Meter interface unit for utility meter reading system

A meter interface unit for interconnecting utility meter reading apparatus to a telephone line to allow the automatic reading of utility usage at the telephone central office in response to an interrogation signal from the telephone central office. The meter interface unit converts meter reading signals to alternating signals for transmission to the telephone central office when a subscriber's telephone is on-hook. The unit also encodes a subscriber or customer identification signal which is transmitted with utility usage data to eliminate the need of any manual reading of the utility meter at the customer's premises. The meter interface unit is powered over the telephone line.

BACKGROUND OF THE INVENTION 
The present invention relates to an apparatus and method of sending data 
over a telephone line and more particularly with sending utility usage 
information over a telephone line in response to receiving an interrogate 
signal from the telephone line. 
The present invention is suited for sending utility usage data and can send 
utility usage information from virtually any utility monitoring device 
over a telephone line. The typical use of the present invention is in an 
automatic utility meter reading system in which the present invention is 
responsible for sending the utility usage information from at least one 
utility monitoring device over a telephone line in response to receiving 
an interrogate signal. 
The automatic utility meter reading system for which the present invention 
is particularly suitable is described in co-pending application Ser. No. 
543,372, filed Oct. 19, 1983 for a Centerpoint Automatic Meter Reading 
System. This meter reading system is generally located at a central 
telephone office where a multiplexor system, best described in co-pending 
application Ser. No. 544,110, filed Oct. 21, 1983 for A Multiplexor for An 
Automatic Utility Meter Reading System, sends a series of distinct 
interrogate signals over a plurality of telephone lines. Each of the 
telephone lines has connected to it at least one of the apparatus of the 
present invention. In response to receiving a particular distinct 
interrogate signal, each of the present apparatus then causes a utility 
monitoring device to deliver its utility usage information which is sent 
over the telephone line to the multiplexor. The multiplexor decodes and 
stores the received meter readings for subsequent retrieval and mass 
storage by a microcomputer. The apparatus of this invention may also be 
accessed from the telephone central office via the metallic test access 
port and the subscriber line by manual dialup of the subscriber number. 
There have been systems for sending utility usage data over telephone 
lines. One such system can be found in U.S. Pat. No. Re. 26,311 to Dumont 
et al. This system uses the telephone companies leakage testing system to 
call up the individual meter installations. Once a meter installation is 
called up, it sends the meter information over the telephone line to a 
central telephone office. However, the Dumont invention requires the use 
of a telephone company's leakage testing system to be operable and such 
leakage testing system can change, requiring an additional large 
investment in new equipment configured to the new leakage testing system. 
As well, not all telephone companies have the same type of leakage testing 
equipment, so that numerous configurations of the meter reading system 
must be devised to fit the numerous types of leakage testing equipment. 
The Dumont invention also requires a power supply, powered either from the 
power available at the meter installation site or from battery power, for 
each of its meter installations. Unlike the present invention, this 
requirement of a power supply makes the Dumont invention costly, more 
difficult to service, and makes the system prone to failures due to common 
power outages at the installation site. 
Unlike the present invention, the Dumont invention requires a complex 
synchronous data output on the telephone line. The synchronous output 
requires that the meter installations send additional sync pulses over the 
telephone line. In the event that either the sync pulses or synchronous 
meter data is momentarily interrupted by even a short noise pulse, which 
is quite common on telephone lines, the meter data will be lost. In 
addition, lines must be read sequentially which greatly slows down the 
process. 
Another system which has been used to send data over a telephone line is 
found in U.S. Pat. No. 3,922,490 to Pettis. The Pettis invention is a 
direct current system where several resistances are switched across tip 
and ring of the telephone line. The current drawn by the several different 
combinations of resistances connected to the telephone line are sensed at 
a central telephone office and any of several conditions are thus 
communicated. Typically, in the Pettis invention, the least significant 
digit pointer of a utility meter makes or breaks a switch depending on 
which half of its rotation the pointer is presently in. The making or 
breaking of the switch causes the resistance across the telephone line to 
change. This change is sensed at the central office and the cumulative 
count of changes in transition are totaled and the meter reading 
determined therefrom. 
