BACKGROUND OF THE INVENTION
'I The present invention relates generally to meters, and more particularly
to a relay control circuit for controlling operation of relays used by an electric meter.
Electric meters are typically implemented with various relays that
perform different functions. For example, an electric meter may utilize a disconnect
relay that can remove electrical service from a customer that is attached to the meter.
Having the disconnect relay under the cover of an electric meter along with a two-way
communication device enables remote activation and deactivation of the relay, so that
the electric service can be reconnected and disconnected. Other relays that may be
utilized by an electric meter include ancillary relays that control specific loads (e.g., a
heater load, circuit breaker, etc.). All of the relays used by an electric meter are
generally controlled by a relay control circuit. There are various types of relay
control circuits that can be utilized by an electric meter having multiple relays. A
relay control circuit utilizing a single winding relay control scheme and a relay
control circuit utilizing a double winding relay control scheme are examples of some
control circuits that have been used with electric meters to control multiple relays.
However, these relay control circuits and their respective control schemes (i.e., a
single winding relay control scheme and a double winding relay control scheme) have
their respective drawbacks with respect to energy usage (i.e., the energy necessary to
operate the elements (e.g., switches and winding coils) associated with a particular
scheme) and the amount of these elements used in each scheme.
BRIEF DESCRIPTION OF THE INVENTION
In one aspect of the present invention, a circuit is provided. The circuit
comprises more than one relay coil each connected to a corresponding relay; a pair of
common control switches connected to each of the relay coils; and a plurality of relay
coil specific switch pairs, each relay coil specific switch pair connected to one of the
relay coils, wherein each relay coil specific switch pair is connected to one of the
relay coils at an end opposite a connection of the pair of common control switches
with each of the relay coils; wherein the pair of common control switches and the
plurality of relay coil specific switch pairs operate cooperatively to selectively open
and close the relay coils which selectively open and close a corresponding relay.
In another aspect of the present invention, a circuit is provided. In this
aspect of the present invention, the circuit comprises more than one relay coil each
connected to a corresponding relay; a pair of common control switches connected to
each of the relay coils, wherein the pair of common control switches connect to each
of the relay coils at a common end; a plurality of relay coil specific switch pairs, each
relay coil specific switch pair connected to one of the relay coils, wherein each relay
coil specific switch pair is connected to one of the relay coils at an end opposite a
connection of the pair of common control switches with each of the relay coils; and a
current limiting mechanism connected to the plurality of relay coil specific switch
pairs and the pair of common control switches.
In a third aspect of the present invention, a utility meter is provided. In this
aspect of the present invention, the utility .meter comprises more than one relay; a
relay control circuit configured to selectively open and close each of the relays, the
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relay control circuit comprising more than one relay coil each connected to a
corresponding relay, a pair of common control switches connected to each of the relay
coils, wherein the pair of common control switches connects to each of the relay coils
at a common end; and a plurality of relay coil specific switch pairs, each relay coil
specific switch pair connected to one of the relay coils, wherein each relay coil
specific switch pair is connected to one of the relay coils at an end opposite a
connection of the pair of common control switches with each of the relay coils; and a
microcontroller, operatively coupled to the relay control circuit, that is configured to
direct the relay control circuit to selectively open and close the relays.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram illustrating an electric meter according to one
embodiment of the present invention;
FIG. 2 is a schematic circuit diagram of a relay control circuit that may be
implemented in the electric meter depicted in FIG. 1 according to one embodiment of
the present invention;
FIG. 3 is a schematic circuit diagram of a relay control circuit that may be
implemented in the electric meter depicted in FIG. 1 according to a first alternative
embodiment;
FIG. 4 is a schematic circuit diagram of a relay control circuit that may be
implemented in the electric meter depicted in FIG. 1 according to a second alternative
embodiment;
FIG. 5 is a schematic circuit diagram of a relay control circuit that may be
implemented in the electric meter depicted in FIG. 1 according to a third alternative
embodiment;
FIG. 6 is a circuit implementation of the diagram illustrated in FIG. 3
according to one embodiment of the present invention; and
FIG. 7 is a circuit implementation of the diagram illustrated in FIG. 5
according to one embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Various embodiments of the present invention are directed to a relay
control circuit used with a utility meter such as an electric meter. In one embodiment,
the relay control circuit is a hybrid of a single winding relay control scheme and a
double winding relay control scheme. In one embodiment, the relay control circuit
comprises more than one relay coil each connected to a corresponding relay, a pair of
common control switches connected to one end of each of the relay coils, and a
plurality of relay coil specific pair switches. Each relay coil specific switch pair is
connected to the other end of the relay coils. The pair of common control switches
and the plurality of relay coil specific switch pairs operate cooperatively to selectively
open and close the relay coils, which selectively open and close a corresponding
relay. In one embodiment, the relay control circuit can have a current limiting
mechanism connected to the plurality of relay coil specific pair switches and common
control switches to avoid shoot through and protect the switches from permanent
damage. In one embodiment, the current limiting mechanism may include a resistor
network. In another embodiment, the current limiting mechanism may include a short
circuit protection logic circuit.
