Power check meter

A power measurement system calculates the power flow within a wire to a customer and transmits an indication of the power flow to a remotely located operator. The measurement system includes both a current transformer that senses current within the wire and generates a first output signal and a voltage input that senses voltage within the wire and generates a second output signal. A measurement device receives both the first and second output signals and in response generates a third signal representative of the power flow within the wire. The measurement device includes both a speech encoding circuit that receives the third signal and in response generates a voice signal, and a transmitter that receives the voice signal and transmits the voice signal to the remotely located operator.

BACKGROUND OF THE INVENTION 
The present invention relates to a power check meter, and in particular to 
a power check meter with improved data transmission characteristics. 
Some electrical power customers tap the electrical power line routed to 
their residence or business at a location prior to their power meter in 
order to steal electrical power from the utility. To reduce the theft of 
electrical power many utilities use a portable kilowatt-hour check meter 
connected to the incoming power line of a suspected dishonest customer to 
monitor the customer's power usage. The portable check meter is normally 
installed high on the power pole near the location that the customer's 
line connects to the utility's main power line. By installing the portable 
check meter in such a location it is difficult for the customer to tap the 
incoming line prior to the portable check meter. The utility compares the 
recorded power usage from both the power meter and the portable check 
meter during the same time period and notes any difference. If the 
measurements are significantly different then the utility has confirmed 
its suspicions and obtained proof that electrical power has been stolen by 
the customer. The utility then takes corrective measures to ensure that 
the customer thereafter refrains from stealing electrical power. 
Customers that steal electrical power are paranoid of being caught and may 
notice the utility employees installing the portable check meter on the 
pole near their location. If the customer notices utility employees 
installing such equipment, the customer will typically refrain from 
stealing power for a period of time. During such a time the utility will 
not be able to detect the theft of power. Traditionally, in order to 
monitor the customer's power usage, utility employees were required to be 
in close proximity to the portable check meter's display indicating power 
usage. This required a utility employee to climb the pole which may alert 
dishonest customers that their power usage is being monitored and cause 
the customer to refrain from stealing power until they are confident that 
their power usage is not being monitored. In addition, it is frequently 
dangerous for utility employees to be near such dishonest customers, 
especially if they are involved in illegal drug activities. 
In order to alleviate the need for utility employees to be within several 
feet of the traditional portable check meter to read the power usage, some 
portable check meters include a radio-frequency transmitter that 
periodically transmits the power usage. The utility employee uses a 
radio-frequency receiver to receive and display the transmitted power 
usage. However, the radio-frequency receiver must still be within 
approximately 100 to 300 feet to receive the power usage. Accordingly, the 
utility employee must still get close to the customer which may 
inadvertently alert the customer that they are being monitored. Also, this 
may place the utility employee in a dangerous situation. In addition, this 
requires the utility employee to drive to the vicinity of the transmitter 
requiring significant time and expense. Further, the utility must obtain a 
specialized receiver to receive the power usage at additional expense. 
Such a system is available from Universal Protection Corporation of 
Atlanta, Ga., known as CMI Diversion Check Meter System. 
An alternative portable check meter available from Universal Protection 
Corporation of Atlanta, Ga., sold under the name CPS I Cellular Phone 
System, further includes a cellular phone link. A radio-frequency 
transmitter is used to transmit power usage from the portable check meter 
to a radio-frequency receiver located in a separate housing. The 
radio-frequency receiver receives the power usage and in response 
retransmits the power usage as digital data to the utility using a 
cellular telephone transmitter. The utility needs a computer, a modem, and 
specialized software to receive and analyze the digital data from the 
cellular telephone transmitter. However, the CPS I system requires two 
separate enclosures to be mounted in the vicinity of the customer which 
increases the likelihood that the customer will notice the check meter. In 
addition, the utility is required to use specialized software operating on 
the computer to receive and analyze the data obtained from the cellular 
phone transmitter. Further, cellular telephone communications are highly 
susceptible to dropouts which then require the data to be retransmitted 
until valid data is received by the utility. The dropouts and potential 
corruption of the digital data increases the likelihood that the utility 
will obtain a false reading of the actual power usage. 