Of course, the Pettis invention, being a D.C. system, does not relate at 
all to the present invention which is an A.C. system for sending data over 
the telephone line. As well, the present invention sends an entire updated 
reading each time it is requested to do so; the Pettis invention requires 
that a first reading be known to the central telephone office and that all 
of the subsequent transitions of the least significant pointer be received 
without interruption for an accurate meter reading to be had. If there is 
any interruption in the receiving of the transitions greater than a 
typical transition period, the central office will have to send someone 
out to the installation site to read the proper meter reading to 
compensate for the lost transitions. 
None of the above described inventions is responsive to alternating current 
interrogation signals, and none have a meter interface device which sends 
alternating current representations (while the telephone is ON-HOOK or 
OFF-HOOK) and is powered from the telephone line in either the ON-HOOK or 
OFF-HOOK state; and, powering a meter interface from the telephone line 
has some extremely important advantages which will be discussed later. As 
well, none of the above described inventions sends current utility usage 
information asychronously over the telephone line. 
SUMMARY OF THE INVENTION 
The present invention is an apparatus and method for sending data over a 
telephone line. The apparatus is an interfacing device comprising a 
converting means coupled to at least one utility monitoring device and to 
the telephone line for converting utility information from at least one 
utility monitoring device into alternating current representations and for 
sending the alternating current representations over the telephone line; 
means coupled to the telephone line for detecting a preselected 
interrogation signal from the telephone line; and, means responsive to 
detection of the interrogation signal for enabling said converting means. 
Each of said means are powered by current on the telephone line. 
The converting means may comprise a means coupled to each of the utility 
monitoring devices for sensing the utility usage information and providing 
a digitally encoded representation of the utility usage information from 
each of the utility monitoring devices; means for converting the digitally 
encoded representations of the utility usage information from each of the 
utility monitoring devices into the alternating current representations; 
and, means for sending the alternating current representations over the 
telephone line. The enabling means may comprise means for producing a 
monitor signal responsive to the detection of the interrogation signal and 
means for enabling the means for sensing the utility usage information 
responsive to the monitor signal. The apparatus may include means for 
encoding and transmitting a customer identifier signal. 
The means for powering the interfacing device from the telephone line may 
include a means for producing an inoperative condition in the device when 
the telephone line is in an OFF-HOOK condition unless the interfacing 
device itself causes the OFF-HOOK state. Powering the interface device 
from the telephone line has several advantages. First, the interface 
device does not have to be installed within a building where it is 
located. This advantage allows for easy installation and servicing. 
Second, the interface device is not dependent on power from the 
installation site. This advantage decreases dramatically the incidence of 
interruption in meter reading caused by power outages. The telephone 
company's power systems are backed up by their own batteries and 
generators so that a power outage from the telephone line is much less 
likely than a power outage from an electrical utility company. 
Third, the cost of the interface device is decreased and fewer components 
are required to comprise a meter interface device. The lower cost is 
important since there may be hundreds of thousands of the interface 
devices in each community used in conjunction with an automatic utility 
meter reading system. The fewer components required to perform the task of 
sending the data over the telephone line generally means that there is a 
lower probability of component failure compared to a system with more 
components. 
Fourth, the feature of being un-powered during subscriber generated 
OFF-HOOK conditions is that, even though the device may have circuitry 
hard wired to the telephone line which would slightly attenuate audio 
signals when active, there is virtually no load (AC or DC) presented to 
the phone line during OFF-HOOK conditions. This is a very important 
characteristic since all normal telephone data or voice communications 
occur OFF-HOOK. Thus, the device is transparent in OFF-HOOK conditions and 
yet needs no relays or switching of any kind to isolate the interface 
device's transmitting output stage which adds complexity and cost. 
The alternating current representations may be in the form of a series of 
pulses of a pulse width modulated single carrier frequency or frequency 
shift keying signals, each carrying representations of a utility usage 
figure and a meter identification figure. 