Technical effects of the various embodiments of the present invention
include an improved relay control circuit that has low costs associated with the energy
necessary to operate its elements in the circuit and low costs in the amount of these
elements used in the circuit. Additional technical effects include a relay control
circuit that performs with high reliability and immunity to noise. Other technical
effects include a relay control circuit that avoids unintentional "CLOSE operations
of a main disconnect relay, and thus obviating safety issues to utility customers.
FIG. 1 is a schematic diagram illustrating an electric meter 100 according
to one embodiment of the present invention. Although various embodiments of the
present invention are described with respect to use with an electric meter and an
electric utility service, the embodiments are not limited to use solely with these items.
Those skilled in the art will recognize that the various embodiments of the present
invention are suitable for use with other metering devices and utility services. A nonexhaustive
list of other metering devices where the various embodiments of the
present invention are suitable for use include gas, water and heat meters. Similarly, a
non-exhaustive list of other utility services where the various embodiments of the
present invention are suitable for use include gas, water and heat services.
As shown in FIG. 1, electric meter 100 includes a set of relays 105
controlled by a relay control circuit 110 and a microcontroller 115. In one
embodiment the set of relays 105 comprises three relays - a service disconnect relay
120, a first ancillary relay 125 and a second ancillary relay 130. Service disconnect
relay 120 enables reconnecting and disconnecting of the electrical service, while first
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ancillary relay 125 and second ancillary relay 130 are for controlling ancillary single
phase loads (e.g., a heated load, circuit breaker, etc.). In one embodiment, service
disconnect relay 120 includes three relays represented as 11. Each I1 relay is used for
connecting/disconnecting one of three phases (i.e., Phase A, Phase B and Phase C).
Although not shown in FIG. 1, the three I1 relays of service disconnect relay 120 are
mechanically connected to form a single relay. For each of the three I1 relays of
service disconnect relay 120, there is a line that connects to the electric service (i.e.,
lines 1, 3 and 5) and a line that connects to a load (i.e., lines 2, 4 and 6). In one
embodiment, first ancillary relay 125 is represented as I2 that connects to an ancillary
load via line 9 and second ancillary relay 130 represented as 13 that connects to an
ancillary load via line 10. FIG. 1 further shows that the set of relays 105 has two
neutral lines (e.g., lines 7 and 8); line 7 connects to the electric service and line 8
connects to the load. Operation of service disconnect relay 120, first ancillary relay
125 and second ancillary relay 130 is dictated by microcontroller 115. In particular,
microcontroller generates control signals representative of a certain operational action
for the relays that are put into effect by relay control circuit 1 10. Those skilled in the
art will recognize that the 11, I2 and I3 relays can be rated to have differing current
values depending on the particular application of each relay. In addition, those skilled
in the art will recognize that the 11, 12 and I3 relays can be all single phase or all
polyphase or a combination of single phase and polyphase depending on the particular
application of the relays.
Note that the implementation of the set of relays 105 in FIG. 1 is only
illustrative of one embodiment and is not meant to be limiting. Those skilled in the
art will recognize that the various embodiments of the present invention are suitable
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for controlling a varying amount of relay configurations. Generally, the various
embodiments of relay control circuit 110 are suitable for use with an electric meter
having more than one relay.
For the sake of simplicity in illustrating various embodiments of the present
invention, those skilled in the art will recognize that not all features and
functionalities associated with electric meter 100 are illustrated in FIG. 1. For
example, those skilled in the art will appreciate that electric meter 100 can have
specialized microprocessors (e.g., an application processor and a meter processor) that
can facilitate the measurement of different electrical services, detection of different
conditions, etc. In addition, electric meter 100 may have a liquid crystal display
(LCD) or other means to display various parameters. Other components that electric
meter 100 may include are memory for storing data and instructions, communication
interfaces, a power supply and various other switches.
