GAS METER WITH GAS THERMAL PROPERTY MEASUREMENT AND AUTO-COMPENSATION

Abstract

An electronic utility gas meter using MEMS thermal mass flow sensor to meter gas custody transfer and MEMS gas thermal property sensor to compensate the metering values due to gas composition variations is disclosed in the present invention. The meter is designed to have a MEMS mass flow sensor to meter the city utility gas consumption independent of environmental temperature and pressure while a MEMS gas thermal property or dual gas thermal property sensors to compensate the tariff due to the gas composition variations for compliance with the current regulation requirements of tariff and remove the major concerns for the wide deployment of the thermal mass MEMS utility gas meters.

Claims

1. An electronic utility gas meter with MEMS mass flow sensors and gas thermal property sensors for compensation of tariff due to gas composition variation in compliance to the current tariff practice, comprising A MEMS mass flow sensor for metering the custody transfer city utility gas, operating with calorimetric sensing principle that is independent of variations in environmental temperature and pressure; A MEMS gas thermal property sensor or dual gas thermal property sensors for in situ measurement of the gas thermal properties providing the feedback to the mass flow measurement to compensation the metrology data such that the gas composition dependent tariff can be eliminated in accordance with the current tariff; A meter body that is constituent of a Venturi flow channel, a pair of flanged or threaded mechanical connection and two component chambers to host the control electronics and power/battery pack, respectively; A control electronics printed circuitry board for acquisition of the data from the sensing elements, processing the data compensation, performing the data communication; managing the power supply, providing the onboard data storage, display the metering information, and managing the failure events; A data communication port with wired and wireless options that enable the data transmission, allow the manual access to the onboard data storage, programming the user specified functions, and diagnosis the meter performance; A pair of flow conditioning apparatus that performs the flow straightening and flow profiling; both are installed at the inlet of the flow channel for maintaining a stable and reproducible gas flow; A battery pack that provides the power to the MEMS mass flow sensor and gas thermal property sensors, as well as to the control electronics printed circuitry board; and A pair of meter covers that seals the battery pack chamber as well as the control electronics chamber with a display window that can be coated with anti-tamper transparent metal film or anti-interference film.

2. An electronic utility gas meter with MEMS mass flow sensors and gas thermal property sensors for compensation of tariff due to gas composition variation in compliance to the current tariff practice of claim 1 wherein said MEMS mass flow sensor will be made with calorimetric sensing that is independent of environmental temperature and pressure variation in favor for the accurate city utility gas metering for tariff.

3. The electronic utility gas meter with MEMS mass flow sensors and gas thermal property sensors for compensation of tariff due to gas composition variation in compliance to the current tariff practice of claim 1 wherein said gas thermal property sensor will be made of MEMS sensing technology which utilizes the heated thermistor to measure the thermal conductivity and thermal diffusivity to measure the thermal capacitance.

4. The MEMS gas thermal property sensor of claim 3 wherein said gas thermal property sensor will be made on silicon substrate with a thermal isolation cavity with silicon nitride and silicon dioxide membrane with a thickness preferably 0.6 to 4 micrometers, and most preferably 1.2 micrometers.

5. The MEMS gas thermal property sensor of claim 3 wherein said gas thermal property sensor will have two identical thermistors in sizes and resistance values as the sensing elements. These thermistors are preferably made of high temperature coefficient materials such as platinum, or nickel or doped ploy-crystalline silicon; and most preferably made of platinum.

6. The MEMS gas thermal property sensor of claim 3 wherein said gas thermal property sensor will have one of the thermistor or sensing element passivated with thermally conductive materials such as silicon nitride or silicon carbide, but most preferably with silicon nitride, while another thermistor will be open to the flow gas medium to be measured.

7. The MEMS gas thermal property sensor of claim 3 wherein said gas thermal property sensor will have the two thermistors on the sensor operating in differential circuitry to eliminate any electrical and external temperature effects.

8. The electronic utility gas meter with MEMS mass flow sensors and gas thermal property sensors for compensation of tariff due to gas composition variation in compliance to the current tariff practice of claim 1 wherein said MEMS sensor assembly will be comprising a MEMS mass flow sensor place at the tip of the assembly probe whereas the gas thermal property sensors will be placed at the steam of the probe in a sealed space that will only have a small window open to the flow gas medium to be measured. The small window will have a filter installed to prevent contaminants such as oil vapor and particles.