The interrogate signal is typically a single or multi-frequency distinct 
tone burst when the interface device is used in conjunction with an 
automatic utility meter reading system. The interrogate tone commands the 
interface device to send data from a utility monitoring device over the 
telephone line. The data is typically sent as a pulse width modulated 
carrier tone when the interface device is reading the typical water meter. 
Thus, in the case of the typical water meter, the usage data from the 
water meter is sent over the telephone line as a series of tone bursts 
representing digital signals. The data sent may also be a series of 
dual-tones, each tone pair indicating a single digit from the utility 
monitoring device. 
The data sent by the interface device from the typical water meter can be 
received in a central telephone office and the usage data from a number of 
interface devices can be compiled. 
The present invention is also a method of sending data over a telephone 
line comprising the steps of receiving a particular distinct interrogatory 
signal from the telephone line; producing a monitor signal in response to 
receiving the particular distinct interrogation signal from the telephone 
line; sensing data from at least one data monitoring source in response to 
the monitor signal; converting the sensed data into alternating current 
representations; and, sending the alternating current representations over 
the telephone line. 
The method of the present invention may also include the step of preventing 
the sending of the alternating current representations when the telephone 
line is in an OFF-HOOK condition. The interface device may retain the 
ability to transmit while in an OFF-HOOK state when the type of telephone 
equipment used requires it. The interface device may contain the ability 
to initiate an OFF-HOOK state upon command to do so as to activate the 
return communication link in some types of commonly used telephone 
equipment. 
Interrogation from the telephone central office may be via the test port by 
dial-up procedures usually used for line testing. This eliminates the need 
for much of the special interrogation equipment.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, the applicant's invention is an interfacing device for 
sending data from a monitoring device over a telephone line. The 
interfacing device of the applicant's invention is particularly suited to 
be a meter interface device for an automatic utility meter reading system 
10, similar to one described in co-pending application Ser. No. 543,372, 
filed Oct. 19, 1983, for Centerpoint Automatic Meter Reading System. In 
the utility meter reading system 10, a plurality of subscriber's telephone 
lines 12 are connected to at least one meter interface device 14 of this 
invention. The meter interface device (MID) 14 of the applicant's 
invention may have one or several utility monitoring devices (UMD's) 16 
which can send a usage figure to the meter interface device 14 upon 
receiving a command therefrom. The MID 14 of the applicant's invention in 
combination with at least one UMD 16 typically comprises an installation 
of the utility meter reading system 10 at the subscriber's site. A typical 
utility monitoring device (UMD) 16 for monitoring water usage can be seen 
in U.S. Pat. No. 4,085,287 to Kullman et al, the disclosure of which is 
incorporated by reference herein. 
The MID's 14 connected to the individual subscriber's telephone lines 12 
are each sensitive to receiving a particular distinct interrogation signal 
from a telephone central office via the metallic test access port normally 
used for testing lines or preferably via a multiplexer system 20, similar 
to one described in co-pending application, Ser. No. 544,440, filed Oct. 
21, 1983 for A Multiplexing System for an Automatic Meter Reading System. 
When a particular interrogation signal is received over a subscriber's 
line 12 by the MID 14, the MID 14 commands a usage figure from one of its 
UMD's 16 which is then sent over the subscriber's line 12. It can be seen 
that numerous meter readings can be sent over a plurality of telephone 
lines in the utility meter reading system 10. 
The plurality of subscriber's lines 12 are typically connected to central 
office 27 and are multiplexed both for the sending of the plurality of 
interrogation signals and for the receiving of the plurality of meter 
readings in the mulitplexor (MUX) stage 22 of the typical multiplexing 
system 20. The meter reading data is sent to a computer 24 which can 
assemble and compile the plurality of usage figures into billing 
information. The computer 24 may be accessed by local terminal 23 and 
printer 25. Since the multiplexing system 20 is typically in a central 
telephone office, the billing information or the meter readings alone may 
be sent to a utility company by high or low speed data lines 26 and 28. 
