GB2041588A - Apparatus for metering and displaying the cost of electrical energy consumption - Google Patents

Abstract

An apparatus is connected in series with the mains conductors supplying an electrical load, for the purpose of calculating the accumulated energy consumption and by reference to cost information provided by the user 21 also to calculate and display 20 the total cost accumulated during the measuring period since initiation by the user. The apparatus incorporates analogue to digital conversion of a succession of samples of a parameter or parameters of the mains supply, a microprocessor operating according to a stored digital program, controlling switches and an alpha-numeric display. <IMAGE>

Description

SPECIFICATION Apparatus for metering and displaying the cost of electrical energy consumption We, Stephen Day and Peter Richard Hutt of Response, Stoner End, Froxfield Petersfield, Hants, GU32 1 DX do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to the measurement of electrical energy consumed by an electrical load connected to a source of electrical supply and more particularly to the calculation and indication to the user of the cost of the electrical energy consumed by the load.

The cost of electrical energy consumption has become increasingly significant in recent years as the price of primary fuels has risen. Consequently it has become of greater importance that consumers of electrical energy can readily monitor the cost of electrical energy being consumed on their premises either by the totality of electrical appliances operating on their premises or more particularly by any individual appliance connected to the supply on their premises.

Consumers of electrical energy are always supplied by the electrical supply authority with a watt hour meter of conventional rotating disc shaded-pole or other type of analogue electrical consumption meter. The disadvantage of this type of meter is that it is of the continuously totalizing type and that to calculate the cost of energy consumed over a period of time is difficult. The dials or number scales are not easy to read, the calculation of units consumed requires careful monitoring over a measured time interval and the number of units consumed has to be multiplied by the electric energy unit cost as charged by the supplying authority. It is a consequence of these complications that consumers of electricity are often not aware of the rate at which they are incurring charges for electricity consumed on their premises by their electrical equipment.

Hitherto monitoring of electrical energy consumption has mostly been performed by conventional analogue measuring instruments. With the advent of digital to analogue converters and complex integrated digital circuitry it has already become feasible to calculate the power taken by an appliance or load on a supply by sensing and converting the electrical current and voltage waveforms driving the load to digital form, storing the waveshapes as a sequence of sufficiently frequently taken samples represented by binary numbers of 8 or more bits and from these samples to calculate the power or volt-amperes being taken by the load averaged over one or several cycles of the mains frequency. Such an invention is described in British Patent specification 1373581 wherein a digital wattmeter operating according to these principles was disclosed.The calculation and display of electrical power from the succession of analogue current and voltage samples requires a large amount of complex digital integrated circuitry. The addition of further facilities to such a digital wattmeter using conventional integrated circuitry would result in an unduly complex sizeable and expensive apparatus.

It is an object of the present invention to provide apparatus for sensing the energy or volt-amperes being taken from a mains source of electrical supply, for the apparatus to totalise the energy taken from the supply over a period of time initiated and terminated bythe user, for the apparatus to be responsive to input of the details of the charging tariff for electricity being supplied and be able to display quantities which include all or several of the total cost of the energy consumed since the beginning of the period, the total amount of energy consumed since the beginning of the period, the details of unit charge and tariff supplied by the user, and the time elapsed since the start of the period of measurement.

In one embodiment of the invention the apparatus may be connected in series with the mains supply entering the premises and be used to monitor total energy consumption on these premises.

In another embodiment of the invention the apparatus may be plugged into a power socket of 13 amp or other maximum nominal rating and the appliance to be monitored then plugged into a supply socket on the apparatus thereby allowing a single appliance or several appliances connected to the one plug to be monitored for energy consumption and cost.

It is a feature of the invention that the apparatus in order to be of a sensible sizband complexity incorporates a microprocessor, the microprocessor operating on digital samples representing instantaneous current and voltage values provided by one or more analogue to digital converters. In one embodiment sensing means are employed which combine voltage and current taken by the load so as to produce a sensing voltage proportional to the instantaneous power being consumed by the load and the microprocessor operates directly on samples of this power sensing voltage. The microprocessor operates according to a program of instructions stored in a non-volatile digital memory and is controlled by a set of switches mounted on the body of the apparatus.The microprocessor in conjunction with the switches drives a display which can be of the seven segment light-emitting diode or liquid crystal or other type.

