Note: Descriptions are shown in the official language in which they were submitted.
1~173~6
- 1 -
"Improvements in or relating to fuel burner control
systems"
. _ .
The invention relates to a fuel burner control
system capable of controlling the supply of air and
fuel to a burner, and to a combustion process contro-
system lncluding such a fuel burner control system.
The quantity of air and fuel supplied to a fuel
burner should be controlled in such a manner that the
fuel is burned completely without having a significant
quantity of excess air. The supply of too little air
results in incomplete combustion and the waste of fuel
whilst the supply of too much air results in the
absorption of some heat by the excess air. For
efficient combustion the ratio of the quantity of the
fuel supplied to the burner to the quantity of air
supplied to the burner should be constant at a value
which provides just enough oxygen for complete combustion
to take place. However, because of the behaviour of the
fuel and the air flowing through the respective control
valves, the ratio of the extent of opening of the fuel
valve to the extent of opening of the air valve to provide
a constant fuel : air ratio is not constant over the
heat supply range of the burner.
Known burner control systems employ mechanically
linked air and fuel supply valves and suffer from the
disadvantage that they are capable of achieving
.
- 2 - 13 17 3~6
efficient combustion of fuel over a small part only
of the burner heat supply range.
It is an object of the present invention to
provide a burner control system capable of improved
performance compared to existing burner control
systems.
13173~6
20648-136~
In accordance with the present invention, there is
provided a control system for a fuel burner, the system comprising
a fuel supply control valve, an air supply control valve, a memory
for holding values of air valve and fuel valve settings~ a
processor connected as part of the control system, means for
manually setting the system selectively, through the processor, to
a commissioning mode or a run mode, manual means for operator
control, through the processor, in the commissioning mode~ of at
least one of the valves in order to effect operator selection of
the settings for that valve, and means for effectlng, through the
processor, in the commissioning mode, the entry into the memory of
a respective comblnation of the settings of the fuel and air
supply valves for each of a plurality of values of an input signal
representing a first variable, the processor being operable, in
the run mode, to provide, from the memory, respective air and fuel
valve settings according to the value of the input signal
representing the first variable, which settings are used to
control the valves.
The valve settlng values are preferably derived from
operator selection of the settlngs of one of the valves and
operator derivatlon of the settings of the other of the valves.
The present invention also provides a fuel burner
control system including a memory for holding values of air valve
and fuel valve settings, a processor connected as part of the
control system, means for manually setting the system selectively,
through the processor, to a commissioning mode or a run mode, and
manual means for operator control, through the processor in the
13173~6
20648-1364
commissioning mode, to effect the generation of output values for
setting a fuel valve and an air valve and the entry, into the
memory, of selected settings for the fuel valve and corresponding
settings for the air valve for each of a plurality of values of an
input signal representing a first variable, the processor being
operable, in the run mode, to provide, from the memory, respective
air and fuel valve settings according to the value of the input
signal representing the first variable.
Preferably, the processor is capable of determining a
setting value for one valve for each value of the first variable,
and is arranged to select increasing setting values for the valve
with increasing values of the first variable over a limited range
of values of the first variable, and outside the limited range, to
select a fixed setting value for the valve.
Preferably, the fixed value setting is the maximum
setting avallable for the valve, when the valve is the fuel valve.
Preferably, the lower llmlt of the limited range
corresponds to the START condition for the system.
Preferably, the limited range of values of the first
variable lies between five and twenty percent of the possible
range of the first variable.
Preferably, the processor includes means for ad~usting
the limits of the limited range of values of the first variable.
Preferably, the control system includes data as to the
number of valve settings the memory is intended to accommodate and
is capable of operating in a run mode only when all the air and
fuel valve settings are present
13~73~
20648-136
in the memory.
Preferably, the memory holds data as to the open and
shut positions of the valves.
Preferably, the first variable is the difference between
second and third variables, and, preferably, the second and third
variables are the actual and desired operating temperatures,
respectively, of a medium arranged to be heated by a burner
controllable by the control system.
Preferably, the control system includes display means
and is capable of displaying the second and third variables
alternately on common display elements.
