Note: Descriptions are shown in the official language in which they were submitted.
WO 91/023~0 2 Q ~ 0 4 2 2 P~/US90/038~;
~JNIV~R8A~ lU~l,OG INPTJ'r
BACKGROUND OF T~E INVENTION
The present invention generally relates to an
input interface circuit and more particularly to a
universal analog input circuit which converts various
types of analog information to analog information of a
given type which can be read by an input channel.
There are many control systems which act upon
information obtained at points remote from the control
systems. Such information is generally obtained from
remote sensors which provide information relative to the
condition sensed in analog form.
One such system is a facility management
system. Such systems are used to control the internal
environment of, for example, an office building or plant
facility. Internal room temperature, humidity, air flow
lighting and security are among some of the conditions
controlled and/or monitored by such systems. These
systems provide this kind of control largely in response
to information obtained from remote sensors which are
connected by multiple wires back to the control systems.
2Q 5uch multiple wires are necessary to both convey the
information relative to the condition sensed back to the
control system and to enable the control system to
provide power to those remote sensors which require
external power. Because many different types of
conditions are controlled by such systems, many different
types of remote sensors are required.
Since many different types of remote sensors
are required, and even though the information conveyed
to the facility management system normally, in each case,
takes the form of analog information, analog information
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WO9l/02300 PCT/US90/03875
2 ~ ~ of many different types may ~e provided by the remote
sensors. For example, a temperature sensor may provide
an indication of the temperature sensed in the form of
a resistance parameter. Other remote sensors may provide
a voltage magnitude indicating the conditions sensed,
and still other remote sensors may provide a current
magnitude indicative of the conditions sensed.
The control portion of facility management
systems usually includes a plurality of input channels
for receiving the analog information from the remote
sensors. In the prior art, each input channel is hard
wired configured to read only one type of analog
information. As a result, an input channel may be
capable of reading only a resistance parameter, another
input channel may be capable of reading only a voltage
magnitude, and another channel may be capable of reading
only a current magnitude.
Because the number of input channels in such
systems is limited, facility management systems of the
prior art have lacked flexibility because each input
channel of such systems has been capable of being
connected to only one type of remote sensor. This lack
of flexibility can limit both the overall system
configuration and, more importantly, the capability of
such a system to adequately control all of the conditions
which are necessary to control.
SUMMARY OF THE INVENTION
The invention provides a control system input
arranged to respond to a plurality of different types of
analog input information received from remote sensors.
The system input includes an input channel adapted to
read a given type of analog information, terminal means
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wog1/02300 2 0 ~ O ~ 2 2 PCTfUS90/03~75
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adapted for connecting a remote sensor to the system, and
interface means disposed between the terminal means and
the input channel. ThP interface means are selectively
operable for converting the type of analog in~ormation
provided by the remote sensor to the given type of analog
information.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure l is a block diagram of a control system
embodying the present invention.
Figure 2 is a schematic circuit diagram of a
universal analog input embodying the present invention
and which may be utilized to advantage in the control
system of Figure l.
Figure 3 is a chart identifying the circuit
jumper posltions and screw terminals used to configure
the universal analog input of Figure 2 for various
different types of remote sensors which may be connected
to the system utilizing the universal analog input.
Figures 4 through l0 are equivalent circuit
diagrams of the various input circuit configurations
which may be obtained by the selection of the circuit `
jumper positions and screw terminals identified in Figure
3 for the dif~erent types of remote sensors which may be
connected to the control system.
.
DESCRIPTION OF THE PREFERRED EMBODIMENT
. ~ ,
Referring now to Figure l, it illustrates a
control System l0 embodying the present invention and,
more particularlyr a facility management system embodying
the present invention. The system lO generally includes
- a main communication bus 12, which may be an Nl LAN -
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WO91/02300 PCT/US90/0387~
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ARCNET bus, a network control module 14, a digital
control module 16, and another bus 18, which may be an
N2 OP~OMUX bus, interconnecting the network control
module 14 to the digital control module 16. LAN ARCNET
and OPTOMUX busses 12 and 18 respectively are of a type
well knows in the art.
