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(11) | EP 0 143 865 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Burner control |
| (57) A control system for an oil burner comprises TRIACs for switching on an air blower,
an igniter and a solenoid valve for oil feed; solid-state drive circuitry for the
TRIACs; circuitry for inhibiting the drive circuitry in response to a lock-out signal;
logic circuitry for providing control signals to the drive circuitry and a lock-out
signal to the inhibiting circuitry and arranged to determine (a) the period for which
the blower and igniter operate together to purge the nozzle, (b) the period for which
the igniter remains operating with the solenoid value also open (when a flame is normally
established), and (c) the period for which the system is locked-out if a flame is
not established when the igniter is turned off (or if a flame, once established, becomes
extinguished); an indicator which is energised when the drive circuitry is inhibited;
and a manual reset for enabling the ignition sequence to be restarted. |
[0002] According to the invention an oil burner control system comprises a thermostat which energises the system upon a call for heat; first, second and third solid-stpte switching means for coupling an air blower motor, an ignition device and a solenoid valve, respectively, to a power source; first solid-state drive means arranged to actuate the first switching mefns upon energising of the system; second and third solid-state drive means for actuating the second and third switching means, respectively, in response to respective drive signals; a first timing means responsive to energising of the system and arranged to provide the drive signal for the third drive means after a first period and to trigger a second timing means arranged to provide the drive signal for the second drive means from energising of the system until the end of a second period; means responsive to the drive signal provided by the second timing means and to the signal from a flame sensor and arranged to provide a first inhibiting signal for inhibiting all three drive means when the ignition sequence has failed to establish a flame or when an established flame goes out; third timing means responsive to the first inhibiting signal for providing a second inhibiting signal for inhibiting all three drive means for a third period (known as a lock-out period); and a manually-operrble reset means arranged to reset the first timing means to stert a fresh ignition sequence.
[0003] There may be an interlock logic circuit to prevent the first timing means from being reset until after the end of the lock-out period.
[0004] The means arranged to provide the first inhibiting signal may be in the form of another timing means which provides the first inhibiting signal at the end of another period unless disabled by a "flame absent" signal from the flame sensor.
[0005] There may be provided an indicator arranged to be energised whilst the three drive means are inhibited.
[0006] Each of the drive means may comprise a resistor arranged to supply to a control electrode of its associated switching means from a voltage supply line, the resistor being coupled by a respective clamping diode to the output of a transistor switch responsive to an inhibiting signal. There may be first and second such transistor switches responsive to the first and second inhibiting signals respectively. Alternatively, there may be a single transistor switch with logic gating circuitry for receiving the first and second inhibiting signals.
[0008] One oil burner control system embodying the invention will now be described with reference to the drawings, in which:-
Figure 1 shows the logic circuitry of the system;
Figure 2 shows interface circuitry which controls the burner ignition, motor and valve in response to signals from the logic circuitry; and
Figure 3 is a circuit diagram of the power supply and flame sensor.
[0009] The control system illustrated is suitable for use in a central heating system. It is only one example of forms which the invention might take.
[0010] A brief description of the operation of the control system will be given first, followed by more detailed description of the circuitry.
[0011] The system is energised by means of a thermostat which can be positioned in a room to sense air temperature or on a weter cylinder or tank to sense the temperature of the water. Initially the motor of the air blower and the ignition are energised for a period of about 15 seconds whilst the solenoid valve remains closed, in order to purge the nozzle region. The solenoid valve is then opened and a steady flame is established at the burner nozzle, its presence being indicated by the signal from an optical sensor. About 12 seconds after the solenoid valve was opened the ignition is switched off, provided that the flame is established, and the burner continues until the desired temperature is reached and the thermostat switches the system off.
[0012] If the flame is not present at the end of the 12-second period, then the ignition, the motor and the solenoid valve are switched off and an indicator is brought on to show that no flame is present. A feedback signal keeps these elements switched off for period of about 75 seconds, after which the control sequence can be started by means of a reset button. The system is also switched off and disabled in the event that the flame, once established, is extinguished, for example by excessive down draught.
[0013] Considering first Figure 3, in normal operation the system is initially energised by the closing of thermostat contacts 10 which are connected to one end of the primary winding 11 of a mains transformer 12 and to a neutral mains terminal 13 via a resistor 14. The other end of winding 11 is connected to a live mains terminal 15. Also connected to terminal 15 are output terminals 16, 17 and 18 which are connected to the ignition device (not shown), the motor (not shown) and the solenoid valve-(not shown), respectively, which are connected to respective TRIACs referred to later in the interface circuitry of Figure 2.