Arrangements of the control system for a fuel burner,
referred to above, may, of course, be included in boiler
installations.
According to another aspect, the present invention
provldes a method of commisslonlng and running a control system
for a fuel burner, the system comprising a fuel supply control
valve, an air supply control valve, a memory for holding values of
valve settlngs, and a processor, the method comprising the steps
of manually setting the system, through the processor, to a
commissioning mode, operating the burner, selecting a respective
combination of air valve settlng and fuel valve setting for each
of a plurallty of values of an input signal representing a first
variable, where the setting of at least one valve ls effected
manually through the processor, and entering the selected
combinations into the memory, manually setting the ~ystem, through
the processor, to a run mode, operating the burner and providing
13173a6
2064~-1364
an input signal to the processor representing a first variable,
which results in the processor obtaining from the memory a
respective value of fuel value setting and a respective value of
air valve setting according to the value of the input signal
representing the first variable, and setting the fuel valve and
the air valve according to the settings obtained from the memory.
5a
~317356
-- 6
A control system for a fuel burner in accordance
with the present invention and a combustion process
control system including the burner control system will
now be described by way of example only and with reference
to the accompanying drawings, in which :-
Fig. 1 is a schematic representation of a com-
bustion process control system arranged as
the central unit of an electrical system
capable of controlling a boiler,
Fig. 2 is a block schematic representation of the
combustion process control system of Fig.
1 ,
Fig. 3 is an illustration of a control panel of the
combustion process control system of Fig. 1,
Fig. 4 is a flow chart representation of the opera-
tion of the combustion process control system
of Figs. 1 and 2,
Fig. S is a graphical representation of the rela-
tionship between the fuel valve setting and,
(i) the deviation of the actual temperature
from the thermostat setting (the upper
abscissa scale), and,
(ii) the temperature relative to the thermo-
stat setting T C (the lower abscissa scale),
for the burner control system and,
Fig. 6 is a diagrammatic representation of the
arrangement of fuel and air valve setting
13173~6
- data in an addressable data store, for the
burner control system.
Referring to Fig. 1, an electrical system capable
of controlling a boiler includes a combustion process
control system 1, an air supply control valve 2, a fuel
supply control valve 3, an air control valve motor 4, a
fuel control valve motor 5, position indicating potentio~
meters 6 and 7, a thermostat 8, and a fuel selector switch
9. The combustion process control system 1 includes a
plurality of input ports by means of which it receives
information from its sensors and output ports by means
of which it provides information to actuators and the .
like. The combustion process control system 1 includes
input ports Fl, F2 one of which is energised by means
of the fuel selector switch 9 to signal the type of
fuel in use, a temperature sensor input port Tl/T2 for
receiving information as to an actual temperature, a
remote load control input port 10,
a boiler thermostat input port S10, an open /
start switch position-sensing input port S13, switch
position-sensing ports S14 and S15, a load control switch
sensing port S7, an air valve position sensing input port
A, and a fuel valve position sensing port F. Also in-
cluded are output ports A+ and A- for controlling the
air control valve motor 4 and output ports F+ and F-
for controlling the fuel valve control
- 8 - 13173~6
motor 5.
Referring to Fig. 2, the combustion process control
system 1, of Fig. 1, includes a microprocessor 100, a
serial timer interrupt controller 101, an electrically
5 erasable memory 102, a plurality of display5103, input/
output controllers 104 and 105, a fixed programme memory
106, a random access memory 107, and an analogue-to-
digital converter 108. The microprocessor is a Type
Z80 integrated circuit which, under the direction of
the fixed programme memory 106, reads the signals at
the various input ports and executes the actions for
providing control signals at the appropriate output
ports in addition to providing information for the
displays 103. The serial timer interrupt controller
15 101, which is a Type MK 3801 integrated circuit, is a
multifunction device providing a USART (Universal
Synchronous/Asynchronous Receiver/Transmitter), four
timers (two binary and two full function), and eight
bidirectional input/output lines with individually pro-
grammable interrupts. The random access memory 107 acts
as a short term store for the signals received from in-
put ports and the signals to be presented to output ports.
