WO2001098736A1

WO2001098736A1 - Gas meter and method for detecting a consumed amount of gas

Info

Publication number: WO2001098736A1
Application number: PCT/IB2001/001069
Authority: WO
Inventors: Felix Mayer; Andreas Martin HÄBERLI; Ralph Steiner Vanha; Urs Martin Rothacher
Original assignee: Sensirion Ag
Priority date: 2000-06-23
Filing date: 2001-06-14
Publication date: 2001-12-27
Also published as: AU2001274372A1; DE10129300A1; CH694474A5

Abstract

The invention relates to a gas meter for the purpose of calculating the charges, which is adapted to measure the mass flow of the gas. Said gas meter comprises a mass flow detector (4), a control (5) and a display (6). The inventive gas meter may further comprises a card reader (7) and a valve (8). The mass flow detector is based on a sensor element that is integrated on a semiconductor chip together with a digital and analogous evaluation unit. Since it is the mass flow and not the flow speed or the volume of the consumed gas that is measured, the value obtained is independent of the pressure and is substantially based on the calorific value of the gas.

Description

Gas meter and method for determining a consumed

amount of gas

Reference to related applications

This application claims priority from Swiss Patent Application 1252/00, filed on June 23, 2000, the entire disclosure of which is hereby incorporated by reference.

background

The invention relates to a gas meter and a method for determining a quantity of gas consumed according to the preamble of the independent claims.

Gas meters are devices with which the gas consumption of a consumer is measured so that the amount of gas consumed can be charged to the consumer. Conventional volumetric gas meters have the disadvantage that their measured values are dependent on pressure and temperature. This leads to an unjust calculation of gas costs.

Presentation of the invention

It is therefore the task of providing a gas meter and a method of the type mentioned at the outset which determine consumption values which are as accurate as possible in order to enable a more just calculation of the gas costs.

According to the claims, this task is solved by determining the mass flow of the gas and integrating it over time. So it is not the volume but the mass of the gas consumed that is determined. There the mass also corresponds to the calorific value of the gas, this allows a fairer fee calculation.

The gas meter preferably has an integrated mass flow sensor with a semiconductor substrate with a membrane and measuring components arranged thereon.

For particularly high accuracy with low manufacturing costs, an analog part and a digital part are simultaneously integrated on the semiconductor substrate. The signals are preprocessed in the analog section, i.e. for example, amplified and then digitized. The digitized data is linearized in the digital part. By integrating the parts all on a common semiconductor substrate, there is a reduction in manufacturing costs. Nevertheless, thanks to the linearization, a high level of accuracy can be achieved, even over a wide range of gas flows.

In order to make the mass flow sensor as robust as possible, a tensile passivation layer can be applied over the membrane. Such a passivation layer can put the membrane under tensile stress. This causes a deflection, which e.g. would cause a reduction in mechanical stability.

Brief description of the drawings

Further refinements, advantages and applications of the invention result from the dependent claims and from the description that follows with reference to the figures. Show:

1 shows a block diagram of a gas meter according to the invention, FIG. 2 shows a schematic representation of a possible embodiment of the mass flow detector. 3 shows a mass flow detector with linear response,

4 shows a section through the sensor element, FIG. 5 shows a plan view of a semiconductor module with sensor element and electronic circuits,

Fig. 6 is a block diagram of the block according to

Fig. 5 and

Fig. 7 is a block diagram of the controller.

Ways of Carrying Out the Invention

Overview:

1 shows a block diagram of an embodiment of the invention in the form of a gas meter 1, as it is e.g. can be used to determine gas costs in a household.

The gas meter has a main channel with an input line 2 and an output line 3 for the gas to be measured. A mass flow detector 4 is provided for measuring the amount of gas, i.e. a sensor with which the mass of the gas flowing through per unit of time is determined. A controller 5 evaluates the results of the mass flow detector 4, operates a display 6 and e.g. a chip card reader 7. It can also control a closing valve 8. A power supply 9 feeds all components, preferably from a battery.

The parts of the gas meter 1 are described in detail below. It should be noted that the use of some of these parts is not limited to a gas meter. For example, the mass flow detector explained below or the sensor element can be used in a large number of fields of application.

Mass flow detector:

The mass flow detector 4 either measures the mass rate, ie the mass per unit of time, or an integer. grail the mass rate, ie the total mass. Instead of the mass or mass flow rate, the respective size per unit flow area of the gas line can also be determined and then converted. Fig. 2 shows schematically the structure of the mass flow detector. In the following, the "mass flow" is understood to mean the mean mass flow pv, where p is the density and v is the velocity of the gas. If the entire mass flow through the main channel 2, 3 is to be determined, p.vjj should be integrated in a known manner, where VJJ is the average flow velocity in the main channel.

