CA1298424C - Electronic remote data recorder for electric energy metering - Google Patents

Abstract

ELECTRONIC REMOTE DATA RECORDER
FOR ELECTRIC ENERGY METERING
ABSTRACT OF THE DISCLOSURE

An electronic remote data recorder records pulses representing usage of a commodity such as, for example, water, gas or electricity from a plurality of consumers. The data from each consumer is stored in a respective data storage device. Each data storage device is associated with an interval data directory which stores the time at which significant events, affecting the data in the data storage device occurred. Thus, the data in the data storage device is compact, without requiring a contemporaneous time code for each data item. Data integrity is retained over a period of power outage in a non-volatile storage device. Initial, post-installation programming is enabled by comparing the data pattern in the non-volatile storage device with a predefined data pattern that is expected to exist once the apparatus has been programmed. A write-protect switch prevents programming during an incoming call after the initial programming. Programming from an external source may be permitted during a telephone call initiated by the data recorder itself. A
telephone line-sharing device permits a plurality of remote data recorders to share a single telephone line without interfering with each other.

Description

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1 ll~ME-l91 EIECTRONIC REMOTE DATA RECORDER
FOR ELECTRIC ENERGY METERIN&

~ACKGROUND OF THE INVENTION

Tha present invent~on relates to data recorders and, more particularly, to digital data recorders adaptad for remote acce~ over dial-up ~elephone lines.
~~~~ Since the earliest days of utilities providing energy in the form of gas and electricity, the consumption o~ energy has been metered at the user's location. Collecting the metered data has been done traditionally by a meter reader visiting the user's consumer' location at regular intervals to note the indicat~on on an indicator auch as, ~or example, dials or drums on an electro-mechanical register or an electronic display or digital readout. In one series of electric meters produced by the General Electric Company, readout accuracy and speed are enhanced by an optical readout device accessing the data through an optical port provided under the trademark Optocom.
The cost o~ electric energy i5 generally considered to consist of two parts: out-of~pocket costs and capital cost.

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Out-o~-pocke~ c06t~ are those required ~or the generation and distrlbution of the electric energy.
Such costs are fairly recovered by a charge based on the actual consumption o~ energy.
Capital costs ars those that the utility must bear to ~e prepared to supply the total electriclty needs of all of its consumers. It is well known that the consumption o~ electrlcity has diurnal, a3 well as seasonal, patternsO In hot summer weather, for example, it i8 well known that peak conGumption is reached in some systems in the late afternoon as consumers return home and turn on their air condi~ioners. In winter, similar peaks arise from lighting loads synchronized by early darkness causing business and residen~ial consumer~ to turn on lighting fixtures at about the same time. Business and industrial consumers produce consumption peaks from motor start-up loads and the energy consumption of air conditioning, lighting and other business and ~0 industrial uses.
The size and cost o~ a plant for generating and distributing electricity are determined by the peak load the plant must accommodate. Thus, the capital cost of building a generation and distribution facility is similarly governPd by the peak load, rather than the averaye load.
Demand metering is concerned with the magnitudes of consumption peaks rather than with the times they occur~ Conventional demand meters accumulate the amount o~ energy usage in each of a continuous sequence of demand interva~s. At the end o~ each demand interval, the energy consumption in the ~.2~

3 ll-ME-~91 interval i6 compared to a stored value repr~senting the maximum demand in all previous demand intervals in a current period. If the demand in the just-ended demand interval exceeds the demand in the pr~vious demand inter~al having highe6t demand, a new highest-demand i8 stored and the previou6 high demand i8 erased. When read out, the maximum demand i~ used to influence the rate at which the consumer' 8 total electric ener~y consumption i8 billed for a period which may extend ~or a period a8 long as a year or more.
The familiar electric meter for residential consumers contains a mechanical register accumulating total energy usage in units of, for example, kilowatt hours. No distinction i8 made for the time during which the consumption occurs or for peaks in energy consumption, as in time-of-use and demand systems.
The timeR (of day, week and year~ during which consumption occurs is critical to time of-use or demand metering.
Electronic demand and time-of-use register generally mimic the funstions of their mechanical ~redecessors. Nost electronic registers add display a~d analysis ~eatures not easily implemented in mechanical registers, but not of interest to the present invention.
Physical reading of registers in electric meters is a substantial burden on the utility pro~iding the electric energy. It is thus desirable to provide means for the utility to read the consumption and time-dependent time-of-use and/or demand data from user's registers without requiring a personal visit ~ .

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by a meter raader.
one way to provide remote reading o~ a register includes a dedica~ed line ~uch as, for example, a dedicate~ ~elephone line be~waen a metering data cenler and a register in a consumer'~ facility. The metering data center is thereby enabled to query the condition of registers in ~he consumer's ~acility at will. From a practical standpoint, an energy con~umer, absent a metering failure, require~ a readout only at intervals o~, ~or example, once a week or once a month. It i5 unlikely that a utillty i5 c06t ~ustified in inkerrogating the ~egister6 o~
even a large energy consumer more frequently than once a day. Thus, the relatively high cost of a dedicated telephone line iR dif~icult to justi~y, even in the case of a large energy consumer.
Another way to provide remote reading includes the use of a dial-up telephone line with an auto-dial, auto-answer MODE~ ~modulator-demodulator) at the user's location. The amount of data that must be transmitted at any time between a metering data center and an energy user fits well with the data transmission rates of which commercial M3DgM devices are capable.
It is preferred that a data-co~munications system used with the present invention be able to share telephone facilities with other uses such as, for example, normal in~oming or outgoing voice communication. Such sharing requires that the system be able to recognize that the telephone line i in usa, and to delay demanding use of the telephone line until it is free. It i~ further desirable that means ~%~2~

5 ll-ME-l91 be provided to permit the da~a-co~munications system to be accessed by an incoming call. Such mean~ may include, for example, an auto answer function in which the system engages the incoming line after a S predetermined number of r~ng~ have elap~ed.
Whenever incoming telephone calls may access a data-communications sy~tem~ the 6ub; ect of data security arises. It i5 not wi6e ~ in a revenue-intensive sy6tem ~uch as a metering data communications sy~tem, to permit unauthorized access to the data and, perhaps more importantly, it is crucial to prevent unauthorized tampering with the data or operating system. One method ~or avoiding unauthorized access to a data system includes the re~uirement that access to data requires input o~ a password. In the absence of the required password, access is denied. A password can consi6t of any combination of alphanumeric and punctuation characters receivable by a ~ODEM.
A ~urther access-security method includes callback control, wherein access to the system re~uires that an incoming call begin with a predetermined user code, e~uivalent to a password, be transmitted by the station calling in. The data communications system then hangs up. I~ it received a correct user code, it calls a telephone numbe~
associated with the us2r code. Only then is communication established. Thus, in order to establish communications, an incoming caller must have the correct user code and access to the particular telephone dialed in response to the user code.