PREFERRED EMBODIMENTS 
A One UMD Embodiment 
The applicant's invention relates to a meter interface device (MID) 14 for 
sending utility usage information over a telephone line, and, referring to 
FIG. 2, a one monitoring device embodiment of the MID 14 of the 
applicant's invention is seen. The tip 40 and ring 42 connectors are 
connected to the subscriber's telephone line 12 which has approximately 
-48 volts on the ring conductor with respect to the tip conductor in an 
ON-HOOK condition. The TIP conductor of a typical telephone line usually 
sits at approximately earth ground potential. In the preferred embodiments 
of the applicant's invention, the MID 14 is powered from the telephone 
line 12. This feature has the obvious advantage of doing away with 
separate power supplies which must be powered from the subscriber's 
location or battery supplies. Also, this feature allows the MID 14 to be 
completely shut off when the telephone line 12 becomes OFF-HOOK, if this 
feature is desired. This will guarantee non-interference with normal 
communications. 
A voltage regulator 50 drops the 48 volt ON-HOOK telephone line 12 supply 
voltages to a range compatable with digital logic integrated circuits. The 
MID 14 can prevent its own operation when the telephone line 12 is 
OFF-HOOK by requiring that the input voltage to the MID 14 be higher than 
a voltage appearing on the OFF-HOOK telephone line 12, typically 2.5 to 8 
volts on most telephone lines. The voltage regulator 50 is responsible for 
furnishing power to an interrogation signal detector 60, a control logic 
circuit 70, a clock circuit 80, a carrier oscillator circuit 90 and an 
output circuit 100 which comprise the operational elements of the MID 
device 14. 
When a particular distinct interrogation signal, to which the MID 14 has 
been designed to respond, is sent over the telephone line 12, the 
interrogation signal detector 60 responds by sending a signal indicating 
the presence of the interrogation signal to the control logic circuit 70. 
The control logic circuit 70 responds by turning on the clock circuit 80, 
powering the output stage 100 and powering the UMD 16 through transistor 
Q4. 
It will be seen that this embodiment of the applicant's invention is 
particularly suited to send utility information from the water meter 
encoder described in U.S. Pat. No. 4,085,287 to Kullman et al. Suffice it 
to say that the Kullman water meter encoder comprises four rotary switches 
represented in simplified for in FIG. 4, which turn as the water is 
consumed. The positions of these four rotary switches indicate the water 
usage figure. The rotary swithes are digitally scanned to output a series 
of pulse width modulated digital signals representing the usage figure 
from the rotary switches together with sentinel figures. Typical pulses 
from the Kullman water meter meter can be seen in FIG. 4a. However, for 
reasons discussed in the section dealing with interfacing the Kullman 
water meter encoder to the MID 14, the typical pulses represented in FIG. 
4a will not be those outputted from the Kullman water meter encoder when 
it is interfaced to the preferred embodiment of the invention. 
The clock circuit 80 of the MID device 14 sets up the timing of the pulse 
train which will be outputted from the water meter UMD 16 of the preferred 
embodiment. The pulses from the Kullman water meter in the preferred 
embodiment are graphically depicted in FIG. 4. These pulses seen in FIG. 4 
pulse the carrier oscillator circuit 90 directly, thus, the carrier from 
the carrier oscillator circuit 90 is turned on for the duration of the 
positive going pulses and shut off during the zero voltage transitions. 
This pulsed carrier is conducted onto the telephone line 12 through the 
output circuit 100 which amplifies the pulsed carrier and rise time 
limiter circuit 110 which limits components of the typical 2000 Hertz 
carrier frequency appearing above 3000 Hertz in frequency. 
Referring now to FIG. 3, the one monitoring device embodiment of the MID 14 
of the applicant's invention is seen in greater detail. The voltage 
regulator 50 consists of Zener diodes D1 and D6 and diode D7 which with 
transistor Q1 prevents conduction in a reverse direction, thus, enabling 
the telephone company to still make accurate line leakage tests by testing 
the line with a reverse battery applied (RING +, TIP -). Diode D7 prevents 
a reverse current from being conducted through the MID 14 whether such 
reverse current is created by telephone company leakage tests or incorrect 
installation of the tip 40 and ring 42 connectors to the telephone line 
12. The power supply 50 with its internal ground 55 is referenced to the 
tip side of the line 12. 