As illustrated in Figure 1, the system
thereshown includes just one network control module and
digital control module for exemplary purposes only, and
it should be understood that additiona:L network control
modules with associated digital control modules may be
connected to the main communication bus 12 in a practical
system. This type of control system is referred to as
a distributed system wherein each network control moclule
is on a par with all other network control modules and
communicates with all other network control modules on
the bùs 12.
The main function of the network control module
is to communicate with other network control modules of
the system on an equal basis and to control its associate
digital control module under its own assigned software
protocol. Such a protocol may include setting
temperature control setpoints, heating schedules,
lighting schedules, etc. The network control module, in
accordance with its protocol, sends high level commands
to the digital control module which then executes on
those commands by performing closed-loop operations by
issuing suitable control signals at its outputs
responsive to sensed input conditions by its remote
sensors.
The control signals issued by the digital
control module can be both in digital or analog form.
A digital control signal can be used to activate relays
to in turn activate fan motor starter windings or to turn
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WO9l/0230~ 2 0 4 ~ ~ 22 PCT/US90~03~7s
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on heaters. An analog control signal can be used to
power a damper motor to set a damper at a desired
position. Hence, the digital control module performs
decision making processes, gathers information from its
remote sensors, digitizes the information, and executes
control functions to satisfy the high level commands of
the network control module.
The digital control module ]L6 thus processes
digital information for performing various different
types of closed-loop control operations within the
system. To that end, the digital control module 16 may
include ten output channels identified as OCHl through
OCH10. The outputs OC~l through OC~10 provide the
control signals to control the various different types
of control elements of the systems, such as relays or
damper motors, to provide the desired control of the
internal environment of, for example, an office building.
As previously mentioned, relays controlled by the outputs
of the digital control module 16 may, for example, turn
on or off fan motors to establish desired air flow or
heaters to establish desired room temperatures. Damper
motors controlled by the digital control~module }6 may
:; be utilized to set a damper to also control air flow such
as return air flow within a heating system.
In order to provide closed-loop control, the
digital control module 16 may include ten input channels
designated CHl through CH10. These input channels
receive various different kinds of information from
remote sensors within the system, which remote sensors
provide analog input information of various types
indicative of the conditions being sensed by the remote
sensors. Since the information provided by the remote
sensors is in the form of analog information, the input
channels CHl through CH10 are arranged to read analog
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WO91/02300 PCT/US90/~3875
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input information. The analog information readable by
each of the input channels i5 of a given type of analog
information, and, in accordance with this preferred
embodiment, is a voltage which may be applied across the
inputs of a differential amplifier such as, for example,
a differential voltage or a singlle-ended voltage
referenced to a fixed potential.
As previously mentioned, various types of
remote sensors may be required within a ~aciIity
management system. Because various types of remote
sensors may be required, the analog information provided
by the remote sensors may be of various different types
of analog information. For example, a temperature sensor
may take the form of a temperature dependent resistance
so that the temperature sensor provides a resistance
having a magnitude which is indicative of the temperature
being sensed. Other types of remote sensors may provide
analog information of the condition being sensed in the
form of voltage magnitudes or current magnitudes carried
through a two wire current loop. As a result, the
universal analog input of the ~present invention
interfaces the remote sensors with the digital' control
module to convert the various different types of analog
information provided by the remote sensors to the given
type of analog information readable by the input channels
C~1 through CH10 of the digital control module. In
accordance with this preferred embodiment, the gi~en
analog information is a voltage which is applied across
the inputs of a differential amplifier. This voltage can
be, for example, a differential voltage or a single-ended
voltage referenced to system ground or to a digital
control module power supply voltage.
To that end, the control system lO of Figure
1 is illustrated as including a remote sensor 20 which
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wo 91/02300 2 0 4 0 4 2 2 PCT/US90/03875
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is coupled to the first input channel (CHl) of the
digital control module by an input interfase embodying
the present invention which includes a terminal block 22
and a universal analo~ input circuit (IAU) 24.
