Patent Application
20190293467
The present disclosure pertains to devices for flow measurements of fluids.
The disclosure reveals a mass flow sensor assembly that contains an absolute pressure sensor for compensating via electronics an output reading of mass flow of a fluid through a channel. The flow and pressure sensors may be built in close proximity to each other in the channel. The mass flow sensor assembly incorporating the absolute pressure sensor may be fabricated using MEMS (micro electro mechanical systems) techniques.
The present system and approach may incorporate one or more processors, computers, controllers, user interfaces, wireless and/or wire connections, and/or the like, in an implementation described and/or shown herein.
This description may provide one or more illustrative and specific examples or ways of implementing the present system and approach. There may be numerous other examples or ways of implementing the system and approach.
Aspects of the system or approach may be described in terms of symbols in the drawing. Symbols may have virtually any shape (e.g., a block) and may designate hardware, objects, components, activities, states, steps, procedures, and other items. The term “fluid” may refer to a gas or liquid.
When calibrating a mass flow sensor to output in pressure drop, an absolute pressure may be critical to achieving an accurate output from the mass flow sensor. A pressure drop across a part at a given mass flow may change based on changes in the absolute pressure, but the output of the sensor would remain the same. When calibrating a mass flow sensor to an output in pressure drop, the absolute pressure appears critical to achieving an accurate output.
Some people may use analog mass flow sensors that are uncompensated, and are used in applications where a differential pressure is desired. They may look to an upgrade for their next generation of products of digital high resolution compensated sensors. Competitors may make a compensated pressure drop sensor that does not necessarily correct for absolute pressure. This disclosure may exhibit a competitive advantage by providing more accurate performance.
An absolute pressure sense die may be placed either in a sensor flow path or with a pneumatic connection to flow path to measure absolute pressure within the sensor flow path. Absolute pressure may be controlled with sensed pressure data during calibration and the pressure data may be used to mathematically compensate a flow sensor output versus pressure drop for fluctuations in absolute or atmospheric pressure.
The system may have a software component. The sensor may be a hardware device with some embedded software measuring/detecting and transmitting data (e.g., temperature, pressure, motion). Embedded software may run in a device/unit (e.g., firmware).
When a non-zero fluid flow 24 is present in the fluid channel 12 and the heater element 22 is heated to a temperature higher than the ambient temperature of the fluid in the fluid flow 24, the symmetrical temperature distribution may be disturbed and the amount of disturbance may be related to the flow rate of the fluid flow 24 in the fluid channel 12. The flow rate of the fluid flow 24 may cause the upstream sensor element 21 to sense a relatively cooler temperature than the downstream sensor element 23. In other words, the flow rate of the fluid flow 24 may cause a temperature differential between the upstream sensor element 21 and the downstream sensor element 23 that is related to the flow rate of the fluid flow 24 in the fluid channel 12. The temperature differential between the upstream sensor element 21 and the downstream sensor element 23 may result in an output voltage differential between the upstream sensor element 21 and the downstream sensor element 23.
In another illustrative embodiment, the mass flow and/or velocity of the fluid flow 24 may be determined by providing a transient elevated temperature condition in the heater element 22, which in turn, causes a transient elevated temperature condition (e.g., heat pulse) in the fluid flow 24. When there is a non-zero flow rate in the fluid flow 24, the upstream sensor element 21 may receive a transient response later than the downstream sensor element 23. The flow rate of the fluid flow 24 can then be computed using the time lag between the upstream sensor element 21 and downstream sensor element 23, or between the time the heater is energized and when the corresponding elevated temperature condition (e.g., heat pulse) is sensed by one of the sensors, such as the downstream sensor 23.
In
A table, equations and solutions relevant to flow rate of an airflow sensor are indicated below. Many of these items may be in the public domain. A flow path through the sensor may behave as a combination of pipe and orifice type flow.
One may note at a given mass flow rate, a pressure drop may be affected by density of the fluid. It seems that if one has a measured delta pressure between the two ends of the pipe, then the mass flow rate may be calculated. There may be other bases for calculations. Another delta pressure may between a tap to the first end of the pipe, and still another pressure delta may be between the tap and the second end of the pipe. These mass flow rates may be used to verify or compensate a flow sensor reading of the fluid flow through the channel of the sensor assembly. If all of the variables, except density, are known, then density may be calculated and aid in identifying the fluid. If there is just one unknown, then of course it may be calculated.
When a mass flow sensor is calibrated to pressure drop, an issue is that delta pressure may fluctuate with density changes. So a purpose of adding a pressure sensor may be to adjust for changes in atmospheric pressure, such as from weather changes, altitude, and even local effects in test equipment.
