GB2133594A - Electrical power consumption costing device - Google Patents

Abstract

A device for the measurement and display of electrical power drawn from a supply, comprising a means (10) for deriving a first electrical signal proportional to the instantaneous current level being drawn from the supply, a means (16) for deriving a second electrical signal proportional to the instantaneous voltage level of the supply, and a means (14) for electronically operating on said first and second signals to provide a third signal representative of the instantaneous power being consumed. A keyboard (34) enables information as to, inter alia, unit cost to be introduced by a user. A microprocessor (22) operates on the third signal and the information entered on the keyboard (34) to derive a value for the cost of power consumed during a prescribed period. Calculated information is displayed to the user on an electronic digital display (30). <IMAGE>

Description

SPECIFICATION Electrical Power Measurement Device The present invention relates to devices for the measurement and display of electrical power.

All domestic and commercial premises are fitted wth meters for the display and measurement of the electrical power which is consumed on those premises. Conventional meters are, however, not particularly informative since (a) the units which they display are not ones with which the average person is familiar and (b) the cumulative total of the units consumed is displayed so that, at the very least, one has to do a mental subtraction to arrive at the number of units used in a particular period, e.g. since the meter was last read. It is not surprising therefore that consumers are usually totally unaware of the likely size of any particular electricity bill until it is received - by which time it is too late to take steps to adjust the consumption to a desired rate.

There thus exists a need for a device which would inform the consumer in recognizable units of the amount and cost of his electrical power consumption actually as it is happening, rather than at the end of the quarter when it is too late to do anything about it.

Accordingly, it is an object of the present invention to provide a device which can provide the user with detailed information about his consumption of electricity in order that he may more easily regulate the amount used.

According to the present invention, there is provided a device which comprises: (a) means for deriving a first electrical signal proportional to the instantaneous current level being drawn from the supply; (b) means for deriving a second electrical signal proportional to the instantaneous voltage level of the supply; (c) means for electronically operating on said first and second signalsto provide a third signal representative of the instantaneous power being consumed; (d) means to enable information as to, inter alia, unit cost to be introduced by the user; (e) means for operating on the third signal and the information entered on the keyboard to derive a value for the cost of power consumed during a prescribed period; and (f) means for providing calculated information to the user, at least items (c) to (e) being disposed in a selfcontained housing locatable at a position to suit the user.

Preferably, the operation on the third signal and the user-entered information is performed by a microprocessor contained in said housing.

In one embodiment, the first and second signals are supplied to an analogue switch which is controlled by the microprocessor alternatively to pass the first and second signals to an RMS to DC converter the resulting analogue D.C. signals being converted to digital signals in an analogue to digital converter. The microprocessor multiplies the resulting two digital signals to derive a further digital signal representative of instantaneous power consumed. This can be displayed. The microprocessor also multiplies the latter signal by the "cost per unit" entered by the userto provide a display of the actual cost of the units consumed in the prescribed period, e.g. since the last meter reading.

In another embodiment, the first and second signals are applied to an analogue multiplier to derive a product signal which is then applied to a voltage to frequency converter. The resulting pulses, suitably calibrated, represent power consumed and can be displayed accordingly. This approach simplifies the processor software.

The invention is described further hereinafter, by way of example, with reference to the accompanying drawings in which: Figure lisa simplified block circuit diagram of one embodiment of a device in accordance with the present invention; and Figure 2 is a circuit diagram of part of a second embodiment illustrating one manner for achieveing current-frequency conversion.

The embodiment illustrated in Figure 1 uses a current transformer 10 which comprises a laminated iron core (not shown) which splits into two pieces to enable it to be clipped around one of the mains leads to the existing electricity meter or main fuse. The ability to split the core ensures that the transformer may be fitted without disconnecting or breaking the main conductor, no direct electrical connection being required at this point. In the conventional manner for current transformers, a winding on the iron core has a current induced in it which is proportional to the alternating current flowing in the conductor and through the electricity meter. A calibration amplifier 12 with variable gain provides a voltage Awhich may be adjusted to produce a signal of convenient size proportional to the current in the mains conductor.