Similarly, another remote sensor 26 is shown coupled to
the tenth input channel (CH10) by an :Ldentical terminal
block 22 and an identical universal anialog input circuit
24.
The terminal blocks 22 provide terminal mea~s
adapted for connecting the remote sensors to the control
system. The universal analog input circuits 24 provide
interface means disposed between the terminal blocks and
the input channels. The universal analog input circuits,
as will be more fully described hereinafter, are
selectively operable for converting the type of analog
information provided by their associated remote sensors
to the given type of analog information readable by their
associated input channels.
Since the digital control module includes ten
output channels, it may perform up to ten separate
closed-loop control operations, each having a unique
input and output. one such closed-loop control operation
is illustrated in Figure l in connection with the tenth
output channel (CH10). Output channel OCHlO is coupled
to an output functional module 30. The output functional
module 30 may be of many different types, and! for
purposes of this description, will be assumed to be a
relay. The output functional module 30 is coupled to a
heater 32 through a terminal block 34. When the relay
of the output functional module 30 closes, the heater 32
is turned on for heating an internal space such as a room
of a building. The temperature of the room may be sensed
by the remote sensor 26 which provides analog information
in the form of a resistance having a magnitude indicative
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WO91/02300 PCT/US~0/03875
2 ~ 2 2 -8- ~
of the temperature being sensed. The resistan~e analog
information provided by the remot~ sensor 26 is coupled
to the tenth input channel (C~10) by the terminal block
22 and the universal analog input circuit 24 as
previously mentioned. The temperature infoxma~ion from
the remote sensor 26 is converted from a resistance
magnitude to the given type of analog information, such
as a differential voltage by the input interface formed
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by the terminal block 22 and the universal analog input
circuit 24. When the differential voltage read at the
tenth input channel (CHlO) indicates that the room being
heated by the heater 32 is at the desired temperature
indictated by the high level command of the network
control module, the digital control module 16, through
output channel OCHl0, will open the relay of the output
functional module 30 to turn off the heater 32. When the
room temperature falls below the desired temperature,
that condition is sensed by the remote sensor 26, is
converted to a differential voltage by the input
interface comprising terminal block 22 and the universal
analog input circuit 24 to a differential voltage, which
then causes the digital control module to close the relay
- contacts of the output functional modulé 30 by-its output
channel OCHlO. The foregoing closed-loop process
continues until it is interrupted by either an operator
manually placing the output function module 30 into a
manual mode, or by a command from the network control
- module 14 to the digital control module 16 through the
bus 18. Such a command may be initiated under software
control of the system. Such a software command may be
desirable, for example, when the heat provided to
portions of an office building is to be turned off at
night or over weekends.
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Wosl/o23oo 2 ~ L104 2 2 PCT/US90/0387~
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Referring now to Figure 2, it illustrates a
control system input or input interface 40 embodying the
present invention. The input interface illustrated in
Figure 2 is arranged for interfacing a single remote
sensor with a single input channel of thQ digital control
module 16. If all ten input channels of the digital
control module are coupled to a remote se!nsor, each input
channel would be associated with an input interface 40
as illustrated in Figure 2.
The input interface 40 generally includes a
terminal block 22 and a universal analog input circuit
24. The terminal block 22 includes six screw terminals,
screw terminal 1 through screw terminal 6. As
illustrated, screw terminals 1, 2, 4, and 5 are available
for connection to a remote sensor. Screw terminals 3 and
6 are not utilized and therefore are connected to ground
potential. However, where noisy electrical environmental
conditions exist, screw terminals 3 and 6 may be utilized
for connecting the shields of shielded cables to ground.
