Background to the Invention.

Electronic utility meters are becoming more widespread in use; utility companies are now specifying that new meters should be of this type whereby meter reading may be performed with high accuracy. This is because a transfer of meter reading may be performed by electro-optical means. That is to say a meter reader would visit the premises of a utility consumer, place his meter reading device against a specific reader window of the meter to enable a meter reading to be conducted without the possibility of an erroneous transfer of data because of human error. This type of system is known as a non-contact optically isolated interface system.

Utility meters are fitted with energy consumption indicators, that may be used when calibrating and checking the accuracy of the meter. Such indicators are typically fitted so that they are visible from the front of the meter. The indicator is typically a mark on a rotating disc or a light source such as a light emitting diode (LED) that flashes.

The speed of rotation of the disc or rate of flashing of the LED is typically proportional to the rate of energy consumption.

The reasons for using an optically isolated interface are that it ensures electrical isolation between the meter and the communication equipment, and also, the communication to the meter may be made when the meter has been fully assembled where the internal circuit is otherwise protected from external effects. The non-contact optically isolated interface to the meter traditionally uses two optical devices, in the meter, for communication. One device is used to transmit information and the other device is used to receive information. Using two devices has clear cost penalties from both the cost of the part and the cost of fitting the parts, and it would therefor be of benefit if the number of parts could be reduced. By reducing the number of parts, the reliability is also increased. There are existing methods of bi-directional communication between a meter and some external equipment. The most commonly used method is that specified in IEC 1107, where two optical devices are used, one of these is used to transmit information and the other is used to receive information.

A second method, which is used, is to make direct electrical connection between the circuitry of the meter and the external equipment. The disadvantage of this is that while direct electrical contact to the circuitry can be made before any external enclosure has been fitted, it is not possible to allow the same connection to be made after an enclosure has been fitted to the meter unless a salable method of isolation be provided in the enclosure. The requirements for a salable cover in the enclosure are required from the point of safety and anti-fraud. l The manufacture of electronic utility meters often requires that parameter values specific to the operation of that individual meter are assigned and stored in circuitry within the meter. These values could be related to the measurement accuracy calibration or the'tariff'structure, which the meter conforms to when operating, but are not restricted thereto. This information is conveniently stored on a circuit board in some form of non- volatile memory device, which a microprocessor may read from and write to. When the information is read from the memory it is able to make use

of the values to ensure that the individual meter operates as required.

Before the microprocessor is able to operate the meter, the information must first be placed into the memory. To place the information into the memory, it is possible using existing techniques to write directly into a semiconductor device using electrical contact between the PCB and some external equipment, but this can be undesirable from a safety point of view. Also it is possible to use the microprocessor to write the information to the memory device by communicating the information to the microprocessor which will then perform the write operation.

As discussed above, it is common practice in the utility metering industry to provide a visible indication representing the consumption of energy which is being measured. It is also known to combine the feature of the meter reading non-contact optically isolated communication port with an LED indicator.

Object of the Invention The present invention seeks to provide an improved metering apparatus.

It is also an aim of the present invention to provide an energy consumption indicator for a metering apparatus at reduced cost.

A further aim of the present invention is to provide a relatively low cost bi-directional optical communication circuit for a utility meter.

Statement of Invention In accordance with a first aspect of the invention, there is provided a utility meter and a meter reading device, wherein: the meter comprises an optical utility consumption rate indicator, an optical indicator of consumed utility and an optical detector, the meter being operable to provide an

indication of consumed utility upon receipt by the detector of interrogation signals from the meter reading device, wherein a single LED device is operable to provide utility consumption rate signals, signals indicative of an amount of utility consumed by virtue of an exchange of digital signals and receive interrogation signals from the meter reading device.

The signal could comprise an on-off signal with an on period indicative of an amount of utility consumed.

The signal could comprise an on-off signal with a repetition frequency indicative of the rate of consumption of the utility.

The signal indicative of rate of utility consumption may be calibrated. An error in the accuracy of the meter could be determined by the meter reader.

The signals received from the meter reader could change its mode of operation to enable a tariff data change, e. g. to provide for the signalling of off-peak consumption data. Other functions could also be provided as would be known to a skilled man.