Portable check meters normally include both a voltage input (or 
transformer) that is directly connected to the wire to sense voltage and a 
current transformer that encircles the wire to sense current flowing 
within the wire. The voltage and current measurements are multiplied 
together to obtain the power usage. Unfortunately, utility employees 
periodically install the current transformer in the reverse direction 
thereby causing the current induced in the current transformer to have the 
wrong polarity. The improper current polarity may result in the portable 
check meter calculating an incorrect power usage. If the current 
transformer is not properly connected to the wire then the utility 
employee must return to and reconnect the current transformer to the wire 
with the proper orientation. The utility employee returning to the check 
meter increases the likelihood that the customer will detect the 
monitoring of their power usage and also subjects the utility employee to 
further danger. 
What is desired, therefore, is a portable check meter that reduces the 
likelihood of transmitting false data to the utility. Also, the check 
meter should eliminate the need for a computer and specialized software to 
receive and display the power usage while minimizing the amount of 
equipment installed at the customer. Further, the check meter should 
minimize the time necessary for installation and ensure that the utility 
employee orientates the current transformer in the proper direction. In 
addition, the check meter should reduce the need for utility employees to 
be in the vicinity of the customer after installation. 
SUMMARY OF THE PRESENT INVENTION 
The present invention overcomes the aforementioned drawbacks of the prior 
art by providing an improved power measurement system for calculating the 
power flow within a wire to a customer and transmitting an indication of 
the power flow to a remotely located operator. The measurement system 
includes both a current transformer that senses current within the wire 
and generates a first output signal and a voltage input that senses 
voltage within the wire and generates a second output signal. A 
measurement device receives both the first and second output signals and 
in response generates a third signal representative of the power flow 
within the wire. The measurement device includes both a speech encoding 
circuit that receives the third signal and in response generates a voice 
signal, and a transmitter that receives the voice signal and transmits the 
voice signal to the remotely located operator. 
The use of the voice signal in the present invention operates on the basis 
of relying on the recognition of the human brain to understand voice or 
speech, even if slightly or severely distorted by limitations in cellular 
telephone transmission technology. If a few bits are dropped in the voice 
pattern or a dropout occurs, the speech pattern is still recognizable by 
the utility employee. 
In the preferred embodiment the measurement also includes internal 
circuitry that detects the polarity of the current transformers. This 
involves detection of the duration which the voltage and current signals 
have the same and different polarities. If the voltage and current signals 
over a cycle have different polarities more than they have the same 
polarity then the internal circuitry reverses the polarity of the current 
transformer. This assures that the polarity of the current transformer is 
proper, regardless of the orientation in which it was installed. 
The foregoing and other objectives, features, and advantages of the 
invention will be more readily understood upon consideration of the 
following detailed description of the invention, taken in conjunction with 
the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, a utility customer 10 has an incoming power line 12 
which normally includes two hot wires and a common wire. The power line 12 
is typically connected to a main line 14 at a utility pole which belongs 
to a power utility 15. A standard power meter 16 is located adjacent to 
the customer 10 in order to determine the customer's power usage for 
periodic billing purposes. If the utility 15 suspects that the customer is 
stealing power then the utility 15 installs a check meter 18 on the 
utility pole to monitor the customer's power usage. Unfortunately, the 
installation of the check meter 18 may alert the customer 10 that the 
utility is monitoring their power usage, and subject utility employees to 
danger during installation and subsequent adjustment of the check meter 
18. 
Referring to FIG. 2, the check meter 18 of the present invention includes a 
microprocessor 20. The microprocessor 20 is preferably a Motorola 
MC68HC711E9 which includes internal analog-to-digital and 
digital-to-analog converters. A system clock 22 provides a clock signal to 
the microprocessor 20. A temperature sensor 24 allows the check meter 18 
to provide the utility 15 with temperature measurements and also internal 
temperature compensation for the electronics within the check meter 18. 
