Ventilation Fan System With Smoke Detector Speed Control

Abstract

This invention relates to a ventilator wherein an electronic circuit is actuated when a detecting element detects the existence of any smoke or gas while a fan is in a manually selected slow rotating node of operation or in a stand-by halting position, and then the fan is automatically put into full rotation in order to expel smoke or such gas as carbon monoxide, and also for a specified period after completion of this expelling operation the fan is kept rotating during the above operation through the function of a delay-off circuit, with a shutter of a ventilating window being kept open by means of a switch network.

Description

BACKGROUND OF THE INVENTION

This invention concerns a field of automatic ventilator commonly used in households or the like, but which is particular in that when smoke or gas from cooking, etc. is filling a kitchen, etc. or when unusual smoke or carbon monoxide, etc. is emerging due to a fire, while the fan is in low rotation or even idle, an electronic circuit is actuated by a detecting element and automatically activates the ventilating fan.

There have been prior art devices wherein ventilator have been actuated by detecting elements through electronic circuits. However, their manual starting and automatic motivation have been independently operated without co-relation between them. Consequently, in such a conventional ventilator, even if the detecting element detected smoke or gas in its manually started operation, it has been unable to shift into automatic operation. Especially in case of its low speed operation, it has been unable to expel such detected dangerous smoke or gas. Furthermore, in such conventional ventilator, it cannot automatically shift from the circuit connection for manual operation into the circuit connection for automatic operation, and hence, when manually shifting the circuit connection into the automatic operation, a shutter which is interlocked with a manual starting switch first has to close itself and then to open itself anew, thus producing bothersome noises while closing and reopening itself.

SUMMARY OF THE INVENTION

The object of this invention is to actuate an electronic circuit of a ventilator whenever smoke or gas appears while a ventilating fan is operating at low speed or inoperative of a detecting element which is sensitive to smoke or gas, which circuit switches the fan into high speed operation. In this invention, the word "smoke" is defined to mean "smoke or gas."

The apparatus of this invention is provided with a switch designed for manually selecting three kinds of circuit connections, that is, for manually selected high speed operation, for manually selected low speed operation and for automatic control. When the detecting element detects smoke, no matter which connection of said switch was selected, the electronic circuit actuates an electromagnetic relay switch and automatically shifts the operation from manual control into automatic control and to high speed rotation.

The shift back from high speed operation into low speed turning off the apparatus of this invention is achieved by short-circuiting a speed control coil. For this purpose, an electromagnetic relay switch which closes a normal-open contact is provided, together with a ventilating fan motor having a main coil connected in parallel with a branch which connects an auxiliary coil, a resistor and the speed control coil in series. When shifting back from high speed to low speed or automatic operation after expelling smoke, said speed control coil is short-circuited by means of said manual operation switch, electromagnetic relay switch and another switch.

The apparatus of this invention is provided with a switch which maintains manual-open condition of a ventilator shutter while the fan shifts from manually started low speed operation into an automatic operation as a result of smoke detection. Accordingly, the wasteful opening and closing of the shutter which are usual in the prior art devices when shifting from the manually started operation into automatic operation can be avoided.

The electronic circuit to be actuated by the detecting element in the apparatus of this invention has a sensitivity adjusting circuit and a delay-off circuit part, as well as an electromagnetic relay switch which disconnects the delay-off circuit when adjusting sensitivity for operating the ventilating fan in accordance with due density of smoke. Accordingly, by watching a sensitivity adjusting lamp controlled by the electromagnetic relay switch, the sensitivity can be adjusted.

As mentioned above, the electronic circuit to be actuated by the detecting element is provided with the sensitivity adjusting circuit and the delay-off circuit part, and it is further provided with a switch for disconnecting the delay-off circuit while adjusting sensitivity in order to drive the ventilator in accordance with the density of smoke. Hence, such adjustment can be made by watching the movement of the ventilator.