The random access memory 107 acts also as a scratchpad
memory for the microprocessor 100. The input/output
25 controllers 104 and 105 control the activation and de-
activation of the ports as instructed by the micropro-
cessor 100 and the serial timer interrupt controller 101.
The signals from
- 9 - 13173~6
the temperature sensor port (T1 - T2) and the valve
motor position indicator ports (F, A) are subjected to
analogue-to-digital conversion by the analogue-to-
digital converter 108. The signals from the remote
load sensing port 10 and other port3 in its group
(S7, S10, S13, F1, F2) are each subject to modification
by means of a level-translating circuit 109 which also
provides electrical isolation by means of optical
coupling. There are provided manual controls capable
of effecting the operations listed below. The manual
controls are identified on the ront panel represented in
Fig. 3.. The manual controls are switches connected to
a plurality of control input ports shown in Fig. 2.
The operations referred to above are :-
1. Placing the combustion process control system
in either the commiqsioning mode or the run
mode, and, in the commissioning mode :-
2. Increasing or decreasing the fuel ~upply.
3. Increasing or decreasing the air supply.
4. Increasing or decreasing the desired tempera-
ture.
5. Signalling to the system the positions of the
air and fuel valves relative to their
respective open and closed positions.
Referring to Fig. 4, the operations carried out
by the combustion process control system commence with
switch-on and the selection of fuel (1). The system
then checks whether or not it has a look-up memory with
information for the fuel selected (2) and, if not,
. ~
1317356
-- ],o,
places itself in the commissioning mode permitting
control by means of the manual controls shown in Fig. 3
and illuminating the CLOSE POSITION and ENTER ~EMORY
displays at the control panel (3). The manual control~
for the air and fuel valve motors are then used by the
operator to close both valves (indications of the
positions of the valves are given at the control panel)
and the operator presses ENTER MEMORY on the front
panel when he is satisfied that the valves are closed
(4). The system then illuminates a SET STAT display,
indicating that the operator should enter a temperature
setting at which the burner is to be extinguished in
order to prevent a further rise in the temperature of
the medium being heated e.g. water in a boiler. The
OPEN POSITION and ENTER MEMORY displays on the control
panel are next illuminated ~7) and the operator uses
the manual controls to open both valves fully and presses
ENTER MEMORY on the first panel when he is satisfied
that both valves are.open (8). The system next purges
waste gases from the combustion chamber (9) after which
it illuminates the START POSITION display on the control
panel (10, 11, 12). The manual controls are then used
by the operator to open partially both valves to allow
ignition and combustion of fuel and he then presses
START POSITION ( 13) to initiate boiler operation. The
system then illuminates the HIGH POSITION and ENTER
MEMORY displays on the front panel (14 ? . The manual
ll 13173~
controls are used by the operator to obtain, from the
burner, a maximum heat output suitable for the inAtalla-
tion in which it is being used while ensuring efficient
combustion at the maximum heat demand (15). This part
of the operation is executed with the aid of combustion
analysis equipment and requires an.operator skilled in
the use of such e~uipment. When the operator is satis-
fied that efficient combustion is taking place at the
high heat demand setting he presses ENTER MEMORY (15).
10 The system then decides whether subsequent operation is
to be ~or the entry of intermediate or start data (17),
and,for the entry of intermediate data, illuminates the
lNTER POSITION and START displays on the front panels
(16). For the entry of intermediate data, the operator
15 presses INTER ( 18), selects ~ome fuel valve setting
below the maximum value set previously, adjusts the
air valve to provide efficient combustion at this new
intexmediate heat demand setting, and when he is satis-
fied that the combustion is efficient he presses ENTER
20 MEMORY (19). The system continues to illuminate the
INTER and START displays (return to 16) until the
required number of locations in the look-up memory are
filled with values for intermediate fuel valve and air
valve settings. On completion of the entrie~ for
intermediate settings the START and ENTER MEMORY
displays are illuminated (20), the operator uses the
manual controls to set a selected START position for the
fuel valve, adjuststheair valve forefficient combustion
.