9. The MEMS sensor assembly of claim 8 wherein said gas thermal property sensor placed in a sealed space will be preferably to have the sealed space splitting into two identical sized spaces, of which one space will have a gas thermal property sensor completely sealed with reference gas such as methane, nitrogen or air, but most preferably sealed with methane. The other space will have another identical gas thermal property sensor installed but having a small window open to the flow gas medium to be measured. The small window will have a filter installed to prevent contaminants such as oil vapor and particles.

10. The electronic utility gas meter with MEMS mass flow sensors and gas thermal property sensors for compensation of tariff due to gas composition variation in compliance to the current tariff practice of claim 1 wherein said sensor assembly will be inserted into the flow channel with the mass flow sensor at the tip of the probe of the sensor assembly being placed at the central position of the throat of the Venturi flow channel where the flow speed is the highest.

11. The electronic utility gas meter with MEMS mass flow sensors and gas thermal property sensors for compensation of tariff due to gas composition variation in compliance to the current tariff practice of claim 1 wherein said flow restrictor will be comprised a flow straightener and a flow profiler that shall be sequentially installed at the inlet of the flow channel for the purpose of maintaining a reproducible flow profile. The distance between the flow profiler and the straightener shall be one sixth to one half of the diameter of main flow channel but preferably one third of the diameter of the main flow channel. In case of a low pressure drop across the flow channel is required, the said flow conditioning apparatus could be comprised of only flow straightener.

12. The electronic utility gas meter with MEMS mass flow sensors and gas thermal property sensors for compensation of tariff due to gas composition variation in compliance to the current tariff practice of claim 1 wherein said control electronics will provide the data process of the acquired mass flowrate and the gas thermal properties from the said MEMS sensing elements. The control electronics will further keep the data into a plural number of solid memories, and preferably into three separate solid memories such that any electronic malfunctioning will not impact the data safety. In the case that the meter is connected to a network, the control electronics will response to the remote inquires or automatically transmit any data registry to the designated data center or service center while display the same on the meter LCD display. The control electronics will also perform power status monitor and evaluation, and send alarm register at fixed time period that can be programmed in advance before the end of the battery power.

13. The electronic utility gas meter with MEMS mass flow sensors and gas thermal property sensors for compensation of tariff due to gas composition variation in compliance to the current tariff practice of claim 1 wherein said mechanical connectors are preferably the flange type for easy installation and maintenance. Alternatively, threaded connection is also preferred for low flowrate models where the existing mechanical meters can be replaced without changing the original mechanical configuration.

14. The electronic utility gas meter with MEMS mass flow sensors and gas thermal property sensors for compensation of tariff due to gas composition variation in compliance to the current tariff practice of claim 1 wherein said communication port will be able to served as a local data access port as well for manual data download and meter failure diagnosis.

15. The electronic utility gas meter with MEMS mass flow sensors and gas thermal property sensors for compensation of tariff due to gas composition variation in compliance to the current tariff practice of claim of claim 1 wherein said control electronics unit shall provide the interface for wired or wireless transmission apparatus such as NB-IoT, Bluetooth, Zigbee, infrared transmission and/or general packet radio service (GPRS) transmission apparatus, per the local regulations where the said meter is installed.

16. The electronic utility gas meter with MEMS mass flow sensors and gas thermal property sensors for compensation of tariff due to gas composition variation in compliance to the current tariff practice of claim 1 wherein said low power operation based on the battery pack will have the capability of averaged power in microwatt such that the battery power can provide reasonable field operation time, preferably ten years, but not less than three years.

17. The electronic utility gas meter with MEMS mass flow sensors and gas thermal property sensors for compensation of tariff due to gas composition variation in compliance to the current tariff practice of claim 1 wherein said display glass cover will have the capability to withstand external interference by electrical magnetic field and tamper proof. The glass cover will be preferably coated with transparent metal films that will meet the requirements by electrical magnetic compatibility standards.

Description

BRIEF DESCRIPTIONS OF THE DRAWINGS

[0017] FIG. 1: The explosive view of the disclosed utility gas meter assembled with the thermal mass flow sensing technology and simultaneously measured gas thermal properties for compensation of the tariff due to gas composition variations.

[0018] FIG. 2: The perspective view of the disclosed utility gas meter showing the flow channel design and the sensor probe assembly path.

