Note: Descriptions are shown in the official language in which they were submitted.
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POWER SUPPLY
This invention relates to an apparatus for supplying electrical
power to a number of separate outlets.
BACKGROUND OF THE INVENTION
In colder regions of the globe electrical devices are used to heat
automobile engines and interiors to facilitate engine starting and user
comfort. Energy costs and conservation efforts have led to the widespread
use of parking lot controls.
These controls are designed to reduce energy consumption
while still satisfying engine starting and user comfort constraints. Numerous
algorithms have been devised to limit this consumption, ranging from simple
timers to the most current proportional temperature controls (the colder it
gets the more power is delivered).
Current parking lot controls are centralized, whereby all the
loads of a parking lot are switched together on or off by a central contactor.
Many inherent restrictions and limitations are imposed by this form of
centralized control. Central contactor controls carry substantial installation
and maintenance costs, with typical installation pay back periods in the
order of five years or more. The longevity of mechanical contactors depend
heavily on regular maintenance adding to operational costs.
Many lots impose a limit on power use for each vehicle. But
since no adequate means of enforcement exists, it is left open to abuse.
Often enough users abuse the set limits to trip the main breaker for a lot,
inconveniencing all patrons. In addition, individual parking stall breakers are
tripped due to temporary short circuits, overloads, etc. Since no feedback
as to the presence of power is provided for users or maintenance personnel,
this stall maybe without power for several days.
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SUMMARY OF THE INVENTION
It is one object of the present invention to provide an improved
device for supplying power to a number of electrical outlets.
According to one aspect of the invention there is provided an
5 apparatus for supplying electrical power to a plurality of electrical outlets
comprising a central power supply, a plurality of outlet receptacles each for
mounting at a respective one of a plurality of separate positions for
supplying electrical power to a plurality of separate electrical loads, electrical
wiring for communicating current from the central power supply to the
10 receptacles in parallel, each receptacle having an outer casing and at least
one electrical outlet socket mounted thereon for receiving a connector plug
of a respective one of the electrical loads and means for controlling a supply
of current from the central power supply to the electrical outlet sockets of
the outlet receptacles connected thereto comprising a plurality of control
15 elements, each mounted in a respective one of the receptacles and each
associated with at least one of the electrical outlets of the respective
receptacle; each control element comprisin~: a reprogrammable
microprocessor; communicating means for communicatin~ with the
microprocessor from the exterior of the respective receptacle; switch means
20 operable by the microprocessor for selectively supplying power from the
central power supply to said at least one electrical outlet; detector means
responsive to the insertion of a connector plug connected to one of said
electrical loads into the respective outlet socket; and comparison means
actuated by said detector means for comparing a current drawn by the load
25 with a predetermined maximum allowable current and for only allowing
supply to the outlet in response to a current less than said predetermined
maximum.
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According to a second aspect of the invention there is provided
an apparatus for supplying electrical power to a plurality of electrical outletscomprising a central power supply, a plurality of outlet receptacles each for
mounting at a respective one of a plurality of separate positions for
5 supplyin~ electrical power to a plurality of separate electrical loads, electrical
wiring for communicating current from the central power supply to the
receptacles in parallel, each receptacle having an outer casing and at least
one electrical outlet socket mounted thereon for receiving a connector plug
of a respective one of the electrical loads and means for controlling a supply
10 of current from the central power supply to the electrical outlet sockets of
the outlet receptacles connected thereto comprising a plurality of control
elements, each mounted in a respective one of the receptacles and each
associated with at least one of the electrical outlets of the respective
receptacle; each control element comprising: a reprogrammable
15 microprocessor; switch means operable by the microprocessor for
selectively supplyin~ power from the central power supply to said at least
one electrical outlet; detector means responsive to the insertion of a
connector plug connected to one of said electrical loads into the respective
outlet socket; comparison means actuated by said detector means for
20 comparing a current drawn by the load with a predetermined maximum
allowable current and for only allowing supply to the outlet in response to a
current less than said predetermined maximum and means for pro~ramming
said microprocessor to vary said predetermined maximum allowable current.
