WO2013070064A1

WO2013070064A1 - Dual turbine gas meter

Info

Publication number: WO2013070064A1
Application number: PCT/NL2012/050746
Authority: WO
Inventors: Raymond Richards
Original assignee: Flow Meter Group B.V.
Priority date: 2011-10-25
Filing date: 2012-10-25
Publication date: 2013-05-16
Also published as: EP2771650A1

Abstract

A turbine gas meter comprises a housing provided with a gas inlet hole and a gas outlet hole, two turbine wheels (9, 11) located in the housing, and two counters (29) connected each to a turbine wheel for counting the number of revolutions of the turbine wheel. The turbine gas meter further includes a processing unit connected to the two counters, which averages the values of the two counters and compares them to each other and emits a signal in case of a difference that exceeds a predetermined maximum permissible difference value. Reducing means (17, 19) are located between the turbine wheels and the counters so that the counters may be fed by batteries. The turbine wheels preferably have different configurations.

Description

DUAL TURBINE GAS METER

DESCRIPTION:

Field of the invention The invention relates to a turbine gas meter comprising a housing with a gas inlet hole and a gas outlet hole, at least one turbine wheel located in the housing, and a counter connected to the turbine wheel for counting the number of revolutions of the turbine wheel.

Turbine gas meters are regularly used measuring instruments for determining quantities of gas. The principle is based on the given that the number of revolutions of the turbine wheel is proportional to the gas flow through the wheel (through the blades). The gas flow rate multiplied by the orifice of the wheel (between the blades) represents the quantity per unit of time. The revolutions of the turbine wheel are transferred to a counting mechanism by means of a transmission (electronically by means of pulses or mechanically by means of gears). In order to create uniformity in the flow between the blades and to avoid the flow obtaining a deviating inlet angle relative to the blades as a result of a shift in the gas flow, a flow straightener is installed in front of the blade wheel.

State of the art

For turbine gas meters as described hereinabove there is widespread use for purposes of settlement of accounts and they are to be calibrated as such. The typical field of application is medium-sized to very large amounts of gas with pressures from atmospheric up to 100 bars. In nearly all gas receiving stations, where delivery takes place from transmission companies to distribution companies, the amount of gas delivered is settled over turbine meters. Since the delivery pressure of these gas receiving stations is relatively high (4 to 16 bars), the measured amount expressed in normal m 3 (normal m3 is the number of m3 calculated backwards to atmospheric conditions) is large. A minor measuring error caused by whatever reason has large financial consequences. In order to avoid large financial calculating errors, turbine meters are to be checked (recalibrated) on a regular basis, which entails hefty charges because recalibrations are to be executed under comparable conditions (i.e. high-pressure natural gas), and the meter as a whole is to be removed from and reinstalled in the pipe section.

If for any reason a significant error were ascertained during the recalibration operation, the meter would have to be overhauled. However, there is then the issue of how long this error has occurred in practice, leading to the fact that more often than not costly and lengthy legal processes are conducted between supplier and client.

Summary of the invention It is an object of the invention to improve the known turbine gas meter. For this purpose the turbine gas meter according to the invention is characterized in that the turbine gas meter further includes a further turbine wheel as well as a further counter, and an averaging unit 31 connected to the two counters, which averages the values of the two counters. The renewed turbine meter (Fig. 1) concept utilizes two turbine wheels in one meter housing. The signals of both wheels are scaled in a battery-fed processing unit (for example one revolution of the shaft connected to the first wheel equals 0.3564 m and the second wheel 0.40085 m ) and subsequently added up per wheel. For the total readout the sum of the two counting registers is taken and divided by two. As a result of the addition and the subsequent division by two, the two wheels count towards the total represented quantity (essential) only for half. This achieves that if either of the wheels should produce an error for whatever reason, this error would affect the total only for half. For example: wheel 1 has poor bearings and therefore indicates 2% short and wheel 2 revolves as new. The error in the total readout is now only 1%. In a conventional turbine meter having only 1 wheel, the error would be double this value. The scale factors are determined on calibration of the meter.