The feature of automatically shutting off the MID 14 when the telephone 
line 12 is in the OFF-HOOK position is included in the diagram of FIG. 3. 
Typical value of zener diode D1 is 8.2 volts and the typical value of 
zener diode D6 is 16 volts. Therefore, it can be seen that the voltage 
between tip 40 and ring 42 must be somewhere over 24 volts to cause D1, D6 
and D7 to allow current to allow voltage to be conducted to power line 58; 
since the typical OFF-HOOK voltage is between 8 and 2.5 volts, it can be 
seen that the MID 14 will be inoperative at typical OFF-HOOK voltages 
insuring non-activation during a telephone conversation and also 
increasing the impedance the MID impresses on the line to insure no 
attenuation or distortion of OFF-HOOK voice or data signals. It can also 
be seen that at a typical ON-HOOK voltage which is 48 volts, the voltage 
on power line 58 is typically -7.3 volts DC. The MID 14 is referenced to 
TIP with a resultant negative supply voltage used because with TIP close 
to ground potential, less current will be conducted to ground from the 
telephone line in the event of a meter, meter drop, or MID malfunction 
causing leakage to ground. (The UMD's 16 drop wire can leak to ground if 
damaged). 
If the MID 14 of FIG. 3 develops a short circuit either at the UMD input 
lines 61, 62 and 63 or in other components of the MID 14, the telephone 
line 12 will see only the value of resistances R9 and R10 across its tip 
and ring connections. The line sees 5,000 ohms across its tip and ring 
conductors. Therefore, the telephone line 12 is protected from short 
circuits which may develop in the MID 14 or the UMD 16 so that the 
telephone service will not be interrupted. 
UMD Isolation 
The MID of this invention has been designed to minimize leakage current 
between the telephone line and ground which could result from a 
deteriorating in-ground cable which connects the MID to the UMD. This is 
particularly important in the case of the UMD being connected to a water 
meter since the UMD may be itself submerged in ground potential water in 
some areas at some times of the year. 
These potential leakage currents are minimized by referencing the voltage 
regulator 50 output and therefore all of the MID's circuitry to the TIP 
side of the line which normally is at near ground potential. In addition, 
a UMD isolation circuit is provided which allows the UMD to "float" in 
potential relative to the MID during idle and OFF-HOOK conditions. 
Referring specifically to FIG. 3, the UMD isolation circuit comprises 
transistors Q3 and Q4, diodes 9 and 10 and capacitor 12. 
Operation 
In operation, the received interrogation signal in the form of an AC tone 
burst from the telephone central office is amplified by transistor Q8 and 
associated components and then put through a Schmitt trigger inverter 
integrated circuit U1 connected to a phase lock loop integrated circuit 
U2. The phase lock loop U2 is set up to respond to a single tone 
interrogation signal. When the single tone interrogation signal is 
detected, NOR gate U3, inverter U4, NOR gates U5 and U6, and inverter U7, 
which typically comprise the control logic circuit 70, turn on the clock 
circuit 80. The frequency of the UMD clock carrier oscillator circuit 90 
is determined by the values of resistor R13 and capacitor C10 which are 
connected to the input of an inverter U8. 
The control logic circuit 70 also turns on the carrier oscillator circuit 
90. The frequency is determined by R18 and C13 which drives into 
complimentary emitter follower amplifier output stage 100 which sends the 
pulsed carrier to the rise time limiter circuit 110 which typically 
consists of capacitor C11 and potientiometer R16 or, alternatively, an 
operational amplifier (not shown) with line AC feedback to enable 
auto-adjust of the output level. One purpose of the rise time limiter 
circuit 110 is to limit the rise times of the carrier pulses to 0.167 
milliseconds maximum to prevent frequency components above 3 kilohertz 
from being produced when the carrier has the typical frequency of 2 
kilohertz. However, it must be noted that frequencies from about 300 to 
about 3500 Hertz may be used as a carrier frequency and still be 
consistent with the applicant's invention. 