Also as mentioned above, said electronic circuit to be actuated by a signal from the detecting element is provided with the adjusting circuit for adjusting the sensitivity of the system and the delay-off circuit for operating the ventilating fan for a specified period after expulsion of smoke. These two circuits are combined by an electromagnetic relay switch which controls the sensitivity adjusting lamp of the adjusting circuit during the adjustment and also sets the delay-off circuit. Hence, the sensitivity of the electronic circuit for operating the ventilator can be adjusted while watching the sensitivity-adjusting lamps.

Said sensitivity adjusting circuit of the electronic circuit to be actuated by the detecting element is provided with a semi-fixed resistor for compensating the threshold sensitivity, another semi-fixed resistor for presetting the position of an adjusting knob inbetween and a variable resistor for determining the operating sensitivity of the electronic-circuit. Hence, in case of varying the resistance of the variable resistor for determining the operating sensitivity of the electronic circuit, a due sensitivity can be set in an inbetween position.

The apparatus of this invention is provided with a manual switch operated for instance, by a pull string and having separate contacts for high speed, low speed and automatic operations, an electromagnetic relay switch capable of activating the ventilator in response to detected smoke with the detecting element at any of said contact, an "automatic" lamp which lights while the pull string switch is connected with the "automatic" contact, a "manual" lamp which lights while connected with "high speed" or "low speed" contact, and a circuit which lights either one of the "manual" and "automatic" lamps while the other one is cut off due to voltage division between the power source and the pull string switch. Hence, the state of the ventilator, whether in "manual" operation or in "automatic" halt, can be clearly indicated.

The apparatus of this invention is provided with the adjusting circuit including the detecting element, an amplifying circuit for amplifying signals of said adjusting circuit, and the delay-off circuit part for operating the ventilator after said amplifying circuit is disconnected, wherein said adjusting circuit and amplifying circuit part are combined, said amplifying circuit and delay-off circuit are combined via the electromagnetic relay switch, and said delay-off circuit and an output circuit part are connected via the electromagnetic relay switch. Therefore the ventilator of the output circuit is activated whenever the detecting element detects smoke.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a front view of a ventilator of an example of this invention,

FIG. 2 is a diagram of an electronic circuit of said ventilating fan,

FIG. 3 is a diagram of an electronic circuit of a ventilator of another example, and

FIG. 4 is a characteristic diagram of a detecting element.

DETAILED DESCRIPTION OF THE INVENTION

The first example of this invention will be described in detail referring to FIGS. 1, 2 and 4. In the figures, numeral 1 indicates a ventilator frame, numeral 1' indicates a shutter which has a known constitution and is driven by an electromagnet. Numeral 2 indicates a fan to be driven by a motor 12, numeral 3 a pull string for manual switching between "automatic" and "manual" operations, numerals 4 and 5 "automatic" and "manual" indication lamps, respectively, numeral 6 indicates an inlet for smoke or gas (hereinafter referred to only as "smoke") accumulating below a front frame 7 of the ventilator frame 1, numeral 8 an adjusting knob for regulating the sensitivity of the detection against the density of accumulating smoke to automatically change over to high speed operation, numeral 9 a sensitivity-adjusting neon lamp for guiding the position of the adjusting knob 8 in regulating the sensitivity. A series resistor 91 is connected in series to the neon lamp 9.

To regulate the system, the adjusting knob 8 is turned clockwise first from an L side (position of the lowest potential) to an H side (position of the highest potential) to find the position where the sensitivity-adjusting lamp 9 goes off and the fan 2 starts rotating. By reversing the knob 8 from this position in the direction of the L side, a point is found where the sensitivity-adjusting lamp is lit and the fan 2 continues rotating through actuation of delay-off circuit 531, 54, 55 and 57 shown in FIG. 2. The knob 8 is stopped at this point; then if smoke accumulates and enters through the inlet 6, an electronic circuit is actuated and automatically activates the fan 2 into high speed operation.

Numeral 10 indicates a detecting element provided with a pair of electrodes in a gas-sensitive semiconductor, being heated to a specified temperature by a weak current and having a characteristic of decreased resistance across the electrodes by the adsorption of smoke. This detecting element 10 is provided inside the inlet 6.