A pair of split core current transformers 26a and 26b sense the current 
level within the respective hot wire 27a and 27b of the power line 12, and 
in response each current transformer 26a and 26b generates an output 
voltage proportional to the current level within the respective wire 27a 
and 27b. The current transformers 26a and 26b may be any type of device 
that senses the current flowing in a wire. A respective phase and gain 
circuit 28a and 28b receives the output voltage from the respective 
current transformer 26a and 26b. The microprocessor 20 through lines 30a 
and 30b adjusts the voltage gain of respective phase and gain circuits 28a 
and 28b. The gain values are set during calibration of the check meter 18. 
In addition, the phase and gain circuits 28a and 28b rectify the received 
voltage signals. The microprocessor 20 and the phase and gain circuits 28a 
and 28b determine if the phase of each of the sensed current signals is 
correct, as described later. Rectified analog voltage outputs 31a and 31b 
from the respective phase and gain circuits 28a and 28b are representative 
of the current level within the respective wire 27a and 27b. 
A pair of voltage inputs (or voltage transformers) 32a and 32b are 
connected to the respective wire 27a and 27b. The voltage inputs 27a and 
27b are preferably clips connected directly to the respective wire 27a and 
27b. A pair of signal conditioning circuits 34a and 34b amplify, rectify, 
and filter the voltage output from the respective voltage inputs 32a and 
32b. The voltage output 29a and 29b of each of the signal conditioning 
circuits 34a and 34b is a rectified analog voltage representative of the 
voltage level within the respective wire 27a and 27b. The rectified analog 
voltage outputs from both the signal conditioning circuits 34a and 34b and 
the phase and gain circuits 28a and 28b are sampled and converted by 
analog-to-digital converters within the microprocessor 20 to a set of 
digital values for further processing. A nonvolatile RAM 40 stores sampled 
data and other suitable data for the check meter 18. 
Zero volt crossover detector circuits 36a, 36b, 36c, and 36d detect the 
zero crossover of each of the respective input voltage signals that may be 
used to determine the start of each period of the current and voltage 
waveforms within the wires 27a and 27b by the microprocessor 20. The 
current and voltage waveforms within the wires 27a and 27b are generally 
periodic. 
To determine the customer's power usage, each of the respective sampled 
voltage signals from the voltage inputs 32a and 32b and current 
transformers 26a and 26b are multiplied together to obtain a set of 
instantaneous power measurements (Power=Current*Voltage). The 
instantaneous power measurements obtained during a period of time, such as 
one cycle, are summed together to obtain the power usage per unit time. 
The period of the cycle may be determined based on the outputs from the 
crossover detectors 36a-36d or a timing sequencer 56, described later. 
Unfortunately, the polarity of the output voltage from one or more of the 
current transformers 32a and 32b may have the incorrect polarity if 
improperly connected to the respective wire 27a and 27b by the utility 
employee. If one or both of the current transformers 32a and 32b is 
improperly connected, the utility employee previously had to return to the 
check meter 18 to reverse the orientation of the current transformer which 
adds expense to the surveillance, may jeopardize the secrecy of the 
surveillance, and may place the utility employee in further danger. 
The combination of the crossover detectors 36a-36d, the phase and gain 
circuits 28a and 28b, and the microprocessor 20, collectively determine if 
the polarity of the output voltages from the current transformers 32a and 
32b are correct. 
Referring to FIG. 3, each of the crossover detectors 36a-36d is principally 
a voltage comparator 52 that produces a positive voltage output (logical 
1) when its inverting input voltage is negative and produces a negative 
voltage output (logical 0) when its inverting input voltage is positive. 
Each of the phase and gain circuits 28a and 28b includes a phase circuit 
50 and the timing sequencer 56. One phase and gain circuits will be 
described for one wire with the other being the same. The positive and 
negative rectangular waveforms from the crossover circuits 36c and 36d are 
the input voltage waveforms 54a and 54b to the phase detector 50. The 
phase detector 50 is preferably an XOR gate (exclusive OR), and produces 
the following outputs: 
______________________________________ 
Voltage Current 
Input Transformer Phase 
Comparator 36c 
Comparator 26d 
Detector 
Output Output 50 Output 
______________________________________ 
High Volts ("1") 
High Volts ("1") 
Low Volts ("0") 
High Volts ("1") 
Low Volts ("0") 
High Volts ("1") 
Low Volts ("0") 
High Volts ("0") 
High Volts ("1") 
Low Volts ("0") 
Low Volts ("0") 
Low Volts ("0") 
______________________________________ 
The output waveform from the phase detector 50 has a zero basis value (low 
volts) when both the voltage inputs have the same polarity. This indicates 
that the current and voltage in the respective wire have the same 
polarity. An output waveform with a (high) logic 1 voltage, indicated by a 
logic 1 or positive voltage pulse, indicates the time during which both 
the voltage and current signals do not have the same polarity. The 
duration which the current and voltage signals have the same and different 
polarities is illustrated in FIG. 4. 