It must be noted that it is totally consistent with the applicant's 
invention to send utility information from virtually any utility meter, 
such as water meters, watt-hour meters and gas meters, by interfacing the 
MID 14 with each of such utility meters. As well, numerous data 
transmission schemes may be used in creating the alternating current 
representations of the usage information from a UMD 16. Furthermore, the 
applicant's invention may be configured to respond to numerous types of 
interrogation signals sent over the telephone line 12. The single tone 
concept is far the simplest and yet effective. 
Interfacing to a Water Meter 
As previously discussed, the one monitoring device embodiment of the MID 14 
of the applicant's invention is particularly suited to send utility 
information from a water meter encoder of the type described in U.S. Pat. 
No. 4,085,287 to Kullman et al. This Kullman water meter UMD 16 of FIG. 2 
requires a clock input line 61, data output line 62 and a ground line 63. 
The clock input line 61 (22 in FIG. 5 of U.S. Pat. No. 4,085,287) powers 
the Kullman water meter encoder through a diode (25) and capacitor (26) to 
ground. With the typical 10 kilohertz, 50% duty cycle clock input, the 
rectification from the diode and filtering by the capacitor provide an 
adequate, stable input voltage. However, as will be discussed, it is 
advantageous to reduce the clock frequency to about 200 Hertz to get the 
optimum characteristics of the pulse width modulated carrier for 
transmission on the telephone line 12. This reduced frequency clock will 
not allow proper powering of the Kullman water meter UMD 16 at a 50% duty 
cycle. This 50% duty cycle at a frequency of 200 Hertz will produce 
significant sags in the voltage resulting on the voltage input line (27 on 
FIG. 5 of U.S. Pat. No. 4,085,287). If the Kullman water meter is leaking 
current to earth ground by becoming immersed in water, the current 
requirements are heightened and the sags become even more significant. The 
current sags will cause the Kullman water meter UMD 16 to operate 
improperly. Therefore, at the reduced frequency clock of 200 Hertz, the 
clock pulses must have a higher duty cycle which is typically 99 percent. 
A clock pulse frequency of 200 Hertz with a 99% duty cycle on the positive 
going pulse has been found to be the preferred characteristics of the 
clock pulse input. However, increasing the duty cycle of the clock input 
pulse has the adverse effect of overriding the mark pulse seen in each 
pulse train example in FIG. 4a (also shown as 88 of FIG. 8 of U.S. Pat. 
No. 4,085,287) which is a negative going pulse at the start of each digit 
of data. This is caused because the mark pulse, in the Kullman water meter 
encoder is proportional in width to the negative going period of the clock 
pulses. However, this overriding effect does not make it impossible to 
recover the data from the Kullman water meter UMD 16. The relative pulse 
widths of the data from the Kullman water meter UMD 16 can be sensed at 
the multiplexors 22 of FIG. 1 and the data can be determined from the 
relative pulse widths of the data pulse train received. 
Referring to FIG. 4a, mid-regions of several typical output data pulse 
trains are shown. An 0 bit followed by an 0 bit has the largest bit 
period. An 0 bit followed by a mark bit has the next highest bit period 
and so forth. As can be seen, the mark bit is too short to be detectable 
and is represented by a thin line where the mark bit should have been. 
However, the Kullman water meter UMD 16 sends out a series of BCD 14's 
(see FIG. 18 of U.S. Pat. No. 4,085,287) which can be used to set the 
relative bit periods and relative 4 bit character periods which comprise a 
single digit of the meter reading. The multiplexor 22 as disclosed in our 
above referenced co-pending application, looks for the series of BCD 14's 
in the data received and sets the bit period and 4 bit character period 
for which the rest of the data digits will be compared to detect the 
Kullman water meter reading. The relative pulse durations in each 
character period are then compared to all possible combinations of 
relative pulse durations for the characters of the meter reading and a 
meter identification figure. 
This feature of comparing the relative pulse durations in each character 
period of the pulse train also allows for the pulse widths of the pulse 
train from the MID 14 to drift over large ranges and still be able to send 
accurate meter readings over the telephone line 12. This is because the 
relative pulse widths are first stored and then compared at the 
multiplexor 22 of FIG. 1; so long as the pulse width relativity is intact, 
the meter readings can be received and decoded by the multiplexor 22. 