[0014] The transformer 12 has a centre-tapped secondary winding 20 which feeds a pair of diodes 21 arranged for full- wave rectification uith their anodes connected to an output terminal 22. A capacitor 23 is connected between terminal 22 and an output terminal 24 which is connected to the centre-tap of the secondary winding 20. A further secondary winding 25 is also provided: this feeds a bridge rectifier 26 whose output is connected to an output terminal 27 and the output terminal 22. A smoothing capacitor 28 is connected betueen output terminals 22 and 27.
[0015] The transformer is selected so that, relative to terminal 24, terminal 22 provides a 3-volts negative power supply line and terminal 27 provides a 12-volts negative power supply line.
[0016] A bridge rectifier 30 has its input terminals connected across the resistor 14 and its output terminals connected to a smoothing capacitor 31. Connected in a series circuit across the capacitor 31 are a light-responsive resistor 32, a LED transmitter 33 of an optical coupler, and a resistor 34, comprising a flame sensor circuit.
[0018] Thus, upon closing of the thermostat contacts 10 the power supply lines are energised, and so is the flame sensor circuit.
[0019] Considering now Figures 1 and 2, line 35 is connected to terminal 24, line 36 is connected to terminal 27 (-12 volts) and line 37 is connected to terminal 22 (-3 volts). Capacitor 38 is directly connected to line 36 and is connected to line 35 via series-connected resistor 40 and variable resistor 41. The junction of capacitor 38 and resistor 40 is connected via resistor 42 to the inputs of NAND gate 43 whose output is connected via resistor 44 to the inputs of NAND gate 45 and via resistor 46 to the inputs of NAND gate 47. The output of gate 47 is connected to a line V which is connected via resistor 48 to the base of a control transistor 49 whose emitter is connected to line 35 and whose collector is connected via a load resistor 50 to line 37.
[0020] A TRIAC 51 is connected between line 35 and a terminal 52 to which the solenoid valve (not shown) is connected. The gate of TRIAC 51 is connected via a pair of series-connected forward-biased diodes 53 to the collector of transistor 49 via a resistor 54 to line 35. A voltage-dependent resistor 55 is connected between terminal 52 and line 35.
[0021] Initially, the capacitor 38 is in a discharged state having discharged through the power supply via a diode 56 connected across resistors 40 and 41. This renders the inputs of gate 43 high (i.e. towards line 36 relative to line 35) for a time delay determined by capacitor 38 and resistors 40 and 41. This delay is set at approximately 15 seconds in this particular embodiment.
[0022] Thus, the output of gate 47 is high during this delay, and transistor 49 is conducting, so that there is no current flow through diodes 53 to switch on TRIAC 51 and the solenoid valve remains unenergised.
[0023] A similar TRIAC control for the blower motor (not shown) comprises TRIAC 57, resistor 58, voltage-dependent resistor 59, a pair of diodes 60 and terminal 61; and a further similar TRIAC control for the ignition device (not shoun) comprises TRIAC 62, resistor 63, voltage-dependent resistor 64, a pair of diodes 65 and terminal 66.
[0024] Diodes 65 are connected to the collector of a transistor 67 having a load resistor 68 and a base resistor 69 in the same manner as transistor 49, but diodes 60 are coupled to line 37 via a load resistor 70 with no corresponding control transistor so the blower motor becomes energised as soon as the power lines become established upon closing of switch 10.
[0025] The output of gate 45 is connected via a resistor 71 and a clamping diode 72 to another RC delay circuit comprising capacitor 73, resistor 74, and variable resistor 75, which is set to provide a delay of approximately 12 seconds. The junction of capacitor 73 and resistor 74 is connected via resistor 76 to the inputs of a NAND gate 77 whose output is connected to a line T which is connected to base resistor 69 of control transistor 67.
[0026] During the first delay period of 15 seconds the output of gate 45 is high and clamps the input of gate 77 high so that its output on line T is low and control transistor 67 is non-conducting. TRIAC 62 is thus on and the ignition device is energised.
[0027] Gate 77 is also connected via a resistor 78 to the inputs of a NPND gate 79 whose output is connected via a resistor 80 and a series-connected clamping diode 81 to a capacitor 82 connected to line 36. The junction of diode 81 and capacitor 82 is connected via resistor 83 to the inputs of a NAND gate 84 uhose output is connected via resistor 85 to the inputs of a NAND gate 86 whose output is connected to a line 8; and this junction is connected to line 35 via series-connected resistors 87 and 88.