Although it increases the complexity of the apparatus means can be provided to enter the information to the apparatus from a remote point over a pair or several parallel wires and to relay the information over a pair or several parallel wires to the same or different remote point for display or provision of information to another information accepting apparatus.

Although the apparatus provided by the invention is most accurate when energy consumption is calculated from digital samples of both current and voltage or digital samples of instantaneous power one embodiment of the invention employs only samples of the current being supplied it being assumed by the apparatus that the voltage of the supply has its nominal value supplied by the electricity supply authority.

In another embodiment of the invention further accuracy is sacrificed by assuming that the current taken by the load is sinusoidal it then being sufficient for the apparatus to make an approximate calculation of energy consumption based on the peak to peak value of the current together with the peak to peak value of the voltage or an assumption of the voltage having its nominal supply value.

In any embodiment which employs the total waveform of current drawn by the load it is necessary for reasonable accuracy to measure a number of regularly spaced samples of the current at points distributed evenly through the cycle of the current waveform. For an approximate estimate of the true power ten or twenty samples per half cycle of mains voltage is required whereas a more accurate estimate requires 50 or 100 samples per half cycle of mains voltage. Similarly in any embodiment which measures the actual supply voltage a similar number of samples is required at exactly corresponding times. Again where power is sensed directly a similar number of samples are required.

It is a feature of the sampling process that if the number of samples per half-cycle is an even number and is even as few as 8 samples per half cycle the estimate of energy consumed by a load drawing a sinusoidal current from a sinusoidal voltage supply is almost exactly correct depending only on thé accuracy of the analogue to digital conversion. When the apparatus is to be used to measure consumption and cost of a load drawing non-sinusoidal current such as a triac-switched-controlled device or appliance, in order to achieve high accuracy it is necessary to take of the order of 50 or 100 samples per half cycle. For simplicity of implementation one embodiment of the apparatus takes only 8 samples per half-cycle and this is considered sufficient for the purpose.In this case it is considered that the reduced accuracy for non-sinusoidal loads is immaterial since the purpose of the embodiment is only to provide information on the approximate cost of supplying the load. For an embodiment of the apparatus to be used for metering and charging costs to a consumer a large number of samples per half-cycle is required to ensure correct and accurate billing.

In an embodiment where the energy consumption is calculated from an assumed or measured peak-to-peak value of the mains voltage the actual voltages at the times of the current samples can be assumed to be those corresponding to the known time of occurrence after the last time of instantaneous occurrence of zero voltage of the supply. In such an embodiment the zero crossings of the voltage waveform are detected by a comparator, which may be an integral part of the microprocessor input circuitry.

In certain embodiments the voltage of the supply is determined by measuring the instantaneous voltage of the supply using only one voltage sample taken at the known time of occurrence after the detection of an instantaneous zero voltage of the peak of the sinusoidal supply voltage. For a 50-cycle supply the peak value of the voltage occurs 5 milliseconds after the occurrence and detection of the last zero crossing.

Accuracy of the energy consumption calculations is also effected by the analogue to digital conversion process. In an embodiment which requires high accuracy over a large range of power consumption by the load 8 bit samples of the current may not be sufficient to give high accuracy at low currents. One embodiment of the invention employs a current sensing load which is non-linear and possessing two outputs. One of these has a sensitivity several times greater than the other. The more sensitive output is used at low powers and the less sensitive one at high load powers. The non-linear nature of the load allows the more highly sensitive output to be restricted to a voltage which will not damage the analogue to digital conversion device.

In the precise forms of embodiment of the invention energy consumed in a cycle and hence power or volt-amperes is calculated from a complete set of current and voltage samples taken in a mains cycle or half-cycle. The calculation of energy per cycle may be effected by storing all the samples before calculating the energy. Alternatively in another form of embodiment the energy may be calculated for each sampling interval as it occurs and a running total accumulated continuusly sample period by sample period without reference to mains cycle. In any embodiment it is not necessary to calculate the energy on every cycle of mains it being sufficient if desired to calculate the energy of volt-amperes consumption rate every second or so and to assume constant consumption until the ensuing calculation on the next selected mains cycle or half-cycle.

