Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a sys-tem for remote
monitoring of several different power consumers by using one host
computer.
In particular, the present invention relates to a
solid-state system which can monitor and record the electric power
used by individual users in existing distribution schemes such as
those found in an apartment building without the need of
installing separate kilowatt hour meters in each apartment unit.
In many larger apartment buildings, it is not possible to
correctly apportion electrical power usage on an apartment by
apartment basis since each apartment does not have a separate
kilowatt hour meter. In such cases, the landlord cannot charge
each tennant a rental rate plus a power usage rate; the power
usage must be part of the landlord's overhead. Of course,
separate kilowatt hour meters could be installed for each
apartment unit, but this could be quite expensive particularly
where a large number of apartment units are involved. The present
invention provides for a solid-state apparatus which can be used
to properly apportion hydro usage on an apartment by apartment
basis without the need of installing a separate kilowatt hour
meter in each apartment, and at a considerable cost saving.
The present system can be broken down into four key
areas; a current/voltage transducer, a sampling unit which will
record measurements, a data pathway, and host computer. The
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transducer can monitor the current ror the main hydro line as
well as branch lines which will be provided to each user. At
regular time intervals, the sampling unit can measure the
voltage across each individual line and at the same time take a
measurement f rom the current transducer. Using these two
measurements, the true power being consumed at a particular
instant in time can be obtained. The sampling unit can then be
used to monitor and collect data from the transducers, and will
be capable of sampling multiple transducers by means of
multiplexing transducer signals. The host computer will be used
to poll sampling units. The sampling unit will transmit
collected data to the host computer when addressed by the host
computer. The host computer will then identify the data and
store it. The host computer must also monitor the central line
feeding the distribution system. The power measured here will
give the total power consumption, and this value allows the host
computer to calculate the ratio of individual consumption to
that of the total use. The ratios can then apportion the total
bill supplied by hydro on an apartment by apartment basis. The
size and configuration of the electrical distribution system
will determine the number and location of the sampling devices.
In accordance with the present invention there is
provided an apparatus for monitoring and apportioning electrical
power consumption by a number of consumers, each consumer being
provided with an unmetered branch power transmission line
connected to a metered main power transmission line, including:
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at least one sampling unit comprising i) at least one current
transducer for measuring current in said branch lines at
predetermined time intervals; ii) at least one voltage
transducer for measuring voltage on said main transmission line;
iii) multiplex means for causing selected current signals to be
transmitted to a current peak detector at predetermined time
intervals; iv) timing means associated with said current peak
detector for initiating voltage sis~nal sampling upon detection
of a current signal peak; v) means for converting said current
peak values, and corresponding voltage signal values from analog
to digital form; and vi) serial/parallel interface means
connected to said multiplex means (iii) and said converting
means (v) for collating and transmitting serial current and
voltage values for each said branch line to a Central Processing
Unit.
The present invention will now be described with
reference to a preferred embodiment which will be made with
particular reference to the following drawins~s.
Figure 1 is a block diagram generally showing the
system.
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Figure lA is a detailed block diagram generally showing
the complete sampling unit.
Figure 2 is a block diagram showing transducer
connections.
Figure 3 is a block diagram showing the sampling unit.
Figure 4 is a diagram showing a current transducer.
Figure 5 is a circui-t diagram showing the current
transducer conditioning circuit.
Figure 6 is a schematic diagram showing the voltage
transducer conditioning circuit.
Figure 7 is a diagram showing the multiplexing circuit.
Figure 8 is a circuit diagram showing the current peak
detector circuit.
Figure 9 shows the analog to digital converters.
Figure 10 shows the sampling unit communications
interface.
Figure 11 shows the network protocol.
Referring to Figures 1 and lA, the system can generally
be configured as shown. There must be at least one host computer
10, one network interface 24, and one sampling unit 12. There
must also be at least one current transducer 13 per sampling unit
12, and one voltage transducer 14 per sampling unit 12. There can
be as many as 128 sampling units 12, 64 current transducers 13 per
sampling unit 12, and two voltage transducers 14 per sampling unit
12. As shown in Figure 2, the current transducer 13 will moni-tor
the current for the main hydro lines 25 and send this information
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to the sampling unit as shown in Figure 3. The voltage transducer
14 also monitors the voltage for the main hydro line 25 and
provides this information to the sampling unit Figure 3. On the
distribution side of maln fuse box 26, current transducers 13 are
provided across each of the individual lines and will monitor the
current for each of the individual lines and send this information
to the sampling unit 23. The sampling unit shown in Figure 3
accepts these inputs and multiplexes input transducer signals on
an apartment by apartment basis. The multiplex signals are
converted from analog signals to digital signals by A/D converters
21 and 22 at specific sampling times determined by peak detector
23, and then sent into a network interface 24 between the sampling
unit of Figure 3 and the host computer 10 by way of a data pathway
network. The host computer 10, shown in Figure 1, can poll the
sampling units, identify the data, and store it. The host
computer 10 is also monitoring the central line feeding the
distribution system so that it can calculate the total power
consumption.
In order to measure the true power being consumed by a
load, it is necessary to obtain a voltage and current
representation of load conditions. It is also necessary to obtain
the phase relationship between the current and voltage since if
the current and voltage are not in phase, the true power
consumption cannot be obtained unless the phase angle is known.
Real power can be obtained from the product of the peak to peak
current with the peak to peak voltage and the cosine of the phase
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angle between the current and voltage. From this equa-tion~ it can
be seen that if peak current could be measured and at the same
time the voltage measured, the product of these two numbers at any
instant in time will automatically give the real power since the
product includes the cosine of the phase angle. Accordingly, the
real power being consumed by the load is the peak current times
the voltage at the same instant in time.