Each of the other screw terminals, screw
terminals 1, 2, 4, and 5 is coupled to one of the inputs
42, 44, 46, and 48 of the universal analog input circuit
24. More specifically, screw terminal 1 is-coupled to
input 42, screw terminal 2 is coupled to input 44, screw
terminal 4 is coupled to input 46, and screw terminal 5
is coupled to input 48. The four screw terminals enable
any of the remote sensors to be utilized within the
system to be coupled to the system. Screw terminals 1
and 2 are utilized for receiving the analog information
from the remote sensors. Screw terminals 4 and 5 are
utilized for providing power to a remote sensor when
required. The power at screw terminal 4 is provided by
a current limited voltage source 50 within the digital
control module 16 which is coupled to the screw terminal
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WO91~02300 PCT/US90/03875
2~0422 -lO-
4 through the universal analog inpu~ circuit 24. Screw
terminal 5 is utilized for the power supply return from
screw terminal 4. Screw terminal 5 may also be utilized
for connecting a remote sensor to a constant current
source. The constant current available at screw terminal
5 is provided by a constant current source 52 within the
digital control module 16 which is coupled to the screw
terminal 5 through the universal analog input circuit 24
when required.
The universal analog input circuit 24 also
includes four outputs, 62, 64, 66, and 68 which are
coupled to corresponding inputs 82, 84, ~6, and 88 of the
digital control module 16. The inputs 82, 84, 86, and
88 of the digital control module comprise one input
channel of the digital control module 16.
. The digital control module 16, in addition to
the current limited voltage source 50 and the constant
current source 52, includes a differential amplifier 54.
. The differential amplifier 54 includes a positive input
56 and a negative input 58. The differential amplifier
. 54 along with input resistors 51, 53, 55, and 57 enable
. the reading of the given type of analog information, such
. as a differential voltage or a single-ended voltage in
a conventional manner.
The universal analog input circuit 24 includes
internal circuitry which, through two sets of circuit
jumpers 70 and 90 provides selectable circuit
configurations for converting any one of the various
types of analog input infor~ation from the remote sensors
to a differential voltage readable by the input channel
of the digital control module 16. The first set of
circuit jumpers 70 includes circuit jumpers Sl, S2, and
S3. The second set of circuit jumpers 90 includes
circuit jumpers S4, S5, S6, and S7. Each circuit jumper
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Wogl/0230~ 2 0 ~ O ~ 2 2 PCT/US9O/03875
is illustrated as including a pair of terminals. In
actual practice, the pair of terminals of each circuit
jumper are preferably aligned so that a conductive
shorting pin may be inserted into the center of each
s terminal pair for shorting the terminal pair together and
selecting a particular circuit jumper. As can be noted
from Figure 2, the terminals o~ circuit jumper S1 are not
coupled to any other portion of the universal analog
input circuitry. This circuit jumper is utilized when
neither circuit jumper S2 .or S3 is required, thus
providing a convenient storage place for the shorting pin
when it is not actually used.
Except for circuit jumper Sl, each of the First
terminals of the circuit jumpers is coupled to one of the
inputs of the universal analog input circult 24 through
a fuse. More specifically, the first terminal 7:L of
circuit jumper S2 is coupled to the input 46 of the
universal analog input circuit 24 by a fuse 100. The
first terminal 73 of circuit jumper S3 is coupled to the
input 42 by a ~use 102. The first terminal 91 o~ jumper
S4 is coupled to input 48 through a fuse 104 and the
first terminals 93, 95, and 97 of circuit jumpers S5, S6,
and S7 respectively are coupled to input 44 through a
fuse 106. The fuses lO0, 102, 104, and 106 are provided
to protect the digital control module circuitry from
possible excessive current or voltage conditions which
may result due to a defective remote sensor coupled to
the terminal block 22.
To comp}ete the description of the circuit
jumper connections, the second terminal 72 of circuit
jumper S2 is coupled to the first terminal 73 of circuit
jumper S3 and to the input 56 of the differential
amplifier 54 through the resistor 51. The second
- terminal 74 of circuit jumper S3 is coupled to a resistor
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WO~I/02300 Pcr/US90/0387
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25 which in tuxn is coupled to the input 58 of the
differential amplifier 54 through a resistor 55. The
common node of resistors 25 and 55 are also coupled to
the input 44 of the Universal analog input circuit 24 and
to the first terminals 93, 95, and 97 of circuit jumpers
S5, S6, and S7 respectively. The function of resistor
25 will be described in more detail hereinafter.