[0019] FIG. 3: The design of the M EMS flow sensing assembly with the key elements.

[0020] FIG. 4: The design of the MEMS flow sensing assembly with the gas thermal property sensors packaged in close proximity to the flow sensing element.

[0021] FIG. 5: Alternative version of MEMS flow sensing assembly to further improve the performance of the gas thermal property sensor.

[0022] FIG. 6: The final assembly of the disclosed utility gas meter with gas thermal property measurement and auto-compensation.

[0023] FIG. 7: The design of a MEMS gas thermal property measurement sensor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The explosive view of the gas meter using MEMS sensing elements for the metrology and gas thermal property measurement of city utility gas disclosed in this invention is shown in FIG. 1. The gas meter is having a metal molded meter body (100). The meter body is constituent of a flow channel having the standard connection sizes of the city utility gas pipes (130), a control electronics chamber hosts the data acquisition, communication and display electronics (110), and the power/battery pack chamber (120). Further, the pipe connection is preferable to be flange type for easier installation and maintenance but it can also be threaded when replacing some of the existing mechanical meters. The meter body (100) will be made with cast aluminum alloy or stainless steel in compliance with the utility industry standards for surviving in the long term filed service time. The MEMS sensor assembly (200) having the mass flow sensing and gas thermal property sensing elements will be made into an insertion probe formality that can be placed into the flow channel for data acquisition. The control electronics printed circuitry board (300) will have the functions of acquisition of the raw data from the MEMS sensing elements, amplification and conversion of the analog data via a high precision analog to digital converter (ADC) into digital ones for processing by the microcontroller (MCU) where the digital data are compared to those installed at the calibration to output the correct metering value. Simultaneously, the gas thermal property will also be acquired from the gas thermal property sensors and compared to those stored at the calibration. The MCU will then invoke the algorithm for the gas thermal property or gas composition variation compensation once such variation is detected. Each compensation event and the corresponding data will also be stored on the same board at plural numbers of solid memories for data safety. The remote data communication is preferably to be performed via the industry standard protocol such as NB-IoT or GPRS or other standards depending on the geographic locations. The Display (320) is preferable to be a liquid crystal display (LCD) for the desired low power operation of the said meter. Additional tasks by the control electronics will include the detection of battery power status, flowrate abnormality and others which are interests to the users and be pre-programmed. The meter cover (140) will be made with the same materials as the meter body and the seal to the meter component chambers will be done via gaskets and screws to meet the protection class requirement since the meters are usually placed outdoor with direct exposure to the open space in the environment. The power battery pack chamber (120) will hosts the sealed battery pack (400) and the connection terminal (310) that connects to both the control electronics supplying the power and data port. For the data safety, a local data port with a data cable (500) will provide the data access by the users in case the remote communication will be disrupted for various reasons. This data port will also serve for the local GPRS connection and external power supply in case the battery cannot support the required communication power consumption. In order to achieve the custody transfer or tariff required accuracy, a pair of the flow dynamic constrainers will be installed at the inlet of the flow channel of the said utility gas meter. The outer block (150) is a flow straightener which removes the turbulent instability and it is then followed by a flow profiler (160) which forces the flow into a desired profile to ensure the measurement repeatability and accuracy. The straightener and the profiler are normally separated at a distance which is not longer than half of the flow channel diameter for the best performance.

[0025] The component chamber is designed and made into two separated but closely connected ones. The control electronics chamber is normally sealed with tamper proof as it serves the metering tariff data. The seal can be done by a third authorized party per the local regulation requirements. This will ensure the integrity of tariff data and prevent any tamper. The independent battery pack chamber also makes the change of the battery easier as the battery pack would be required to be changed since the battery may be consumed in a much shorter time than the meter service lifetime. The other detailed components used for making of the disclosed 1 utility gas meter are illustrated in FIG. 2 by the perspective view of a portion of the preferred meter in FIG. 1. The flow channel (105) is made with a Venturi shape where the sensor assemble is inserted into the flow channel at its throat from the control electronics chamber through opening (201). The Venturi profile will provide an acceleration of the medium flow speed at its throat position where the sensor will have the enhanced sensitivity.

