EP1571395A1

EP1571395A1 - Burner flame control unit

Info

Publication number: EP1571395A1
Application number: EP04425138A
Authority: EP
Inventors: Attiliano Gambaretto; Andrea Marini Celadon; Giuseppe Toniato
Original assignee: Riello SpA
Current assignee: Riello SpA
Priority date: 2004-03-02
Filing date: 2004-03-02
Publication date: 2005-09-07
Also published as: CN1664443A

Abstract

A unit (1) for controlling the flame of a burner. The unit (1) has a first programmable control device (9) for controlling fuel feed devices and combustion air ventilation devices of the burner by means of a number of control outputs (6, 7, 8) controlled by respective switch blocks (16, 17, 18), and for safely controlling overall operation of the unit (1). The unit (1) also has a second control device (20) for further safety control independent of that performed by the first device (9). And the unit (1) is characterized in that the second control device (20) comprises a hardware watch-dog.

Description

The present invention relates to a single-control-channel unit for controlling the flame of a burner, in particular a gas or vapourized liquid fuel burner.
As is known, a gas or vapourized liquid fuel burner is supplied with a fuel and combustion air mixture. The composition and combustion of the mixture are controlled by a flame control unit, which regulates combustion air flow to the burner by means of a fan, and regulates fuel flow by means of solenoid valves.
The flame control unit is normally equipped with at least one electronic control device (microcontroller) for processing physical flame combustion parameters and regulating the fuel and combustion air mixture according to the desired calories. In other words, the electronic control device processes certain parameters of the burner system to supply control signals for controlling burner system actuating devices, such as the fuel feed solenoid valves and the electric motor applied to the fan.
The flame control unit must be made to specific operating safety standards.
For example, the control unit must cut off fuel supply immediately, upon the electronic control device determining processing errors or malfunctioning of the actuating devices.
In known flame control units, the problem is solved using two- or even three-channel architectures, in which the electronic control devices of the units are substantially doubled and tripled respectively.
Moreover, multiple-control-channel architecture calls for additional comparing devices to compare the results of the various channels, and to determine, in the case of two channels, or even solve, in the case of three channels, any fault on one of the channels caused by failure of the flame control unit component parts or electronic devices.
The theoretical advantage, in terms of reliability, of multiple-control-channel solutions is partly offset by the large number of electronic components involved, which in effect increases the likelihood of failure and malfunctioning, besides, obviously, increasing manufacturing cost in the case of limited-scale production.
It is an object of the present invention to provide a fuel burner single-control-channel flame control unit designed to eliminate the aforementioned drawbacks.
According to the present invention, there is provided a fuel burner single-control-channel flame control unit, as claimed in Claim 1 and, preferably in any one of the following Claims depending directly or indirectly on Claim 1.
According to the present invention, there is also provided a fuel burner flame control method, as claimed in Claim 7.
A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which:
Figure 1 shows a block diagram of the fuel burner single-control-channel flame control unit according to the present invention;
Figure 2 shows a main flow chart of the fuel burner flame control method according to the present invention;
Figures 3 to 6 show, in increasing detail, various modules and submodules of the main flow chart in Figure 2.
The present invention will now be described with reference to the accompanying drawings showing a non-limiting embodiment.
Number 1 in Figure 1 indicates as a whole a single-control-channel flame control unit for a two-stage fuel burner (not shown). Control unit 1 comprises a number of inputs 2, 3, 4, 5 for receiving signals from sensors of the burner; and a number of control outputs 6, 7, 8, which comprise a motor control output 6 connected to the electric motor applied to the combustion air fan (not shown) of the burner, and a first solenoid valve control output 7 and a second solenoid valve control output 8, each connected to a respective fuel supply solenoid valve (not shown) of the burner.
Control unit 1 comprises a control device (microcontroller) 9, which controls control outputs 6, 7, 8 on the basis of the signals from inputs 2, 3, 4, 5, and on the basis of a number of signals 10, 11, 12, 13, 14, 15 generated within control unit 1, to conform with specific operating safety requirements.
Control device 9 controls control outputs 6, 7, 8 by means of respective switch blocks 16, 17, 18. More specifically, a first switch block 16 is associated with motor control output 6, a second switch block 17 is associated with first solenoid valve control output 7, and a third switch block 18 is associated with second solenoid valve control output 8.
Control device 9 performs safety actions on control outputs 6, 7, 8 whenever malfunctioning of control unit 1 is determined on the basis of an undervoltage signal 12, generated by first switch block 16 when the mains voltage 19 of unit 1 falls below a predetermined threshold, a motor output fault signal 13, a first solenoid valve fault signal 14, and a second solenoid valve fault signal 15.
Control unit 1 also comprises a hardware watch-dog device 20, which provides for further safety control, independent of that performed by control device 9, by acting directly on first and second solenoid valve control outputs 7, 8. More specifically, watch-dog device 20 is connected substantially two-way to second switch block 17, which is located upstream from and in series with third switch block 18. In other words, disabling of first solenoid valve control output 7 also disables second solenoid valve control output 8.
Watch-dog device 20 is connected to control device 9 so that the two devices 9, 20 control each other.
More specifically, in actual use, control device 9 sends a periodic signal 10 of given characteristics to second switch block 17. Upon control device 9 determining a malfunction of control unit 1, the periodic signal 10 loses its given characteristics, thus disabling watch-dog device 20 and so opening second switch block 17. Similarly, a malfunction of second switch block 17 or of watch-dog device 20 disables watch-dog device 20 and so opens second switch block 17. Watch-dog device 20 communicates the malfunction to control device 9 by a watch-dog feedback signal 11 to disable control device 9.
In the event of either type of malfunction, the opening of second switch block 17 opens third switch block 18, thus disabling first and second solenoid valve control outputs 7, 8.
Inputs 2, 3, 4, 5 comprise a thermostat input 2, a gas pressure switch input 3, an air pressure switch input 4, and a flame sensor input 5. Control device 9 controls a switch 21 for enabling or disabling thermostat input 2, gas pressure switch input 3, and air pressure switch input 4; and disabling of the above inputs corresponds to enabling of a reset block 22, which resets control device 9 when a respective reset button 23 is pressed.
Control unit 1 also comprises a non-volatile (EEPROM) memory 24 for memorizing diagnostic data for supply to an external computer connected to control unit 1 over a serial data output 25 (RS232).
A lighter 26 is also integrated in the unit to generate the flame ignition spark under the control of control device 9.
Control device 9 is programmed with class C firmware, i.e. complex firmware for devices operating to specific safety requirements, to control control outputs 6, 7, 8 as a function of the signals from inputs 2, 3, 4, 5, and as a function of a number of signals 10, 11, 12, 13, 14, 15 within the unit, according to a given control method.
The fuel burner flame control method according to the present invention will now be described in detail with reference to the Figure 2 to 7 flow charts.
Operation of control unit 1 is defined by a state machine, the state transitions of which are controlled by the flame control method according to the invention.
The states, as shown in Figure 5, are the following:

INIT state 101, in which control device 9 is initialized;
WAITING state 102, in which control outputs 6, 7, 8 are all disabled;
PREPURGE state 103, in which motor control output 6 is enabled, and solenoid valve control outputs 7, 8 are disabled;
PRE_IGNITION state 104, which corresponds to the period between enabling lighter 26 and enabling first solenoid valve control output 7;
IGNITION state 105, which corresponds to the period between enabling first solenoid valve control output 7 and the appearance of the signal at flame sensor input 5;
POST_IGNITION state 106, which corresponds to the period between the appearance of the signal at flame sensor input 5 and disabling lighter 26;
RUNNING state 107, in which the burner is running;
SHUT_DOWN state 108, in which solenoid valve control outputs 7, 8 are disabled;
LOCKOUT state 109, in which solenoid valve control outputs 7, 8 are disabled, and which is only exited by manually pressing reset button 23.

The flame control method comprises the following main steps performed cyclically, and as shown in the main flow chart in Figure 2:

perform (110) a start-up self-diagnosis (INIT state 101) when a switch connected to thermostat input 2 is closed, to reset control device 9 and determine the internal integrity of device 9;
perform (111) a main self-diagnosis to check undervoltage signal 12; to check the internal time base of control device 9 by comparison with an external signal locked to the mains frequency; and to determine the integrity of an internal volatile (RAM) memory (not shown) of control device 9;
generate (112) a main time base, for use in control unit 1 (polling), from the internal time base of control device 9;
read (113) the input signals 2, 3, 4, 5, 10, 11, 12, 13, 14, 15 of control device 9 required to operate a state machine governing operation of control unit 1;
manage (114) non-volatile memory 24;
repeat the start-up self-diagnosis in the event of a return to start-up conditions, i.e. in the event the switch connected to thermostat input 2 closes again after being opened;
execute (115) an application module controlling a series of actions characterizing operation of control unit 1, as shown in the Figure 3 flow chart;
command (116) control outputs 6, 7, 8 and lighter 26;
refresh (117) an internal software watch-dog device of control device 9.