FIG. 4 is a characteristic diagram of the detecting element 10, showing the relation between variation of resistance value R(ko) and time t(minutes) on the ordinate and abscissa, respectively. According to this FIG. 4, when heating current and voltage are supplied, the resistance value radically drops during about the first 20 seconds, but becomes stable in about 5 minutes at the specified resistance value. The dotted line indicates such radial decline of resistance value by the adsorption of smoke at such stage.

Numeral 11 indicates an AC source terminal, to which usually 100 volts is applied. Numeral 12 indicates a motor for the fan, wherein a branch connecting a speed control coil 13, a capacitor 14 and an auxiliary coil 15 of the motor in series and a main coil 16 of the motor are connected in parallel. This motor 12 runs at a high speed when an AC voltage is applied across its terminals a-b, and runs at a low speed when the same voltage is applied across its terminals c-b and the coil 13 connected between the terminals a-c is short-circuited.

Numeral 17 indicates an electromagnetic coil for opening and closing a shutter connected in parallel with said motor 12 for the fan 2, and numeral 18 indicates a switch for changing over among manual-high, manual-low and automatic operations by means of the pull string 3. The switch 18 comprises a manual-low speed operation contact 19, a manual high-speed operation contact 20 and an automatic operation contact 21. Numeral 22 indicates a switch interlocked to said switch 18 and adapted to be turned "ON" when said switch 18 is connected to said "low" contact 19 or "high" contact 20 and to be turned "OFF" when switch 18 is changed over to said "automatic" contact 21. The function of this switch 22 is to keep the electromagnetic coil 17 continuously excited while the moving arm of switch 18 is being changed over from the "low" contact 19 to the "high" contact 20 or while being suddenly changed over from the manually selected "low" contact 19 or "high" contact 20 to the "automatic high" operation in order to expel smoke. This entirely eliminates the bothersome noise of a flapping shutter.

For the "automatic" indication lamp 4 and the "manual" indication lamp 5, neon lamps are preferably used, one of which is on while the other is off. Numeral 23 indicates a series resistor of the "automatic" lamp 4, numeral 0 and 24 indicate series resistors of the "manual" lamp 5, and numeral 25 indicates a by-pass resistor connected in parallel with a branch consisting of series connection of the "automatic" lamp 4 and the series resistor 23.

Numeral 26 indicates a switch of an electromagnetic relay 29 comprising a normal-closed contact 27 and a normal-open contact 28, which switch 26 is changed over from the side of normal-closed contact 27 to the side of normal-open contact 28 by excitation of an electromagnetic coil 30; in other words, while the density of smoke is below a specified value and the fan is in operation by the manual "high" contact 20 or "low" contact 19 selected by the switch 18 with the pull string 3, the normal-open contact 28 of the switch 26 is OFF and the normal-closed contact 27 is ON.

In such a manual operation, when the electromagnet 29 is deenergized and the switch 26 is connected on the side of contact 27, the series resistor 0 is shortcircuited, and therefore, the source voltage is applied across a series connection linking the series resistor 24, the "manual" lamp 5, and the by-pass resistor 25. Due to the short circuiting of the resistor 0, the "manual" lamp 5 is lit in a brighter phase. Also, due to existence of the by-pass resistor 25, the "automatic" lamp 4 is not lit. In this manual operation, when the switch 26 of the electromagnetic relay 29 is connected to the side of the contact 28 by energization of the electromagnet 29 upon detection of smoke, the series resistor 0 becomes inserted in said series connection. Accordingly the "manual" lamp 5 is less brightly lit on account of the voltage drop in said resistor 0. Also the automatic lamp 4 is inoperative on account of said by-pass resistor 25.

In case the switch 18 is changed over to the "automatic" contact 21 by pulling the pull string but there is no smoke to detect, the source voltage is applied across the "automatic" lamp 4 and the series resistor 23 through the normal-closed contact 27 of the switch 26 and the "automatic" contact 21 of the switch 18, and hence, the "automatic" lamp 4 is lit. Since the switch 18 is selecting the "automatic" contact 21, both ends of the branch connecting in series the "manual" lamp 5 and the series resistor 24 are short-circuited, and consequently, the "manual" lamp 5 goes out.