With respect to the second set gO of circuit
jumpers, the second terminal 92 of circuit jumper S4 and
the second terminal.94 of circuit jumper S5 are coupled
to the constant current source 52 within the digital
control module 16. The second terminal 96 of circuit
jumper S6 is coupled to a negative voltage power supply
at terminal 59 which is external to the universal analog
input circuit 24. Lastly, the second terminal 98 of
circult jumper S7 is coupled to system ground external
to the universal analog input circuit 24 as illustrated.
By virtue of the circuitry just described with
respect to the universal analog input circuit 24,
different circuit configurations of the universal analog
input circuit can be selected by the proper selection of
the circuit jumpers and screw terminals on the terminal
block 22 to connect any one of the various types of
remote sensors which may be utilized in the system to the
input channel of the digital control module 16 so that
the information provided by the remote sensor can ~e read
by the input channel of the digital control module.
Figure 3 identifies the proper circuit jumper and screw
terminal selections for seven different types of remote
sensors which may be utilized in the system.
Referring now to Figure 3, it can be seen that
for a 2-wire resistance temperature device, circuit
jumpers S2 and S5 are used along with screw terminals 1
and 2 of the terminal block 22. For a 4-wire resistance
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WOgl/02300 2 0 ~ O ~ 2 2 PCT/US90/03875
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temperature device, circuit jumpers Sl and S4 are
selected along with screw terminals }, 2, 4, and 5. Each
of the resistance temperature dependant devices provide
analog information in the form of a resistance magnitude.
The 4-wire device requires four wires as will be seen
herein after to provide a more accurate determination of
the resistance than in the case of the 2-wire resistance
temperature dependant device. In both cases, the
selection of the circuit jumpers and screw terminals
identified in Figure 3 configure the terminal block 22
and the universal analog input circuit 24 for converting
the resistance magnitudes to a differential voltage to
permit the input channel of the digital control module
to read the resistance analog information providecl by
these remo~e sensors.
As can also be noted in Figure 3, when the
remote sensor provides a voltage magnitude of 0 to 10
volts to be read by the input channel of the digital
control module, circuit jumpers Sl and S7 are used along
with screw terminals 1, 2, and 4. This selection of
circuit jumpers and screw terminals configure the
terminal block 22 and universal analog input circuit 24
for applying the voltage magnitude as-a single-ended
voltage across the inputs of the differential amplifier
54.
When a remote sensor comprises a potentiometer
from which it is necessary to read the resistance setting
of the potentiometer, circuit jumpers Sl and S7 are used
along with screw terminals l, 2, and 4. As will be seen
hereinafter with respect to the equivalent circuit of
Figure 7, when this combination of circuit jumpers and
screw terminals are used, the setting of a potentiometer,
- which is a resistance, can be converted to a single ended
voltage and applied across the inputs of differential
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WO91/02300 PCT/US90/03875
2040422 -14-
amplifier 54 to thus be read by the input channel of the
digital control module 16.
When a remote sensor takes the form of a 3-
wire transducer of the type providing an output voltage
up to ten volts, circuit jumpers Sl and s6 are used along
with screw terminals 1, 2, and 4. With this selection
of circuit jumpers and scraw terminals, a supply voltage
of twenty-five volts is supplied to the transducer by
screw terminals 4 and 2. The output voltage of the
transducer is made available at screw terminal I with
respect to screw terminal 2 to provide a single-ended
voltage referenced to the negative supply voltage and is
applied across the inputs of differential amplifier 54.
When a remote transducer is configured as a
true 2-wire current loop device, which thus provides its
analog information in the form of a current magnitude,
circuit jumpers ~3 and 56 are used along with screw
terminals 1 and 4. For this configuration both power and
signal are available on the same two wires by supplying
twenty-five volts to the transducer through resistor 25.