The meter can provide its dual light emission/detection properties by means of a circuit such that it is forward biased in a transmit mode and is reverse biased in a receive mode.

Conventionally, the communication LED and detector operate in the invisible portion of the optical spectrum. To provide an indication visible to the human eye, an LCD display segment associated with the meter may be provided to"flash" ; this will enable a'comfort factor'relating to a rate of utility consumption to be visible whilst enabling the LED and detector devices to operate in, for example the infra-redportion of the spectrum.

This may enable greater efficiency in the operation of a bi-directional communication circuit.

The utility may be electricity, when the consumption of electricity would be measured in units, say KW/hours : in the case of water or gas the consumption would be measured in volumetric units, say m3 ; in the case of waste fluids, the consumption would relate to a volume of effluent. In accordance with a further aspect of the invention, there is provided a method of operating a utility meter in conjunction with a meter reading device wherein; in a first mode a LED device operates to provide a visible indication of utility consumption rate; in a second mode the LED device receives an interrogation signal from a meter reader device; and in a third mode the LED device transmits signals indicative of the amount of utility consumed.

The invention provides, in another aspect, a utility meter operable to provide a visible indication of utility consumption rate, an indication of an amount of utility assumed and to detect interrogation signals from a meter reading device.

In contrast to known meters and in accordance with the invention, a single LED device is operable to provide a utility consumption rate signal, a signal indicative of an amount of utility consumed and to receive an interrogation signal from a meter reader device.

Brief description of the figures The invention may be understood more readily, and various other aspects and features of the invention may become apparent from consideration of

the following description and the figures as shown in the accompanying drawing sheets, wherein: Figure 1 shows a typical example of a prior art utility meter; Figure 2 and 3 shows a schematic view of the functions of a bidirectional optical communication system ; Figure 4 shows a first example of a meter made in accordance with the invention; and Figure 5 shows a circuit operable to enable a bi-directional signal functionality.

Detailed description of the invention There will now be described, by way of example, the best mode contemplated by the inventors for carrying out the invention. In the following description, numerous specific details are set out in order to provide a complete understanding of the present invention. It will be apparent, however, to those skilled in the art, that the present invention may be put into practice with variations of this specific.

Referring now to Figure 1, there is shown a prior art mechanical utility meter, 10. Behind a glazed cover 12, the front face of the device shows mechanical rotating digit display 14. A rotating disc 16 has a mark 18 placed on a circumferential edge. This mark is visible during a period during the revolution of the disc. The indication of utility consumption can be provided in other ways and, in the case of electrical meters is typically provided by means of a flashing LED light operating in the visible region of the optical spectrum.

Figures 2 and 3 show an overview of the process involved in meter reading using a meter 22 having a bi-directional optical communications port 28. The meter is also provided with a LCD visible display 27. The port 28 is provided with a ring 30 which aids positive location of a

correspondingly shaped portion 29 of meter reading device 24. The ring 30 is conveniently magnetic. In use, and as best shown in Figure 3, the portion 29 of the meter reading device 24 is placed against ring 30. A trigger 26 may be depressed to start a measurement, when an interrogation signal would be transmitted from a light source within the meter reader device. In known systems this signal would be received by a detector within the meter; the meter would transmit consumption data by means of a separate transmitter device (not shown). Reference numeral 31 indicates an LED light source operable to indicate that consumption of utility is occurring.

Figure 4 shows a utility meter 40, corresponding substantially with meter 20, having opto-port 28 with locator ring 30. Display 42 differs in that is can be a LCD display which shows an optional LCD indicator which is operable to enable a simple indication that utility is being consumed-the decay time for a visible display would typically prevent any meaningful determination of rate of assumption. Other types of display could also be used such a LED and VFD (Vacuum Fluorescent Display).

An embodiment of the present invention will now be described with reference to Figure 5; the invention makes use of a single LED (Light Emitting Diode). The LED could be manufactured so that its operated in a visible or invisible (infra-red) part of the spectrum. Properties of an LED are that the diode will emit light when biased in a forward direction; this is the traditional method of operation an LED as a transmitter.