Next, the electronic circuit for actuating the electromagnetic relay 29 will be explained. This circuit comprises

an adjusting circuit A including the detecting element 10.

an amplifying circuit for amplifying the signal of the adjusting circuit, and

a delay-off circuit D for driving the fan for a specified period after cutting off the amplifying circuit.

Numeral 31 indicates a power transformer, numeral 32 a diode for rectification, and numeral 33 a capacitor for reducing ripple. Numeral 34 indicates a resistor connected between the electrodes of said detecting element 10 in order to limit variation of output corresponding to the variation of resistance of said detecting element 10 from moisture and heat.

The primary winding of transformer 31 is connected to the A.C. input terminal 11. The upper secondary winding feeds a D.C. current through rectifier 32 to transistors 40, 43 and 55 and so forth. The lower secondary winding or transformer 31 moderately heats the element 10.

Numeral 35 indicates a series resistor for the detecting element 10, and numeral 36 a variable resistor for compensating the threshold sensitivity. Numeral 37 indicates a semi-fixed resistor for preset adjustment to start the fan by detecting smoke while in the "automatic" operation with the adjusting knob 8 in its half-way position. Resistors 34, 35, 36 and 37 are all of high resistance and, consequently the D.C. electronic circuit receives very little current through these resistors. Numeral 38 indicates a variable resistor to be turned by the adjusting knob 8 for manual setting. Numeral 39 is a diode connected across the base and the emitter of a transistor 40 and numeral 41 is a resistor connected to the collector of the transistor 40. Numeral 42 is a coupling capacitor connected between the collector of the transistor 40 and the base of a transistor 43 while numeral 44 is a diode connected across said coupling capacitor 42 and the base of said transistor 43. Numerals 45, 46 & 47 are resistors, numeral 48 is an electromagnetic coil of an electromagnetic relay 49 connected to the collector of said transistor 43, numeral 50 is a switch of said electromagnetic relay 49 having a normal-closed contact 51 and a normal-open contact 52, and numeral 53 is a smoothing condenser connected across said electromagnetic coil 48. During the period when the switch 50 is changed over to the side of the normal-closed contact 51, the sensitivity-adjusting lamp 9 is kept lit, indicating the condition that the smoke-detecting function is entirely suspended.

Numeral 531 indicates a capacitor connected between the normal-open contact 52 of said switch 50 and the positive outlet of the power source, numeral 54 is a resistor connected between said normal-open contact 52 and the base of a transistor 55, numeral 56 is a diode for protection from surge voltage connected in parallel with the electromagnetic coil 30 connected to the collector of said transistor 55, and numerals 57 and 58 are resistors.

Next, the abovementioned electronic circuit will be explained. Adjusting circuit includes such elements as the detecting element 10, the variable resistor 38, the semi-fixed resistor 37, and the threshold-compensating variable resistor 36, etc. The electric potential to drive the transistor 40 ON must be determined in relation with the size of output of the detecting element 10. The adjustment of this base potential is made by turning the sensitivity-adjusting knob 8 and thereby moving the sliding piece of the variable resistor 38. When the adjusting knob 8 is turned to the L side, a sliding piece of the variable resistor 38 slides toward the variable resistor 36 for compensating the threshold sensitivity and the base input voltage of the transistor 40 is divided to low voltage, and hence, the transistor 40 does not become ON until smoke reaches a certain density.

When the power source terminal 11 is connected to an AC source and the adjusting knob 8 is turned toward the H side, the sliding piece of the variable resistor 38 slides toward the semi-fixed resistor 37 and raises the base potential of the transistor 40. Hence, the AC output of the collector of the transistor 40, which imparts the AC output to the collector even if the density of smoke or gas is small and the AC voltage output is small, is applied to the base of the transistor 43 via the capacitor 42 and the diode 44 and turns the transistor 43 ON. Accordingly, the electromagnetic coil 48 connected to said collector of the transistor 43 is excited, opening the normal-closed contact 51 of the switch 50 and shifting switch 50 to contact 52.