6 ll-~E-l91 Numarous other security techniques including, for example, encryption, are well known to those skilled in the ark and thus do not require ~urther description.
Best advantags can be tak2n of access through a dial-up telephone line if the line can be used for other purposes when not needed by the data communication~ system. For example, the data communications system may be connected in parallel with the user's existing telephone line. Except for a few relatively short periods when the data communications 5y tem is in the process of communicating data with the metering data center, the user's line is undisturbed by the presence of the data communications system. Steps must be taken to prevent the data communications system from interfering with other uses and to prevent other uses from corrupting the transmitte~ data.
Besides a data-communications system, an electronic remote data reaorder requires holding and recovery techniques to survive an intentional or unintentional power outage. Holding may be performed with battery backup ~or the most critical components and data. Recovery requires that recording resume without losing revenue data and with time-dependent functions updated according to actual clock time, regardless of the conditions that prevailed when the power 1065 occurred. In addition, means for programming the functions of the electronic remote data recorder, preferably over a telephone line, are desirable. An ability to reprogram remotely suggests that special security measures be provided to avoid unau~horized tampering with ~his function.

OBJECTS ~ND SUMMARY OF THE INVENTION

It is an object of the in~ention to provide an electronic remote data recorder which overcomes the drawbacks o~ the prior art.
It is a ~urther ob~ect of the in~ention to provide an electronic remote data recoxder having means for holding data durlng a power outage and for recovaring after power resumption.
It iB a still further object of the invention to provide an electronic remote data recorder having means for permitting telephone line eharing with other uses.
It is a still further object of the invention to provide an electronic remote data recorder having means for freezing changeable data during data transmission.
It is a s~ urther object of the invention to provide an electronic remote data recorder having programmable write protection.
It is a still further ob;ect of the invention to provide an electronic remote ~ata recorder having means for detectiny a telephone line condition indicating that the telephone line i6 in use.
It is a still ~urther ob;ect of the invent$on to provide an electronic remote data recorder having means for initializing programmable output switch conditions according to an internal clock time.
It is a still further objeot of the invention to 8 11-ME-l9l provide an electronic remote data recorder having simplified meanR for storing in~erval demand data and for tracking a load profile through a programming change or a time reset.
Briefly ~ated, the pre~ent invention provides an electronic remote data recorder which records pulses representing usage o~ a commodity such as, for example, water, gas or electricity from a plurality of consumers. The data fro~ each consumer i8 ~tored in a respect~ve data etorage device. Each data storage device i5 a~sociated with an interval data directory which ~tores the times at which significant events, af~ecting the data in the data storage device occurrad. Thus, the data in ~he data ~torage device is compact, without r~quiring a contemporaneous time code ~or each data item. Data integrity i~ retained over a period of power outage in a non-volatile storage device. Initial, post-inetallation programming is enabled by comparing the data pattern in the non-volatile storage device with a predefined data pattern that i6 expected to exist once the apparatus has been programmed. A write-protact switch prevents programming during an incoming call after the initial programming. Programming ~rom an external source may be permitted during a telephone call initiated by the data recorder itself. A
telephone line-sharing device permits a plurality of remote data recorders to share a single telephone line without interfering with each other.
According to an embodiment of the invention, there is provided a power ~ail detector a~d recovery apparatus for an electronic remote data recorder, the g ll~ l91 electronic remote data recorder including a processor therein, comprising: means ~or producing a power failure signal in response to a ~irst predetermined voltage reduction in a power ~ource to the electronic re~ote data ~ecorder, the electronic remote data recorder being responsive to the power fail signal by halting oparation o~ the proces~or, a non-vola~ile storage device for ~toring con~ents of the proce6sor in the non-volatile storage upon occurrence of the power ~ail si~nal, means rOr res~oring operation of the processor upon a second predetermined voltage increase in the power source above the f irst predetermined voltage, the mean6 for restoring including means for comparing a pattern o~ the contents in the non-volatile storaga with a predetermined data pattern indicating a programmed electronic remote data recorder, and ~or producing an enable signal when a pattern of the contents indicates that the proce~or ha~ not been previously programmed, and means responsive to the enable signal for connec~ing programming data from an external source to the processor for initial programming thereof.
According to a feature of the invention, there is provided a data recording channel for an electronic remote data recorder comprising: a data memory, means for storing pulse data in the data memory, a data direc~ory, m~an~ for storing in the data direc.tory time and event-type data related to the pulse data in the data directory memory, and the time and event type da~a being rela~ed to the stored pulse data to permit after-the-fact reconstruction of ll-ME-l91 time informatlon in the data memory.
According to a further feature of the invention, there is provided a data recording channel for an electronic remota data recorder comprising~ a da~a memory, means for storing pulse data in the data ~emory, a ~irst-inPirst-out register, the pulse data passing through the first-in- ~irst-out register before being stored in the data memory, and means responsive ~o data communication in progre~ for storing incoming data in the first-in-fir t-out register, whereby stationary data i8 transmitted during the data communication.
According to a still further feature of the invention, there is provided an electronic remote data recorder for recording data in a using facility, the using facility including at least one function controlled by at least one programmable switch responsiva to signals from the electronic remote data recorder, comprising: mean~ ~or controlling the at least one programmable switch in response to a clock, a programmable switch library including a relationship o~ a condition of the at least one pregrammable switch and at least one time, and means responsive to power restoration following a power outage for controlling the at least one programmable switch according to a content of the programmable switch library.
According to a still further feature of the invention, there is provided apparatus for sharing a single telephone line among at least first and second MODEMs, comprising: the first MODEM including a first line sharing circuit asæociated therewith, the 11 ll-ME-l91 second MODE~ including a second line sharing circuit associated therewith, the f~rst and second line sharing circuits simultaneously monitoring the same tel~phone line/ the first line-sharing circuit being a master, the second line-sharing circuit being a slave, means in the first line-sharing circuit for responding to an incoming call on a telephone line with an answer signal, means in the s~cond line-sharing circuits for recognizing a first unique identity code and for producing an answer signal in response thereto, the first line-sharing circuit including means for recognizing the first unique identity code and for extinguishing its an6wer signal in response thereto, whereby control of communications is transferred to the second MODEM, means in the first line-sharing circuits for recognizing a second unique identity code and for producing an answer signal in response thereto, and the second line-sharing circuit including means for recQgniæing the ~econd unique identity code and for extinguishing its answer signal in response thereto, whereby control o~ communications is transferred to the first MODEM.
Tha above, and other objects, features and advantages of the present invention will become apparent from th~ following description read in conjunction with the accompanying drawings, in which li~e reference numerals designate the same elements.