In a precise form of embodiment employing for example 100 samples per half-cycle the average volt-ampere consumption in a cycle is calculated according to the following formula.

Where P is the average volt amperes being delivered to the load vk is the binary representation of the k th voltage sample after the last voltage zero ik is the binary representation k th current sample after the last voltage zero.

Embodiments which make an approximate estimate of power use the same principle though using fewer samples andlor assuming nominal values for the various vk. Accuracy of an embodiment is dictated by the application anticipated for that embodiment.

In an embodiment of the invention which is used to measure consumption by an electricity authority for domestic billing purposes high accuracy is necessary and a highly accurate embodiment is employed.

Where an embodiment is to be employed for the purposes of estimating the approximate rate at which energy is consumed by a single appliance or a few appliances sharing one mains socket a lower accuracy is sufficient and a more approximate embodiment can be employed.

Features and advantages of the present invention will become apparent from the following description of embodiments thereof, given by way of example with reference to the accompanying drawings in which Figure lisa diagram illustrating the sensing of current and voltage applied to the load by use of simple resistive sensing.

Figure 2 is a diagram illustrating the use of transformers to sense current and voltage.

Figure 3 is an electric circuit diagram illustrating the construction of a non-linear load for deriving two sensing voltages having different sensitivities.

Figure 4 is an electric circuit diagram of the current sensing portion used in a simple embodiment of the invention.

Figure 5 is a block schematic diagram representing a complete embodiment of the invention.

Figure 6 is a circuit diagram of a particular embodiment of the apparatus where the analogue to digital converter is separate from the microprocessor and employs a separate program memory.

Figure 7 is a circuit diagram of a second particular embodiment of the apparatus where the analogue to digital conversion process, the program memory and the microprocessor are all incorporated in one device.

Figures is a circuit diagram of a particular embodiment of power supply incorporating a particular form of zero-voltage, SYNC, detection.

Figure 9 is a drawing of the appearance of an embodiment of the apparatus to be used for monitoring consumption by asingle appliance.

Figure 10 is a particular example of a logical flow diagram representing the calculating and controlling program executed by a microprocessor within the apparatus.

Figure 1 illustrates the principle of current and voltage measurement by the measuring apparatus 4. The live, neutral, and where appropriate also the earth conductors from the supply pass into the apparatus. The instantaneous mains voltage, VL, is sensed directly or as in Figure 1 a proportion of the mains voltage, vv, is obtained by the resistive divider chain 2, 3. The instantaneous current iL is sensed by the series resistance, 1, in series with the live or preferably the neutral conductor this series resistance being of such low value that the mains voltage across the load is not significantly affected. The sensing voltage generated, vv, is essentially of the order of a volt or less if power lost in the sensing resistance is to be kept low.

In order to raise the current sensing voltage to a more reasonable level a current transformer can be employed as illustrated in Figure 2. The current transformer, 6, generates a secondary current through the current sensing load 7. The current sensing load may be a resistance or set of series resistances having a total value of several tens or several hundreds of ohms. It may also incorporate non-linear elements in order to restrict sensing voltages, yell, vl2, generated to tolerable levels for the input to the analogue to digital conversion stage to be described later. The sensing voltage yv may be obtained from a separate transformer or as illustrated in Figure 2 from a special winding or tapping on the electronic power supply transformer, 8.

The power supply, 9, produces power at voltage Vcc to activate the devices in the apparatus and a stabilised voltage VREF for the analogue to digital conversion circuitry. It also can operate to produce a voltage zero crossing reference time or SYNC pulse occurring 100 times per second. In the event of mains supply failure battery backup is shown capable of allowing the apparatus to recommense operation sensibly when power is restored.

Figure 3 illustrates the use of a non-linear load for the current sensing load across the secondary winding of the current transformer. The secondary winding current is independent of the nature of the secondary sensing load provided that the equivalent series sensing load in the mains supply path is low compared with the main electrical load and has a low impedance in comparison with the transformer primary inductance.