According to a third aspect of the invention there is provided
25 an apparatus for supplying electrical power to a plurality of electrical outlets
comprising a central power supply, a plurality of outlet receptacles each for
mounting at a respective one of a plurality of separate positions for
supplyin~ electrical power to a plurality of separate electrical loads, electrical
2 1 1 57 1 0
wiring for communicating current from the central power supply to the
receptacles in parallel, each receptacle having an outer casing and at least
one electrical outlet socket mounted thereon for receiving a connector plug
of a respective one of the electrical loads and means for controlling a supply
of current from the central power supply to the electrical outlet sockets of
the outlet receptacles connected thereto comprising a plurality of control
elements, each mounted in a respective one of the receptacles and each
associated with at least one of the electrical outlets of the respective
receptacle; each control element comprising: a repro~rammable
microprocessor; switch means operable by the microprocessor for
selectively supplying power from the central power supply to said at least
one electrical outlet; detector means responsive to the insertion of a
connector plug connected to one of said electrical loads into the respective
outlet socket, said detector means being arranged to detect a point in time
of insertion of a connector plug carrying a load and to communicate said
point in time to said microprocessor; and comparison means actuated by
said detector means for comparing a current drawn by the load with a
predetermined maximum allowable current and for only allowing supply to
the outlet in response to a current less than said predetermined maximum.
One particular area of potential use of present invention is to
provide an improved apparatus for controlling and monitoring electrical
automobile heating loads for the purpose of energy conservation.
Redistributing control of parking lot electrical loads to each parking stall hasmajor advantages over centralized control schemes. Capital costs of
implementation are drastically reduced to pay back periods in the order of
one year. This is due in part to the elimination of the central high current
contactors and their associated wiring. Other gains are realized through
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better demand management control, energy conservation algorithms and
user service as well as lower maintenance costs.
By fittin~q each outlet box (which controls two stalls) of a
parking lot with a reprogram able microcontroller greater flexibility is
5 realized. This increases the diversity of possible energy conservation
algorithms that can be implemented. Helping management staff to meet
patron requirements, maximize energy conservation and meet ever
increasing budgetary constraints. Further, conservation algorithms can be
updated, customized, or changed as new techniques become available since
10 the device is reprogrammable. Apparatus for the measurement of
temperature or wind-chill is also provided enabling the most current
conservation algorithms to be implemented.
One novel feature included is the ability to detect each load as
it is asserted or removed. This enables the device to delay delivery of
15 power to a newly asserted load for sometime. Reasonin~q that the vehicle
has just arrived, it is still warm and should be for sometime. The length of
this delay could be a fixed amount of time or calculated based on current
temperature, wind-chill, etc. This feature may also assist local utilities with
peak power demand management. Peak demand periods occur between 8
20 and 9 a.m., when people arrive at work and again 5 to 6 p.m., when people
return home. The burden of these automobile heating loads maybe averted
during these times with this new technique.
By includin~q apparatus for sensing current being delivered to
each load another dimension in control is added. This enables the effective
25 enforcement of power consumption limits for each vehicle, assisting in local
demand power management. Maintenance costs are reduced and user
service is increased by the detection of overloads or short circuits. Enabling
these loads to be switched "off" before the associated breaker can trip.
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Added safety is provided by helping to prevent faulty loads from starting
fires or damaging property. This apparatus enables the use of economical
solid-state contactors for delivering power to attached loads, reducing
maintenance costs and boosting reliability.
Feedback to patrons is provided by visual or auditory
apparatus. In the case of visual feedback two light emitting diodes (LED's)
are provided, one green the other red for each stall. As an example, when a
user asserts a load the presence of power is identified by a quick flash of
the green LED (load within acceptable limits) or the red LED is lit solidly
(overload is rejected). For auditory feedback different tones identify load
acceptance or rejection and the presence of power.