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12 ll-ME-l91 BRIEF DESCRIPTION OF THE DR~WINGS

Fig. 1 is a simplified global block diagram o~
an energy-using ~acility whose data i5 stored and communica~ed to a metering data center by an electronic remote data recorder according to an embodiment o4 the invention.
Fig. 2 is a simpli~ied block diagram o~ the electronic remote data recorder of Fig. 1.
Fig. 3 is a bloc~ diagram of a data storage device of Fig. 2.
Fig. 4 is a lo~ic diagram of a power fail and recovery circuit of Fig. 3.
Fig. 5 is a logic diagram of a data storage channel of Fig. 3.
Fig. 6 is a block diagram o~ a communications control circuit of Fig. 2.
Fig. 7 is a ~mplified schematic diagram of a telephone system with which an other-phone detector of Fig. 6 is employed.
Fig. 8 is a curve showing typical variations in voltage on a typical telephone line, as seen by t~e other-phone detector of Fig. 7.
F~g. 9 is a block diagram of the other-phone detector of Fig. 7.
Fig. 10 is a block diagram o~ the signal conditioner of Fig. 9.
Fig. 11 is a simplified block global diagram of a plurality of electronic remote data recorders including means for all recorders to be polled on a common telephone line without mutual interference.

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13 ll-ME-l91 DETAIT~D DESCRIPTION OF THE PREFERRED E~BODIMENT

Referring to Fig. 1, an electric energy consumer lO which may be, for example, a business, residential or manufacturing establishment. Electric ener~y consumer 10 includes electricity-consuming equipment (not shown) whose ener~y consumption i8 measured by one or more kilowatthour meters 12, 14 an~ 16. As represented by t~e vertical dashed line between kilowatthour meters 14 and 16, electric energy consumer 10 may contain any required number of 0 kilowatthour metersO
one skilled in the art will recognize that metering of energy consumption ~ay take other forms besides kilowatthour metering. For example, some utility systems may be interested in measuring kilovoltampere hours instead of, or in addition to, kilowatthours. In addition, a large in~tallation is frequently metered on a time-of-use and/or demand basis. Thus, instead of kilowatthour meters 12, 14 and 16 metering energy consumptio~ from different loads, they may all be applied to metering different aspects of energy consumption of a single load. For example, if kilowatthour meter 14 is changed from a kilowatthour meter to a kilovoltampere hour meter monitoring the same load as kilowatthour meter 12, then both the real and reactive components of the load are monitored. Further, if kilowatthour meter 14 is changed from a kilowatthour meter to a kilowatthour demand or kilovoltampere hour demand meter, three different aspects of the load 2~

14 11-~E 191 consumption are measured.
It is conventional in electric ener~y metering to produce ou~put pulses, each of which memorializes the consumption of a predetermined quantu~ of the aspect of electric energy being metered. The pulses conventionally consist of switch closuxes of, for example, a mercury~wetted relay, solid state relay, or optical sensor. The outp~t pulse& are connected from kilowatthour meters 12, 14 and 16 on lines 18, 20 and 22, respectively, to an electronic remote data recorder 24.
Data is communicated between electronic remote data recorder 24 and a meterlng data center 26 on a telephone line 28.
Re~erring now to Fig. 2, electronic remote data recorder 24 contains a data storage device 30 and a communications control unit 34. Data storage de~ice 30 receives and 6tores data pulses incoming on lines 18, 20 and 22. In addition to data pulses, storage of time-dependent data such as, for example, data from which demand or time-o~-use is to be reconstructed, may also ba accompanied by data indicating the times at which the time-dependent data is produced. For economy, a conventional telephone instrument 36 may share use of telephone line 28 with electronic remote data recorder 24.
The data in data storage device 30 is updated each time a data pulse is received. If a period during which data is read out of data storage devics 30 e~compasses a time when an input pulse is received by data storage device 30, an a~biguity may result in the data sent out on telephone line 28. Data ll~E-~sl storage device 30 includes means for preventing such ambiguity by ~reezing a snapshot o~ the data in data storage device 30 at the in~tant that data communications be~ins. ~hus, an internally consisten~ se~ of data is available Por transmission to metering data center 26. New data pulses occuxring during a transmission ara not discarded, completion o~ their en~ry into data storage device 30 is merely delayed until the end o~ transmission.
Then, they are added to tha data, whereby they are available for transmission at the next readout.
Communications control unit 34 performs the functions required to permit access to the stored data in data storage device 30 and those required to prevent conflict in shared use of telephone line 28 with telephone instrument 36. These ~unctions include a MODE~ (modulator-demodulator) ~or converting serial binary (on-off) data to tone data suitable for transmission on telephone line 28, off-hook detection by a user o~ telephone instrument 36 and data security. Besides these functions, communications control unit 34 may be programmed to initiate a call to metering data center 26 under certain circumstances. Such circumstances may include, ~or example, the occurrence of a power outage and restoration, detected probability of data corruption or scheduled routine data transmissions. Also, communications control unit 34 may be enabled to receive and answer a call initiated by metering data center 26, whereby special interrogation, troubleshooting or programming may be per~ormed without requiring an on-site visit.

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16 ll-~E-l91 An optional programmable switch asse~bly 3~ is provided for controlling external functions of a using facility zuch as~ for example~ lighting, blowers, air conditioners or heating plant~. In one embodiment o~ the invention, programmable switch assembly 38 contains a plurality of switches controlled according to time of day ~o con~rol the above functions in an energy-management 6y6tem for automatic control and for reducing peak loads.
Programmabl~ ~witch assembly 38 receives time informatlon on a line 40. Th~ output~ of progra~mable switch as6embly 38 are connected on a line 42 to the controlled element~, the exact identification o~ which are unimportant to the present disclosure.
Referring now to Fig. 3, data storage device 30 includes a plurality of data storage channels 44, 46 and 48 for receiving and storing pulse data from lines 18, 20 and 22, respectively. Data storage device 30, as well as the remainder of electronic remote data recorder 24, operates under control of a central processing unit 50 which may be, for example, a suitably programmed microprocessor. Central processing unit 50 receives a signal on a line 123 indicating that a telephone has gone off line in the consumer's facilityO In response to this info~mation, central processing unit 50 may produce a signal requiring that its MODEM (not shown in Fig. 3) go off line to permit access to the telephone line by another user. In addition, central processing unit receives a sample of an AC line voltage for use in its internal timing functions.

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17 ll~ME-191 A programmable switch library 52 contains information governing control of programmable switch assembly 38 according to ~ime. The data in programmable switch library 52 may be changed by control signals on a line 54 from central processing ~nit 50.