The transducer modulates its output resistance and
therefore modulates the current on the current loop.
This is read as a-voltage drop (differential voltage)
across resistor 25.
Lastly, when a remote sensor is self-p`owered
and is configured as a remote current loop, circuit
jumpers S3 and S4 are selected along with screw terminals
1 and 2. For both current loop type remote sensors, the
circuit jumper selections place resistor 25 across the
input 58 and input 56 of the differential amplifier 54
for converting:the current magnitude provided by the
remote sensors to a differential voltage. For a 2-wire
current loop, screw terminal 4 is used to provide power
to the remote sensor. Screw terminal 4 is not used for
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WOg~/02300 2 0 4 0 ~ 2 2 PCTtUS90/03875
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the remote current loop sensor since this type of sensor
is selfpowered. ~;
Referring now to the equivalent circuit
diagrams of Figures ~ through 10, Figure 4 illustra~es
the equivalent circuit diagram of the t:erminal block 22 ;
and universal analog input circuit 24 when the remote
sensor is a 2-wire resistance temperature dependent
device. That remote sensor is illustrated as a variable
resistance 110. Also, for purposes of simplification,
the resistors 51, 53, 55, and 57 along with the specific
circuitry of the current limited voltage source 50 have
been omitted from the equivalent circuit diagrams.
Referring again to Figure 4, the 2-wire
resistance temperature device is illustrated as a
variable resistor 110. With the selection of circuit
~umpers S2 and S5 along with the screw terminals 1 and
2, it can be seen that one side of the variable
resistance is connected to the positive input
di~ferential amplifier 54 through screw terminal 1 and
the fuse 102. Also with the selection of circuit jumper
S2, the resistor 110 is coupled to the positive voltage
source 50 of the digital control module. With the
; selection of circuit jumper S5 and screw terminal 2, the
iother end of resistor 110 is coupled to the negative
input 58 of the differential amplifier 54 through the
fuse 106 and to the constant current source 52 through
the circuit jumper S5. As a result of the ~oregoing, a
constant current is provided to the resistor 110 so that
any change in its resistance will result in a
proportionate change in the differential voltage applied
across inputs 56 and 58 of the differential amplifier 54.
The circuit configuration of Figure 4 can also
be used to sense binary contacts. When such contacts are
closed, the resistance will be low and when the contacts
WO9l/02300 PCT/US90/03875
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are open, the resistancP will be high. The difference
in resistance values will provide either a low or high
differential vsltage across inputs 56 and S8 of
differential amplifier 54 for reading the corresponding
contact conditions. With this approach, very good noise
immunity is obtained due to the differential (balanced)
nature of the system.
Referring now to Figure 5~ it illustrates the
equivalent circuit of the terminal b:Lack 22 and the
universal analog input circuit 24 when t:he remote sensor
is a 4-wire resistance temperature dependant device and
when circuit jumpers S1 and S4 are selected along with
screw terminals 1, 2, 4, and 5. This remote sensor is
represented as a variable resistor 112. It will be noted
that this remote sensor is coupled to the terminal block
22 using four wires. One wire connects the first end of
resistor 112 to the current limited voltage source 50 of
the digital control module 16 through screw terminal 4
and fuse 100. The first end of the resistor 112 is also
coupled to the positive input 56 of di~ferential
amplifier 54 through screw terminal 1 and fuse 102. The
second end of the resistor 112 is coupled to the negative
input 58 of the differential amplifier 54 through screw
- terminal 2 and fuse 106. Lastly, the second:end of
resistor 112 is coupled to the constant current source
52 through screw terminal 5, fuse 104, and circuit jumper
S4. As will be noted in this configuration, separate
wires are utilized to connect the resistor 112 to the
voltage source 50 and the constant current source 52.