In an embodiment of the turbine gas meter according to the invention the values (overall, per unit of time or per quantity passed) of the individual wheels are compared with each other in a difference determining unit. With this unit it can be ascertained whether the wheels show an error and an alarm can be generated if too large an error has been detected. In the previous example this diagnosis function will detect that there is a 2% difference between the two wheels. As long as the difference is smaller than the maximum permissible error (laid down in various standards and/or regulations) a meter need not be recalibrated and can be continued to be utilized for fiscal purposes.

The difference in the ratio of the blade wheels determined during the calibration (shaft rotation and the scale value) is an exact measure for the error, assuming that the two wheels are not affected to the same degree at the same moment and that the two wheels are completely independent (i.e. a disturbance of the first wheel must not affect the second wheel, because otherwise the comparison of the numbers of revolutions is not correct). In the manner described errors as a result of bearing damage, blade wheel wear and pollution are clearly noticeable and quantifiable.

A further embodiment of the turbine gas meter according to the invention is characterized in that reducing means are located between the turbine wheels and the counters. By means of a gear train the number of revolutions of the two wheels is reduced to such extent that complete revolutions of the shaft (output shaft downstream of the gear train) can be sensed by means of sensors. A revolution of the strongly speed-reduced shaft represents a quantity passed.

A still further embodiment of the turbine gas meter according to the invention is characterized in that the processing unit is a battery-fed processing unit. Reducing the number of revolutions is desired for minimizing the energy consumption of the sensors so that the sensors and the signal processing electronics can operate based on the battery supply. In case of a strongly reduced number of revolutions the sensors and the processing electronics can partly remain passive and will not be activated until a complete revolution of the shaft is to be expected. By way of illustration: with a maximum speed of 1 revolution per second the sensors and processing electronics would only have to be briefly activated once a second. The position of the shaft can be determined by means of an encoder system (Fig. 2), which may be a grey-code disc with optical sensors or three (or more) magneto- sensitive sensors, activated by a magnet installed on the rotating shaft (these sensors are positioned such that from the switch frequency can be derived the position and direction of rotation of the shaft). For determining/computing a count state based on a shaft rotation it is of importance that no information is missed and that the direction of rotation is recognized.

Yet a further embodiment of the turbine gas meter according to the invention is characterized in that the turbine wheels have different configurations. By having different physical configurations for the two blade wheels, for example by varying the height and the angle of the blades, it is highly improbable for a disturbance of any kind whatsoever to generate simultaneously the same error for both wheels.

Preferably, the turbine gas meter further includes two flow straighteners the first one of which being located between the inlet hole and the turbine wheel and the second one of which being located between the two turbine wheels. Since the two wheels are to register mutually independently, the flow is built up again by means of a flow straightener between the two wheels. In front of the first wheel a flow straightener has already been installed for rendering the overall measurement as much as possible insensitive to installation specific flowing profiles and whirling motions which could affect the real measuring behaviour (relative to the calibration). However, the possibility cannot be discounted that extreme disturbances of the flow can nevertheless affect the measuring accuracy in practice. When two independent wheels are used, while the second wheel is additionally protected by the second flow straightener, these extreme disturbances will be able to affect the first wheel but not the second wheel. Therefore, by comparing the two wheels, these extreme disturbances, caused by the installation, will be detected.

Brief description of the drawings

The invention will be elucidated more fully hereinbelow based on an example of embodiment of the turbine gas meter according to the invention while reference is made to the appended drawing figures, in which:

Fig. 1 shows an embodiment of the turbine gas meter according to the invention comprising two measuring wheels;

Fig. 2 gives a diagrammatic representation of the turbine gas meter shown in

Fig. 1;

Fig. 3 shows a first embodiment of the encoder system of the turbine gas meter; and

Fig. 4 shows a second embodiment of the encoder system of the turbine gas meter. Detailed description of the drawings

Fig. 1 shows an embodiment of the turbine gas meter according to the invention. The turbine gas meter 1 comprises a housing 3 provided with a gas inlet hole 5 and a gas outlet hole 7. The housing accommodates two turbine wheels 9 and 11 of different configurations, as well as two flow straighteners 13 and 15, the first one 13 of which flow straighteners is located between the inlet hole 5 and the turbine wheel 9 and the second flow straightener 15 is located between the two turbine wheels 9 and 11.