A power fail detection and recovery unit 56 receives a sample o~ the AC line voltage available to electric energy aon~umer 10 on a line 58. In the event that a voltage oondition iB detected which threatens valid proces~ing of data, power fail detection and reoovery unit 56 produces a number of signals for application on lines 60 and 62 which bring processing to a halt in processor 50 before even further lowerîng of line voltage can produce data corruption. Power fail det~ction and rscovery unit 56 also detects a voltage condition indicating restoration of power. The signals on lines 60 and 62 enable resumption of normal operation with due regard ~0 for tagging the data in data storage channels 44, 46 and 48 with indications o~ ~he power outage, in order to permit resumption of the accumulation of pulse data inputs. Lines 62a and 62b communicate the condition of the line voltage to other elements in electronic remote data recorder 24, as will be seen in the following.
All time-dependent functions in data storage device 30, as well as elsewhere in electronic remote data recorder 24, are controlled according to a master timing signal produeed by a system clock 64.
System clock 64 is preferably backed up by a long-life battery (not shown) to permit it to ,' ,'' .......... ' ' ' ' ' ~ :
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maintain synchronism with real time even when electronic remote data recorder 24 experiance~ a prolonged period out o~ service due, for example, to a lengthy pow~r oukage. System clock 64 receives a control signal from central procas6in~ unit 50 a~
well as a power fail ~ignal fed back from power fail detection ar.d recovery unit 56, ~entral processing unit 50 rPceive~ a signal on a line 123 indicating that ~ ~econd telephone has gone of~ hook whila electronic remote data recorder 24 is engaged in communication~. In response to this signal, central processing unit produces a ~ignal effective for placing electronic remote data recorder 24 on hook, thereby enabling another user in the facility to use the telephone.
Data is read out from data ~torage channels 44, 46 and 48 under control of ~ignal~ from c~ntral processing unit 50, onto an output data line 66.
Data is connected to central processing unit 50 on a data line 68. Programming data for central processing unit 50 i~ first connected on a programmin~ data line 70 ~o power fail detection and recovery unit 56 which examines whether or not central processing unlt 50 previously has been programmed. I~ central processing unit 50 is in an unprogrammed condition, indicating that initial programming should be permitted, or if other required conditions are satisfied, the program data is connected from power fail de~ection and recovery unit 56 to central processing unit 50 on line 60. If cenkrai processing unit 50 has been previously programmed, as indicated by the pattern of data ~2~2~

19 ll~ l9 1 therein, the condition of a write-protect switch in power fail detection and recovery unit 56, as well as other considerations, determines whether or not programming data is connected to central processing unit 50.
Under most circumstances, it i~ not desirable to permit progr~mming of central processing unit 50 in response to an incoming telep~one call. Even with password control, the danger of illegal entry to such a revenue-sensitive ~ystem make~ such a prohibition a good choice. However, the need does exist ~or reprogramming to permit, for example, resetting system clock 64 and for accommodating changes in tariffs. one technique permits reprogramming on a secure basis only during data communication initiated by electronic remote data recorder 24 to metering data center 26 (Fig. 1). That i6, at predetermined times, or in response to specific events such as, for example, a malfunction or power outage, an auto-dial MODEN (not shown) in electronic remote data recorder 24 is enabled by central processing unit 50 to dial the telephone number of metering data center 26.
Nhen such a communication is in progress, central processing unit 50 provides an enable signal on line 60 to power fail detection and recovery unit 56 bypassing the write-pro~ect switch. After an automatic ~xchange of passwords, electronic remote data recorder 24 is enabled to communicate a trouble, or other message, to metering data center 26 and, while still connected, metering data center 26 is enabled to supply reprogramming data through power fail detection and recovery unit 56 to central ~9~z~

ll~ l91 processing unit 50.
Referring now to Fig. 4, a power fail/recovery threshold 72 receives ~he sample of the line voltage from line 58. The term ~sample of the line voltagP"
is intended to mean a voltage whose amplitude is related ar~thmetically to the actual AC line voltage available to electric energy consumer 10. Such a sample may be the line voltage itsel~ or the output voltage o~ the ~econdary w~nding o~ a trans~ormer who~ primary winding reaeive~ the line voltage.
Although the particular voltage~ at which certain even~s take place are governed by the amplitude of the original line voltage, for concreteness, it is harein assumed that the nominal value of the line voltage on line 58 is 115 volts RMS.
Power fail/recovery threshold 72 produces two output signals, an AC OK signal on ~C OK line 62a and a power fail signal on a power fail line 62b. When the line voltage is in a normal xange exceeding about 80 volts RMS, the power fail signal on power fail line 62b enables central processing unit 50 to continue collection of energy usage data. When the AC voltage drops below 80 volts RMS, the power fail signal applied to central processing unit 50 causes it to inhibit further collection of eneryy usage data. All data necessary for permitting electronic remote data recorder 24 to resume operation without loss of previously recorded data is contained in non-volatile storage 80. If the line voltage continues to drop below about 50 volts, the signal on AC OK iine 62a causes central processing unit 50 to go into a sleep mode in which power is shut of~ to all 2~L

components.
After a power ~hutoff, when the line voltage increases beyond about 75 volts, the AC OK signal on AC OK line 62a enables central processing unit 50 to command reconnec~ion o~ power to all device~ in electronic remote data recorder 24, but operation of electronic remote data recorder 24 remains inhibited until the power-fail signal on power ~ail line 62b returns to an Qnabling condition at about 92 volts ~MS. The hysteresi~ between tha voltage levels for removal and restoration o~ thQ power fail and AC OK
signals prevents dithering.
The circuits in power fail/recovery threshold 72 are conventional threshold, gate and multivibrator devices with which everyone skilled in the art is completely familiar. It i6 believed that a detailed description thereof would lead only to prolixity and is thus omitted.
When power fail signal resumes, the enable signal applied from power fail line ~2b to an input of an AND gate 76 permits the contents of non-volatile storage 80 to be fed through AND gate 76 for examination in a CPU RAM status verification circuit 82. If the present applica~ion of power to ~5 electronic remote data recorder 24 is the first time that power has been applied following installation, the pattern of data in non-volatile storage 80 is random, as opposed to the ordered pattern of data existing in storage 80 at all other times. If a disordered pattern of data indicating an initial turn-on is found, CPU RAM s~atus verification aircuit 82 applies an enable signal on a line 84 to one input 22 ll~ME-l91 of an AND gate 86. A second input of ~N~ gate 86 receives program data from programming data line 70 which may originate in metering data center 26 (Fig.
1~ or may be input from a local programmerO The output of AND gate ~S i~ applied through an OR gate 88 and line 60c to central processing unit 50. Thus, upon initial startup of elec~ronic remote data recorder 24, programming o~ central proce~ing unit 50 i~ enabled.
