Residential Ultrasonic Gas Meters Published in Electronics and Telecommunications (ISETC), 2014 11th International Symposium on DOI: 10.1109/ISETC.2014.7010758 pp. 101-105 Laurentiu Gavra Timişoara, Romania Ciprian Sălăgean Timisoara, Romania Abstract The natural gas is a non-regenerable energy source. Because of this natural gases must be managed and adequately protected for the next generations Management in an appropriate manner of natural gas reserves requires the achievement by the company that distributes natural gases to beneficiaries of a system for monitoring and submetering the consumption of natural gas. Submetering and billing of natural gas consumption by the population is made traditionally with residential gas meter [1]. For solving some problems related to natural gas consumption billings have been achieved gas smart meters. In this situation we present an intelligent gas meter G4 EUS Keyword domesticl gas meters, inteligent gas meters, I. INTRODUCTION ultrasonic utility meters, Revenue collection is one of the core activities of any utility distribution company (electrical or heat energy, gas and water). This was has always achieved using conventional meters like diaphragm gas meter by reading these counters regularly at 1-3 months by specialized personnel. This process is expensive. He creates numerous inherent problems for both utility and customers. To solve some of these problems are developing new gas meters known as residential smart gas meters 1. This type of meter offers benefits to both parties. In this context we presented in this paper an enhanced version of residential ultrasonic smart gas meter [1] manufactured in Romania by SC AEM SA from TIMISOARA. Monica Sabina Crainic Timişoara, Romania or monicacrainic@yahoo.com Petru Pupşa Timisoara, Romania Ultrasonic gas meter is designed and manufactured to measure the volume of natural gas having maximum working pressure of 0.5 bar within a measurement range of 40-6000 L/h. A. Measurement Principle In a transit time ultrasonic gas meter (see fig. 1) there is pair of transducers. Each pair has its own transmitter and receiver. The transducers are placed on the pipe wall. One (set) is placed on the upstream (transducer 1 or T up ) and the other (set) on the downstream (transducer 2 or T down ). The transit-time of the ultrasonic signal propagating in the flow direction t 12 is shorter than the transit-time of the signal propagating against the flow direction t 21. A transit-time difference, Δt, can thus be measured and allows the determination of the average flow velocity 2 L t v (1) 2Xt t 12 21 based on the propagation path of the ultrasonic signals. The larger the difference, the higher the flow velocity. II. ULTRASONIC GAS METERS [1] The ultrasonic gas meters complies with EN14236:2007, UNI TS 11291_1, UNI TS11291_8. 1 Smart meters are electronic measurement devices used by utilities to communicate information for billing customers. Fig. 1 Gas flow measurement Therefore, the gas flow rate Q v k S (2)
where A is the cross-sectional area of the USM flow path and k is called meter factor. This factor expresses the influence of the flow velocity profile. B. Construction [1-3] Having no moving mechanical parts (see Fig. 2) the structure of ultrasonic gas meter is much simplified. the ultrasonic module and the temperature sensor are powered down. The meter does not record anything; no events are stored in the internal event log. The communication, real time clock and display are fully functional. The meter can be placed in inspection mode for metrological verification. When the inspection mode ends, all the values in the volume registers are erased Table 1 Some metrological characteristics of ultrasonic gas meters [1-4] Fig. 2 Structure of a ultrasonic gas meter [1] The ultrasonic measurement unit for gas meter is made by Panasonic Corporation [3]. The meters are made from pressed steel. This type of housing ensuring robustness, external tightness, resistance against external and internal corrosion and resistance to high environment temperatures [1-2]. Ultrasonic measurement unit (see fig. 2) is mounted inside the meter case on the run way of the gas flow. The meter contains a shut off valve on the inlet path. When it is detected an abnormal gas flow rate, the shutoff valve automatically interrupts the gas flow. The valve can be controlled local or remotely [1]. The electronic circuit, include the ultrasonic sensor module. This module is powered from a local battery. The life time of battery is of minimum 10 years. The electronic parts are distributed in two compartments. First compartment has a metrological functionality. This compartment is completely sealed. The second compartment has a communication modem, a valve driver, and monitors battery functionalities. This compartment can be open without breaking the metrological seal. In this compartment is mounted battery which feeds with power the ultrasonic sensor module [1]. C. Metrological Characteristics The gas meter developed by us is a residential model. Maximum flow rates for ultrasonic module are of 7200 L/h. Table 1 shows other metrological characteristics of the ultrasonic gas meters. Operating temperature -25 + 55C Measurement performance 40 to 600L/ within ±3%, with EN 14236:2007 600 to 6000L/h within ±1.5% acc with EN 14236:2007 Accuracy class 1,5 Pressure loss less than 200 Pa acc with EN 14236:2007 Class of protection IP54 Humidity 95%,at atmosphere temperature 0~35 C, for Ta>35 C max amount of water vapor is 37.6 g/m b) Normal mode. The meter is switched from an unconfigured mode to the normal mode by setting the meter date and time, its redelivery point ID and the billing schedule information (gas day, gas hour, number of months between 2 self-readings). In this mode, both the ultrasonic module and the temperature sensor are active. The meter records all events specified in the UNI/TS 11291 standard in the event log. c) Service mode. Is similar to normal mode, but no events are stored in the event log during this mode. Additionally, the meter can be placed in inspection mode for metrological verification. Additionally, for metrological verification purposes, another (temporary) meter mode is defined, called inspection. In this mode, all volume values are displayed with 4 decimal places. Additionally, the ultrasonic module can be configured to enter its own inspection mode, where the flow rate is determined every 125 ms as opposed to once every 2 s. This mode is temporary; the meter can stay in this mode for a configurable amount of time, ranging between 4 and 255. 2. Ultrasonic module The ultrasonic module (USM) used in the meter is supplied by Panasonic. Its performances are presented in: D. Technical Description 1. Modes of operation The meter has 3 modes of operation, defined in the UNI/TS 11291-6 standard. These are: a) Unconfigured mode. The meter can only be in an unconfigured mode initially, just after production, and requires breaking the metrological seal. In this mode both Table 2 Some technical specifications of ultrasonic module [2] Measurement range Measurement accuracy of propagation time 3L/h 7200 L/h < 100 ps (<0,1 ns)
Supply current 330 mah/year The USM needs a correction coefficient to correct the influence of assembly conditions. This correction coefficient is written during the calibration phase and cannot be changed afterwards. Normally, the USM sends a telegram every 2 seconds (and every 125 ms in inspection mode). All volumes stored in the gas meter are at base conditions (Vb). The meter has a precision of ±1.5% for flow rates in the 600 L/h 6000 L/h range, and ±3% for flow rates in the 40 L/h 600 L/h range. 3. Tariff management Tariff management is a superset of the UNI/TS 11291-6 Italian standard. The meter can have a maximum of 2 tariff plans. The structure of a tariff plan is as follows: The year is split in a maximum of 12 different periods, each of them being assigned one of 4 different seasons, Each season has 3 different types of days: Monday Friday, Saturday, Sunday and public holidays, Each day is split in a maximum of 12 different intervals, each of them being assigned one of 3 different tariffs. There are 2 types of tariff plans i.e. Active tariff plan which is the plan currently used in the meter. It cannot be deleted or modified, only completely replaced. Latent tariff plan which is the plan that will become the new active tariff plan once the activation date is reached. If no tariff plans are configured, tariff 1 is used as default. However, once a tariff plan has become active, there will always be an active tariff plan in the meter. The second tariff plan, if there is one configured, is used as the latent tariff plan coming into effect at a preset date. If the date of the latent tariff plan is earlier than the current date, it automatically becomes the active tariff plan, overwriting the old one. Each tariff plan has a unique ID, called a tariff plan ID. This ID is written in each self-reading, to identify the tariff plan that was active at the time of the self-reading. Changing the tariff plan automatically triggers the creation of a new self-reading. The meter is capable of holding up to 48 recurring (4 per month) and 40 non-recurring (4 per year, max. 10 years) public holidays. 4. Display [1, 4] The ultrasonic gas meter is fitted with a LCD display. The visible surface of the LCD display is 57 mm x 24 mm. The meter is capable of displaying 8 digits with either 3 or 4 decimal precision for gas volume. Seven of the 8 digits have 11 segments, while the 8th has 7 segments. The display can also show measurement units and special characters for signaling. There are 2 display sequences. The primary one is active during each meter state apart from the inspection state. The secondary display sequence is only active during inspection state. Each display sequence is configurable; any of the values above can be added to it, although only once. A short press of the display button will change the value on the LCD to the next one in the display sequence. A long press of the display button (> 3s) will trigger the automatic cycling through the values in the display sequence. The amount of time each value is displayed is also configurable (between 5 and 15 seconds). Another short press of the display button will stop the automatic cycling. LCD display sequences can be changed using a button on the display module. Displayed values such as data and hour, total volumes in base condition and in alarm mode, billing period, status of the meter and shut-off valve are the in accordance with UNI/TS 11291-6. 5. Stored values The ultrasonic gas meter is equipped with a non-volatile memory. In this memory are stored both billing values and recorded events as follows [1-2]: the daily consumption values for the last 70 days; the last 2 billing records; the events register, with a capacity of 180 events. The events are [1-2]: date and hour for each event recording; type of event; ID number of the operator who generated the event (if applicable); previous and new value of the parameter used for volume calculation (if applicable); the total volume value in reference conditions at the moment when the event was recorded Main events recorded in the non-volatile memory [1-2] are: battery missing, 10% of battery remaining life, 90% of events register full, events register full, opening of the metrological and battery compartment, measured temperature exceeding the working temperature range (-25 C...+55 C) back flow recorded and error when closing the valve. Other potential events are: clearing of the events register; changing of the value of the base temperature; changing of the tariff program; battery replaced; updating the firmware version of the communication card 6. Shut-off valve The shut-off valve behaves differently based on the state the meter is in unconfigured state where the valve cannot be operated, or in normal state where the valve is automatically closed when the main lid is removed. The valve can also be closed remotely via an external communication command. The valve can only be reopened by following the steps described in chapter 6 of the UNI/TS 11291-6 standard:
A valve reconnection is sent to the meter from an external command system via GSM or the optical port. The user presses the valve button during this interval If no gas flow is detected for 30 minutes, the valve remains open. However, if gas flow is detected during the 30 minutes, the valve automatically closes. The user has 2 more attempts to open the valve during the interval when the valve is authorized for reconnection. If all 3 attempts fail (due to gas flow detected) or the interval when the valve is authorized for reconnection elapses the valve remains closed. In service mode: the valve is operated via the shut-off valve button 7. Communication interface The ultrasonic gas meter has two communication channels an optical port and a remote communication interface [1-2, 4] Optical port is used for local communication purpose. The optical interface complies with EN 62056-21. The communication speed is 9600 baud with 8 data bits, no parity, and 1 stop bit. The remote communication interface can be equipped with M-Bus radio modem having 169MHz/868MHz carrier frequency. This type of interface complies with EN 13757-3 and EN 13757-4 Both channels use the same communications protocol, DLMS/COSEM E. Fraud Detection The gas meter stores up to 180 events in an internal event log. The event buffer can store: parameter or state changes: like: base temperature, base pressure or working pressure, clock resynchronization, tariff plan, valve state, meter state Abnormal events like: primary battery missing, 90% of battery consumed, event buffer 90% full, generic alarm, event buffer full, clock is unsynchronized, volume calculation error (ultrasonic module failure or voltage under 3.0 V), corrupt database, valve close test fail, valve open test fail, temperature under min. value (-25 C), temperature over max. value (+55 C), flow rate over max. value (7200 L/h), reverse gas flow detected, lower lid open (lid on communication board), upper lid open (lid on metrology board) Illegal access attempts (wrong password). Each entry in the event log has a timestamp (dd.mm.yyyy hh:mm:ss format) and the total volume at the time of the event occurrence. Additionally, for parameter changes, the user that modified the change, as well as the old and new value of the parameter are also saved. When the 179th event is stored in the event log, an event buffer full event is also generated on the last position, the 180th. Any new event that arrives after this point will overwrite the penultimate position in the event log. F. 169 MHz Radio Module The 169 MHz Radio M-BUS wireless module with basic performance presented in table 3 has 2 main functions: 1 The modem communicates (wireless) with the Data Concentrator (DC) and provides data such as Index on tariffs, monthly self readings at a specific time, profile load, instantaneous values. 2. The modem communicates (local - UART) with the meter and collect/send specific date Table 3 Some basic performance of 169 MHz radio module Frequency Band 169 MHz Transmission Power +30dBm (1000mW) ( typ ) (antenna input level) Frequency {MHz] 169.406250 Data Rate [kbps] 4.8 Deviation [khz] 2.4 Modulation GFSK III. CONCLUSIONS Smart gas meters use an advanced metering infrastructure (AMI). This type of infrastructure use a technology that allows two-way communication between gas meters and company that distribute natural gas to beneficiaries In this context, in this paper we have presented a new intelligent residential gas meter. This counter is an ultrasonic gas meter equipped with a communication module, a thermal compensation system and an inner valve. The major benefits associated with introducing smart gas meters to the natural gas system are [1, 5]: a) for customers: better information, bills based on actual consumption, the possibility to offer dynamic pricing and innovative tariffs, b) benefits for suppliers: better frequency and quality of billing data, improved load profiling and forecasting, c) benefits for network operators: reduction of load, system security, easier detection of network losses, d) benefits for society as a whole: reduction of greenhouse gas emissions, increases in energy efficiency. REFERENCES [1] Laurentiu Gavra, Monica Sabina Crainic, Petru Pupsa, Gheorghe Popa Residential Smart Gas Meters in, Proceedings of 2012 10 th International Symposium on Electronics and Telecommunications, p. 37-40 [2] *** Ultrasonic Gas Meters G4EUS Prospect SC AEM SA Timisoara, ROMANIA 2014 (version 0.1 2014)
[3] *** Ultrasonic Measurement Unit Prototip Specification Home Appliances Company. Panasonic Corporation 2011 [4] *** Mounting, operation and maintenance of the G4EUS Ultrasonic Gas meter Technical Manual SC AEM SA Timisoara, ROMANIA version 2 2014 [5] *** Final Guidelines of Good Practice on Regulatory Aspects of Smart Metering for Electricity and Gas European Regulators Group for Electricity and Gas Ref: E10-RMF-29-05 8 February 2011