Since the relative pulse widths may vary, there is no need for expensive 
time bases, thus, the cost of each of the MID 14s is greatly reduced. 
Also, since the relative pulse widths are first stored, there is no time 
limitation on the subsequent task of decoding. In central office computer 
software, this time advantage enables use of quite sophisticated 
techniques enabling the reconstruction of a very marginal reading. 
Suffice it to say, the outputted data pulse train on the data output line 
from the Kullman type meter encoder 62 turns on the carrier oscillator 90 
of FIG. 3 with every low to high transition of the outputted data pulse 
train and turns it off with every high to low transition of the outputted 
data pulse train. Therefore, the typical output of the carrier oscillator 
80 is a series of asynchronous pulses of a single carrier tone with the 
pulses having several pulse widths. However, it must be noted that there 
are different ways of sending the utility information over the telephone 
line 12 suitable for a different type of UMD 16 which may be used and 
still be consistent with the applicant's invention. 
The data pulse train is sent over the telephone line 12 for typically one 
and one-half times the time necessary to send a single meter reading so 
that no data bits can be lost if the sending starts somewhere after its 
beginning point. This one and one-half time period constitutes a wrap 
around of the data bits from the Kullman water meter UMD 16. 
The frequency found to be the most preferred for the carrier frequency of 
the MID 14 of the applicant's invention is about 2 kilohertz, and, the 
preferred duration of the average pulse width of the 2 kilohertz carrier 
has been found to be about 10 cycles or about 5 milliseconds when the 
Kullman water meter UMD 16 is used to monitor the water usage information. 
A 2 kilohertz frequency was chosen because it is in the mid-range of the 
human voice which telephone lines 12 are made to carry. Being in the 
mid-range of the human voice allows the carrier to be transmitted over any 
direct wire or carrier-derived telephone lines 12. As well, the 2 
kilohertz frequency is not in conflict with any known frequency used by 
telephone companies for testing purposes, therefore, this frequency will 
not interfere with existing telephone operations. 
The average pulse width of the 2 kilohertz carrier was chosen by 
considering that an increased pulse width will give a greater amount of 
reliability to the receiving of the pulse train on the opposite side of 
the telephone line 12 by increasing its immunity to noise pulses. At the 
same time, the shorter the time required to send a Kullman water meter 
reading the better since there may be numerous such MID's 14 to be read. 
The preferred compromise between the two considerations has been found to 
be the 5 millisecond average pulse width. It must be noted that since the 
pulse widths vary from the Kullman water meter UMD 16, it is the average 
of these pulse widths which is 5 milliseconds. 
The pulse width modulated carrier from the carrier oscillator has the 
advantage of drawing a significantly lower average current than other 
modulations, such as frequency shift keying, where the carrier is always 
on. With a lower average current draw, the MID 14 can be powered from the 
telephone line 12 and not have an OFF-HOOK condition occur because the MID 
14 is drawing excessive current during transmission of data. In addition, 
a higher carrier signal level can be used since FCC signal power 
regulations restrict levels on a 3 second average. This is the reason why 
pulse width modulation was chosen; however, it is important to note that 
other modulation methods may be used to transmit utility information from 
an UMD 16 and still be consistent with the applicant's invention. 
Referring to FIG. 5A and 5B, the components of the one monitoring device 
embodiment of the MID 14 are typically mounted on a printed circuit board 
130. This printed circuit board 130 can be configured to fit over the tip 
and ring 40 and 42 (FIG. 5a) connectors of a common telephone line 
protector block 140. This line protector block 140 typically houses 
lightning protectors 142 and 144 which protect telephone equipment from 
lightning induced overvoltage conditions. The entire one monitoring device 
embodiment of the MID 14 on the printed circuit board 130 may be housed 
inside the line protector block 140 housing (unshown). 
The mounting of the printed circuit board 130 in the line protector block 
140 allows for easy installation of the MID 14 at a subscriber's site. 