This allows the sensing load to incorporate non-linear elements. In Figure 3 the resistances R and 7R are in series at voltages from the secondary of the order of 3 volts peak-to-peak or less and V12 is a highly sensitive sensing voltage. When the voltage increases as for higher electrical load current the triac, 10, is switched on preventing further rise in voltage v12. The sensing voltage, v11, which in this illustration is nominally one eighth of vl2 is now of sufficient amplitude to allow accurate analogue to digital conversion to occur on V11.

Figure 4 illustrates an embodiment of the invention where the current sensing device is a simple resistance 11. The range of variation of the voltage is centred within the range of the analogue to digital conversion device by the resistive divider chain 12, 13 consisting of two approximately equal resistances. The range of analogue conversion possible is approximately 0 volts to VREF volts, VREF being approximately a 5 volts stabilized voltage.

Figure 5 represents a complete embodiment of the invention, shpwing how the sensing circuits of Figures 1 to 4 can be employed in a complete apparatus. In this example of an embodiment a current transformer, 15 in series with the neutral conductor supplying the electrical load, 14, supplies secondary current to the current sensing load 16. In this embodiment there are provided two current sensing voltages which are used as inputs to the analogue to digital converter as previously explained by reference to Figures 2 and 3. The analogue to digital conversion circuitry, 18, contains two analogue to digital converters the output of one being used for low peak-to-peak load currents the other for high peak-to-peak load currents. The analogue to digital conversion circuitry is provided with a reference voltage Ref from the power supply, 17, of approximately 5 volts which acts as a voltage reference for comparison with the current sensing voltage made by the analogue to digital circuitry. The analogue to digital converter output consists of a sequence of digital samples of the current waveform. The digital calculating controlling and display driving circuitry, 19, controls the times at which analogue to digital conversions are made, responds to the operator control switches 21, and displays the results of calculations on the indicators 20.

In the embodiment as represented by this Figure the voltage waveform is assumed to be sinusoidal and equal to the nominal mains voltage so that it is only necessary to sense the zero crossing time of the mains voltage by the comparator, 22. This embodiment of the apparatus could be modified so that instead of only using the zero crossings of the voltage and assuming values thereafter an analogue to digital converter would operate on a proportion of the mains voltage as previously explained by reference to Figures 1 and 2.

Another form of modification would allow the voltage sensing winding to be sampled 5 milliseconds after zero crossing this point being the known peak of the mains supply cycle. In this diagram the SYNC is not employed, synchronization being derived from the voltage sensing winding by the comparator.

In the form of embodiment represented by Figure 5 means are provided whereby the apparatus can be operated from a remote location by means of remotely situated controls which transmit signals over a single or group of data-transmitting wires to the data-receiving portion of a Data Transmitter and Receiver, 22A.

The signals are then made available to the main apparatus thereby controlling its operation. Also provided are means whereby the data-transmitting portion of the Data Transmitter and Receiver can transmit data from the apparatus over the same or similar group of wires to a remotely situated device. Such a remote device will normally consist of an indicating device operable to display the results of calculations performed by the main apparatus The nature of the connections to the Data Transmitter and Receiver, 22A, are such that this embodiment of the invention may be employed using remote operation, remote indication, or be operated and employed in a purely local mode not requiring any external data connecting wires. The data connecting wires, when employed may be used to communicate with other data manipulating, calculating or controlling apparatus.

Figures 6 and 7 show the details of two separate embodiments of the invention as just broadly described with reference to the commonly applicable block diagram of Figure 5. The detailed embodiments of Figures 6 and 7 differ mainly in respect to the type and arrangement of devices used for the analogue to digital conversion, the voltage comparison, the digital program storage, and the digital computation process. In these two detailed embodiments data communicating means are not included in the description though such a facility could be incorporated by quite simple modification to either apparatus. Firstly the detailed embodiment of Figure 6 will be described.This embodiment employs an INTEL 8035 microprocessor, 23, operating at a basic clock rate of 3.2 MHz, which in this embodiment is derived from the resistance and capacitance time constant reference connected to inputs XT1 and XT2, which could equally well be estabiished by a quartz crystal reference in parallel with a 1 M resistance connected between the same terminals.