FIG. 2 is a schematic circuit diagram of one embodiment of a relay control
circuit 200 that may be implemented in electric meter 100. As shown in FIG. 2, relay
control circuit 200 comprises winding relay coils L3, L4 and L5 that connect to a
corresponding relay (not shown in FIG. 2). A pair of common control switches
(Switch 1 and Switch 2) is connected to relay coils L3, L4 and L5. Control circuit
200 further includes relay coil specific switch pairs coupled to relay coils L3, L4 and
L5. In particular, Switch 3 and Switch 4 connect to relay coil L3, Switch 5 and
Switch 6 connect to relay coil L4, and Switch 7 and Switch 8 connect to relay coil L5.
As shown in FIG. 2, Switch 1, Switch 3, Switch 5 and Switch 7 are connected to a
voltage supply, while Switch 2, Switch 4, Switch 6 and Switch 8 are connected to
ground.
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In operation, common control switches, Switch 1 and Switch 2, operate in
conjunction with each pair of the relay coil specific switch pairs (i.e., Switch 3 and
Switch 4, Switch 5 and Switch 6, and Switch 7 and Switch 8) to selectively turn on
and off relay coils L3, L4 and L5, which control corresponding relays (not shown in
FIG. 2). In particular, common control switches, Switch 1 and Switch 2, and Switch 3
and Switch 4 turn on and off relay coil L3, which will control a corresponding relay
(not shown in FIG. 2); common control switches, Switch 1 and Switch 2, and Switch
5 and Switch 6 turn on and off relay coil L4, which will control corresponding a relay
(not shown in FIG. 2); and common control switches, Switch 1 and Switch 2, and
Switch 7 and Switch 8 turn on and off relay coil L5, which will control a
corresponding relay (not shown in FIG. 2).
In one embodiment, if one wanted to turn on (i.e. close) relay coil L3, then
Switch 1 and Switch 4 would be closed. On the other hand, if one wanted to turn off
(i.e. open) relay coil L3, then Switch 2 and Switch 3 would be closed. In another
embodiment, if one wanted to turn on relay coil L4, then Switch 1 and Switch 6
would be closed. If one wanted to turn off relay coil L4, then Switch 2 and Switch 5
would be closed. In another embodiment, if one wanted to turn on relay coil L5, then
Switch 1 and Switch 8 would be closed. If one wanted to turn off relay coil L5, then
Switch 2 and Switch 7 would be closed. Those skilled in the art will recognize that by
reversing the relay coil connection the logic can be changed. For example, by
connecting the relay coil L3 in reverse direction by controlling Switch 1 and Switch 4
the relay L3 can be turned off. Similarly, relay L3 can be turned ON by controlling
Switch 2 and Switch 3.
FIG. 3 is a schematic circuit diagram of a relay control circuit 300 that may
be implemented in electric meter 100 according to a first alternative embodiment. In
this embodiment, a current limit mechanism formed from a network of resistors Rl,
R2 and ~3 is used to avoid shoot through when two switches on the same leg (any
one of the pairs of switches (Switch 1 and Switch 2, Switch 3 and Switch 4, Switch 5
and Switch 6, and Switch 7 and Switch 8) are turned on, which can cause permanent
damage. For example, if it was desirable to open relay coil L3 (i.e., close Switch 2
and Switch 3) and close relay coil L4 (i.e., close Switch 1 and Switch 6), then Switch
1 and Switch 2 would get shorted. In another example, any external noise may cause
Switch 1 and Switch 2 to turn on simultaneously, which could cause permanent
damage as well. Another example in which two switches on a leg can short may
occur if microcontroller 115 inadvertently causes the switches to close. All of these
examples can result in physical damage due to the shorting of the switches.
The current limit mechanism provided by resistors R1, R2 and R3 provides
a passive approach to controlling the current through the switch pairs (Switch 1 and
Switch 2, Switch 3 and Switch 4, Switch 5 and Switch 6, and Switch 7 and Switch 8).
As shown in FIG. 3, resistor R2 is connected to the leg of switch pair formed from
Switch 5 and Switch 6, while resistor R3 is connected to the leg of switch pair formed
from Switch 7 and switch 8. In this embodiment, the switch pair formed from Switch
3 and Switch 4 does not have a resistor connected to that leg because the service
disconnect relay 120 needs a high current to control as compared to relays 125 and
130. As a result, the current rating of Switches 1, 2, 3, and 4 are higher than the
ratings of the other switches (i.e., Switches 5, 6, 7 and 8). Consequently, resistor R1
would be sufficient to protect Switches 1,2, 3 and 4, while protecting Switches 5,6,7
and 8 requires the use of additional resistors (i.e., R2 and R3) added to their legs.