There will be no necessity to go into a subscriber's building to install 
or service the MID 14. The wire drop 18 from connections 61, 62 and 63 may 
be run to a UMD 16 at the subscriber's site. As previously stated, the UMD 
16 may be virtually any type of monitoring device since the MID 14 can be 
interfaced to vitually any type of UMD 16. 
Four UMD Embodiment 
Referring now to FIG. 6, a four monitoring device embodiment of the MID 14 
is seen. The circuitry of the four UMD embodiment allows for sequential 
sending of utility information from four separate UMD's 16, namely, UMD A, 
UMD B, UMD C and UMD D. The circuit of FIG. 6 shows interfacing for four 
Kullman water meter UMD's 16, each Kullman water meter of the type 
described in U.S. Pat. No. 4,085,287. It is, however, totally consistent 
with the applicant's invention to have a watthour meter, a gas meter, a 
Kullman water meter or other UMD 16 connected to the MID 14 to transmit 
utility usage information over the telephone line 12. The embodiment of 
FIG. 6 is basically the circuit of FIG. 3 with the capability of 
transmitting data from four meters in sequence from one subscriber 
station. 
Again, as described in the single monitoring device embodiment of FIG. 3, 
two resistors R34 and R35 prevent the UMD 16 or MID 14 from interrupting 
telephone service which would be caused by shorts developing in either of 
the UMD 16 or MID 14. In the situation of a dead short in the MID 14, the 
telephone line 12 will only see resistors 34 and 35 in parallel or 
approximately 5.1 kilohms across its tip and ring connectors. 
The S1 and S2 switches are option straps which enable a choice of three 
different output stages: (1) normal manual adjustment, (2) auto 
adjustment, and (3) OFF-HOOK (subscriber carrier output current loop 
stage, Q19). 
Customer Identification Embodiment 
I have found that certain conditions can exist in a telephone system when 
the identity of the line being interrogated can be lost and an ambiguity 
exist if two meters in sequence have identical readings. To absolutely 
avoid that possibility, I have developed a MID which encodes each customer 
with a unique 6 digit code. The code is transmitted with each data reading 
for processing at the telephone central office. 
The customer encoding MID is shown in FIG. 7 connected to the tip and ring 
connectors 42 and 40, respectively of a telephone line. It includes a 
protector 200 similar to earlier embodiments and an optional OFF HOOK 
TRANSMIT STAGE 201 which allows the MID to transmit a reading even when 
the receiver is off hook, if interrogated. This stage which is ahead of 
the normal voltage regulator 210 and includes transistors 202, 203, 204 
and adjustable resistance 205. 
The voltage regulator or power supply for the MID, similar to earlier 
embodiments includes Zener diodes 211 and 212 and transistor 213. Reverse 
polarity protection is provided by diode 214. 
The interrogation tone detector 215, similar to earlier embodiments senses 
the presence of an interrogation signal on the line to enable the 
transmission of meter readings. An off hook detector 220 including 
transistor 221 which allows the MID to be used on lines including party 
lines with high voltage off hook conditions. 
The control logic section 230 includes NOR gates U3 and NAND gate U5. Meter 
read sequencing is provided by meter sequencer 335 comprising basically 
integrated circuit U4, preferably a type MC140 7. 
Customer identification and signalling is accomplished due to the presence 
of U8 and a series of six ten position thumb wheel or equivalent switches 
capable of providing six digit numbers for encoding similar to data. For 
purpose of simplicity of explanation, the switches are shown as a six by 
four line matrix with the switches binary encoding the six lines with a 
four bit code. 
The customer encoding MID also incudes its own meter clock circuit 240 to 
control the baud rate; on-hook automatic level output stage 250; its 
carrier oscillator 260 and individual UMD drive and isolation circuitry, 
the last, individual for each meter A-D. 
Employing this embodiment, the customer identification number is encoded, 
similar to data but as six digits followed by a pause and then the four 
meter readings in sequence. 
The above described embodiments of the applicant's invention are merely 
descriptive of its principles and are not to be considered limiting. The 
scope of this invention instead shall be determined from the scope of the 
following claims, including their equivalents.