In the present embodiment, a bypass 10 is provided on the main channel, which runs parallel to a section 11 of the main channel 2, 3, with an input 12 and an output 13. A sensor element 14 is provided in the bypass 10.

At least in an area 15 between the mouths of the bypass 10 there is an area shown in gray in FIG. 2, in which the flow resistance of the gas is increased in comparison to the rest of the main channel in order to increase the pressure drop Δp between the mouths.

A measuring arrangement is preferably arranged in the sensor element 14, which has a heating element and symmetrically two temperature sensors. A preferred embodiment of this arrangement is described below.

The temperatures at the temperature sensors of such a sensor element depend on the product of the flow velocity vg in the bypass 10 and the density p of the gas. The output signal S of the sensor element is therefore a function f of the mass flow pv- _β , where vg denotes the gas velocity at the location of the sensor element 14 in the bypass 4, ie

S = s (pv _B ) (1) By means of suitable linearization, a signal proportional to the mass flow can be generated, so that

S = kpv _B , (2)

where k is a constant.

The gas flowing through the bypass 10 generates a pressure difference Δp between the mouths of the lines 12 and 13. The pressure difference Δp is dependent on the gas velocity v _B in the bypass 10, ie

Δp = f _B (v _B ), (3)

the function f _{B describes} this dependency.

On the other hand, this pressure difference also depends on the flow velocity vpj in the main channel, i.e.

Δp = f _H (v _H ). (4)

where the function f _{H describes} the dependence of the pressure drop on the flow velocity in the main channel.

The functions f _B and fjj depend on the geometry of the main channel and the bypass. For laminar flow conditions, f _B and fjj are linear functions. With turbulent flow conditions or with dynamic pressure, f _B and fjj can also depend on higher powers of the respective speed, in particular on the square of the speed.

From equations (3) and (4) we get:

v _B = f _B -l (f _H (v _H )) = F (v _H ) (5)

The properties of the mass flow detector can be optimized by suitable selection of the function F or the functions f and fjj. 3 shows an embodiment of a mass flow detector with a linear response. A linear flow resistance 15 'is arranged in the main channel, so that Δp is proportional to _jj . The flow resistance can consist, for example, of a large number of parallel, narrow channels. The bypass also has a linear flow resistance, so that v ° = VJJ.

Sensor element: Fig. 4 shows the structure of a sensor element

14, with which the mass flow pv _{B of} a gas can be measured.

The general functional principle of such a component is described in detail in "Scaling of Thermal CMOS Gas Flow Microsensors: Experiment and Simulation" by F. Mayer et al., In Proc. IEEE Micro Electro Mechanical Systems, (IEEE, 1996), pp. Llβff described.

The sensor element 14 is arranged on a semiconductor substrate 21 made of monocrystalline silicon, in which an opening 22 has been etched out. The term “opening” is understood to mean both a simple depression in the semiconductor substrate 21 and an opening extending entirely through the semiconductor substrate 21. The opening or depression 22 is covered by a thin membrane 23 made of a dielectric A resistive heater 24 composed of three resistors is arranged in membrane 23. Two thermocouples 25, 26, which serve as temperature sensors, are provided symmetrically to heater 24. Strictly speaking, these are thermopiles consisting of several thermocouples connected in series With this description and the claims, the term thermocouple is understood to mean both a single element and a thermopile

Temperature sensors have the advantage that they are practically none Have drift and are also relatively insensitive to bending of the membrane 23.

The thermocouples 25, 26 and the heater 24 lie in the direction of flow 27 such that the gas first sweeps over the first thermocouple 25, then the heater 24 and finally the second thermocouple 26.

A typical size of the membrane 23 is, for example, 300 X 500 μm ² .

The sensor element 14, and in particular the area of the membrane 23, is covered with a passivation layer 28. This can e.g. consist of silicon oxide, silicon nitride or a polymer, in particular polyimide. The passivation layer 28 prevents diffusion of undesired molecules, e.g. Water, in the components integrated on the semiconductor substrate 21.

The passivation layer 28 also has to perform a mechanical task. For this purpose, it is designed to be tensile, with a tensility at operating temperature of preferably more than 100 MPa. It is therefore exposed to tensile stress so that it tightens membrane 23 and thus keeps it stable. Thanks to this stress compensation, the membrane 23 still works perfectly even with a pressure difference of more than 3 bar. The tensility of the passivation layer 23 can be controlled by means of known methods by suitable selection of the production parameters, see for example Dominik Jaeggi, "Thermal Convertes by CMOS Technology", dissertation at the Swiss Federal Institute of Technology in Zurich No. 11567, 1996 As already mentioned, with a 4, the mass flow of the gas is determined, for this purpose the temperatures above the thermocouples 25, 26 are measured, which depend on the product of the flow velocity v _B and the density p of the gas.