~3~7~
and then presses the ENTER MEMORY display/switch to
effect entry of the settings into the memory ~
The system then illuminateq the RUN display on the
front panel to indicate that it is ready for operation
(22) which is effected by pressing RUN (23).
When the RUN control is operated at the end of the
commisqioning phase the combustion process control
system deactivat~s all of the front panel controls
with the exception of the COM (commission) and RUN
controls and thereafter functions as a burner control
system capable of providing it~ stored valve setting
data in response to a remote load control input.
Following the operation of the RUN control as
described above, the system waits for 20 second (24)
and then responds to the remote control, checking periodi-
cally for a change in demand ~25).
Further shown in Fig. 4, the combustion process
control system may be reprogrammed by switching it off
and on (return to 1), and then operating the COM control
on the front panel which returns it to the commissioning
cycle via check point (27) and decision (2a).
Referring still to Fig. 4, should the flame be
extinguished by external influences, the system switches
off (29) and will restart when the pilot flame is
reestablished (30 to 37).
The programmer/operator is required to set, by
means of a presettable control forming part of the
apparatus, an "offset" temperature difference to be
- 13 - 13173~6
~,
used by the apparatus in normal operation. The function
of the "offset" temperature difference and the relation-
ship between the START, INTERMEDIATE, and ~IGH settings
will now be explained with reference to Fig. 5.
In Fig. 5, the relation~hip between the fuel valve
~etting and the deviation of th~- actual temperature from
the thermostatically set temperature is represented by a
graph having two straight portions, one (the first)
portion rising at a constant rate to meet the other
portion which has zero slope. The first portion of the
graph represents an increasing fuel valve setting, that is,
the extent of opening of the fuel valve, from the START
value to the HIGH value. The increase in the fuel valve
setting from the START value to the HIGH value occurs
over a change from 0 C to 10 C in the deviation of
the actual temperature from the thermostatically set
temperature. The fuel valve setting then remains con-
stant at the HIGH value for temperature deviations in
excess of 10C. It will be appreciated that the thermo-
statically set temperature T C is represented by a O Ctemperature deviation and T - 10 C is represented by a
10 C deviation, as shown in the alternative temperature
scale of Fig. 5. The"offset" temperature difference
referred to above is, in Fig. 5, the 10 C difference at
which the change occurs in the slope of the graph. Values
of fuel valve setting which lie on the rising part of the
graph are the intermediate fuel valve etting values.
13~7356
~he equipment is capable of "constructing" the graph of
Fig. 5 by calculation, since it is given the START
value, the HIGH value, and the "offset"temperature
difference. As stated above the HIGH value represent~
the setting for the maximum heat output which may be
used with the particular installation, e.g. a boiler,
which incorporates the burner control system.
The fuel burner control system, according to the
invention, in operation, monitors the actual temperature
of a medium e.g. water in a boiler, which is being
heated by the fuel burner and compares the said actual
temperature with a thermostatically set temperature for
the medium. The fuel burner control system is capable
of calculating the deviation of the actual temperature
from the thermostatically set temperature and also of
performing the operations necessary to obtain a value for
fuel valve setting for any temperature deviation value in
accordance with the relationship represented by Fig. 5.
Therefore the fuel burner control system selects the
START value of fuel valve setting if the temperature
deviation is zero and selects the HIGH value of fuel
valve setting if the temperature deviation is 10 C or
more. For a temperature deviation between 0 C and 10 C,
the fuel burner control system calculates the fuel
valve setting (angular position in degrees) in accord-
ance with the relation3hip :-
Fuel valve rHIGH fuel START fuel 1X temp.deviation
po~ition ~alve ~etting valve settingJ 10
~ 13~7356
Also shown in Fig. 5 are alternative forms of therelationship between fuel valve settings and temperature
deviation having break points at X C (less than 10 C)
and Y C (more than 10 C), respectively, the break
points representing a range of values of temperature
deviation which may lie between five and twenty per cent
of the possible range of temperature deviation. The fuel
burner control system shuts off the fuel supply if the
temperature deviation becomes negative.