[0028] The receiver part 89 of the optical couples is connected between line 36 and the junction of resistors 87 and 88.
[0029] The low output of gate 77 drives the output of gate 79 high which clamps the input of gate 84 high, so causing line B to be high. This signal is fed via a resistor 90 to the base of an NPR transistor 91 whose emitter is connected to line 36 and whose collector is connected to line 35 via a resistor 9?, to the bpse of a PNP transistor 93 via a resistor 94 and to the base of a PNP transistor 95 via a capacitor 96.
[0030] The emitters of transistors 93 and 95 are connected to line 35. Transistor 93 has a load resistor 97 connected to line 36, and its collector is connected to diodes 53, 60 and 65 via respective diodes 98, 99 and 100, and to a forward-biased diode 101 which in turn is connected to line 36 via series-connected resistor 102 and LED 103.
[0031] Thus transistors 91 end 93 are non-conducting and diodes 98, 99 and 100 are reverse-biased via resistor 97 and do not disable the TRIAC drives.
[0032] The collector of transistor 95 is connected to line FB feedback which is connected vie diode 104 and resistor 105 to the input of NAND gate 106, and the junction of diode 104 and resistor 105 is connected via parallel- connected resistor 107 and capacitor 108 to line 36. The output of gate 106 is connected to line A which is connected to the base of a PNP transistor 109 via a resistor 110, the collector is connected to line 36 and the emitter is connected to line 35 via a resistor 111 and to the base of a PNP transistor 112 via a resistor 113. Transistor 112 has a load resistor 114 connected to line 36 and its collector is connected to diodes 53, 60 and 65 via respective diodes 115, 116 and 117 and to resistor 102 via diode 118.
[0033] Initially, transistor 95 will be non-conducting because transistor 91 is non-conducting, and the input of gate 106 uill be held high via resistors 105 and 107. Thus line A will be low and transistors 109 and 112 will be non-conducting and diodes 115, 116 and 117 are reverse-biased via resistor 114 and do not disable the TRIAC drives.
[0034] At the end of the first delay period of 15 seconds the input of gate 43 goes low and hence the signal on line V goes low resulting in control trensistor 49 becoming non-conducting and TRIAC 51 switching on to energise the solenoid velve for the flow of oil to the nozzle. Also, the output of gate 45 goes low and removes the clamping action on the input of gate 77 and allows the second delay period of 12 seconds to begin, with capacitor 73 charging via resistors 74 and 75.
[0035] At the end of this second delay period the input of gate 77 goes low and the signal on line T goes high which results in control transistor 67 turning on. TRIAC 62 is thus switched off and the ignition device is de- energised. Also, the output of gate 79 goes low and removes the clamping action of the input of gate 84 and allows a further delay period of about 1/2 second to begin, with capacitor 82 charging via resistors 87 and 88 in the event that the flame has not established itself and receiver 89 is thus non-conducting.
[0036] At the end of this further delay period (i.e. for no established flame) the input of gate 84 goes low end the signal on line 8 goes low which turns on transistor 91. This results in transistor 93 turning on and switching off all the TRIACs via diodes 98, 99 and 100, and energising the alarm LED 103. Also capacitor 96 starts to charge via the base-emitter junction of transistor 95 causing it to conduct while capacitor 96 charges, and pull the input of gate 106 low via diode 104. The signal on line A thus goes high which causes transistors 109 and 112 to conduct whereby diodes 115, 116 and 117 act to switch off the TRIACs, and LED 103 is also energised via diode 118. The collector load for transistor 95 is resistor 107 and capacitor 108 which charges to nearly 12 volts.
[0037] When capacitor 96 becomes fully charged, there is no base current for transistor 95 which then ceases conducting and allows capacitor 108 to start discharging via resistor 107 back to its normal level. The delay set for this is approximately 75 seconds and during this period the signal on line A remains high thus inhibiting any action of the TRIRC circuits in response to signals on lines T rnd U, and energising the alarm LED 103.
[0038] A manual reset push-button 119 is connected across cap- aoitor 38 and, upon actuation, short-circuits capacitor 38 to provide a high signal to the input of gate 43. Thus gates 45 and 79 provide high outputs uhich discharge capacitors 73 and 82 via diodes 72 and 81, respectively, and the ignition timing sequence is ready to recommence.