The sensor element 14, ie the heater 24, is operated in a pulsed manner, for example with a pulse length between 5 and 50 ms. However, the time delay between the heating pulse and the thermocouple signals is preferably not measured, since this only depends on the flow rate and not on the mass flow. Rather, the temperature signals of the two thermocouples 25, 26 are compared with one another, for example by determining the difference between the signals or the quotient of the signals. This size depends primarily on the mass flow.

The pulsed operation of the heating has the advantage that the power consumption is reduced.

Thanks to its construction, the sensor element 14 is mechanically robust and can be mounted in any position.

An evaluation circuit and driver circuits for the heater 24 can also be integrated on the semiconductor substrate 21. A possible structure of all these parts on a common substrate is shown in FIG. 5, and a corresponding block diagram in FIG. 6. The components combined on the semiconductor substrate 21 are divided into three groups and comprise a sensor part 30, an analog part 31 and a digital part 32. The sensor part 30 contains the sensor element 14 described above. It extends over the entire width of the semiconductor substrate 21. Since it comes into contact with the gas to be measured, no circuit elements are arranged in the sensor part. The analog part 31 mainly comprises analog circuit blocks, the digital part 32 predominantly digital circuit blocks. The three groups can each be arranged on individual semiconductor substrates, but the arrangement on a common substrate is preferred for reasons of cost and because of the lower susceptibility to interference.

The circuits are implemented in CMOS technology. The smallest gate lengths of the transistors, in particular the digital switching transistors, are preferably in the range from 0.2 to 0.8 μm, in any case below 1.0 μm. Thanks to the high integration density, it is possible to accommodate all components on a semiconductor substrate 21 with an area of, for example, only 15 m ² .

5 or 6 can be supplied with a voltage of less than or equal to 5.5 volts, preferably with 3 volts.

For connection of the supply voltage and for communication with external components, 32 connection pads 39 are provided on the semiconductor substrate 21 in the area of the digital part.

The functions of the analog part 31 and the digital part 32 are described in more detail below. It should only be briefly mentioned here that the analog part 31 serves for the analog processing of the signals of the sensor element 14 and for the conversion into digitized data. A linearization of the digital data takes place in the digital part 32. The digital part also generates the clock signals of the individual components, and it has a memory in which calibration and operating parameters and / or linearization coefficients can be stored. The linearization coefficients are preferably stored in an EEPROM.

The geometry of the arrangement of the components on the semiconductor substrate reduces interference. The analog part 31 is between the

Sensor element 14 and the digital part 32 arranged so that the weak sensor signals are influenced as little as possible by the switching signals of the digital part.

Furthermore, the sensor element is arranged at one end of the semiconductor substrate, so that the remaining parts of the semiconductor substrate cannot come into contact with the gas to be measured.

As can be seen from FIG. 5, the sensor element 14 is arranged essentially symmetrically with respect to a central longitudinal axis 37 of the semiconductor module. In particular, the heater 24 is symmetrical about this axis, so that thermally induced voltages in the sub- stay strat low. Furthermore, the analog part 31 has two differentially operated channels for evaluating the measurement signals. So that these channels are influenced in the same way by the temperature gradient generated by the heater 24 in the substrate 21, their components are arranged in areas of the same temperature, if possible.

The operation of the analog part 31 is explained in more detail below.

As shown in FIG. 6, the analog part comprises a heating controller 50, a part 51 called MUX / amplifier for selecting the signals to be processed and for their pre-amplification, and an A / D converter 52.

The heating control 50 serves to keep the temperature, the current or the output of the heating constant. In a simple version, the heater can also be connected directly to the (external) supply voltage.

Furthermore, the analog part 31 also comprises a temperature sensor 40 with an A / D converter 40a for measuring the ambient and / or substrate temperature. This temperature can influence the signals of the thermocouples 25, 26. It is therefore linked to the data from the temperature sensors 25, 26 in order to reduce the dependence of the end result on the ambient and / or substrate temperature.

The temperature sensor 40 can also be arranged in the sensor part 30, in particular on the membrane 23.