A bi-directional infrared data communication interface is
included increasing utility. From time to time general maintenance of
parking lots are performed requiring power tools. To facilitate this whole
parking lots are disabled with centralized controls. While with the present
invention only required individual outlets need be disabled. With this data
link operational modes and limits can be easily set and changed. Since this
link is bi-directional the device can be used to collect operational data to be
down loaded periodically at request. Providing management and
maintenance with such diverse information as frequency of use, number of
overloads and short circuits seen, amount of power delivered, temperature
trends, etc. This information may then be used to help design better energy
conservation algorithms and maintenance schedules.
An interface is provided to allow the microcontrollers program
or firmware to be changed, making it field programmable. This increases
the useful life and reduces manufacture costs. Useful life is increased by
the fact the energy conservation al~orithms can be kept up to date and
customized to a particular application. Manufacturing costs are reduced by
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having to produce only one generic model and by reprogramming the
devices with self test and calibration routines, manufacture costs are further
reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
One embodiment of the invention will now be described in
conjunction with the accompanyin~ drawings in which:
Figure 1: Overall Block Diagram of Circuit
Figure 2: Infrared Communication and programminy Interface
Figure 3: "Hot" Power Supply Circuitry
Figure 4: Current Sense Apparatus
Figure 5: solid-state Contactor Circuitry
Figure 6: Temperature or wind-chill Measurement Circuitry
Figure 7 is a schematic illustration of a control system for
supplying electrical power to a plurality of electrical outlets in a parking lot.
Figure 8 is a diagram showing the operation of the current
sense apparatus of Figure 4.
DETAILED DESCRIPTION
In Fi~ure 7 is shown an overview of the whole system which
includes a main power supply 69 for supplying electrical power to a plurality
of outlets 71, most of which are shown only schematically but one of which
indicated at 72 is shown in an exploded isometric view. The electrical
power is supplied through wirin~ 73 which is again shown only
schematically without distinguishing between the hot, neutral or ground
wires.
The main power supply comprises basically only a main breaker
and possibly a number of subsidiary breakers to a number of different
circuits depending upon the number of outlets to be supplied.
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It is a conventional practice to provide the outlet as paired
outlets with each pair within a separate receptacle mounted at a spaced
position around the car park to be supplied. The one outlet illustrated in
detail therefore comprises a metal box or receptacle 74 which is mounted on
5 a suitable support for example of wooden post, fencing or the like. The
receptacle 74 has an open front face which can receive a rectangular
extension box module 75 which in turn carries a standard duplex outlet 81
and cover plate 82. The extension box module is fastened in place by a
conventional screw arrangement 85 which connects with screw holes
10 supplied on the receptacle 74. The standard outlet 71 is fastened to the
receptacle 74 through holes provided by the extension box module 75 in a
standard arrangement by screws 83. The standard cover plate 82 is
fastened by screws 85 and/or 84. A suitable gasket or other sealing
arrangement can be provided to prevent moisture penetration but this is not
15 illustrated as it is well known to one skilled in the art.
The extension box module 75 contains a control unit 80 which
enables the independent control of each outlet of an attached duplex outlet
81. A conventional electrical terminal arrangement is provided on the rear
face of the extension box module 75 so as to be insertable into the
20 receptacle 74 for electrical supply connection, protection, and containment
thereby. Wires are provided within the open front face of the extension box
module 75 so as to enable the standard connection of a standard duplex
outlet 81.
The control of the power supply to each outlet is effected by
25 the control unit 80 contained within the extension box module 75, without
the necessity for any central control intelligence. In this way the system
can be implemented into existing receptacles and wiring simply by inserting
the extension box module 75 between the conventional outlet 81 cover
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plate 82 and the supply receptacle 74. This allows installation at a relatively
inexpensive price. In addition individual programming of the outlets can be
provided .
On the side facing forward of the extension box module is also
5 shown a first LED 76, 79 which is green for indicating normal or proper
operation of the power supply after application of a load. A second LED
indicated at 77, 78 is red and this is used to indicate an unacceptable load
as described hereinafter. Further ports 20 and 21 are provided for bi-
directional communication as again described hereinafter.