The arrangement of the programme store, 24, and display driving devices 25,26, operated by the 8035 microprocessorfollows conventional practice. Forthe sake of completeness their operation in conjunction with the power sensing device, analogue to digital converter, 27, switches, 28, and display, 29, will be described.

The power supply module, 30, derives operating power from the live and neutral conductors of the supply via a mains transformer incorporated in the power supply module, this is illustrated in more detail by reference to Figure 8. The power supply module in this embodiment also provides the sync pulse, as illustrated in Figure 8, corresponding to zero-crossings of the mains voltage, although a modification allows a special transformer winding to be used for this purpose as previously described by reference to Figure 2.

Referring again to Figure 6 the neutral conductor passes through a current transformer, 31, which presents a low reflected resistance in the primary neutral conductor of the sensing resistance, 32. The sensing resistance is of the order of a hundred to 1000 ohms while the turns ratio of the transformer is such that the primary reflected resistance in series with the neutral mains conductor is of the order ofmilliohms. In this embodiment a simple resistive load is employed, having a single output of constant volts-per-mains-amps sensitivity. A modification allows a non-linear load having 2 or more outputs to be employed as has been explained by reference to Figures 3 and 5.The sensing voltage is biased by the two potential divider resistances, 33, so that the zero voltage point on the mains current sensing voltage corresponds to the middle of the conversion range of the analogue to digital converter, 27. In this embodiment the digital to analogue converter is an ADC0816 made by National Semiconductor which converts the current sensing voltage, vt, to an 8-bit parallel number on outputs D1 to D8 of the device.

In this embodiment only one sensing voltage is measured by the analogue to digital converter, though the apparatus could be modified to measure two or more current sensing voltages of differing sensitivities and could also be modified to make measurements on a sensing voltage proportional to the supply voltage.

The mains conductors in this embodiment enter on a lead which is plugged into a mains supply socket and are connected within the body of the apparatus to a mains supply socket on the apparatus so that an electrical appliance may be plugged into the apparatus and its consumption and cost of electricity monitored.

The apparatus embodies 4 push-button switches, 34, and one toggle switch, 35, although the push-button switches could be modified to be capacitative contact or proximity switches. One function of the 4 push-button switches is to enter the information concerning the cost of electricity into the data memory contained within the 8035 microprocessor. This is performed when the toggle switch is in the 'pence per unit' position as can be seen by reference to Figure 9. When the toggle switch is in the electricity bill position the push-buttons perform the function of allowing a check to be made on the consistent and continuous operation of the device. Pushing 'check' as illustrated in Figure 9 causes the previously entered cost per unit to be displayed thereby verifying continuous and proper operation of the apparatus.Pressing 'start' causes the apparatus to commence totalization of energy consumption and calculation of energy consumption cost since first pressing of start. Pushing the 'stop' button stops further totalization of energy and cost. Pushing 'time' causes the time elapsed to be displayed on the displaying device in minutes and seconds, or hours and decimal hours, or days and decimal days according to the time elapsed since 'start' was first pressed. When no button is pressed and the toggle switch is in the 'electricity bill' position the totalized cost is displayed as multiples of .001 of a penny, for small costs, in multiples of 0.1 of a penny for 1 p to 99p in multiples of .01 of a pound or multiples of .1 of a pound for sums up to 10 or 100 respectively.The display device, 29, in this embodiment is of the 4-character 7-segment light emitting diode type each with a decimal point. Other types of display such as liquid crystal or other type could be employed with simple modification. The displays are of the 7-segment + decimal point addressable type and the display is multiplexed character by character so that segments are illuminated on appropriate characters in turn in a cycle repeating approximately every millisecond.