The signals from the analog part 31 to the digital part 32 and those from the digital part 32 to the analog part 31 are buffered. For this purpose, a buffer 64 is provided for each signal. The use of buffers 64 reduces the transmission of high-frequency interference signals from the digital part 32 into the analog part 31. The analog part 31 thus fulfills a wide range

Tasks and includes at least 100 transistors. Controller:

The control part 5 of the device is shown in FIG. 7. It comprises the microcontroller 73 and an EEPROM 72, with the latter e.g. accesses via the digital part 32 of the mass flow detector 4. The digital part 32 can also access the EEPROM, so that the linearization coefficients for the linearization of the measurement signals can be stored. The microcontroller 73 can e.g. be a microprocessor with integrated ROM. It accesses the EEPROM 72 in order to store accumulated charges there. Furthermore, the microcontroller 73 controls the data to be displayed on the optional display 6 and the optional card reader 7.

A radio interface 76 can also be provided, via which the microcontroller 73 e.g. can communicate with a center 84 via a cellular telephone network, for example using GSM. For example, the gas meter automatically forward the gas consumption to the control center 84. It is also conceivable that the control center 84 transmits a tariff rate according to which the gas consumption is to be calculated to the gas meter by radio.

Instead of or in addition to the radio interface 76, a further interface 77 can be provided. This can be a wireless or wired interface, which e.g. can be used for the local reading of the gas meter.

The microcontroller 73 also controls the valve 8.

The control part can also have an electronic clock 78. This can e.g. can be used to process time-dependent tariff rates.

The control part reads the instantaneous mass flow in the bypass 10, as determined by the mass flow detector 4, via the interface 71 of the digital part 32 and integrates this value over time. Furthermore he converts the mass flow in the bypass 10 to the mass flow in the main channel 2, 3. At regular intervals, for example whenever a certain amount of gas has been used or when gas has been consumed for a certain amount of charges, it saves the corresponding intermediate value in EEPROM 72, so that a fault or loss of power supply does not lead to data loss ,

It is also possible to monitor the supply voltage. As soon as this begins to drop, the last intermediate value is written into the EEPROM. In this case, an appropriate buffer must be used to ensure that there is enough time to save the data in the event of a sudden voltage drop. Since the control part 5 thus integrates the mass flow of the consumed gas over time, it calculates the mass of the gas consumed. A corresponding fee is calculated from this mass, which can also be done either in control section 5 or externally. The control section 5 displays the amount of gas consumed (or a corresponding charge) as a value on the display 6. This value can be encrypted so that there is less risk of manipulation.

If a reading device 7 is provided, the user can insert a value card 80 into this device. This card contains a non-volatile memory 82 with a credit for a certain gas mass. The microcontroller 73 does not open the valve until such a value card 80 is inserted into the card reader 7 and tracks the credit in the memory 82 in accordance with the gas mass consumed. For example, after inserting the card, he can subtract a unit of charge or quantity from the value in the memory 82 and then keep the valve open until a corresponding amount of gas has been consumed. Then he subtracts a next unit of charge or quantity from the value in the memory 82, etc. As soon as such a subtraction is no longer possible, the valve 8 is closed.

If a radio interface 76 is provided, the gas costs or the gas mass consumed can be transmitted to a control center 84 via the radio interface 76.

The digital part 32 can work independently of the microcontroller 73, i.e. he can carry out the calibration and linearization of the measurement data without the help of the microcontroller 73. The microcontroller 73 only needs to query the results from the digital part 32. This allows the microcontroller 73 to be operated only intermittently and / or at a reduced clock rate. This reduces the electricity consumption of the gas meter. In addition, disturbances generated by the microcontroller 73 can hardly reach the analog part 31.

The components arranged on the semiconductor substrate 21 do not have to be in continuous operation. You can use the microcontroller 73 e.g. only be switched on periodically in order to carry out measurements at regular intervals. This leads to a reduction in electricity consumption. For example, Measurements are only carried out every 2 seconds.

The microcontroller 73 can also determine the accuracy of the measurements by specifying the number of averages carried out by the digital part 32 or the pulse length of the heating pulses. To reduce electricity consumption, e.g. a high accuracy measurement is performed first, and then lower accuracy measurements until the latter indicate that the mass flow has apparently changed. Then a high-precision measurement must be carried out again.

The components arranged on the semiconductor substrate can work in continuous operation or in intermittent operation, the corresponding operating mode being selected by microcontroller 73 and controlled by digital part 32. In intermittent operation, when the semiconductor chip is activated by the microcontroller 73, the following steps take place:

A) The heating and the measuring electronics are switched on.