An overall block diagram of the circuit is shown in Figure 1.
The "Hot" power supply 1 supplies all the required power for normal
operation of the device. Communication and reprogramming features are
supplied by the infrared communications and reprogramming interface 2.
The system operation clock for the microcontroller 5 is provided by the CPU
15 clock circuitry 3. The microcontroller 5 controls both outlets of a dual outlet
receptacle through the outlet interfaces 4 and 6. Each outlet interface is
identical in construction composed of solid-state contactor circuits (7 and
10), a standard outlet where electrical loads may be attached (8 and 11)
and current sense apparatus (9 and 12). The temperature/wind-chill
20 measurement apparatus 13 enables the microcontroller 5 to measure the
ambient temperature or wind-chill. To~ether these circuits provide a novel
and particularly useful function for the purpose of energy conservation.
The bi-directional infrared communication and reprogramming
interface is shown in Figure 2. This figure shows one possible
25 communications link to the external world via an infrared data link. The
infrared data link is similar to those found in televisions and VCR recorders
with the exception that this is bi-directional. Points 14 and 15 are
connected to two separate l/O ports of the microcontroller. The l/O port
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connected to point 14 controls the infrared emitting diode 21 through
resistor 16, transistor 22 and resistor 23. This circuit allows the device to
communicate with maintenance personnel via infrared light. The l/O port
connected to point 15 is always configured as an input. Configuration and
5 control information is passed to the device through the infrared detector
circuitry 20 (such as Sharp model IS1U60 infrared receiver), resistor 19 and
point 15 to the l/O port. With this infrared link maintenance personnel can
communicate configuration, control, and retrieve collected information. It is
through this interface that most data will be communicated. One other
10 interface is provided via the five pin connector 24. This interface is
primarily used to reprogram the microcontroller for entirely different energy
conservation algorithms or applications. Connector 24 interfaces with the
microcontroller through Vpp (the programming voltage pin of the
microcontroller), Vdd (the plus power supply to the microcontroller), Vss
15 (the ground or return supply to the microcontroller), I/O ports connected to
points 14 and 15 via resistors 17 and 18 respectively. Other
communication methods are also suitable such as power line carrier
technologies .
The "Hot" power supply circuitry is shown in Figure 3. This
20 circuit provides all the necessary power needed for normal operation of the
device. The word "Hot" is to imply that the circuit derives the energy
required directly from the AC power line without using a transformer. The
Neutral line is connected directly to the plus Vdd supply of the circuit.
Current is "pumped" into the power supply on the negative slope of the Hot
25 terminal with respect to the Neutral terminal through diode 30. The positive
slope current is returned to the AC supply through diode 29. The AC supply
current is limited by resistors 25, 26 and capacitor 28. Resistors 25 and
26 are relatively small in value and are used to limit the surge current
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2 1 1 57 1 0
through capacitor 28. In the event of AC power being removed resistor 27
discharges any residual charge left on capacitor 28 as a safety precaution.
This pump current charges capacitors 31 and 33 through diode 30 for
capacitor 31 and diode 30 and resistor 32 for capacitor 33. The negative
5 trigger supply voltage l-VT) is supplied by the charge across capacitor 31.
