurements of a first position of a first location on the flow tube based on detecting the first light beam;
a second optical sensor (<NUM>) configured to output second measurements of a second position of a second location on the flow tube based on detecting the second light beam; and
control circuitry configured to determine at least one of a mass flow rate through the flow tube or a density of the fluid in the flow tube (<NUM>) based on the first measurements and the second measurements;
characterised in that
the at least one beam splitter is configured to direct the first light beam (<NUM>) and the second light beam (<NUM>) in opposite directions, and the first optical sensor and the second optical sensor are positioned on opposite sides of the at least one beam splitter to receive the first light beam and the second light beam, respectively, from the at least one beam splitter.