An advantage of these displays is that they can be conveniently driven by the microprocessor to provide a limited form of alphabetic display. A modification would allow full aiphanumeric displays of the sixteen segment 'union jack' or 35-dot matrix or other type to be employed, but the seven-segment type is presently preferred for simplicity and economy. Examples of the letters and figures displayed in this embodiment by the display are ".01 5P" "L7.85" L99.2 for totalized cost, and "23.8h" and "99.6d" for elapsed time.

the displays in this embodiment are driven by display LED cathode drivers DS8871 and display MOS to VLED drivers type 75491 since the 8035 microprocessor does not provide sufficient power to drive the displays directly.

The data bus of the microprocessor consists of 8 wires accessible either by the analogue to digital converter, 27, by the switches via the hex bus driver type 74367 ref. 36 in Figure 6, the address latch type 8212 ref. 37 in Figure 6, and the 2K byte program memory store type 2716 of ultraviolet light erasable kind, 24. The data bus is employed to address the memory, 24, in conjunction with outputs P20, P21, P22 of the 8035 ref. 23 and under control of the ALE, address latch enable, signal of the microprocessor. The microprocessor controls the various devices assessing the address/data bus by appropriate enabling of the devices attached to the bus by means of appropriate activation of PSEN, P22, P23, RD signals under control of the digital program stored in the 2716.The operation of the ACD081 6, analogue to digital converter, 27, is controlled by the WR signal to start conversion, and a conversion clock is provided from the TO output at approximately 1 MHz by internally connecting the internal machine clock to the TO output of the microprocessor.

The end of an analogue to digital conversion is signified to the 8035 on the T1 input by the EOC signal on the ADC0816. The switches are read periodically by enabling them onto the data bus by P22 and RD signals.

The state of the switches is conveniently sensed by the microprocessor on every occurrence of the zero crossing interrupt by the sync input to the interrupt input, INT. This occurs at 1 Oms intervals for a 50 cycle mains supply.

The operation of the microprocessor according to its stored program and in conjunction with its peripheral devices embodying the total apparatus shown in Figure 6 is conveniently illustrated by the flow diagram of Figure 10. The microprocessor is initialised when first power is applied by the low voltage on the RESET input. This action clears the data stored in an internal 64-byte random access memory (RAM) and performs a number of other initializing functions. If at this time the 'cost per unit' switch in Figure 9 is 'set' to this position the timer interrupts will be disabled and the microprocessor will be awaiting input of cost information from the four push-button switches. Each switch effects an advance of the adjacent display digit every time it is pressed and released and is debounced by reference to the 10ms interrupt.

On switching the 'cost per unit' switch to 'ELECTRICITY BILL' the four main portions of the flow chart are followed by the microprocessor. An internal sampling timer is started and commences to generate internal interrupts every 1.25 ms, that is 8 times per half cycle of mains frequency. This is sufficient to maintain adequate accuracy for mains currents which are not sinusoidal and leads to precise accuracy for currents which are sinusoidal. For higher accuracy with non-sinusoidal, e.g. triac switched loads, the apparatus can be modified to take more frequent samples.

On each 1 0ms interrupt the elapsed time stored in the microprocessor RAM storage is updated. The half-cycle energy from the previous half cycle is multiplied by the stored unit cost and added to the total already accumulated cost stored in RAM. The half-cycle accumulated charge stored in RAM is then zeroed ready for the next calculation for the next half-cycle.

The switches are scanned to ascertain any change due to operation by the user and their stored status is updated. Any change in status results in appropriate action by the microprocessor such as stopping totalization or effecting display of a different quantity, such as time elapsed instead of cost or other action according to the program which dictates the detailed performance of the apparatus.

The lower half of the flow diagram is followed each time a 1.25 ms internal timer interrupt occurs. On occurrence of this interrupt the timer is restarted for the next sampling period. The ADC is instructed to take a sample of the current sensing voltage. The power orvoltamperes consumed in the last sampling period is calculated and added to the total for the current half-cycle with reference to the nominal voltage stored in data memory for the corresponding times in the cycle. One particular character is illuminated as appropriate to the figures or letters currently to be indicated so that each character when 'on' is illuminated 200 times per second.