Fig. 2 gives a diagrammatic representation of the turbine gas meter. An encoder disc 21, 22 is coupled to each turbine wheel 9, 11 by means of two worm worm wheel transmissions 17, 18 and 19, 20. The rotation of each encoder disc is sensed by three sensors 23, 24. From this sensed value can be determined both the direction of rotation and the number of revolutions. The turbine gas meter has an electronic processing unit to which sensors are connected. This electronic processing unit comprises two logic units 25, 26, one for each set of sensors 23, 24, which emit a signal which is converted by value determining units 27, 28 into a signal that represents a revolution of the encoder disc. Counters 29, 30 count the number of revolutions of the encoder discs. The values coming from these units are averaged in an averaging unit 31. Then a difference determining unit 33 determines the difference between the two counters (preferably with a large time interval, for example per hour or per day). Signalling means 35 emit a light signal if the difference exceeds a limit value and the measurement is unreliable. The average value found is output via a communication unit 36 and shown on a display 37. The counters 29, 30 are fed by batteries 39. When two turbine wheels are utilized with diagnosis, redundancy is large: three or more sensors per wheel and mutual comparison of the turbine wheels.

Furthermore, the turbine gas meter is provided with further encoders 41, 42 which are connected to the turbine wheels and via an interface 43 can be coupled directly to a computer.

The encoder discs and sensors may be in the form of an optical or magnetic disc. Fig. 3 shows the optical variant. The encoder disc 21 ' has recesses and is monitored by three optical sensors 23'. Fig. 4 shows the magnetic variant. In this configuration the encoder disc 21" has a permanet magnet 45 which is monitored by coils 23".

For bringing back the system from an energy engineering point of view to a level at which one or more batteries 39 can keep the processing unit operational for a guaranteed minimum period of 10 years, the two encoder discs will have to be low-speed discs. In the bearing block the speed of the shaft of the encoder disc can be reduced by a factor of 100 to 1000 by means of 2 or 3 worm worm wheel transmissions. Since no torque need be transferred (only a disc is driven), this transmission can be realised in a very compact and cost effective manner.

Since each turbine wheel is coupled to an encoder (encoder disc and sensors) of its own, the downstream encoder processing electronics can execute exactly the same calculations so as to come to a total volume. After linearisation of the two encoder discs and averaging of the two counts, a value is obtained from which the quantity passed can be calculated. Albeit the invention has been described in the foregoing with reference to the drawings, it should be observed that the invention is not by any manner or means restricted to the embodiment shown in the drawings. The invention also extends to all embodiments deviating from the embodiment shown in the drawings within the spirit and scope defined by the claims.

Claims

CLAIMS:

1. A turbine gas meter comprising a housing (3) with a gas inlet hole (5) and a gas outlet hole (7), at least one turbine wheel (9) located in the housing, and a counter (29) connected to the turbine wheel for counting the number of revolutions of the turbine wheel, characterized in that the turbine gas meter further includes a further turbine wheel (11) as well as a further counter (30), and an averaging unit (31) connected to the two counters, which averages the values of the two counters (29, 30).

2. A turbine gas meter as claimed in claim 1, characterized in that the turbine gas meter further includes a difference determining unit (33) which compares the values of the two counters (29, 30) to each other and emits a signal in case of a difference that exceeds a predetermined maximum permissible difference value.

3. A turbine gas meter as claimed in claim 1 or 2, characterized in that reducing means (17, 18, 19, 20) are located between the turbine wheels (9, 11) and the counters (29, 30).

4. A turbine gas meter as claimed in claim 1, 2 or 3, characterized in that the processing unit is a processing unit fed by batteries (39).

5. A turbine gas meter as claimed in any one of the previous claims, characterized in that the turbine wheels (9, 11) have different configurations.

6. A turbine gas meter as claimed in any one of the previous claims, characterized in that the turbine gas meter further includes two flow straighteners (13, 15) the first one of which being located between the inlet hole and the turbine wheel and the second one being located between the two turbine wheels.