Resistor 32 and capacitor 33 form a low pass filter reducing voltage ripple
across capacitor 33. The charge voltage on capacitor 33 is supplied to the
voltage regulator circuit made of resistor 35, transistor 37, zener diode 36
and resistor 34. The combination of the zener diode 36 and the base-
10 emitter junction of the transistor 37 sets the voltage between the Vdd andVss (or ground) terminals. This value is specified by the zener diode 36 plus
0.7 volts for the base-emitter junction of transistor 37. The voltage on
capacitor 33 must be ~reater than this re~ulation value with the remaining
voltage dropped across resistor 34 in order to activate the regulator. The
15 collector terminal of transistor 37 provides a reset signal for the
microcontroller throu~h diode 38 and across resistor 39. If the voltage
across capacitor 33 is insufficient to drive the regulation circuitry transistor37 is off. Hence, no current will flow through transistor 37, diode 38 and
resistor 39. No, voltage will be dropped across resistor 39 and the voltage
20 at the reset terminal will be low holding the microcontroller in reset. This
ensures that the microcontroller will be in a predefined state even during
brown-out conditions of the AC power line. The reset pin of the
microcontroller doubles as the programming supply voltage (VPP) pin. VPP is
typically much greater than VDD with respect to VSS, hence diode 38 is
25 provided to block this programming voltage from interfering with the
regulation circuitry. This voltage is supplied from the interface connector 24
of Figure 2.
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The Current Sense Apparatus is shown in Figure 4. Current
transformer 40 provides a current proportional to the current delivered to
the load. By placing a resistive burden 41 across the current transformer
output terminals the proportional current signal is converted to a
5 proportional voltage signal. This sense voltage is processed by a window
comparator 43 and voltage divider network 42. The window comparator
provides a digital output which is either "low" or "high" depending if the
load current sensed is "over" or "under" a set current limit respectively.
The operation of the window comparator is illustrated in Figure
10 8 where the set current is indicated at C. As explained hereinafter, the
microprocessor has an input providing information on power line zero
crossings as indicated at Z so that it has information on the point T1 as
shown. The window comparator therefore provides state changes at points
T-2 and T-3 which occur at the times where the sensed current becomes
15 ~reater than the set current and subsequently at T-3 becomes less than the
set current.
The set current limit detected by the window comparator is
determined by the voltage divider network 42. The window comparator
output is connected to one of the microcontrollers digital input/output ports.
20 The set current limit should be chosen to be the smallest peak load current
required to be detected for an application. Then by simply timing the
window comparators output "low" pulse-width, currents over the set
current limit can be measured with good resolution. This gives ~reater
flexibility to the device by allowin~ overcurrents for an application to be set
25 within software and not hardware. The comparison of the current supplied
with a predetermined current is thus effected for each half cycle. The
measurement of the current is effected by detecting the differences in time
between events T1 and T2 or between the events T2 and T3. It will be
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appreciated that for larger currents the time period between T1 and T2 will
be reduced while the time period between events T2 and T3 will be
increased. The microprocessor thus detects one or both of these time
periods and compares this with a software table giving a calculation of the
5 actual current drawn in relation to variations in the time periods. The
microprocessor can then be programmed with the required predetermined
maximum current. This predetermined maximum current can thus be set in
software and can be readily varied by the communication system described
herein before. For example, therefore, the predetermined maximum current
10 can be set at a current which will provide power to only an engine block
heater so that any additional current drawn above this amount will trigger
the microprocessor to disconnect supply as described hereinafter. If
required for custom application, the predetermined maximum current can be
increased to allow one or more outlets within the parking lot to allow an
15 increased current for example to drive an interior vehicle warmer.
Temporarily the microprocessor can be programmed to yet further increase
the maximum allowable current for example for power tools and the like.
In the event that an overcurrent is detected, the microprocessor
determines the degree of overcurrent. In the event that the overcurrent is
20 very large indicating a short circuit, the microprocessor disconnects supply
and prevents reconnection of supply until the load is disconnected and a
new "load applied". It is of course possible for the load to go short circuit
duriny operation and accordin~ly it is necessary to detect this possibility and
then to prevent any further connection which would otherwise cause
25 damage to the control unit.
In the event that the overcurrent is beyond the predetermined
maximum but less than that indicative of a short circuit, the microprocessor
is arranged to continue to supply power for a predetermined number of
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further detection cycles to ensure that the overcurrent is not simply a
resultant for example a switching within the load which only temporarily
provides an overcurrent.
The window comparator 43 output is of the open collector
5 type. This enables the l/O Port to become an output to drive the red
indicator LED 45 through resistor 44, transistor 46, and resistor 47,
providing a means of visual feedback to users and maintenance personnel.