As stated, execution (115) of the application module is shown in the Figure 3 flow chart, and comprises:

transmitting (118) a portion of the data in the internal volatile memory to serial data output 25;
every ten cycles of the main flow chart:
- acquiring (119) the signal of flame sensor input 5;
managing (120) reset block 22 as shown in the Figure 4 flow chart;
setting (121) control unit 1 to WAITING state 102, if undervoltage signal 12 indicates mains voltage 19 is below the threshold;
updating (122) the operating state of control unit 1 by making a transition between the nine possible states 101, 102, 103, 104, 105, 106, 107, 108, 109, as shown in Figure 5;
managing (123) gas pressure switch input 3 and air pressure switch input 4;
managing (124) motor control output 6, as shown in the Figure 6 flow chart;
managing (125) lighter 26;
managing (126) first solenoid valve control output 7;
managing (127) second solenoid valve control output 8.

As stated, management (120) of reset block 22 is shown in the Figure 4 flow chart, and comprises:

setting (128) control unit 1 to LOCKOUT state 109 if a hardware fault is detected, or if a non-hardware fault is detected and reset button 23 has not yet been pressed;
setting (129) control unit 1 to INIT state 101 if a non-hardware fault is detected and reset button 23 was pressed at the previous cycle;
resetting (130) non-volatile memory 24 if control unit 1 has returned to INIT state 101;
setting (131) a post-ventilation, i.e. enabling motor control output 6, even with the switch of thermostat input 2 open, when reset button 23 is pressed and control unit 1 is not in LOCKOUT state 109.

As stated, management (124) of motor control output 6 is shown in the Figure 6 flow chart, and comprises:

indicating (132) a hardware fault if the switch of air pressure switch input 4 is open;
disabling (133) motor control output 6 if the switch of air pressure switch input 4 is stuck, or the switch of air pressure switch input 4 operates correctly and control unit 1 is in any one of INIT state 101, WAITING state 102, SHUT_DOWN state 108, LOCKOUT state 109;
enabling (134) motor control output 6 if the switch of air pressure switch input 4 operates correctly and control unit 1 is in any one of PREPURGE state 103, PRE_IGNITION state 104, IGNITION state 105, POST_IGNITION state 106, RUNNING state 107.

The main advantage of the present invention is that of providing a single-control-channel flame control unit 1 comprising only one control device 9, and capable of meeting the same operating safety requirements as known multiple-channel control units, while at the same time simplifying the circuitry and so improving the overall reliability of unit 1.
The above advantage is achieved by altering the hardware architecture of control unit 1 by providing a hardware watch-dog device 20 independent of control device 9, and by enhancing the software architecture (class C firmware) by which control device 9 governing control unit 1 is programmed.

Claims

A unit (1) for controlling the flame of a burner; the unit (1) comprising a programmable control device (9) for controlling fuel feed devices and combustion air ventilation devices of said burner by means of a number of control outputs (6, 7, 8) controlled by respective switch blocks (16, 17, 18), and for safely controlling overall operation of said unit (1); the unit (1) also comprising further control means (20) for further safety control independent of that performed by the control device (9); and the unit (1) being characterized in that the further control means (20) comprise a hardware watch-dog device (20).
A unit (1) as claimed in Claim 1, the unit (1) being characterized in that the watch-dog device (20) supplies a watch-dog feedback signal (11) to disable the control device (9) in the event of malfunctioning of the watch-dog device (20).
A unit (1) as claimed in Claim 1 or 2, wherein the number of control outputs (6, 7, 8) comprises a motor control output (6), a first solenoid valve control output (7), and a second solenoid valve control output (8).
A unit (1) as claimed in Claim 3, wherein a first switch block (16) controls the motor control output (6), a second switch block (17) controls the first solenoid valve control output (7), and a third switch block (18) controls the second solenoid valve control output (8).
A unit (1) as claimed in Claim 4, wherein the third switch block (18) is located in series with the second switch block (17).
A unit (1) as claimed in Claim 5, wherein the watch-dog device (20) is connected substantially two-way to the second switch block (17) to automatically disable the first and second solenoid valve control outputs (7, 8) in the event of malfunctioning of the second switch block (17) and the watch-dog device (20).
A single-control-channel method of controlling a fuel burner; the method being characterized by implementing safety actions generated by a multiple-state machine (122) assisted by independent automatic safety actions (11) generated by a particular hardware architecture (17, 20).