GB914786A - Improvements in control devices for space heaters - Google Patents

Abstract

914,786. Controlling burners. RHEOSTATIC CO. Ltd. May 13, 1960 [May 19, 1959], No. 16878/59. Class 75 (1). A device for controlling a burner heating a building comprises a unit 1, Fig. 1, located outside the building and containing a thermostatic switch 4 and a heating resistance 3, and a further switch 7 in parallel with the thermostatic switch 4 and actuated by a cam 10 which in one rotation determines a first period during which the switch 7 is open and a second period during which the switch 7 is closed. Both switches energize the heating resistance 3 and a motor 9 rotating the cam 10 and connect the A.C. mains terminals 5, 6 to terminals 8, 6<SP>1</SP> connected to a burner which supplies heat when the terminals 8, 6<SP>1</SP> are energized. When the outside temperature falls the thermostatic switch 4 closes to energize the motor 9 and the heater 3 and to start the burner. The heater 3 is unable to open the thermostatic switch 4 during the first predetermined period when the switch 7 is open so that the burner produces heat during both periods and closes down when the cam 10 again opens the switch 7, the thermostatic switch 4 having opened during the second period. The apparatus shown in Fig. 2 comprises a cam driven two-way switch 20 in place of the switch 7 of Fig. 1, a motor 28 for supplying the burner with fuel oil or a gas valve, a fluestat 29 or a photoelectrical device controlling an ignition transformer 33 and a self-locking relay 33, and a warning light 36. When the thermostatic switch 4 closes the cam motor 9 is energized and the burner motor 28 is energized through contact 22 of the two-way switch 20. The ignition transformer 33 is energized through cold contact 31 of the fluestat 29 and the relay 34 is short circuited by the twoway switch 20. If ignition is successful the fluestat 29 de-energizes the ignition transformer and closes its hot contact 32 so that the burner motor is supplied independently of the cam switch 20. When the latter opens its contact 22 and closes its contact 23 the cam motor 9 is energized independently of the outside switch 4 and the burner continues to operate until the cam switch again changes its contacts. If ignition is not successful the fluestat does not close its hot contact 32 and when the camoperated switch 20 opens its contact 22, the self-locking relay 34 is energized in series with the burner motor 28. The energization of the burner motor 28 in this way is insufficient so that it stops. The relay 34 closes contacts 35 to energize the warning light 36 and opens contacts 27 so that the outside thermostatic switch 4 is ineffective. The cam motor 9 continues to rotate until it again closes contact 22 of the two-way switch 20. The relay is reset manually. A three-way switch 26 provides a normal position or a continuous run position or an off position. The cam 10 may operate a switch 38 to relieve the outside thermostat 4 of the load when making the circuit and a further switch may be operated by the cam to break the circuit to the heater 3 before the switch 20 closes its contact 22. In an installation, Fig. 3 (not shown), having an indirect cylinder for providing hot water from the same boiler as the central heating, the terminals 8, 6<SP>1</SP> of Fig. 1 are connected to a relay coil which operates a pair of contacts to control a burner motor and a second pair of contacts to control a pump for circulating the water through the building. A two position thermostat having a large operating differential is located in the indirect cylinder and connects the burner motor to the supply when the temperature is low and the pump to the supply when the temperature is high. The control device of the invention can be applied to a solid fuel fired burner by controlling the supply of combustion air as though the air was the fuel.