Patent GB-1424616-A (GB)
Title: Ventilator
IPC: A62C2/06
Filed: 1973-03-16
Abstract: 1424616 Ventilators MATSUSHITA SEIKO CO Ltd 16 March 1973 [28 July 1972 (4) 2 Aug 1972] 12720/73 Heading A5A [Also in Divisions F4 G3 and H2] A ventilator comprises a fan, a smoke or gas detector, a fan motor operable at high and low speeds, a first switch by which high speed operation, low speed operation or automatic operation of the motor may be manually selected and an electronic circuit connected to the detector and controlling the motor such that upon a preselected smoke density threshold being detected by the detector, the fan motor is connected by a second switch controlled by the circuit to operate at high speed regardless of the position of the first switch. Ventilator construction. Figure 1 shows a frame 1 containing a shutter 1' of known construction and driven by an electromagnet, a fan 2 driven by a motor 12, a string 3 for manual switching between automatic and manual operating conditions, lamps 4, 5 respectively indicating automatic and manual operation, an inlet 6 for smoke or gas and inside which is located a detecting element 10 in the form of a gas-sensitive semiconductor, which is heated to a specified temperature by a low current and has the characteristic that its resistance decreases rapidly upon absorption of smoke or gas Fig. 4 (not shown), an adjusting knob 8 for regulating the smoke density threshold which will cause high speed operation of the fan, and a neon lamp 9 for use when adjusting the position of the knob 8. Motor control circuit, lamp operation and calibration. Figure 2 shows an induction motor 12 having a main winding 16, an auxiliary winding 15 and capacitor 14, and a speed control winding 13, the windings 15, 16 being permanently connected through point b to an AC supply 11 and windings 13, 15 being connectible to this supply through points a, c and switches 18-21 and 26-28, which respectively constitute the first and second switches. A further switch 22, gauged to the first switch, controls the energisation of a coil 17 for opening and closing the shutter 1'. The supply 11 also feeds a transformer 31 having two secondary windings respectively supplying the detecting element 10 and the electronic circuit, which comprises an adjusting circuit part A (including element 10), an amplifying part having members 40..47 and a timing-out part D to drive the motor for a predetermined period after the smoke density has dropped below the preselected threshold. Lamps 4, 5 are connected with resistors 23, 24, 25 and 0 of which the latter has a high value. When the smoke density is below the threshold, a coil 30 is de-energised so that the second switch controlled by this coil is in position 26, 27 to shunt the resistor 0. Movement of the first switch contact 18 to contact 19, 20 or 21 respectively produces low speed operation, high speed operation or de-energisation of the motor 12, the current in circuit 4, 5, 23, 24, 25 being sufficient to 'fully light lamp 5 but insufficient to light lamp 4 in positions 19, 20. Switch 22 maintains coil 17 energised during movement of 18 between 19 and 20. When the smoke density reaches the threshold value, the signal from resistor 38 makes transistors 40, 43 successively conductive to energise a coil 48 and change a switch contact 50 from 51 to 52. Transistor 55 is thereby switched on to energise the coil 30 and charge capacitor 531. Contact 26 changes to position 28 to energise the motor 12 at high speed irrespective, of the position of contact 18, energise the coil 17 (if switch 18 is on contact 21) and insert resistor 0 into circuit, the latter action producing a voltage difference between terminals a, c causing high speed operation if switch contact 18 is in position 19 and also causing lamp 5 to be lit dimly. Lamp 4 is lit when contact 18 is on contact 21. When the smoke density falls below the threshold transistor 40 turns off to return switch contact 50 to position 51, but transistor 55 is kept on by capacitor 531 until it has discharged to a predetermined voltage. Thus .contact 26 changes back to contact 27 after a further predetermined high speed operation of the motor 12 to expel smoke from remote corners of a room containing the ventilator. A lamp 9 controlled by the switch 50, 51, 52 is on or off according to whether the smoke density is below or above the threshold. This lamp is also used to calibrate the circuit part A to produce high speed operation at a desired threshold, the knob 8 adjusting the tap of resistor 38 towards resistor 36 (preset together with resistor 37) or towards resistor 37 to determine the points at which the lamp 9 goes out and the motor starts, and the lamp is lit and the motor continues to operate for a predetermined time. A typical calibrating operation is described. In a modification. Fig. 3 (not shown) the lamp 9 is omitted and a normally-closed switch is provided in series with the capacitor 531, this switch being 'opened during calibration to disable the timing-out circuit D to determine the instants of switch-on and switch-off of the motor. A resistor 34 limits variation of the output of element 10 caused by moisture and heat.