This current sensing apparatus enables the device to enforce
load limitations on users, prevent short circuits or overloads from tripping
10 breakers, use economical solid-state contactors and helps to increase user
safety.
Other methods for measuring current are also suitable such as
the use of an Analog to Digital converter (ADC). This method simplifies the
needed software but increases hardware costs. The rnethod presented is
15 meant to describe only one possible method of very many, which is
apparent to one skilled in the art.
The solid-state contactor and load detection circuitry is shown
in Figure 5. Solid-state contactor 48 provides the means to deliver power to
attached loads 59. The snubber network 49 prevents false triggering of the
20 solid state contactor when in the presence of inductive loads. While resistor 55 prevents false triggering due to static discharge, etc. Voltage zero
crossings of the power line are provided in di~ital form at point 51 to an
input/output port of the microcontroller. Resistor 50 is used in conjunction
with the protection diodes of the microcontrollers l/O port to shape this
25 analog signal into a digital one. This information is used to derive a real
time clock and determine when the contactor should be triggered. To
achieve radio frequency interference free power delivery the contactor
should be triggered "on" at power line zero crossings only.
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Point 57 is used to detect if loads are attached. In order to
determine this, the contactor must be in the "off" or high impedance state.
If no load is attached the voltage at point 57 will follow the value of the
"Hot" terminal throu~h snubber network 49 and resistor 56 and is clamped
5 to a di~ital signal by the l/O port protection diodes. Otherwise, if a load isattached the voltage at point 57 is tied to neutral through the attached load
59, current sense apparatus 61 and resistor 56. Then by monitoring point
57, if its level remains unchanged throughout the course of a full cycle of
the power line a load is attached, otherwise no load is connected.
The microcontroller triggers the solid- state contactor 48
through the l/O port connected to point 52. When a "low" output pulse is
applied to point 52 the triac 48 will enter its low impedance state or turn
"onn. This trigger current is supplied to the triac 48 through resistor 53,
transistor 54, green LED 58 and resistor 60 to the negative trigger supply
15 voltage (-VT). Durin~ this trigger pulse the green LED 58 will be lit providing
visual feedback to the user. The user will therefore see on inserting the
connector plug and applyin~ the load a flash of the green LED also shown in
Figure 7 (76, 79).
The detection of the allowable current as described above is
20 effected each half cycle and the triggering of the contactors is effected on
each zero crossin~ to maintain control over the power supply.
Solid state contactors can be damaged by excessive currents
such as those associated with short circuits. It is most probable that a load
if short circuit will be short circuit when it is first applied to the system. As
25 explained above, therefore, the microprocessor is arranged to detect the
presence of a new load by continually monitorin~ the presence or absence
of a load. In the event that a detected absence of a load is followed by a
detected presence of a load, the microprocessor is arranged to firstly
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provide a test of that load to determine whether it is short circuit. This is
effected by triggering the contactor instead of at a zero crossing at a
position close to the next zero crossing at which time it will shut off. The
amount of current thus supplied to the load is controlled in that the volta~e
5 at the point of triggering is relatively low in comparison with the peak
voltage. The resulting load current is then monitored by the current sense
apparatus of Figure 4, to ensure that the current sense apparatus does not
detect a current over the set current limit. If a current over the set limit is
detected despite the reduced voltage, the attached load is deemed to be a
10 short circuit. The microprocessor is arranged to ensure that the contactor
will not be triggered again until this load is removed and a new load is
asserted. By following this simple load qualification scheme solid-state
contactors are used reliably.
The load detection feature can also be used to increase power
15 conservation by the fact we know when a new load is attached. Reasoning
that the vehicle has just arrived, it is still warm and should be for sometime.
We can then delay the delivery of power to this new load for sometime.
The amount of wait time can be determined by the current temperature,
wind-chill, etc. This feature is also beneficial to local utilities in managing
20 peak demand periods.