[0026] The detailed making of the MEMS sensor assembly (200) is illustrated in FIG. 3 which exhibits the mass flow sensor chip (210) that is placed at the tip of the insertion probe (230) sensor assembly. The mass flow sensor (210) will be preferable to be made with MEMS mass flow sensing technology and operate with calorimetic sensing principle that is independent of environmental temperature and pressure variation. The steam of the insertion probe will be preferred to be a circular form while towards its tip where the MEMS mass flow sensor is places the circular form will be changed into a “V” shape (225) for the better flow profile and stability. The MEMS mass flow sensor chip on a carrier printed circuitry board is embedded into the thin tip plate that is preferred to be made of stainless steel. The front side of the plate (220) will have a slope to form the boundary layer in the flow medium such that the flow medium across the plate and being sensed by the MEMS flow sensor will be forced to re-profiled into a laminar flow that results in a best measurement conditions for the MEMS mass flow sensor. The said MEMS sensor assembly will be sealed to the meter flow channel and fixed with screws via the installation positions (240). The seal of the wire connection (260) can be achieved with nonvolatile epoxy (250).

[0027] The placement of gas thermal property sensors is exhibited in FIG. 4. The sensor (211) is preferred to be placed in a sealed space (231) at the steam of the MEMS sensor assembly probe (230). The sealed space will only have one small window open to the flow medium which provides the gas exchanges when the flow medium composition is changed. The window can be further installed with a filter that can be effectively filtering out the impurities such as oil vapors or particles or other foreign materials. The sealed space will allow the gas thermal property sensor not to be impacted by the medium flow which can introduce additional temperature effects for the sensor. The position of the said space to host the gas thermal property sensor will also have the lowest flow rate of the flow due to the flow profile inside a closed conduit or channel. To further improve the performance of the gas thermal property sensor, an alternative configuration is exhibited in FIG. 5 where the said space for the gas thermal property sensor is divided into two with the identical size (232 and 233). Each of the space will have one gas thermal property sensor installed, but one sensor (212) will be completed sealed in the space (232) filled with reference gas such as methane or air or nitrogen, and another identical gas thermal property sensor (213) in the identical sized space (233) will have a small window (236) open to the gas flow medium to be measured. The window will also be installed with the filter that can be effectively filtering out the impurities such as oil vapors or particles or other foreign materials. These two sensors (212 and 213) will be operating in a differential circuitry such that any electrical drifting can be fully eliminated to ensure the high precision of the gas thermal property measurements which is critical for the tariff compensation due to the gas composition (thermal property) variations.

[0028] The design and structure of the said gas thermal property sensor is exhibited in FIG. 6 where the sensor is preferred to be made with the MEMS sensing technology. The said sensor will have a silicon substrate (223) on which a thermal isolation cavity (224) is made beneath a membrane composed of low stressed silicon nitride and silicon dioxide that can be made with low pressure chemical vapor deposition. The gas thermal property sensing elements (thermistors) can be made with materials of high temperature coefficient for better sensitivity such as platinum, nickel or doped polycrystalline silicon. These two thermistors (225 and 226) will be made with the identical size and resistance value but one thermistor (225) will be open to the flow gas medium to be measured while another one (226) will be passivated by a thin film such as silicon nitride. In the actual making process, an etching process to the passivation film can be performed to open the window (227) such that the thermistor (225) will be in direct contact with the flow gas medium. In the static gas environment, the gas thermal conductivity, K, can be measured by the elevated temperature of the heated thermistor, and the thermal capacitance, C.sub.p, can be measured by the elevated temperature of the adjacent thermistor due to the diffusivity, D:

[00001]$D=\frac{\kappa }{\rho C_p}$

Where ρ is the gas density. These two thermistors will be operation in a differential mode such that the thermal instability and temperature effects of the thermistor can be removed for the enhanced gas thermal property measurement accuracy. Each of the thermistors will be connected to the wire bonding pads (228) that are placed symmetrically at the four corners of the silicon substrate.

[0029] The final assembly of the said preferred utility gas meter (100) is exhibited in FIG. 7 where the battery pack chamber (120) is covered and sealed with a sold metal made with the same materials of the meter body, while the control electronics chamber (110) will be sealed with a cover having a glass window and additional tamper proof mechanism which would be dependent on the regulations by the local tariff authority where the meter will be applied. For the ultimate protection and tamper proof, the glass window will be coated a transparent metal film which will be anti-electrical magnetic radiation or other external interferences.