In FIG. 3, resistor R1 is connected between the voltage supply and the node
formed from each of the pairs of switches (Switch 1 and Switch 2, Switch 3 and
Switch 4, Switch 5 and Switch 6, and Switch 7 and Switch 8). In this embodiment,
the function of resistor Rl is to fbrther limit the current flowing through the switches
(Switch 1, Switch 2, Switch 3, Switch 4, Switch 5, Switch 6, Switch 7 and Switch 8).
FIG. 4 is a schematic circuit diagram of a relay control circuit 400 that may
be implemented in the electric meter depicted in FIG. 1 according to a second
alternative embodiment. In this embodiment, a current limit mechanism is formed
from resistor R1 to serve the same function as described with respect to FIG. 3. In
this embodiment, the current limit mechanism formed from resistor R1 would be
suitable for use in scenarios where the relays were all similar current relays, or in
scenarios where the rating of the switches (Switch 1, Switch 2, Switch 3, Switch 4,
Switch 5, Switch 6, Switch 7 and Switch 8) were all the same.
FIG. 5 is schematic circuit diagram of a relay control circuit 500 that may
be implemented in electric meter 100 according to a third alternative embodiment. In
this embodiment, instead of using a current limit mechanism formed from a resistor
network of R1, R2 and R3, .or solely resistor R1, the current limit mechanism is
formed from short circuit protection logic 505, which provides an active approach to
limiting the current going to the switches (Switch 1, Switch 2, Switch 3, Switch 4,
Switch 5, Switch 6, Switch 7 and Switch 8). As shown in FIG. 5, short circuit
protection logic 505 is coupled to relay control circuit 500. In one embodiment, short
circuit protection logic 505 may include the use of a logic gate such as a NAND gate,
1 I
resistors, and capacitors to introduce a delay in controlling the switches. In operation,
the resistors and capacitors introduce a delay that is used to control Switches 1, 2, 3,
4,5,6,7, and 8 between the signal generated from microcontroller 1 15 (FIG. 1) to the
switches. Consequently, if any unintentional operation of Switch 1 and Switch 2
happens simultaneously, then before turning on these switches, short circuit protection
logic 505 will turn off an internal switch (e.g., 46 of FIG. 7) which will protect
Switches 1,2,3,4,5,6,7, and 8 from permanent damage. * FIG. 6 is a circuit implementation of relay control circuit 300 according to
one embodiment of the present invention. In this embodiment, each of the switches
(Switch 1, Switch 2, Switch 3, Switch 4, Switch 5, Switch 6, Switch 7 and Switch 8)
is implemented by using metal-oxide-semiconductor field-effect transistors
(MOSFETs) and Bipolar Junction Transistors (BJTs). As shown in FIG. 6, MOSFET
42, MOSFET 414, MOSFET 43, MOSFET Q15, BJT 44, BJT Q16, BJT Q5, and
BJT 417, correspond to Switch 1, Switch 2, Switch 3, Switch 4, Switch 5, Switch 6,
Switch 7 and Switch 8, respectively. In addition, each of the switches (Switch 1,
Switch 2, Switch 3, Switch 4, Switch 5, Switch 6, Switch 7 and Switch 8) has a switch
0 control 600 that controls the opening and closing of their respective switches. As an
example, if one desired to close Switch 8, then its respective switch control 600 would
turn on BJT Q17 in response to having the voltage supply (e.g., 3.3 volts) turn it on
after BJT 413 received a low input. On the other hand, if one desired to open switch
8, then its respective switch control 600 would turn off BJT 417 by not having the
voltage supply (e.g., 3.3 volts) (and BJT 413 receiving a high input). The operation
of the other switches (Switch 1, Switch 2, Switch 3, Switch 4, Switch 5, Switch 6, and
Switch 7) would work in a similar manner and, thus further explanation is not
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provided. Depending on how the switches are controlled, their outputs are sent to
relay coils L3, L4 and L5 via connection lines 605.
FIG. 7 is a circuit implementation of relay control circuit 500 according to
one embodiment of the present invention. In FIG. 7, each of the switches (Switch 1,
Switch 2, Switch 3, Switch 4, Switch 5, Switch 6, Switch 7 and Switch 8) is
implemented by using BJTs. As shown in FIG. 7, BJT Q8, BJT 420, BJT Q9,
BJTQ21, BJT Q10, BJT 422, BJT Ql 1, and BJT 423, correspond to Switch 1,
Switch 2, Switch 3, Switch 4, Switch 5, Switch 6, Switch 7 and Switch 8,
respectively. In addition, each of the switches (Switch 1, Switch 2, Switch 3, Switch
4, Switch 5, Switch 6, Switch 7 and Switch 8) has a switch control 700 that controls
the opening and closing of their respective switches for operation of relay coils L3, L4
and L5 via connection lines 705. In this embodiment, a current limit mechanism that
includes short circuit protection logic 505 is coupled to relay control circuit 500. For
sake of simplicity in illustrating the concept of this embodiment, the connection of
short circuit protection logic 505 to relay control circuit 500 is not shown, however
this is within the knowledge of skilled artisans.
