GB690655A - Improvements in or relating to combustion control - Google Patents

Abstract

690,655. Control of motors. CROOK, C. March 31, 1952 [April 4, 1951 No. 7816/51. Class 38 (iii) [Also in Group XXXVIII] In apparatus for controlling combustion in a combustion chamber to which air is supplied by an electrically driven fan, a power sensitive device responsive to variations in the electrical energy absorbed by the fan (which is related to the volume of air supplied) controls the operation of a fuel feed apparatus so that the ratio of air to fuel is maintained at a predetermined value. A retort 10 is supplied with fuel by a feed screw 11 driven through a magnetic clutch 13 by an electric motor 12 which also drives a fan 16 supplying combustion air to the retort through a conduit 17 having a damper 31. Fixed and movable dynamometer coils 18, 19 are respectively connected in series with the motor load current and across the supply thereto, and the movable coil 19 rotates a pointer (not shown) and a contact arm 23 against a restoring spring 22, to positionally indicate the power absorbed by the motor and thus the air flow delivered by .the fan. Electric power is supplied to terminals 42, 43, 44, 45 and a motor or clockwork rotates a shaft 25 carrying switching cams 27, 28 and a spiral cam 24 engageable with the arm 23, at e.g., 1 r.p.m., so that normally closed contacts 29, 30 are respectively opened once per cycle during the rotation of the spiral cam through the sectors A and B. The damper 31 is initially open, and closes contacts 32, operates relay 33, and closes contacts 34, 35, 36 to start motor 12, so that arm 23 is positioned according to the motor power and the air flow. The periphery of cam 24 contacts arm 23 at an instant in the cycle dependent on the position of the arm, and energises relay 37 to close contacts 38, 39, 40, 41 so that the relay holds over contacts 41 and the magnetic clutch is operated over contacts 38, 39 to transmit drive to the fuel feed screw. At the end of each cycle, contacts 30 open for a short time and release relay 37 to de-energise clutch 13 until arm 23 contacts cam 24 in the cycle, so that the fuel feed is operative in each cycle for a time dependent on the air flow. Contacts 29 open for a short time immediately prior to the opening of contacts 30, and if contacts 38 are open due to there being no contact between cam 24 and arm 23 in the preceding cycle, relay 33 is released to stop the motor 12. Partial closure of damper 31 manually or e.g. thermostatically during a cycle opens contacts 32, but motor 12 is maintained in operation as long as contacts 38 and 29 remain closed. When the damper 31 is completely closed, arm 23 does not contact cam 24 at any part of the cycle, so that the motor 12 is stopped until the damper is re-opened to close contacts 32 and restart the cycle. Cam 24 is cut so that the point of contact with arm 23 corresponds to the correct supply of fuel over the current cycle in correspondence with the air flow determining the position of arm 23. The dynamometer coils may be iron cored or replaceable by a moving iron repulsion movement responsive to the motor current, and they may be energised through current and voltage transformers. The magnetic clutch drive to the fuel feed is replaceable by an independent motor controlled by contacts 39, 40, or by a servomotor mechanism operating a fuel feed regulator or cut-off device. Correction for air flow temperature is obtained by a directly or indirectly temperature variable resistance across the dynamometer series coil, or by a temperature variable correcting torque applied to the dynamometer spindle. The system is adaptable to 3-phase operation.