The temperature or wind-chill measurement circuitry is shown
in Figure 6. Points 62, 63 and 64 are connected to separate l/O ports of the
microcontroller. Resistor 65 is a negative thermal coefficient (NTC) resistor
or thermistor Iresistance rises with a decrease in temperature). Resistor 66
25 is a calibration resistor with a low tolerance value say one percent. Resistor
67 is used to discharge the capacitor 68. Operation of the circuit is as
follows. First, I/O ports 62 and 63 are configured to be inputs and l/O port
64 is confi~ure to be an output. Placing a logic "O" on point 64 discharges
21 1571~
the capacitor 68 through resistor 67. After the capacitor is totally
discharged l/0 port 64 is flipped to be an input. Next, I/0 port 63 is
changed to an output with a logic "1" value. This starts to charge the
capacitor 68 through resistor 66, the calibration resistor. During this
5 charging the microcontroller counts in a tight loop while monitoring the inputlevel at point 64. When the level at this point turns to a logic "1" counting
is stopped and this value is saved. A~ain, the capacitor is discharged by the
method described earlier. Then again l/0 port 64 configured as an input and
l/0 port 62 is now configured as an output with a logic " 1". The
10 microcontroller now starts counting again until the charge on the capacitor
68 registers a logic "1" at point 64. Now, the count derived from resistor
65is divided by the calibration count from resistor 66 and multiplied by the
value of the calibration resistor. The result is the thermistor 65 resistance
value which is directly related to temperature. Hence, the temperature is
15 measured. To measure wind-chill the thermistor is place near a heat source.
The algorithm by which the microprocessor controls the power
supply is open to very many possibilities so that a detailed description will
not be provided here. It will be appreciated however that the
microprocessor can be programmed to accommodate new power saving
20 schemes or to tailor the control system to the particular requirements of a
particular customer.
However one important control function which generates
significant power savings is that of providing a duty cycle so that power is
supplied to each individual outlet only over a portion of a cycle time. In
25 many arrangements of this type, power is supplied for periods only of one
third of each cycle thus reducing the total power usage to one third of that
which would be otherwise required. This proportion can of course be varied
in dependence upon temperatures as measured including reducing the
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portion to zero above a predetermined maximum temperature. In many
arrangements, the system is only concerned with total power usa~e so that
it is not important whether all of the units supply power simultaneously or
whether they are arranged at different portions of the cycle time.
However some systems require a reduction in the maximum
demand since some utilities utilize this factor in calculating power usage
rates. If it is desired therefore to reduce the maximum demand, it is of
course desirable that, of all the outlets in the system only a portion of them
are supplying power at any one time durin~ the cycle. In a one third duty
cycle, therefore, it will be desirable to arrange the outlet so that only one
third are applyin~ power during a first part of the duty cycle, a second third
supply power during a second part of the cycle and a third portion supply
power during a third part of the cycle. As the control units are in effect
independent and not controlled by the central control unit, it is necessary
therefore to supply a scheme by which this can be achieved. In a first
alternative arrangement, therefore, the individual control elements are
programmed with that part of the cycle within which they are allowed to
supply power. All of the units are then initialized at an initial time by
detecting an initial power-up of the system. The units are then generally
maintained in synchronism by the cycles of the power supply. However,
"brown-outs" can interfere with this synchronism and therefore it is
desirable to re-initialize the control elements on a re~ular basis.
In an alternative scheme, there is no attempt to synchronize the
control elements and instead the control elements supply power to a portion
of the cycle with that cycle commencin~q at the time of first application of
the load. As the application of the load is effectively a random event, as the
control units utilize the same cycle time, the commencement of the cycles
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for each of the units will remain random so that the location of the portion
of time within that cycle time will itself be random.
Since various modifications can be made in my invention as
herein above described, and many apparently widely different embodiments
5 of same made within the spirit and scope of the claims without departing
from such spirit and scope, it is intended that all matter contained in the
accompanying specification shall be interpreted as illustrative only and not in
a limiting sense.