The latter voltage is supplied to an analogue switch 14, together with a suitably calibrated voltage B proportional to the mains voltage, derived by a voltage sensing means 16. The analogue switch 14 is is adapted to select the voltages A and B alternatively and to transmit these voltage levels in turn to an RMS-DC converter 18 at a repetition rate selected by a clock 20 contained within a microprocessor 22. The converter 18 accepts the output signals of the analogue switch 14 and produces a respective D.C.

voltage proportional to the RMS value of each of the input signals supplied to it. The RMS-DC converter is included because errors would otherwise result if the input signals were not pure sine waves-as is likely on many occasions in view ofthe increased use ofthyristor phase control in many appliances now being used both domestically and industrially.

The output of the RMS-DC converter 18 is applied to the input of an analoguetodigitalconverter24which provides a parallel binary word A',B' representing the value of the selected input signal corresponding to the voltage levels A and B.

The two digitised input signals A', B' corresponding to signals A and B are applied to the microprocessor 22 together with signals from a real-time clock/calendar circuit 20/26, the microprocessor being adapted to operate on these signals to calculate and totalise the power used. All data is stored in a non-volatile memory, thus ensuring that no information will be lost in the event of a power failure or inadvertent disconnection. The microprocessor includes RAM and ROM circuits 26,28 and is coupled to an electronic display device 30 and a tone generator 32. A keypad 34 enables information to be manually inserted into the microprocessor, particularly information as to the relevant "cost per unit".

The microprocessor is adapted to be capable of operating on the input information supplied to it whereby a user can, with the aid of the keypad, cause information to be displayed as follows: (a) The current being consumed at the present moment in amps.

(b) The power being consumed at the present moment in watts.

(c) The total power and cost of power consumed during the period since the last reset.

(d) The total power and cost of power consumed during the period between the last two resets.

(e) The total power and cost of power consumed during, say, the last 24 hours.

(f) The total power and cost of power consumed during, say, the previous week.

This list can be expanded or reduced as required to suit any particular class of user.

In addition, the microprocessor can be arranged to normally display the current time and/or date when the user is not requiring information on current or power consumption.

The microprocessor may also be arranged to respond to several alarm conditions when the user is alerted by actuation ofthe tone generator 32, such as: (1) a "power threshold" may be set above which the audible tone generator will be actuated; (2) a "cost threshold" above which the audible tone generator will be actuated.

The microprocessor may also be arranged to respond onlyto a personal code number(s) which will prevent unauthorised changing of items such as "cost per unit", "reset" etc.

In a further embodiment of the device (not illus trated),the input voltage levels A and B proportinal to the instantaneous current and voltage could be multiplied directly in an analogue multiplier, the resulting product signal being applied to the input of a voltage to frequency converter. Suitably calibrated, the resultant pulses (or groups of these pulses) can be arranged to represent watt-hours which would be displayed accordingly. This latter embodiment would serve to simplify the microprocessor software.

Figure 2 illustrates an embodiment ofthe lattertype wherein input voltage levels proportioned to the instantaneous current and voltage levels are multiplied in an analogue multiplier. This embodiment is illustrative of one manner in which current to frequency conversion ofthe power related signal can be attained.

With reference to Figure 2, a current transformer (not shown) is inductively coupled to the mains circuit to be measured and is arranged to develop a voltage across a resistor Ri proportional to the current in the means circuit. The latter voltage is amplified by ICla and applied to one input of an analogue multiplier IC2. A second input of It2 is supplied with a voltage proportional to the mains voltage VIN. The output of multiplier IC2 is representative of the instantaneous power in the measured circuit. The latter output is applied to IC3 which converts this signal to an RMS value.

The current output of IC3 is applied to the input of an integrator IC1 b, the output of which is a negativegoing ramp with a slope proportional to the RMS value ofthe measured power. When the output of 1C3 reaches a reference voltage as set by a variable resistor VR4, a comparator IC4 coupled to the output of integrator IC3 is arranged to switch on analogue switches IC5a, IC5b, and IC5d, thus injecting a current into the integrator via a diode D1 which causes the integrator to ramp rapidly towards 0 volts. When 0 volts is reached, the comparator IC4, which now has a reference voltage of 0 volts due to IC5a and IC5b, switches back and the cycle repeats.