Although this embodiment employs a running totalization of energy consumption during each half-cycle an alternative programming of the microprocessor would allow storage of all samples belonging to a particular half-cycle of supply followed by subsequent calculation on the stored samples, which for preference would continue while the samples for the next half-cycle were being taken. It is not necessary to sample all half-cycles and if a longer calculation time is required it would be satisfactory to sample a half-cycle at intervals of several cycles assuming constant load condition between those cycles selected for sampling.

We have described a first detailed embodiment based on an 8035 microprocessor with reference to Figure 6.

We will now describe an alternative detailed embodiment based on an 8022 microprocessor with reference to Figure 7. This differs from the previous detailed embodiment in that the 8022 microprocessor, 38, embodies program memory which is masked into the device during manufacture. It also incorporates two analogue to digital conversion inputs, AN0, AN1. Consequently this embodiment is more economic in terms of components. The power supply, display and display drives are the same as the previous detailed embodiment. The switches, 39, in this embodiment do not require a buffer since there is a port available for their direct sensing where previously on the 8035 embodiment access was via a data bus.

This embodiment shows a non-linear current sensing load, 40, though it could be easily modified to employ a simple linear resistance load. A current transformer is shown although a modification would allow a simple series resistance in the neutral conductor together with an amplification stage to provide a current sensing voltage.

This detailed embodiment, Figure 7, is housed in the same manner as the previous detailed embodiment, Figure 6, and its external appearance is illustrated by reference to Figure 9. The operation of the microprocessor is described with reference to the same program flow chart as illustrated by reference to Figure 10 and previously described for the embodiment employing an 8035 microprocessor. In this case the digital to analogue conversion is performed within the 8022 device, 38, itself.

The functioning of this embodiment of the apparatus is similar to the embodiment described with reference to Figure 6. Because of the incorporation of previous separate devices into one device this embodiment of the apparatus has a simpler circuit diagram.

The displays are of the same type as in the 8035 embodiment connected by similar display drives 41,42, to port 2 for the anodes of the displays and port 1 for the cathodes.

The current sensing voltage or voltages enter on pins AN0 and AN1 of the 8022 and conversion to 8 bit digital form occurs within the device.

As already indicated Figure 9 represents the external appearance of this detailed embodiment and Figure 10 represents a flow diagram giving the essential characteristics of the operation of the apparatus with its program stored in the 8022 in this detailed embodiment, rather than in the 2716 of the previous detailed embodiment.

We have described two detailed embodiments which are intended to have a medium level of accuracy for the calculation of electrical power taken by one or several appliances powered by a single mains power plug.

Modification to either of these embodiments are possible which would enable them to be highly accurate and incorporate also mains voltage sensing, to be sensitive to input details of tariff structure or fixed electricity charges and thereby allow such embodiments to be modified for monitorings of total electricity cost consumed in a single premises. Such an apparatus is then placed electrically in series with the premises mains supply cable and allows a consumer to monitor his total electricity consumption in terms of energy or units consumed as well as the cost of that consumption, or for an electric supply authority to base his charge made on the consumer on the indications given by such a device.

Claims (22)

1. Apparatus for measuring the cost of electrical power taken by an electrical load from a source of alternating electrical supply, such apparatus comprising means for making measurements on the electrical conductors supplying power to the load, calculating means to derive from a succession of such measurements the power or voltamperes taken by the load, means for providing to the apparatus information concerning the cost of electrical energy being supplied to the load including where appropriate details of any fixed or minimum charge or variable costs or tariff structure and means whereby the said calculating means computes the accumulated cost or rate of accumulation of cost of the connection of the said load to the supply, together with means employable to indicate the said cost or costs.

2. Apparatus according to claim 1 where measurements made on the conductors supplying the load consist of a succession of instantaneous values of the voltage occurring between the conductors and a corresponding succession of instantaneous values of the current flowing through the load between the conductors.

3. Apparatus according to claim 1 where measurements made on the donductors supplying the load consist of a succession of instantaneous values of the current flowing between the conductors and measurements of the times of occurrence of zero voltage between the conductors, and for energy and cost calculation the voltage values employed between the conductors at the times of measurement of the current are pre-stored in the apparatus said voltage values being equal to those occurring for a supply having the nominal voltage attributed to the supply.