An inverted output of CPU RAM statu6 veri~icatlon clrcuit 82 i8 applied on a line 90 to a first input of an AND gate 92. The output of AND
gate 76 is applled on a line 9~ to a s~cond input of AND gate 92. An input on llne 60a from central processing unit 50 indicates that an outgoing call is in progres~. This indication of an outgoing call is connected directly to one input of an AND gate 96 and, through an inverter 98, to a third input of AND gate 92. The output o~ AND gate 92 is connected through OR gate 88 to line 60c. The program data on programming data line 70 is also applied to a second input of AND gate 96. The output of AND gate 96 is connected through OR gate 88 to line 60c.
A write-protect switch 100 is a two-position switch having one terminal connected to an enabling voltage ~V and its other terminal connected directly to a line 84 and through an inverter 102 to an input of AND gate 92.
Write-protect switch lOG i~ normally in the open condition, thereby permitting control of programming to take place under control of the outputs of CPU RAM
status verification circuit 82 and the state o~ the 912~

23 ll ME~l91 signal on line 60a. When closed, write-protect switch 100 inhibi~s AN~ gate 92 and enable6 AND gate 86, regardless of ~he conditions of the outputs of CPU ~AM s~atu~ verification circui~ 82. ThiS permi~s programming remotely over ~he kelephone line or on-site by an authorized person u ing, ~or example, a conventional optical interface such as one supplied by the General Electri~ Company under the trademark Optocom. The program dat~ i~ applied on programming data line 70 through enabl~d AND gate 86 and o~ gate 88 to lin~ 60c ~rom whence it ~ applied to central processing unit 50.
The outgoing-call signal on line 60a, wh~ch may originate in a MODEM (not shown) or in central processing unit 50, permit~ programming data from programming data line 70 to be applied to central processing unit 50 even when write-protect switch loO
is in its i~hibiting position and the condition is other than an initial ~tartup. This makes electronic remote data recorder 24 progra~mable during an outgoing call it has, but prevents programming during an incoming call. This of~ers a layer of s~curity ~o program data, as detailed in the foregoing general description.
In some installations, it is desirable to permit external progra~ming during more than one post-installation programming session. Such a situation may include an installation procedure in which an installer performs testing using test data connected to power fail detection and recovery unit 56 from a local irogramming de~ice. Following installation and checkout, it may be desired to apply programming 2~L

24 ll-ME-lsl data, either locally, or from metering data center 26, representing the operational programming to be used in the actual collection Or metering data. In order to accomplish this, the fir t time write-protect æwitch 100 is placed in the closed position, central processing unit 50 recognizes this change in condition by setting a flag. ~hen, during, for example, the first incoming telephone call subsequent ~o ~etting the write-protect switch in thP
closed posit$on, central processing unit 50 simulates an ~ outgoing call by placing an outgoing-call signal on line 60a. A~ter thi~ second external programming opportunity, central processing unit no longer simulateR an inco~ing call, and thus, the write-protect function goes into operation.
I~ subsequent unscheduled reprogramming is required in the absence Q~ an outgoing call, write-protect switch may be placed in the open position for a first programming opportuni~y. This restores the additional programming opportunity in the same manner as described following initial installation. It can be foreseen that some installations may benefit ~rom the availability of a predetermined number of external programming sessions in excess of two. This is readily accomplished by programming central processing unit 50 to permit more than one additional programming session ~ollowing the first one after write-protect switch is closed.
Referring momentariIy to Fig. 3, data storage channels 44, 46 and 48 are identical, thus, the following description of data storage channel 44 will serve as the description for all.

~9!39L~4~

11 ME-l91 Referring now to Fig. 5, data torage channel 44 includes a first-in first-out memory 104 receiving energy-consumption pulses on line 18 at one of its inputs and a signal on a line 106a indicating that data communicat~on is in progress. An output of first-in first-out memory 104 i8 applied on a line 107 to one input of an ~ND gate 108. An lnterval clock 10g receives sy6tem clock signal~ on a line 110. At reqular lntervals, interval clock 109 applies an enable 6ignal on a line 112 tc a ~econd input o~ AND gate 108, whereby the contents of first-in first-out memory 104 are passed through AND
gate 108 to update the contents of an interval data memory 114. An interval data directory 116 receives a time signal from interval clock 109 on a line 118. In addition, interYal data directory 116 receives a siqnal on a line 106b whenever a time reset or a program change oacurs, and a power-~ail signal on line 106a indicating that processing of data has been halted because of low voltage. Outputs of interval data memory 114 and interv21 data directory 116 are applied to output data line 66. A
data pointer is applied on a line 120 from interval data memory 114 to interval data directory 116.
The data-communication signal on line 106a is also applied to interval data directory 116.
During normal operation, in the absence of data communication, reset or power failure, first-in first-out memory 104 accumulates energy consumption pulses for a continuing sequence of fixed predetermined periods. At the and of each fixed predetermined period, the content~ of first-in 26 ll-ME-l91 first-out memory 104 are read out through ~ND gate 108 and stored as a number in interval da~a memory 114. The number indica~es the total energy consumed in the fixed predetermined period. For compact storage, lnterval data memory 114 is not r~quired to store contemporary ~ime signals.
Interval data direc~ory 116 store6 three numbers each time any of the ~ollowing event~ occurs: data readout, time change, program change or power failure. One of the number6 is the time that the ~vent occurs. Another number iB a pointer lndicating the current storage loca~ion being used i~ interval data memory 114. The third number i~ a flag indicating the type of event.
In a completely uneventful time between data readouts, interval data directory 116 contains only a single trio of number~ indicating the last time that a readout occurred. Given these numbers, and a date stamp indicat~ng the tlme at which the readout occurred, all of the consumption data in interval data memory 114 can be related to the times they oacurred. Accordingly, the data in interval data memory 114 is available with inferred aontemporaneous time data to analyze the load profile for time-of-use and demand billing.
In the case of a power failure, two trios of numbers are stored: the power fzilure kime and the power-resumption time with their related pointers and flags. For example, if data storage channel 44 employs an interval of 15 minutes and updates interval data memory 114 on one-minute boundaries, a triggering event occurring at two minutes following ~2~

27 ll-ME-191 the b~ginning of an interval essent~ally break~ the interval into a two-mlnute portion and a 13-minute portion. The data pointer, event time and event flag stored in interval data dlrectory llS permits interpretation of the data in interval data memory 114 without ambiguity.
Xeferring now to Fig. 6, communications control unit 34 includes an other-phone-detect circuit 122, a telephone line-sharing circuit 124 and a MODEM 126 (modulator-d2modulator). MODE~ 126 is assumed to be a conventional device, pre~erably inrluding an ability to answer an incoming call in response to a ringing signal and to initiate a call under control of signals from cen~ral processing uni~ 50. Since it is conventional, fur~her description of ~ODEM 126 is omitted here~rom.