B) After step A, the digital express 32 waits until the heating temperature has stabilized. Then he first carries out an offset correction and then a measurement. The data is output. C) Then the measuring electronics and the

The heating is switched off and the semiconductor chip is waiting for the next activation by the microcontroller.

In continuous operation, measurement cycles are carried out without interruption, with an offset correction and then a measurement taking place in each measurement cycle.

As can be seen from the above, the invention relates to a wide variety of aspects in the field of semiconductor and sensor technology, and in particular to gas charge meters. However, it should be emphasized that in particular the sensor element or the one described

Semiconductor component with sensor part, analog part and digital part can be used as components for other applications.

While preferred embodiments of the invention are described in the present application, it should be clearly pointed out that the invention is not restricted to these and can also be carried out in other ways within the scope of the following claims.

Claims

claims

1. Gas meter characterized by a mass flow detector (4) for measuring the mass flow of a gas flowing through a main channel (2, 3) and further with means (5) for integrating the mass flow over time.

2. Gas meter according to claim 1, wherein it has a non-volatile memory (72) for storing intermediate values of the integrated mass flow.

3. Gas meter according to one of the preceding claims, wherein it has a card reader (7) for prepaid cards and a valve (8) for interrupting the main channel (2, 3).

4. Gas meter according to claim 3, wherein it is designed to track a value memory (82) in a card reader (7) inserted value card (80) according to a consumed gas mass and to close the valve (8) when the value memory (82) is exhausted - cut.

5. Gas meter according to one of the preceding claims, comprising a radio interface (76) for wireless transmission of a consumed gas mass to a central office and / or for the transmission of gas tariffs from the central office to the gas meter.

6. Gas meter according to one of the preceding claims, wherein it has a sensor element (14), an analog part (31) for analog preprocessing of the signals of the sensor element (14) and for generating digitized data and a digital part (32) for linearizing the digitized data having.

7. Gas meter according to claim 6, wherein the sensor element (14), the analog part (31) and the digital part (32) are integrated together on a semiconductor substrate (21).

8. Gas meter according to one of the preceding claims, wherein it has a microcontroller (73) for integrating the mass flow.

9. Gas meter according to claim 8, wherein the digital part (32) can be operated independently of the microcontroller (73).

10. Gas meter according to one of claims 8 or 9, wherein, in order to reduce the power consumption, the microcontroller (73) is designed to periodically switch the mass flow detector on and off.

11. Gas meter according to one of the preceding claims, wherein it has a main channel (2, 3) for the gas and wherein the mass flow detector (4) comprises a bypass (10) parallel to the main channel (2, 3).

12. Gas meter according to claim 11, wherein the bypass (10) with orifices (12 ^λ , 13) opens into the main channel, a linear flow resistance (15 ') being arranged in the main channel between the orifices.

13. Gas meter according to one of the preceding claims, wherein it is designed for encrypted display of gas consumption on a display (6).

14. Gas meter according to one of the preceding claims, wherein it has an electronic clock (78), and in particular is configured to process time-dependent tariff rates.

15. Gas meter according to one of the preceding claims, wherein it has a mass flow sensor with a semiconductor substrate (21) and a sensor element (14), wherein the sensor element (14) in a semiconductor substrate (21) via an opening (22) arranged membrane ( 23), a heater (24) extending over the membrane and temperature sensors (25, 26) arranged on both sides of the heater (24).

16. Gas meter according to claim 15, wherein an analog part (31) for analog preprocessing of the signals of the temperature sensors and for generating digitized data is integrated on the semiconductor substrate, and that A digital part (32) for linearizing the digitized data is integrated on the semiconductor substrate.

17. Gas meter according to claim 16, wherein at least the analog part (31) and the digital part (32) are designed as CMOS circuits with a minimum gate length below 1 μm.

18. Gas meter according to one of claims 16 to

17, wherein it has a sensor (40) for measuring a substrate temperature and / or an ambient temperature, the digital part (32) being designed to link the substrate or ambient temperature with the digitized data of the temperature sensors (25, 26) in order to link one Reduce the temperature dependence of the digitized data.

19. Gas meter according to one of claims 15 -

18, a tensile passivation layer (28) for tightening the membrane (23) being arranged above the membrane.

20. Gas meter according to claim 19, wherein the passivation layer (28) has a tensility of at least 100 MPa.

21. A method for determining a quantity of gas consumed for the purpose of charge calculation, characterized by the steps of measuring the mass flow of the gas consumed and

Integrating the mass flow over time in order to calculate a fee from the mass determined in this way.

22. The method of claim 21, wherein the mass flow is measured by passing a portion of the gas amount over a mass flow detector having a heater (24), the temperature of the gas being measured before and after the heater.