Since the location of pressure sensor is relatively close to the airflow sensor, an error from a small difference in pressure in the flow path can be calibrated out. The pressure sensor may still track atmospheric pressure.
To recap, a flow sensor assembly may incorporate a housing having a channel, an input port connected to a first end of the channel, an output port connected to a second end of the channel, a mass flow sensor situated in the channel, an absolute pressure sensor having a configuration so that the absolute pressure sensor can detect absolute pressure in the cavity, and an electronics module connected to the absolute pressure sensor and the mass flow sensor. Mass flow rate signals from the mass flow sensor may be sent to the electronics. The electronics may provide an indication of a mass flow rate of a fluid in the channel according to the flow rate signals. Absolute pressure signals from the absolute pressure sensor may be sent to the electronics. The electronics may compensate the indication of the mass flow rate according to the absolute pressure signals. The mass flow sensor and the pressure sensor may be integrated as a single unit.
The housing and the single unit may be fabricated as one or more dies with MEMS fabrication techniques.
The channel may extend in a direction from the first end of the channel along a straight path to the second end of the channel.
The channel may exhibit a circuitous path with one or more bends from the first end of the channel to the second end of the channel.
The mass flow sensor may incorporate a first thermal sensor and a second thermal sensor.
Temperature data may go from the first thermal sensor and second thermal sensor to the electronics.
The electronics may calculate the mass flow rate of the fluid from temperature signals of the first thermal sensor and the second thermal sensor.
The mass flow sensor may further incorporate a heater upstream from at least one of the first and second thermal sensors.
The electronics may incorporate a processor and a memory. The memory may contain one or more items selected from a group incorporating one or more lookup tables and one or more algorithms. The processor may incorporate an analog-to-digital converter (ADC) having inputs connected to the mass flow sensor and the absolute pressure sensor. The processor may digitally determine a compensated mass flow rate of a fluid in the channel from the mass flow rate signals and channel pressure signals as digitized from the outputs of the ADC, in conjunction with the one or more items selected from the group comprising one or more lookup tables and one or more algorithms.
The configuration of the absolute pressure sensor may incorporate a cavity in the housing connected to the channel via a tap, and an absolute pressure detection element situated in the cavity.
The tap to the channel may be at a location between the first end and the second end of the channel.
The location of the tap may be situated as close as possible to the flow sensor.
An error in a pressure indication of a fluid in the channel due to a distance of the tap from the mass flow sensor may be calibrated out.
A compensated flow sensor may incorporate a flow channel having an in port at a first end and an out port at a second end, a mass flow sensor situated in the flow channel, an absolute pressure sensor situated adjacent to the flow sensor, and a controller having inputs for connection to outputs of the mass flow sensor and the absolute pressure sensor, and having an output for an indication of a mass flow rate of a fluid in the channel. The indication of the mass flow rate may be compensated by the controller according to an amount of absolute pressure detected by the absolute pressure sensor.
The controller may implement one or items from a group incorporating a look-up table and an algorithm.
The mass flow sensor and the absolute pressure sensor may be integrated as a unit device.
The mass flow sensor may be a MEMS fabricated device.
An approach for detecting a fluid flow rate in a channel may incorporate situating a fluid flow sensor in a channel, situating an absolute pressure sensor in the channel, processing measurements from the fluid flow sensor and the absolute pressure sensor of a fluid in the channel, calculating a flow rate based on processed measurements from the fluid flow sensor, and compensating the flow rate based on processed measurements from the absolute pressure sensor. The fluid flow sensor and the absolute pressure sensor may be situated adjacent to each other in the channel.
The approach may further incorporate situating a temperature sensor in the channel, processing measurements from the temperature sensor, and compensating the flow rate based on processed measurements from the temperature sensor.
U.S. patent application Ser. No. 14/800,492, filed Jul. 15, 2015, is hereby incorporated by reference. U.S. Pat. No. 7,647,842, issued Jan. 19, 2010, is hereby incorporated by reference. U.S. Pat. No. 8,418,549, issued Apr. 16, 2013, is hereby incorporated by reference. U.S. Pat. No. 8,695,417, issued Apr. 15, 2014, is hereby incorporated by reference.
Any publication or patent document noted herein is hereby incorporated by reference to the same extent as if each publication or patent document was specifically and individually indicated to be incorporated by reference.
In the present specification, some of the matter may be of a hypothetical or prophetic nature although stated in another manner or tense.
Although the present system and/or approach has been described with respect to at least one illustrative example, many variations and modifications will become apparent to those skilled in the art upon reading the specification. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the related art to include all such variations and modifications.