A pulsed output of frequency proportional to instantaneous power is thus outputted via IC7b and IC7d. IC6 enables a frequency divided to F/10 to be obtained, which can be useful for signal handling purposes.

Thus, IC1 b, IC4 and IC5 form a current to frequency converter with a pulse rate proportional to power/ time and can be arranged to operate at, for exampie, one cycle per kilowatt/second.

A microprocessor (not shown) totalises the pulses and provides a display of total power measured over any required period of time.

The use of the present device thus provides the user with detailed information concerning the consumption of electrical energy and the cost thereof so that he may be in a position to more easily regulate the amount used. The operation of the device by the user is simple. He only has to key in the current "cost per unit" and any standing charge. The device is reset, preferably when the electricity meter is read, and it will then keep a total ofthe number of units and the cost of the electricity used. This total may be displayed at any time.

The particular form of the microprocessor is not critical and its programming can be accomplished in accordance with known techniques. Details of the microprocessor itself have therefore not been included herein.

Claims (11)

1. A device for the measurement of electrical power drawn from a supply, comprising (a) means for deriving a first electrical signal proportional to the instantaneous current level being drawn from the supply; (b) means for deriving a second electrical signal proportional to the instantaneous voltage level of the supply; (c) means for electronically operating on said first and second signalsto provide a third signal representative of the instantaneous power being consumed; (d) means to enable information as to, inter alia, unit cost to be introduced by the user; (e) meansforoperating on thethird signal andthe information entered on the keyboard to derive a value for the cost of power consumed during a prescribed period; and (f) means for providing calculated information to the user, at least items (c) to (e) being disposed in a self-contained housing locatable at a position to suit the user.

2. A device as claimed in claim 1, wherein the operation on the third signal and the user-entered information is performed by a microprocessor contained in said housing.

3. Adevice as claimed in claim 1 or2, wherein the first and second signals are supplied to an analogue switch which is contolled by the microprocessor alternatively to pass the first and second signals to an RMS to DC converter, the resulting analogue D.C.

signals being converted to digital signals in an analogue to digital converter, and the microprocessor being arranged to multiply the resulting two digital signalsto derive a further digital signal respresentative of the instantaneous power consumed.

4. A device as claimed in claim 3, wherein the microprocessor multiplies said further digital signal by the "cost per unit" entered by the user to provide the actual cost ofthe units consumed in a prescribed period.

5. A device as claimed in claim 2, wherein the first and second signals are applied to an analogue multiplierto derive a product signal which is then applied to a voltage or current to frequency converter, the resulting pulses being passed to the microprocessor.

6. A device as claimed in claim 5, wherein the current to frequency converter comprises an integratorwhich is arranged to ramp with a slope proportional to the power related current output of said analogue multiplier, the ramp outputofthe integrator being supplied to a comparator which, when said ramp outlet has reached a predetermined level, is arranged to reset the integrator and commence a further cycle, the output of the comparator thereby providing a plurality of pulses of frequency proportional to the power per unit time.

7. A device as claimed in any of claims 1 to 6, wherein the information supplied by the user is entered by a keyboard.

8. A device as claimed in any of claims 1 to 7, wherein said means for providing the calculated information to the user comprises an electronic digital display disposed in said housing.

9. A device for the measurement and display of electrical power drawn from a supply, comprising (a) means for deriving a first electrical signal proportional to the instantaneous current level being drawn from the supply; (b) means for deriving a second electrical signal proportional to the instantaneous voltage level ofthe supply; (c) means for electrically operating on said first and second signalsto provide a third signal representative of the instantaneous power being consumed; (d) a keyboard to enable information as to, inter alia, unit cost to be introduced by the user; (e) means for operating onthethird signal and the information entered on the keyboard to derive a value for the cost of power consumed during a prescribed period; and (f) an electronic digital display for displaying calculated information to the user, at least items (c) and (f) being disposed in a self-contained housing locatable at a position to suit the user.

10. A device for the measurement of electrical Dower drawn from a supply, substantially as hereinbefore described with reference to and illustrated in Figure 1 of the accompanying drawings.

11. A device for the measurement of electrical power drawn from a supply incorporating a circuit substantially as hereinbefore described with reference to and as illustrated in Figure 2 of the accompanying drawings.