Consequently, in case of "automatic" operation, the sensitivity-adjusting lamp 9 is turned off, and the transistor 55 is turned ON since the current flows in its base through the resistors 54 and 58. As a result, the electromagnetic coil 30 on the collector side is excited and the normal-open contact 28 of the switch 26 is turned ON, driving the fan motor 12 into high speed operation regardless of the position of the switches 18 and 22. After about five minutes from the application of the power to the power input terminals 11 with this high speed operation, when the detecting element 10 becomes stable the adjusting knob 8 is slowly turned toward the L side into a position where the transistor 40 goes OFF at a certain point. Therefore, the switch 50 reverts to its normally closed contact 51 lighting the sensitivity-adjusting lamp 9. The adjusting knob 8 is set at this lighting position to complete sensitivity-adjustment.

At this time, the normal-open contact 52 goes OFF, and an electric load charged in the capacitor 531 starts to discharge through the resistor 57, the emitter-base of the transistor 55 and the resistor 54.

During the discharging of the capacitor 531, the transistor 55 is kept ON for a specified duration and the electromagnetic coil 30 connected to the collector is kept excited, and hence, the normal-open contact 28 of the switch 26 is also kept ON, keeping the fan motor 12 in actuation for said specified duration. However, when the charge on the capacitor 531 falls below a specified value, the transistor 55 goes OFF and the electromagnetic coil 30 stops excitation, making the normal-closed contact 27 of the switch 26 ON, and hence, stopping the fan 2 if the switches 18 and 22 are in "automatic" setting, or returning the motor to low speed running if the switches 18 and 22 are set for low speed operation.

The delay-off circuit D consists of the capacitor 531, the resistor 54, the transistor 55 and the resistor 57, and provides the advantage of expelling smoke remaining in remote corners of room by keeping the fan 2 rotating for a specified period after smoke has been cleared away from the main of room. In absence of such delay-off circuit part D, the fan 2 would stop rotating when smoke no longer exists around the inlet 6, and hence, smoke in remote corners of room would very likely remain there.

FIG. 3 shows a modified example. This example is basically the same as that of FIG. 2, except for that it lacks the sensitivity-adjusting lamp 9, and therefore the sensitivity-adjustment is done by watching the fan 2 stop and then by turning the knob 8. Other constituent parts corresponding to those shown in FIG. 2 carry the same numerals, to which the descriptions made referring to FIG. 2 shall apply.

In FIG. 3, numeral 59 indicates a switch connected in series to the capacitor 531. If this switch 59 is kept OFF, the delay-off device does not work, and hence, when the output of the detecting element 10 is extinct, the transistor 55 becomes immediately OFF, but if this switch 59 is kept ON, the delay-off circuit D is kept working by the capacitor 531 as in FIG. 2, and consequently, the halt of rotation of the fan can be delayed for the discharging period of the capacitor 531 after extinction of output of the detecting element as in the example shown in FIG. 2.

Now the adjusting procedure for the apparatus of FIG. 3 is described as follows. Connect the power source terminal 11 to an AC power source and change the switch 18 over to "automatic" contact, confirming it by noticing the lighting of the "automatic" lamp 4. Next, turn the adjusting knob 8 from the end of the L side slowly to the H side. By this turning of the knob 8, the sliding piece of the variable resistor 38 slides from the side of the variable resistor 36 to the side of the semi-fixed resistor 37, and hence, an AC output appears in the collector of the transistor 40 at a certain point.

As a result, the transistor 43 is turned ON, also turning the transistor 55 ON, causing the electromagnetic coil 30 connected to its collector to be excited and the switch 26 to be changed over to activate the fan motor 12 into high speed operation.

After rotating the fan 2 for about 5 minutes to stabilize the circuits including the detecting element 10, turn the adjusting knob 8 counter-clockwise, namely, toward the L side, with the switch 59 in its OFF state. Thereupon, the AC output of the collector of the transistor 40 disappears at a certain point, where the adjusting knob 8 is to be stopped. At this point the transistor 43 becomes OFF, the electromagnetic coil 48 becomes unexcited, the switch 50 is charged over and the normal-open contact 52 becomes OFF.

As stated above, the switch 59 is already OFF, and hence, the transistor 55 becomes OFF. Accordingly, the normal-open contact 28 of the switch 26 becomes OFF and the fan stops.