[0039] The signal on line 8 goes high when push-button 119 is actuated, but as explained, the signal on line A will inhibit the TRIAC circuits for approximately 75 seconds. If an operator actuates the push-button 119 during this period, it will be immediately apparent because the alarm LED 103 will not extinguish. The operator will remain pressing the push-button 119 until at the end of this period the signal on line A goes low and the LED 103 extinguishes.
[0040] If a flame establishes normally during the ignition sequence, then receiver 89 of the optical coupler will be conducting and will provide a high signal via resistor 87 to the input of gate 84. Thus at the end of the further delay period the system is in a steady state with the blower on, the solenoid valve open, the ignition device off and an established flame.
[0041] Should for any reason the flame sensor circuit determine that the flame is not present (this will normally be due to loss of radiation falling on resistor 32, but includes a component failure in the flame sensor circuit), then the receiver 89 of the optical coupler will be non-conducting and capacitor 82 will charge rapidly via resistors 87.and 88. Thus a low signal will be present on line B and the system will be "locked-out" as described for the period determined by capacitor 108 and resistor 107.
[0042] After the end of this lock-out period the signal on line A will be low but the signal on line R will be low, so the system remains off with LED 103 energised. The ignition sequence will now start the instant the operator presses the reset push-button 119.
[0043] In the above-described system capacitor 38 will start charging via resistors 40 and 41 as soon as the operator releases the reset push-button 119. Thus if he attempts a restart during the lock-out period he will have to keep the reset push-button aotuated until the LED 103 extinguishes in order to start the timing sequence at the correct time. If the push-button 119 is released some time before the end of the lock-out period then the 15 second purge period could finish without any purge action having taken place, and the system could go straight into the ignition phase as the signal on line A goes low. If it desired to ensure that capacitor 38 can be discharged by the reset push-button 119 only after the end of the lock-out period, then a suitable logic circuit could be included which would inhibit the reset action while the signal on line A was high.
[0044] The system is switched on when the thermostat switch 10 opens, and the capacitors then discharge. Diode 56 provides protection for the input circuitry of gate 43 when the voltage on line 36 collapses and the positive plate of capacitor 38 tries to go more positive than line 35. Gates 77 and 84 have their input circuitry similarly protected by diodes 120 and 121, respectively.
[0045] In the above described system the signals on lines A and B for inhibiting the TRIACs drive separate transistors 93 and 112. If desired, a single transistor could be used with appropriate gating circuitry receiving the signals on lines A and B.
1. An oil burner control system comprising f thermostat which energises the system
upon a call for heat; first, second and third solid-state switching means for coupling
an air blower motor, an ignition device and a solenoid valve, respectively, to a power
source; first solid-state drive means arranged to actuate the first switching means
upon energising of the system; second and third solid-state drive means for actuating
the second and third switching means, respectively, in response to respective drive
signals; a first timing means responsive to energising of the system and arranged
to provide the drive signal for the third drive means after a first period and to
trigger a second timing means arranged to provide the drive signal for the second
drive means from energising of the system until the end of a second period; means
responsive to the drive signal provided by the second timing means and to the signal
from a flame sensor and arranged to provide a first inhibiting signal for inhibiting
all three drive means when the ignition sequence has failed to establish a flame or
when an established flame goes out; third timing means responsive to the first inhibiting
signal for providing a second inhibiting signal for inhibiting all three drive means
for a third period (knoun as a lock-out period); and a manually-operable reset means
arranged to reset the first timing means to start a fresh ignition sequence.
2. A system according to Claim 1 and comprising an interlock logic circuit to prevent
the first timing means from being reset until after the end of the lock-out period.
3. P system according to Claim 1 or Claim 2 wherein the means arranged to provide
the first inhibiting signal is in the form of another timing means which provides
the first inhibiting signal at the end of another period unless disabled by a "flame
absent" signal from the flame sensor.
4. A system according to any of the preceding Claims wherein there is provided an
indicator arranged to be energised uhilst the three drive means are inhibited.
5. A system according to any of the preceding Claims wherein each of the drive means
comprises a resistor arranged to supply to a control electrode of its associated switching
means from a voltage supply line, the resistor being coupled by a respective clamping
diode to the output of a transistor switch responsive to an inhibiting signal.
6. A system according to Claim 5 and comprising first and second such transistor switches
responsive to the first and second inhibiting signals respectively.
7. A system according to Claim 5 and comprising a single transistor switch with logic
gating circuitry for receiving the first and second inhibiting signals.
8. A system according to any of the preceding Claims wherein each of the drive means
comprises a TRIAC.