As a result, a constant current is provided to the
resistor 112 and any variation in its resistance will
result in an accurate variation in the differential
voltage applied across the inputs 56 and 58 of the
differential amplifier 54. This accuracy is due to the
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Wo91/~2300 2 0 ~ 0 4 2 2 PCT~US90/0387~
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fact that the current passing through the resistor 112
i5 converted to a voltage that is not affected by the
resistance of the input sense lines including fuses 102
and 1~6.
Figure 6 illustrates the equivalent circuit
when the remote sensor is the type which requires
external power and which provides a voltage magnitude of
up to en volts indicative of the condition being sensed.
In this case, the selection of screw terminal 4 connects
the remote sensor 114 to the current limited voltage
source 50 through the screw terminal 4 and fuse 100. The
voltage output of the remote sensor 114 is coupled across
screw terminals 1 and 2 with the positive side thereof
being coupled to screw terminal 1 and the negative side
to screw terminal 2. The positive side is coupled to the
positive input 56 of the differential amplifier 54
through screw terminal 1 and fuse 102. The negative side
of the remote sensor is coupled to the negative input 58
of the differential amplifier 54 through screw terminal
2 and fuse 106. Lastly, with the selection of circuit
jumper S7, the negative side of the remote sensor 114 is
also coupled to system ground. By connecting the
- negative side,of the remote sensor 14 to system ground
through circuit jumper S7, the power circuit to the
remote sensor 114 is completed. The negative input of
the differential amplifier is not actually connected
directly to ground by virtue of the resistor 55 not shown
in Figure 6. As a result of the circuit configuration
illustrated in Figure 6, the voltage magnitude provided
by the remote sensor 14 is applied as a single-ended
voltage to the inputs of the differential amplifier 54
to be read by the input channel of the digital control
- module 16 while power for powering the remote sensor is
,also provided.
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WO91/02300 PCT/US90/03875
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Referring now to Figure 7, it illustrates the
equivalent circuit which results when circuit ~umpers Sl
and S7 are selected along with screw terminals 1, 2, and
4 for connecting a potentiometer to the con~rol system. ;
Here, the potentiometer has been provided with reference
character 116.
As will be noted in Figllre 7, the first end of
the potentiometer is coupled to the current limited .
voltage source 50 of the digital control module 16
through screw terminal 4 and fuse lO0~ The opposite end
of the potentiometer 116 is coupled to system ground
through screw terminal 2, fuse 106, and circuit jumper
S7. The opposite end of the potentiometer is also
coupled to the negative input 58 of the differential
amplifier 54 through screw terminal 2 and ~use 106.
Lastly, the wiper 116a of the potentiometer is coupled
to the positive input 56 of the differential amplifier
54 through screw terminal 1 and fuse }02. As can be seen
from the foregoing, the current limited voltage source
provides a voltage across the potentiometer 116 and the
voltage between the wiper 116a and ground is read across
the inputs of the differential amplifier 54. As a
: . result, the resistance setting~of the potentiometer 116 ~ ~
. may be determined by the digital control module 16. ..
Referring now to Figure 8, it illustrates the
equivalent circuit when circuit jumpers Sl and S6 are
used along with screw terminals 1, 2, and 4 for
connecting a 3-wire transducer which provides an output
voltage of up to twenty-five volts to the control system.
The 3-wire transducer is identified by reference
character 118. As illustrated, such transducers require
the application of external power. To that end, the
transducer 118 is connected to the current limited
voltage power supply 50 of the digital oontrol module 16
.
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WO 91/02300 2 ~ ~ 0 4 2 2 PCT/US90/03875
-19- : ' '
through screw terminal 4 and fuse 100. The positive side
of the voltage output of the transducer is coupled to the
positive input 56 of the dif~erential amplifier 54
through screw terminal 1 and fuse 102. The negative side
of the transducer is coupled to the negative input 58 of
the differential amplifier 54 through screw terminal 2
and fuse 106 and to the external minus power supply
through circuit jumper S6. The connection of the ?
negative side of the tr~nsducer to the minus power supply
59 through circuit ~umper S6 completes the power circuit
to the transducer and scales the voltage output to a
range readable by the input channel. Again, input 58 of
the differential amplifier 54 is not connected directly
to the minus power supply by virtue of the resistor 55
not shown in the equivalent circuit of Figure 8. As can
be seen, this combination of circuit jumpers and screw
terminals enables the 3-wire transducer to be powered and
the voltage magnitude output of the transducer to be
applied across and read at the differential inputs of the
differential amplifier 54. The transducer output voltage
is referenced to the system negative supply voltage.