Referring now to Fig. 7, the problem to be solved by other-phone-detect circuit 122 is illustrated. It i5 assumed that, in ordar to be a good neighbor to another user of the telephone line, electronic xemote data recorder 24 should relinquish the line so that the other user may use it if the other user indicates a desire to use the telephone line while it is being used by electronic remot data recorder 24 for data transmission. Other-phone-detect circuit 122 is connected across a telephone line 128 in parallel with telephone instrument 36. A
telephone system includes a DC power source, here represented by a rentral station battery 130 having a fixed-voltage of from about 42 to about 56 volts. An equivaIent resistor, representing a line resistance 132, i5 shown in series with one side of telephone 9129~

~8 ll-~E-l91 line 12~3 to other-phone detect circuit 122.
The resistance ~r line resistanoe 132 i8 vaxiable in a given installation about a nominal value which may be from a~out 400 to about 1700 ohms.
For prPsent purposes, telephone in~trument 3~ i6 represented by a local load resistanca 134. A hook switch 136 responde to re~oving telephone instrument 36 from it8 cradle by connecting local load re6istance 134 across t~lepho~a lin~ 128. An internal resistancQ of ~ODEM 126 is represented by a MODEM lo~d r~3i~t~nce 13~, which i~ placed in serie~
with a MODEM hook ~witch 140.
Several problems must be recognized and overcome before the desire o~ the other user to use the telephone line can be determined from local load resistance 134 being placed across telephone line 128 by closure o~ hook switch 136. In particular, it is necessary to recognize the condition produced when local load resistance 134 is placed acros6 telephone line 128 while ignoring ex~ernal events. External avents are characterized either by relatively slow variations caused by fluctuation in central s~ation battery 130 or line resistance 132 or by sharp spiXes due, ~or example, to lightning strikes. An off-hook condition of telephone instrument 36, in contras`t, is evidenced by a sharp reduction in voltage acro~s other-phone-detect circuit 122 which thereafter var~es slowly about its lower value with possible positive or negative short~duration superimposed spikes.
The ~agnitude o~ the slowly varying external variations in source voltage and line resistance are ~2~34~9~

29 ll-ME-l91 such that a mere measurement of the voltage acros6 telephone line 128 is insufficient to indicate whethex or not local load registance 134 i6 across telephone line 1~8 in parallel with MODE~ load resistance 138. ~owevert advantage i8 taken o~ the differen~ detectable characteristic~ due to external source~ and those due to telephone in~trument 36 going off hook.
Referring to the curve in Fig. 8, three cond~ tionB which may b~ ~ans~d by other-phone detect circuit 122 are shown. With both telephone instrument 36 and NODEN 126 on hook, a ~oltage region 14~ is seen to be slowly varying and may contain short-duration positive and/or negative voltage spikes (not shown). When ~ODEM 126 goes off hook, ~he voltage is reduced a~ shown at 144. This voltage also includes a slow variation, in addltion to which, it may include one or ~ore positive or negative spikes 146.
When telephone instrumen~ 36 goe6 off hook in parallel with MODEM 126, a lower voltage region 148 begins with a sharp transition 150 from ~he DC level of voltage region 144 to the DC level of voltage region 148. When voltage reglon 148 is detected by other-phone-detect circuit 122, MODEM 126 relin~uishes the line, thereby enabling line use by another user.
In brie~, other-phone-detect circuit 122 employs a comparison of a short ter~ average with a long-term average to detect the transition from voltage region 144 to voltage region 148. When t~e di~erence between the short- and long-term a~erages exceeds a predetermined threshold for a predetermined period of . .

30 ll-ME-l91 time, a step tran~ition i6 detected. I~ the comparison fails, ei~her in magnitude or the duration, detection doe~ no~ occur. That i , ~he short-term average may re~pond to spiXe 146, but the long-term average doec not. The predetermined period of tima i~ selac~ed 50 tha~ a tran~ient event such as spik~ 146 pa~e~, and the 6hort-term average returns to agreement wi~h the long-term average, be~ore ~he end of ths time period. T~ia protec~s other-phone-detect circuit 122 from responding to transient event~. Also, 1~ sharp tran~ition 150 is too shallow to indicate that telephona instrument 36 has gone off hook, an insu~ficient dif~erence between the averages prevents triggering other-phone-detect circuit 122. 80th the 6hort-term and the long-term averages follow the normal slow variation in line voltage and thus avoid triggerinq on this type of change.
Referring to Fig. 9, other-phone-detect circuit 122 consists of a signal conditioner circuit 152 receiving the telephone line voltage on telephone line 12~, and a step-change detector 154. The output of signal conditioner circuit 152 is applied on a line 171 in parallel to inputs of a long-term integrator 158. The outputs of shor~-~erm integrator 156 and long-term integrator 158 are applied to inputs of a differential ampli~ier 160. The output of differential amplifier 160 is applied to the input of a threshold circuit 162. When threshold circuit 162 receives a predetermined difference ignal lasting for at least a predetermined period of time, it produces an other-phone~detect signal to cause ~ ' ' -~ . ~

31 ll-ME-l91 MODEM 126 (Fig. 7) to go of~ line~
The apparatus in Ftg. g can be realized with any conven~ent technology. In partlcular, one skilled in the art would recognize that ~uch apparatus could be imple~ented in analog or digital form without departing from the spirit and S~Op2 oP the invention.
For concretenese, an embodiment of the invention i6 described in tha following paragraphs using digital technique~ for implemen~ing step-change detector 1~4.
lo Referring ~ow to Fig~ 10, ~ignal-conditioner clrcu~t 152 includes an absolut~ valu~ cirauit 164 receiving the telephone line voltage of either positive or negative polarity and producing a unipolar output voltage having an amplitude corresponding to tha~ of the telephone line voltaye.
One convenient implementation of ab~olute value circuit 164 includes a con~entional full-wave bridge rectifier circuit. The unipolax output of absolute value circuit 164 i8 applied to an opto-isolator 166 which prevents large voltage transients on telephone line 128 from affecting succeeding circuits. The output of opto-isola~or 166 passee through a conventional level shifter 168 which adjusts the amplitude limits of the output o~ le~el shifter 168 2~ before application to a voltage-to-freguency converter 170.
Voltage-~o-frequency converter 170 produces a square-wave output signal having a frequency related to the voltage applied to its input. The relationship may be positive or negative. In a preferred e~bodiment, the output freguency of voltage-to-freguPncy converter 170 increases with ~2~ %~L

32 11 ME-l91 increasing voltage. Stated another way, the perio~
of the outpu~ pulses from voltage-to-fre~uency c~nverter 170 decrease~ wi~h increa~ing voltage input. Vol~age-to-~retauency converter 170 may be a conventional timer such as, ~or example, a 555 ~imer, with suitable external components. In thP preferred embodiment, voltage-to-frequency converter 170 i6 a pulse-generating circuit capable of producing a square-wave output having about a 50 percent duty 10 ratio over the entire ~re~uency range.