When an LED is reverse biased, its properties block the flow of current through the device, however, when the semiconducting device is illuminated with light of a wavelength appropriate to the type of device, then it will conduct to allow a current flow which is proportional to the amount of light by which it is illuminated. By making use of the current

flowing through the device when it is illuminated by an external source, the device can be made to operate as a receiver. By arranging suitable circuitry in accordance with the present invention, the LED may be biased in either its forward direction or reverse direction as required during the communication.

In figure 5, a single light emitting diode, LED 1 is shown, with a transistor Ql and resistors RI, R2, R3, and diode Dl. The circuit is connected to the communicating device, which would traditionally be a microprocessor, through clearly it could be an ASIC or some form of discrete logic. The two electrical inputs to the circuit, IP1, IP2 are connected to the part of the communicating device which deals with the transmission of information. The output OP1 is connected to the part of the communicating device which deals with the reception of information.

The input IP 1 is connected to the cathode of the light emitting diode LED1 and to one end of the resistor R3. The opposite end of R3 is connected to the collector of transistor Q1 and the output OP1. The anode of the light emitting diode LED1 is connected to the cathode of the diode D1, the base of the transistor Ql and to one end of the resistor R2. The anode of the diode Dl is connected to one end of the resistor Rl. The other end of the resistor R1, and the other end of the resistor R2 and the emitter of the transistor Q1 are connected to the input IP2.

If the inputs IP1 and IP2 are connected to a microprocessor, the microprocessor can control the settings of the logic levels and hence the voltage levels on the inputs IP1 and IP2 respectively, and the light emitting diode LED1 can be configured to be either forward or reversed biased.

With the input IP1 set to logic low (0V) and the input IP2 set to logic high (+V), light emitting diode LED1 will be forward biased and the

majority of current will flow through resistor R1 and diode D1. The value of resistor Rl is chosen to ensure that sufficient illumination is generated from the light emitting diode LED 1 during transmission of data.

With the input IP1 set to logic high (+V) and the input IP2 set to logic low (0V), the light emitting diode LED1 will be reverse biased.

When the light emitting diode LED1 is illuminated by transmitted data from the communicating equipment, a current will flow through the light emitting diode LED1 into the resistor R2, and current is blocked from going through resistor Rl by the reverse biased diode Dl. If the current flowing through the light emitting diode LED1 is great enough, then the potential formed across resistor R2 will be large enough to forward bias the base emitter junction of the transistor Q1 and the transistor will switch on, causing current to flow through resistor R3, and the voltage in the output OP 1 to go towards that of the input IP2.

If the circuit as described above is used in a dual opto-device method, its sensitivity may be increased by increasing the transmitted optical light level from the communicating equipment.

In a normal mode of operation, the LED will flash at a rate indicative of a rate of consumption. When a meter reading device is positioned against the opto-port 29 and the meter reading device is operated, then an interrogation pulse of light is received by the LED, acting as a detector when not in transmit mode. Typically the flash from the LED will have a duration of 2-3 ms and the period in which the LED operates as a detector would be 100ms or more: sufficient to enable an interrogation to be received. Upon receipt of such an interrogation signal, the meter will transmit data relating to the amount of utility consumed. This data may also be supplemented by meter identification data; tarriff data etc. Whilst meter reading devices do not, as a rule, operate to calibrate the meters since this is typically performed upon assembly at a site of manufactured

or upon installation at a premises, this functionality could also be provided for. During the transmission of consumption data from the meter to the meter reading device, which data transfer may be repeated, the normal transmission of energy consumption rate (pulse/flash) is not performed.

As the invention makes use of a single device for both transmitted and received information, then communication between the meter and the equipment is only possible in half-duplex (i. e. one way at a time). The requirements of existing systems using two optical devices for data transfer only allow half-duplex operation and accordingly, the present invention is suitable for such applications.

A meter incorporating the features of an energy consumption indication and an optically isolated communication port, as known, would comprise a total of three optical devices, consisting of two transmitting devices and an optical receiver device.

The present invention provides a great reduction in the manufacturing and associated costs of meters-which are manufactured in their millions and where each cost reduction can have a significant impact Applicant's calculations have determined a cost reduction greater than two thirds for the manufacture. Moreover, by the reduction in number of components an increase in reliability can be expected.