Referring now to Figure 9, it illustrates the
equivalent circuit obtained when circuit jumpers S3 and
S6 are selected along with screw terminals 1 and 4 for
connecting a remote sensor to the control system which
provides an output current magnitude indicative of the
condition being sensed and which also requires power that
is also delivered from screw terminals 1 and 4. The
remote sensor 120 is coupled across screw terminals 4 and
1. Screw terminal 4 is coupled to the current limited
voltage source 50 of the digital control module 16
through fuse 100. With the selection of circuit jumper
S3, the resistor 25 is placed across the differential .
inputs 56 and 58 of the differential amplifier 54. Also ~
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WOgl/02300 PCT/US90/03875
2 0 40 ~2 -20-
screw terminal 1 is coupled to the resistor 25 throuyh
the circuit jumper S3. The other side of the resistor
2s is coupled to the negative voltage source 59 through
circuit jumper S6. As can be noted from Figure 9, this
circuit configuration provides power to the remote sensor
120 by coupling it to the current limited voltage source
50 and directs the current magnitude output of the remote
sensor 120 through the resistor 25 which is placed across
the inputs of the differential amplifier 54. As a result,
the current magnitude provided by the remote sensor lZo
is converted to a differential voltage which can be read
across the inputs 56 and 58 of the differential amplifier
54 of the digital control module 16.
Lastly,'referring to Figure 10, it illustrates
the e~uivalent circuit which is obtained when circuit
jumpers S3 and S4 are selected along with screw terminals
1 and 2 for connecting a selfpowered remote sensor to the
system which provides a current magnitude indicative of
the condition being sensed. The remote sensor is
. indicated at reference character 122. As will be noted,
-~the remote sensor 122 is coupled across screw terminals
1 and 2 of the terminal block 22. With the selection of
circuit jumper S3, the resistor 25 is again'`placed across
the differential inputs S6 and 58 of'the differential
amplifier 54. Screw terminal 1 is also coupled to
Fesistor 25 through circuit Jumper S3 and the fuse 102.
With the selection of circuit jumper S4, screw terminal
2 is coupled to the junction of resistor 25 and negative
. input 58 through the fuse 104. As can be thus noted from
the equivalent circuit, the current magnitude provided
by the remcte sensor 122 is directed through the resistor
25 which is coupled across the inputs 56 and 5~ of the
differential amplifier 54 by the selection of circuit
jumper S3...As a result, the current magnitude provided
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WO91/0~00 2 ~ ~ 0 4 2 2 PCT/US90/03875
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by the remote sensor 122 is converted by resistor 25 to
a differential voltage which is then read by the
differential amplifier 54 of the digital control module
16.
From the foregoing, it can be appreciated that
the present invention provides a new and improved control
system input for adapting an input channel of a control
system to read various different types of analog
information even though the input channel is configured
for reading a given type of analog information, such as
a voltage applied across the inputs of a differential
amplifier. This is accomplished by the present invention
by converting the analog information provided by each
remote sensor to a voltage applied across the inputs of
a differential amplifier, whether the remote sensor
provides a resistance, a voltage magnitude, or a current
magnitude indicative of the condition which it senses.
In addition, the interface circuit o~ the universal
analog input circuit may be readily selected by an
operator through the selection of circuit jumpers and
screw terminals of the terminal block coupled to the
universal analog input circuit. As a result, the control
system results which has maximum flexibility and which
can accommodate many different types of conditions to be
controlled.
While a particular embodiment of the invention
has been shown and described, modifications may be made,
and it is intended in the appended claims to cover all
such modifications as may fall within the true spirit and
scope of the invention.
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