In the example of FIG. 3, as described above, the fact that transistor 40 is now OFF can be ascertained by stopping the motor. Therefore, if the adjusting knob 8 is set while watching the rotation of the motor 12, the detecting element 10 reduces the resistance value when it subsequently detects smoke and the base potential of the transistor 40 relatively rises, and thus the fan motor 12 can be driven.

In the ventilator of this invention as described in the above examples of FIGS. 2 and 3, a change-over between "automatic" and "manual" operations can be made by means of the pull string 3. In the case of "automatic" operation, it can be done by connecting the switch 18 to the "automatic" contact 21, which means that the fan is in a waiting pause for smoke.

This ventilator is usually installed above a gas range or water geyser liable to produce smoke when in use in a kitchen. Such smoke enters the inlet 6 of the ventilating fan and contacts the detecting element 10, thereby lowering the resistance value considerably and sending an AC signal to the base of the transistor 40. Then the electronic circuit is actuated as described, driving the fan 2 into high speed operation, and simultaneously, sending exciting current to the electromagnetic coil 17 which then opens the shutter to expel smoke or gas. At this time, the "automatic" lamp 4 is lit and the "manual" lamp 5 is off.

Next the "manual operation" made by connecting the switch 18 to the "manual high" contact 20 or the "manual low" contact 19 by means of the pull string 3 will be explained. In this state the "manual" lamp 5 is lit and the "automatic" lamp 4 is tuned off by the by-pass resistor 25. When the switch 18 is connected to the "manual high" contact 20, the fan motor 12 starts high speed operation. When the switch 18 is connected to the "manual low" contact 19, the speed control coil 13 is short-circuited by the circuit linking the contacts 19-18, 27-26, 22, and low speed operation is started. Then if smoke is encountered, the resistance value of the detecting element 10 drops and turns the transistor 40 ON by imparting a voltage to its base, whereby the switch 26 of the relay 29 is changed over to the normal-open contact 28 ceasing said short-circuiting of the speed control coil 13, and the fan motor 12 is operated at high speed.

In such manner, wherever smoke needs to be expelled even while the switch 18 is kept connected to the "manual low" contact 19, the fan is shifted to high speed operation to ensure the function of expelling smoke smoothly and quickly.

When pulling down the pull string 3 in order to change the switch 18 over manually from low speed operation to high speed operation, there is no flapping noise of closing and reopening of the shutter, because the source voltage is almost continuously applied to the electromagnetic coil 17 through the switch 22. Also when changing over from "automatic" low operation to "high" operation by detecting smoke, there is no shutter flapping noise at all, because the switch 22 is kept ON and the shutter is kept in the open state.

Either in case of "manual" high or low speed operation or in case of "automatic" halt state, the ventilator of this invention can be automatically changed over to high speed operation by automatically switching the electronic circuit whenever the detecting element detects smoke or gas. Therefore, this ventilator has the characteristic of being able not only to start automatically from the inoperative state but also it changes over automatically from low speed operation to high speed operation to effect quick ventillation. Thus this ventilator is able to change over from any state into high speed operation by means of the switch 26 of the electromagnetic relay 29 instantly upon detecting smoke.

In case smoke is detected while in "manual high" operation, such high speed operation continues after the electromagnetic relays 49 and 29 have been actuated. In such a case, even if the operation is changed over to "manual low" or "automatic," without noticing the existence of smoke or gas, the operation continues in high speed until smoke or dangerous gas has been expelled to ensure safety.

Since the ventilator of this invention has the switch 22 which keeps the shutter open during the changing over from "manual" to "automatic" operations, the electromagnetic coil 17 is kept excited in all cases of change-over and avoids flapping noise of the shutter.

The ventilator of FIG. 2 has an advantage of making sensitvity adjustment very easy by isolating the sensitivity-adjusting part and the delay-off part of the electronic circuit by means of the switch 50 of the electromagnetic relay 49 and simultaneously flickering the sensitivity-adjusting lamp 9, and also by isolating the delay-off part and flickering the sensitivity-adjustment lamp irrespectively of the rotation of the fan, when adjustment is made.