The total power is the summation of each of the instantaneous power 
calculations where the voltage and current signals have the same polarity 
as indicated by the phase detector output 50 having a low voltage, from 
which the instantaneous power calculations are subtracted where the 
polarity of the voltage and current signals are different as indicated by 
the phase detector output 50 having a high output. This provides the 
correct total power value over a period of time. 
To determine if the current transformers are providing signals with the 
proper polarity, the microprocessor 20 determines if during a cycle there 
are more low voltage outputs from the phase detector 50 indicating the 
current and voltage have the same polarity than the total high voltage 
outputs from the phase detector 50 indicating that the current and voltage 
have different polarities. If this is the case, then the microprocessor 20 
knows that the current transformer is properly oriented. Otherwise, the 
microprocessor 20 automatically corrects the polarity of the current 
transformer by logically inverting (reversing) the phase indication values 
from the phase detector 50. This alleviates the previous need for utility 
employees to return to the check meter 18 and reorient the current 
transformer. The aforementioned power calculation technique is especially 
useful when the microprocessor 20 samples rectified signals, as in the 
present check meter 18, because rectified signals do not contain polarity 
information. The phase detector 50 is preferably an XOR gate. 
The timing sequencer 56 receives the output from the voltage crossover 
detector 36c and generates an output trigger signal 57 that indicates the 
start of each cycle of the generally periodic voltage waveform within the 
wire. The timing sequencer 56 identifies each cycle of the input signal so 
that each cycle can be identified and sampled individually. 
Referring to FIG. 5, the power is more specifically calculated by 
reconstructing a power wave (Power=Current*Voltage) from a large number of 
voltage, current, and phase determinations. Each sample taken requires a 
few bytes to store its voltage, current, and phase values. A high clock 
rate would be needed to sample the waveform at high rates. In order to 
reduce the need for high clock speeds and excessive memory to store the 
samples, the check meter 18 samples multiple cycles and overlays them to 
obtain a more accurate resultant power usage. Multiple power data samples 
are obtained in groups, each group measuring at points that are shifted 
slightly later in time, so as to fill in the gaps between the sample of 
the previous sample groups. The first data acquisition group, as shown in 
FIG. 6, obtains the data samples starting at the positive edge of the 
voltage crossover point, and then proceeds to acquire the next sample just 
a few hundred microseconds later, until the final sample is near, but, not 
over the negative going edge of the voltage crossover point. At the 
negative going edge voltage crossover point, the data sampling begins 
again, obtaining samples at exactly the same spacing as in the positive 
half cycle. When the first data acquisition group has finished, the data 
samples are evaluated and combined into a single partial power usage. The 
second data acquisition group, as shown in FIG. 7, in like manner obtains 
its data samples, however, the starting sample is delayed slightly in time 
from the voltage crossover points. This is to cause the sampling of data 
to be slightly shifted to later points all across the waveform. When the 
second data acquisition group has finished, the collected data samples are 
evaluated and added to the first partial power usage. Preferably 256 
samples are obtained across the power wave which may require several 
cycles. The result has a high degree of accuracy, especially for distorted 
waveforms and current phase shifting. 
The present inventors determined that using a cellular phone transmitter to 
transmit digital data to the utility 15 is prone to errors due to the 
inherent limitations of cellular phone transmissions. Also, specialized 
software, a computer, and a modem are not always available to receive and 
display the data. The present inventors came to the realization that they 
could eliminate the digital data transmission limitation, not by including 
redundant check bits or transmitting the digital data multiple times to 
the receiving computer, but instead relying on the recognition of the 
human brain to understand voice or speech even if severely distorted. If a 
few bits are dropped in the voice pattern or a dropout occurs, the speech 
pattern is still recognizable by the utility employee. Referring again to 
FIG. 2, the check meter 18 includes a cellular phone interface 74 which 
includes cellular phone receiver and transmitter circuitry. The utility 
employee calls the cellular phone number of the desired check meter 18 and 
issues in commands by selected combinations of touchtone (DTMF) numbers. 