Returning now to F~g. 9, tha ~unctions per~ormed by step-change detector 154 are done in a digital processor and, most preferably, in a mi~roprocessor.
The periods of the pulses from ~ignal-conditioner circuit 152 may be measured in the processor by convantional means and the short~term and long-term averages logically illustrated a~ ~hort-term integrator 156 and long-term integrator 158 can be derived fro~ the measured periods using conventional arithmetic techni~ues. A running dif~erence between the two averages, logically illustrated by differential amplifier 160, may also be taken by subtraction in the processor. Finally, the thresholding and dela~ function~ logically, illustrated by threshold circuit 162, can also be performed in the processor.
~ he presence of absolute value circuit 164 make~
signal-conditionex circuit 152 and step-change detector 154 indifferent to the polarity of a step change or a transient. When a kelephone call is being dialled by electronic remote data recorder 24, other-phone-detect circuit 122 continues to monitor 33 ~l-~E-l91 the voltage~ on telephone line 128. If, during such dialling, another telephone instrumen~ 36 shoul~ go ~`; off h~ok, it i~ likely that a person li~t~ning on ~uch an instrumen~ would hear the dialling tones and would place tha~ instrument on hoo~. A~ a good neighbor; it 18 de~irable that, ~en~ing ~hat ano~her user i 8 attempting to place a telephone call, electronic remote data recorder 2~ ~hould go on hook.
Due to the presence o~ absolutQ value circuit 164, a sharp voltagQ tran~tion pxoduced by the other telephone going on hook, opposite in polarity to that shown in Fiq. 8, is detected in the same manner described ~or another telephone going off hook during the body of a telephone ses~ion. Thus, other-phone-detect circuit 122 produces a detect signal on line123 causing eleGtronlc remote data recorder 24 to go on hook, thereby permitting the other user to proceed with its intended call.
Referring now to Fig. 11, telephone line-sharing circuit 124 i8 an optional feature permitting a plurality of electronic remote data recorders 24, 24' and 24" to be polled using a single shared telephone line without inter~ering with each other. One of electronic remote data recorders 24, 2~' and 24" is considered a master and the remainder, slaves. For present purposes, electronic remote data recorder 24 is considered to be the master, and electronic remote data recorders 24' and 24" the slaves. Outgoing calls may be initiated by any telephone line~haring circuit 124. For incoming calls~ each telephone line-sharing circuit 124 recponds to a uni~u code on telephone line 28 by turning on its transmitting ~298~

34 ll ME-lsl carrier, wherehy communication~ are initlated by placing the MODEM carrier on ~he line. It al80 responds to reception of a unique code of any of the other telephone line-~haring circuits 124, not its own, by turning of~ its carrier.
A carrier i8 required from a MODEM before communications can be e~tablished. Upon the occurrence o~ an incoming call, maeter telephone line-sharing circuit 124 triggers its ~ODEM 126 to produce an an wer carrier and to mainta~n it at least until oommunloations are Qstablished. I~ th~
incoming call addresses master electronic remote data recorder 24, t~en communications can proceed without further protocol, other than the normal security codes. Telephone line-sharing circuits 124l and 124"
monitor telephone line 2~, listening for their unique identification codes. I~ the incoming call i~
addressed to an electronic remote data recorder other than master electronic remote data recorder 24, once communications are established with MODEM 126, as noted above, the incoming call contains the unique code of the electronic remote data recorder being called. Master telephone line-sharing circuit 124, hearing an identity code other than its own, triggers MODEM 126 to turn o~f its carrier. ~he slave telephone line-sharing circuik, hearing its own identity code, triggers its MODEM to turn on its answer carrier. The transition between the master and slave carriers is fast enough to permit the calling MODEM (not shown) to ignore any small gap in answer rarrier which may occur during the changeover.
The foregoing description has employed logical ~2~4%4 ll-ME 191 elements 6uch a~, for example, gate~, comparator~ and ~hreshold circuits, to illustrate the ~unctions performed by thC apparatus of the invention. It would be clear to one skilled in ~h~ art that substantially a~l o~ the dsscribed function may be performed by a ~ui~able digital processor and such an embodiment i5 fully encompa~sed within the 6COp~ 0 thQ invention.
Having de~cribed preferred e~bodiments o~ the 0 invention with reference to the accompanying drawing~, it ~g to ~ under~tood ~at ~he inventicn is not limited to those precise embodi~ents, and that varioua hanges and ~odifications may be effected therein by one skilled in the art without departing from the scope or spixit of the i~vention as defined in the appended claims.

Claims (13)

1. A power fail detector and recovery apparatus for an electronic remote data recorder, said electronic remote data recorder including a processor therein, comprising:
means for producing a power failure signal in response to a first predetermined voltage reduction in a power source to said electronic remote data recorder:
said electronic remote data recorder being responsive to said power failure signal by halting operation of said processor;
a non-volatile storage device for storing contents of said processor in said non-volatile storage device upon occurrence of said power failure signal;
means for restoring operation of said processor upon a second predetermined voltage increase in said power source above said first predetermined voltage;
said means for restoring including means for comparing a pattern of said contents in said non-volatile storage with a predetermined data pattern indicating a programmed electronic remote data recorder, and for producing an enable signal when a pattern of said contents indicates that said processor has not been previously programmed; and means responsive to said enable signal for connecting programming data from an external source to said processor for initial programming thereof.

2. Apparatus according claim 1, further comprising:
a write-protect switch having first and second positions;
means responsive to said write-protect switch being in said first position for preventing programming of said processor from an external source; and means responsive to said write-protect switch being in said second position for permitting programming of said processor from an external source.

3. Apparatus according to claim 2, wherein said means responsive to said write-protect switch being in said first position further includes means for connecting programming data from an external source to said processor for a predetermined number of times following placing said write-protect switch in said first position.

4. Apparatus according to claim 3, wherein said predetermined number of times is two times.

5. Apparatus according to claim 1, further comprising means for permitting connection of programming data to said processor from a telephone line when a telephone call is initiated by said electronic remote data recorder.

6. An electronic remote data recorder for recording data in a using facility, said using facility including at least one function controlled by at least one programmable switch responsive to signals from said electronic remote data recorder, comprising:
means for controlling said at least one programmable switch in response to a clock;
a programmable switch library including a relationship of a condition of said at least one programmable switch and at least one time; and means responsive to power restoration following a power outage for controlling said at least one programmable switch according to a content of said programmable switch library.