The ventilator of FIG. 3 has the advantage of making sensitivity-adjustment by opening the switch 59 to deactivate of the delay-off circuit and watching the movement of the fan motor, without using the sensitivity-adjusting lamp.

The vantilator of this invention has the advantage of accurately adjusting sensitivity within the turning range of the adjusting knob 8 because the sensitivity-adjusting part is provided with the variable resistor 36 for compensating threshold sensitivity as well as the semi-fixed resistor 37 for adjusting change-over point.

The ventilator of this invention has the further advantage of making alternate lamp indications, for instance, when the "automatic" lamp 4 is on, then the "manual" lamp 5 is off, and vice-versa, in accordance with selection of the operations.

Claims

What is claimed is

1. A ventilator system including a ventilating fan comprising: a smoke detecting element;

a fan motor for driving the ventilating fan, said motor being operable at a low speed and a high speed;

a manual change-over switch having a high speed position, a low speed position and an automatic position and associated contacts, operably connected to said fan motor; and

an electronic circuit means connected to said detecting element and said fan motor, said electronic circuit means being actuated by said detecting element when said element detects smoke and said electronic circuit means automatically switching said fan motor to high speed when actuated by said detecting element regardless of the position of said manual change-over switch.

2. The device of claim 1, wherein said fan motor includes a main coil, an auxiliary coil, a capacitor and a speed control coil, said main coil connected in parallel with a series combination of said auxiliary coil, said capacitor and said speed control coil seriatim, the junction of said capacitor and said speed control coil connected to the low speed contact and the junction of said speed control coil and said main coil connected to the high speed contact, whereby said speed control coil is short-circuited by said manual change-over switch in the low speed position thereof, producing low speed operation of said fan motor.

3. The device of claim 2 wherein said electronic circuit means comprises an electromagnetic relay and a normally open switch, said electromagnetic relay connected to said normally open switch such that activation of said relay when smoke is detected closes said normally open switch, said switch being connected to said main coil of said fan motor when closed, thereby driving said motor at high speed.

4. The device of claim 1, further comprising:

a delay-off circuit means operatively connected to said electronic circuit means for maintaining said fan motor in its high speed position for a predetermined time period after said detecting element no longer detects smoke; and

switch means connected to a ventilating window shutter for keeping said shutter open when said fan motor changes speed.

5. The system of claim 4 wherein said electronic circuit means further comprises means for adjusting the threshold sensitivity of the system to smoke, said means including a sensitivity adjusting lamp and a manual switch for isolating said delay-off circuit means.

6. The system of claim 4 wherein said electronic circuit means further comprises means for adjusting the threshold sensitivity of the system to smoke and gas, said means including a sensitivity adjusting lamp and a switch connected to said lamp and said delay-off circuit means for controlling said sensitivity adjusting lamp during adjustment and for setting said delay-off circuit means.

7. The system of claim 6 wherein said sensitivity adjusting means further comprises a first variable resistor for adjusting threshold sensitivity, a semi-fixed resistor for positioning an adjusting knob within the adjustable range of said knob and a second variable resistor for adjusting the working sensitivity of said electronic circuit means.

8. The device of claim 1 further comprising an automatic operation indication lamp connected to automatic operation contact of said manual change-over switch and a manual operation indication lamp connected to both the high speed operation contact and said low speed operation contact of said manual change-over switch whereby said manual operation indication lamp becomes operative when either of said high speed and low speed contacts are in use and circuit means operatively connected to said lamps for alternative operation of said lamps.

9. A ventilating fan system including a fan comprising: a sensitivity-adjusting circuit including a detecting element (10); an amplifying circuit for amplifying signals detected by said sensitivity-adjusting circuit; a delay-off circuit for keeping the fan rotating after said amplifying circuit is isolated the sensitivity-adjusting circuit and the amplifying circuit being operably coupled and the amplifying circuit and the delay-off circuit being coupled through a switch (50) of an electromagnetic relay (49),; and an output circuit connected to said delay-off circuit through a switch (26) of an electromagnetic relay (29).