The check meter 18 includes a DTMF transceiver (dual-tone multi-frequency) 
72 that receives and interprets touchtone inputs from a touchtone phone. 
In response, the check meter 18 provides the requested data and encodes it 
using a voice synthesizer 70 in a human voice. The generated voice signals 
are transmitted to the utility employee using the cell phone interface 74. 
Alternatively, the measurement system may use any type of 
telecommunication transmission and reception system that permits the use 
of voice transmissions. The utility employee may query the check meter 18 
from anywhere that he has access to a phone. Voice synthesis reduces the 
effects of the dropouts inherent in cellular phone technology because the 
human brain can interpret voice patterns even if some of the data is 
missing. 
The telephone DTMF commands that may be issued to the check meter 18 
include, for example requests for: 
(a) date; 
(b) repeat last information requested; 
(c) current amperage detected; 
(d) current voltage detected; 
(e) kilowatt-hour reading; 
(f) resetable kilowatt-hours; 
(g) peak amps; 
(h) temperature; 
(i) clear resetable kilowatt-hours; 
(j) clear peak amps; 
(k) begin investigation; and 
(l) complete investigation. 
The current amperage command for each current transformer 26a and 26b 
instantly permits the utility 15 to determine if the amperage is unusually 
high, which could be indicative of when the customer 10 is likely stealing 
power. The current voltage command for each voltage input 32a and 32b 
permits the utility 15 to verify that a suitable voltage is being provided 
to the customer. The peak amps command preferably also includes the date 
and time so that the utility can tell when the customer 10 is likely 
stealing power, as described later. Clear peak amps command permits the 
peak amp reading to be set to zero. The resetable kilowatt-hours command 
is the same as the kilowatt-hours command, except that the resetable 
kilowatt-hours can be cleared to zero unlike the kilowatt-hours. During an 
investigation, described below, the resetable kilowatt hours is used to 
directly read the kilowatt hours of power consumed during an investigation 
without having to subtract the previous kilowatt-hour reading from the 
current kilowatt-hour reading to determine the total power usage. 
One method of using the check meter 18 is to first determine if the 
customer is likely stealing power by noting any difference between the 
check meter 18 and the power meter 12 readings. Thereafter the utility 
employee can use the peak amperage command to determine when it is likely 
that the customer 10 is stealing power. As an example, some customers 
attempt to steal power when they believe it is less likely that they will 
be detected, such as during the early morning. During the daytime the 
customer may simply use a normal amount of power. Accordingly, the utility 
employee will attempt to determine those times that the amperage or peak 
amperage is unusually high and attempt to obtain a court order to enter 
the premises while the customer is likely actually stealing power. 
An investigation is an automatic method of obtaining useful information 
during a period of time. The beginning of an investigation involves the 
microprocessor 20 (1) saving the time and date, (2) saving the 
non-resetable kilowatt-hour reading, (3) saving the amps reading, (4) 
clearing the peak amps reading, and (5) clearing the resetable 
kilowatt-hour reading. At the end of the investigation period the 
microprocessor 20 does the following: (1) saves the present time and date, 
(2) saves the non-resetable kilowatt-hour reading, (3) saves the resetable 
kilowatt-hour reading, (4) saves the amps reading, and (5) saves the peak 
amps reading. Upon request, the accumulated data is transmitted to the 
utility employee. 
The actual circuit layout of the check meter 18 is shown in FIGS. 8-20. The 
check meter could be designed, with minor modifications, for use in a 
three phase system. 
The terms and expressions which have been employed in the foregoing 
specification are used therein as terms of description and not of 
limitation, and there is no intention, in the use of such terms and 
expressions, of excluding equivalents of the features shown and described 
or portions thereof, it being recognized that the scope of the invention 
is defined and limited only by the claims which follow.