7. A data recording channel comprising:
(a) a data memory having addressable storage locations;
(b) means for periodically storing pulse data in addressable storage locations of said data memory to form a profile of data accumulated over time;
(c) a data directory having addressable storage locations; and (d) means for storing in addressable storage locations of said data directory, at the time of occurrence of an event, event-type data specifying a type of event occurring in said data recording channel and time data specifying the time of occurrence of the specified type of event, the type of event and time data being related to the pulse data in said data memory and being usable in a prescribed manner to permit an after-the-fact reconstruction of a profile of that data accumulated in the addressable storage location of said data memory up to the time of occurrence of the stored specified type of event.

8. A data recording channel according to claim 7 further comprising:
(a) a first-in-first -out register for receiving said pulse data and passing said pulse data therethrough for storage in said data memory by said means for periodically storing pulse data; and (b) means, responsive to the occurrence of a specified type of event representative of data communication in progress, for storing incoming pulse data in said first-in-first-out register during said data communication to enable a frozen snapshot of the data accumulated in said data memory to be transmitted.

9. A data recording channel comprising:
(a) a data memory having addressable storage locations;
(b) means for periodically storing pulse data in addressable storage locations of said data memory to form a profile of data accumulated over time;
(c) a data directory having addressable storage locations; and (d) means for storing in addressable storage locations of said data directory, at the times of occurrence of each one of a plurality of different types of events, event-type data specifying a type of event occurring in said data recording channel, time data specifying the time of occurrence of each specified type of event and a data pointer associated with each specified type of event, the associated data pointer for each specified type of event identifying a specified addressable storage location in said data memory containing pulse data and being related to the pulse data in said data memory and being usable in a prescribed manner to permit an after-the-fact reconstruction of a profile of that data accumulated in the addressable storage locations of said data memory between the occurrence of different specified types of events.

10. In an electricity metering system, the combination comprising:
(a) an electricity meter for generating pulse signals, each representative of a quantum of electrical energy consumption:
(b) a metering data center; and (c) an electronic data recorder in communication with said electricity meter and said metering data center, said electronic data recorder including, (i) an interval data memory, having a plurality of addressable storage locations, for accumulating the pulse signals from said electricity meter as interval data representative of a load profile of the amount of electrical energy consumed in each of a plurality of contiguous intervals, said interval data memory generating, at an output thereof, data pointer signals representative of a data pointer continuously identifying the current interval

11-ME-191 Claim 10 continued:

data memory storage location in which interval data is being stored;
(ii) means for generating a plurality of event-type data signals, each specifying a different type of event occurring in said electronic data recorder, and time data signals specifying the time of occurrence of each specified type of event;
(iii) an interval data directory, in communication with said means for generating and with said interval data memory, responsive to an event type data signal of a first type for storing information identifying a first type of event, the time of occurrence of the first type of event and a first data pointer identifying a first interval data memory storage location for the storage of interval data, and responsive to an event-type data signal of a second type for storing information identifying a second type of event, the time of occurrence of the second type of event, and a second data pointer identifying the last storage location in said interval data memory in which interval data was stored at the time of occurrence of the event type data signal of the second type, and (iv) means for transmitting, to said metering data center, the interval data accumulated in said interval data memory, and the first and second type event information, the time information of each of the first and second types of events and the first and second data pointers stored in said interval data directory for use in said metering data center in reconstructing a load profile of the interval data accumulated in said interval data memory between the occurrence of the first and second types of events.
11. In an electricity metering system of the type including a metering data center, an electricity meter for generating pulse signals, each representative of a quantum of electrical energy consumption, and an electronic data recorder, in communication with said metering data center and said electricity meter, for communicating with said metering data center and for accumulating the pulse signals as interval data representative of the amount of electrical energy consumed in each of a plurality of contiguous intervals, each interval having a predetermined time period during which the pulse signals are accumulated, said electronic data recorder comprising:
(a) an interval data memory, having a plurality of addressable storage locations, for accumulating interval data to form a load profile of the amount of electrical energy consumed in each of a plurality of contiguous intervals, said interval data memory generating, at all output thereof, data pointer signals representative of a data pointer continuously identifying the current storage location in which interval data is being stored:
(b) means, in communication with said electricity meter, for periodically storing the pulse signals as interval data in addressable storage locations of said interval data memory;
(c) means for generating event type data signals specifying a type of event occurring in said electronic data recorder, and time data signals specifying the time of occurrence of the event; and (d) an interval data directory, having addressable storage locations and being responsive to an event type data signal for storing the event type and time data signals from said means for generating, and the data pointer signals from said interval data memory as information related to the accumulated interval data in said interval data memory and usable, by said metering data center, to reconstruct the load profile of the electrical energy consumed in all contiguous intervals up to the time of occurrence of an event by, identifying the type of event, the time of occurrence of the event, and an address pointing to the last storage location in said interval data memory in which interval data was stored at the time of occurrence of the event.

12. A data recording channel comprising:
(a) a data memory having addressable storage locations;
(b) means for periodically storing pulse data in addressable storage locations of said data memory to form a profile of data accumulated over time;
(c) a data directory having addressable storage locations;
(d) means for storing in addressable storage locations of said data directory, at the time of occurrence of an event, event-type data specifying a type of event occurring in said data recording channel and time data specifying the time of occurrence of the specified type of event, the type of event and time data being related to the pulse data in said data memory and being usable in a prescribed manner to permit an after-the-fact reconstruction of a profile of that data accumulated in the addressable storage locations of said data directory up to the time of occurrence of the stored specified type of event;
(e) a first-in-first-out register for receiving said pulse data and passing said pulse data therethrough to said means for periodically storing before being stored in said data memory; and (f) means responsive to a type of event representative of a data communication in progress for storing incoming pulse data in said first-in-first-out register, whereby a frozen snapshot of data in said data memory is transmitted during the time that said data communication is in progress.

13. Apparatus for sharing a single telephone line among at least first and second MODEMs, comprising:
said first MODEM including a first line sharing circuit associated therewith;
said second MODEM including a second line sharing circuit associated therewith;
said first and second line-sharing circuits simultaneously monitoring the same telephone line;
said first line-sharing circuit being a master;
said second line-sharing circuit being a slave;
means in said first line-sharing circuit for responding to an incoming call on a telephone line with an answer signal;
means in said second line-sharing circuit for recognizing a first unique identity code and for producing an answer signal in response thereto;
said first line-sharing circuit including means for recognizing said first unique identity code and for extinguishing its answer signal in response thereto, whereby control of communications is transferred to said second MODEM;
means in said first line-sharing circuit for recognizing a second unique identity code and for producing an answer signal in response thereto; and said second line-sharing circuit including means for recognizing said second unique identity code and for extinguishing its answer signal in response thereto, whereby control of communications is transferred to said first MODEM.