A current transducer can be constructed from a Siemens'n
R3~ toroid 50 with 275 turns of number 26 wire as shown in Figure
4. The wire 51 through which the load current is flowing can be
placed through the toroid 50, and the peak voltage that appears
across the secondary of the current transformer will be
proportional to the peak load current. The output of the current
transducer can be interfaced to the sampling unit with a current
transducer conditioning circuit such as one shown in Figure 5.
This interface circuit serves to scale the output of the
transducer from zero to five volts for a primary current of from
zero to one hundred amps.
A voltage transducer conditioning circuit can be
constructed from a step down transformer with the primary winding
connected across the load and the secondary winding interfaced to
the sampling unit with a voltage transducer conditioning circuit
such as that shown in Figure 6. This circuit will scale the
output from zero to five volts for a load voltage of from zero to
one hundred and seventy volts.
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The sampling unit shown in Figure 3 serves as the
interface between the current/voltage transducers (13 and 14) and
the host computer 10. The sampling unit of Figure 3 has a
capacity to connect to sixty-four current transducers and two
voltage transducers. The basic func-tions of the sampling unit can
be broken down into five components, namely a multiplexing
circuit, a peak detection circuit 23, analog to digital converters
21 and 22, a communications interface 24, and control logic.
The multiplexing circuit as shown in Figure 7 is used to
multiplex the signals from the current transducers 13 and voltage
transducers 14 to form two signals; one for current and the other
for voltage. The multiplexed current transducer signals are sent
to the current peak circuit detector 23 as shown in Figure 8. The
outputs from the voltage transducer circuit 31 are sent to a
voltage analog to digital converter 22. The same analog to
digital converter chip may be used for both the current and
voltage, such as a ADC0804l~.
The current peak detector circuit 23 is shown in Figure
8, and is used to detect the peak of the multiplex current signal.
An input is accepted from the current multiplexer 30 as shown in
Figure 7, and the signal output of the current peak detector 23 is
used to start a current/voltage sample. The output is sent to the
control logic circuit which sends a"start conversion" signal to
the analog to digital converter circuit shown in Figure 9.
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The analog to digital converters shown in Figure 9 are
used to conver-t the transducer signals into a binary
representation that can then be transmitted to the host computer
10 for evaluation. There are two A/D converters per sampling
unit, in order to digitize the current and voltage signals
simultaneously, and thus enabling the real power equation to be
used. The resolution of the A/D converters, in the preferred
embodiment is 8 bits which transforms, for a current resolution of
approximately .75 amps, and for a voltage resolution of
approximately 1 volt. The outputs from the A/D converters are
seni to the network interface shown in Figure 10. Of course, the
resolution can be 16 bits by obvious software modifications and
changing the A/D converters.
Figure 10 shows the sampling uni-t communications
interface. The communications interface serves as a link to the
host computer 10. The interface has the capability of being
addressed by the host computer 10 to allow the host 10 to talk to
a maximum of 128 sampling units. The sampling unit communications
interface circuit in Figure 10 contains a 6.144 megahertz crystal
which is divided to provide a 307.2 kilohertz clock pulse. Using
a demultiplexer circuit, individual signals which were multiplexed
can be sampled. The host computer, supplied by the end user, must
have a user programmable serial port, such as an APPLE'~ II+, an
IBM'~PC, or a COMMOnORE'~ 64.
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The host computer lO serves as the data collection
nucleus of the I-peak system of the present invention. The host
computer 10 consists of two major components, a network interface
and a host I-peak software. The network interface interfaces the
host computer to the sampling units. This interface in the
preferred embodiment is a four wire full duplex interface
configured to operate with eight bits data, even parity bit, start
and stop bit and a transmission rate of 4800 bits per second. The
communications protocol for the network is implementad in software
such as that shown in Figure 11. The data received from the
sampling units is uncalibrated data and thus must be manipulated
to obtain a true wattage figure from the current voltage data.
This can be done in obvious ways.
During operation, the following sequence of events takes
place.
1. The host computer places an address on the serial line
which enables the sampling unit with the same address.
2. The host computer then issues a command to select which
current and voltage transducer are to be sampled.
3. The serial/parallel interface IC on the sampling unit
sends the command to the multiplex control section of the
board (see Figure 2).
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4. The multiplex control turns on the selected current and
voltage demultiplexer circuit.
5. The selected current signal is sent to the current peak
detector.
6. The current peak detector uses the sample timing control
circuit to activate the current and voltage A/D
converters when the current reaches its peak within a
cycle.
7. The A/D converters convert their input analog signals to
an eight bit digital signal and places the signal at the
inputs of the serial/parallel convertor.
8. The conversion process must last for 16.7 milliseconds to
ensure that a current peak has been attained.
9. The conversion duration is timed by the computer. At the
end of the delay, the host computer issues a second
command to the selected sampling unit.
10. This second command causes the serial/parallel interface
IC to convert the current and voltage da-ta to serial
format and send it to the host computer.
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11. When the serial data is sent to the host computer, the
sampling unit disables itself, so the host computer must
now issue another address to repeat the sampling
procedure using another transducer.
The system just described provldes an eight bit conversion of
voltage and current that may be usecl by the host computer to
calculate instantaneous power. If the customer required a higher
resolution (i.e. 16 bits), this cou]d be accomplished by changing
the A/D converters and modifying the software in the host computer
to accommodate the extra data transfers required.
With the scheme described above, 32 separate power sources
could be monitored by one sampling unit and 128 sampling units
could be monitored on one serial I/O port of the host computer.
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