In operation, the resistors and capacitors introduce a delay that is used to
control Switches 1, 2, 3, 4, 5, 6, 7, and 8 between the signal generated from
microcontroller 115 (FIG. 1) to the switches. Consequently, if any unintentional
operation of Switch 1 and Switch 2 happens simultaneously, then before turning on
these switches, short circuit protection logic 505 will turn off an internal switch 46
which will protect Switches 1, 2, 3, 4, 5, 6, 7, and 8 from permanent damage. The
operation of the other switches (Switch 1, Switch 2, Switch 3, Switch 4, Switch 5,
Switch 6, and Switch 7) in conjunction with short circuit protection logic 505 would
work in a similar manner and thus further explanation is not provided.
While the disclosure has been particularly shown and described in
conjunction with a preferred embodiment thereof, it will be appreciated that variations
and modifications will occur to those skilled in the art. Therefore, it is to be
understood that the appended claims are intended to cover all such modifications and
changes as fall within the true spirit of the disclosure.

WE CLAIM:
1. A circuit (1 1 O), comprising:
more than one relay coil each connected to a corresponding relay (120, 125 or
130);
a pair of common control switches connected to each of the relay coils; and
a plurality of relay coil specific switch pairs, each relay coil specific switch
pair connected to one of the relay coils, wherein each relay coil specific switch pair is
connected to one of the relay coils at an end opposite a connection of the pair of
common control switches with each of the relay coils; wherein the pair of common
control switches and the plurality of relay coil specific switch pairs operate
cooperatively to selectively open and close the relay coils which selectively open and
close a corresponding relay (120, 125 or 130).
2. The circuit (1 10) according to claim 1, wherein the more than one
relay coil comprises three relay coils.
3. A circuit (1 1 O), comprising:
more than one relay coil each connected to a corresponding relay (120, 125 or
130);
a pair of common control switches connected to each of the relay coils,
wherein the pair of common control switches connect to each of the relay coils at a
common end;
a plurality of relay coil specific switch pairs, each relay coil specific switch
pair connected to one of the &lay coils, wherein each relay coil specific switch pair is
connected to one of the relay coils at an end opposite a connection of the pair of
common control switches with each of the relay coils; and
a current limiting mechanism connected to the plurality of relay coil specific
switch pairs and the pair of common control switches.
4. The circuit (1 10) according to claim 3, wherein the pair of common
control switches and the plurality of relay coil specific switch pairs operate
cooperatively to selectively open and close the relay coils which selectively open and
close a corresponding relay (120, 125 or 130).
5. The circuit (1 10) according to claim 3, wherein the more than one
relay coil comprises one of a three-phase service disconnect relay coil, a first singlephase
load control relay coil, and a second single-phase load control relay coil.
6. The circuit (1 10) according to claim 3, wherein the current limiting
mechanism comprises a resistor network.
7. The circuit (1 10) according to claim 3, wherein the current limiting
mechanism comprises a resistor.
8. The circuit (1 10) according to claim 3, wherein the current limiting
mechanism comprises short circuit protection logic (505).
9. A utility meter (loo), comprising:
more than one relay (120, 125 or 130);
a relay control circuit (1 10) configured to selectively open and close each of
the relays (120, 125 or 130), the relay control circuit (1 10) comprising more than one
relay coil each connected to a corresponding relay (120, 125 or 130), a pair of
common control switches connected to each of the relay coils, wherein the pair of
common control switches connects to each of the relay coils at a common end; and a
plurality of relay coil specific switch pairs, each relay coil specific switch pair
connected to one of the relay coils, wherein each relay coil specific switch pair is
connected to one of the relay coils at an end opposite a connection of the pair of
common control switches with each of the relay coils; and
a microcontroller (1 15), operatively coupled to the relay control circuit (1 lo),
that is configured to direct the relay control circuit (1 10) to selectively open and close
the relays (120, 125 or 130).
10. The utility meter (100) according to claim 9, wherein the utility meter
comprise an electric meter.
Dakd w -th"
MANISHA S I N ~ HNA IR
Agent for the Applicant [IN/PA- 7401
LEX ORBIS
Intellectual Property Practice
70917 10, Tolstoy House,
15- 17, Tolstoy Marg,
New Delhi- 1 1000 1