Referring now to Fig. 6, data required by the fuel
burner control system in its operation is stored as fuel
valve settings in a first addressable data store, repre-
sented diagrammatically on the left in Fig. 6, and as air
valve settings in a second addressable data store, repre-
sented diagrammatically on the right in Fig. 6. Once the
fuel burner control system has determined a fuel valve
setting, as described above with reference to Fig. 5, it
locates the said fuel valve setting, in the fuel valve
setting data store (or the fuel valve setting closest to
the said valve setting), notes the address at which the
relevant fuel valve setting was located, and selects the
air valve setting data at a corresponding address in the
air valve setting data store. Once the fuel burner control
system has acquired both fuel valve and air valve setting
data it proceeds to apply the fuel valve setting data to
its fuel valve control output port and to apply the air
valve setting data to its air valve control output port.
Referring to Fig. 6, the fuel valve setting data
available in the first data store includes control
, . . .... , . . . . ~ . _ . ... _ , , .. _ _ _ _ _ _ _ _ _ _ _
` - 16 _ 13173~6
data glving the following positions of the fuel valve :
CLOSED, at which the fuel valve is shut.
OPEN, at which the fuel valve is open fully.
HIGH, at which the fuel valve is open to a position
which provides the maximum heat output which the
installation, e.g. a boiler, can use.
INTERMEDIATE 1 to INTERMEDIATE N, a set of positions
along the sloping part of Fig. 5 representing pro-
gressive opening of the fuel valve for a minimum
heat output START position to the maximum heat
output HIGH position. There may be 25 such INTER-
MEDIATE positions chosen along the sloping part of
Fig. 5 ~N = 25).
START, at which the fuel valve is slightly open to
provide enough heat to compensate for heat losses
of the system in order to maintain the medium being
heated at the thermostatically set temperature
~T in Fig. 1).
The data store also includes an indication of the
value of N ~the number of INTERMEDIATE positions of the
fuel valve available in the data store), so that the
system can check on whether or not it holds a full set of
INTERMEDIATE data.
Referring again to Fig. 1, the accuracy of control
of the air and fuel valves 2 and 3 is of the order of a
quarter degree and the valve positions are read as those
of the motors 4 and 5 by the feedback provided by the
potentiometers 6 and 70 The positions of the motors
.. . : . . . _ _ _ . ._. _ _ . .
~3173~6
- 17 ~
are checked eight times per second.
Referring again to Fig. 3, the front panel displays
include "fuel ~elected" indicators, "commission" and
"run" indicators, and a temperature indicator which
displays the desired and actual temperatures alternately.
The front panel al~o includes an 2 display and ~etting
control for establishing an optimum level of oxygen in
the exhaust gases during commissioning. The system may
be arranged to maintain a boiler to provide the optimum
oxygen level in the exhaust gases by fine control of
the valves (over and above the fixed control set on
commis~ioning). The 2 display is arranged to display
the actual and desired values alternately.
In the equipment described above the temperature
(or more precisely the difference between the actual and
desired temperatures) of the boiler water is used as a
variable con.rol quantity. It is also possible to use
other variables; for example the steam pressure of the
boiler, the temperature of the products of combustion
20 of the boiler, the process or output temperature of the
boiler, or a variable re~ated to the heat load re~uire-
ments of, for example, a building heated by the
boiler.
~ .
13173~6
-- 18 --
As is explained above, the control system will provide,
from the memory, in response to each of a plurality of
input signal values representing values of output heat
demand, respective values for air valve and fuel valve
settings. Examples of the operation of the system are
as follows:-
(i) The control system will select fuel valveand air valve setting values from the memory and apply
them to the output ports without alteration if the
memory holds valve setting values corresponding exactly
to the current input signal value.
(ii) In addition to carrying out (i) above, the
control system will select fuel valve and air valve
setting values from the memory and alter them before
applying them to the output ports if the memory does
not hold valve setting values corresponding exactly to
the current input signal value. The values taken from
the memory are those corresponding to input signal
values closest to the current input signal value and the
control system provides intermediate values from the
values taken from the memory.