4. Apparatus according to claim 1 where measurements made on the conductors supplying the load are the peak or peak-to-peak values of the current flowing between the conductors and the peak or peak-to-peak voltage between the conductors and for the purpose of energy calculation both current and voltage are taken to be sinusoidal in form possessing the said measured peak or peak-to-peak values.

5. Apparatus according to claim 1 where measurements are made on the conductors supplying the load and consist only of the peak or the peak-to-peak value of the current flowing between the conductors and for the purposes of energy calculation it is assumed that the current is sinusoidal having said measured peak or peak-to-peak value and that the voltage is assumed sinusoidal and equal in value to the nominal voltage attributed to the supply, said voltage value being previously stored in the apparatus.

6. Apparatus according to claim 1 where sensing means are employed to measure the supply voltage and supply current, combining means are employed to produce a power sensing voltage proportional to the instantaneous volt-amperes flowing in the load and a succession of instantaneous values of said power sensing voltage are employed by the apparatus as measurements on the electrical conductors supplying the load.

7. Apparatus according to any of claims 1 to 5 employing as voltage sensing means a voltage transformer and analogue to digital converter.

8. Apparatus according to any of claims 1 to 5 employing as voltage sensing means a comparator.

9. Apparatus according to any of claims 1 to 5 employing as current measuring means a current transformer supplying secondary current to a load, thereby generating a sensing voltage or voltages dependent on the current being drawn from the supply said sensing voltage being converted to digital form by an analogue to digital converter.

10. Apparatus according to claim 9 wherein the sensing voltage orvoltages are generated across a linear sensing load.

11. Apparatus according to claim 9 where current sensing voltage or voltages are generated across a non-linear load in such a manner as to suppress the occurrence of damaging sensing voltages in the presence of high supply current while maintaining a sensing voltage output having high measuring sensitivity at low supply currents.

12. Apparatus according to claim 11 whereby.a non-linear sensing load contains one or several switching or sensing devices.

13. Apparatus according to claim 1 where measuring means operate to make a number of separate measurements on the electrical conductors supplying the load during the time of one half-cycle of the supply voltage.

14. Apparatus according to claim 1 where the measurements having being converted into digital form are stored in a random access memory while awaiting subsequent computation.

15. Apparatus according to claim 1 where calculating means consist of a microprocessor operating on measurements converted into digital form by an analogue to digital converter which is controlled by said microprocessor operating in association with a digital program stored in program memory storage means.

16. Apparatus according to claim 1 where the calculating means bodily incorporates an analogue to digital converter or analogue to digital converters or program memory or voltage comparators or a combination thereof.

17. Apparatus according to claim 1 where means for providing information on the cost of electrical energy being taken from the supply consists of a plurality of switches operable to store the information in a memory device, said information being accessible by calculating means.

18. Apparatus according to claim 1 where means are provided to provide information on the cost of electrical energy being taken from the supply by a remotely operable device operating in conjunction with a wire or wires to transmit the information to the apparatus from said remotely operable device.

19. Apparatus according to claim 1 where calculating means are employed incorporating control and activating means to operate an alphanumeric display device so as to display letters and figures indicating the cost per unit of electrical energy being consumed, the time that has elapsed since the commencement of a cost measuring period, the total cost accumulated since commencement of said measuring period, the rate of incurring of cost, the rate of energy consumption by the load, the total energy consumed since the commencement of the measuring period or a combination of such quantities.

20. Apparatus according to claim 19 whereby commencement of a measuring period and quantities displayed on indicating means incorporated in the apparatus are controlled by a plurality of switches in conjunction with calculating means and a program memory device.

21. Apparatus according to claim 19 incorporating means whereby the said quantity or quantities can be indicated on an indicating device remote'from said apparatus.

22. An apparatus for measuring electrical power consumption, digital calculating means for deriving accumulated cost, accumulated energy consumption, and elapsed measurement time and control means to effect display of such quantities as hereinbefore particularly described with reference to the drawings 1 to 10 accompanying the provisional specification.