BACKGROUND OF THE INVENTION

!• Field of the Invention

This invention relates generally to the detection of the products of combustion and, more particularly, to the detection of the toxic gaseous products of combustion.

2. Description of the Related Art

In recent years, publicity has been given to devices which indicate the presence of combustion. These devices have been and are being widely deployed in private and commercial buildings to alert residents of a potentially dangerous situation. In order to insure that the devices are operational, a requirement has been imposed that devices must be capable of being tested, in situ, to insure availability when needed. In a sense, the information provided with respect to the solid particular detectors of particles of combustion has been deceptive. The detectors generally referred to as smoke detectors are, in fact, solid particle detectors. The mechanisms upon which the solid particle detectors operate are typically radiation induced or photo-induced conduction. When particulate matter is introduced into the chamber of the solid particle detector, the particulate matter causes ionization of the air in the chamber. The ionization of the air causes a decrease in voltage in the sensing chamber, the decrease in voltage, when sufficiently large, resulting in activation of an alarm device.

The solid particle detectors suffer from two major disadvantages. First, the material detected is typically more prevalent when active and complete combustion is taking place, and not during a smoldering stage (i.e., with incomplete combustion) . Second, the principal harmful ingredient from complete or incomplete combustion

is carbon monoxide, a gas which is not detected by the solid particle ionization or photo-electric detectors. In the test procedure of these devices, the voltage across the chamber is lowered (without becoming zero) to determine if the alarm device is activated when voltage is decreased a predetermined amount.

Recently, a true smoke detector, identified as the Figaro Gas Sensor TGS 813 or the improved TGS 203 (having two heater elements to increase the sensitivity to carbon monoxide) has been distributed in the United States by the Figaro USA, INC of Wilmette, II. This device is filling the need for a device that is able to detect gases and, more particularly, to detect carbon monoxide. The sensor element of the smoke detector is comprised of a sintered bulk semiconductor consisting principally of tin oxide (Sn0 ₂ ) . When an appropriate gas is introduced into the smoke detector, the resistance across the smoke detector falls. However, the smoke detector unit has not been provided with the test circuits that would permit on location testing, the test circuits that would make the unit acceptable by Underwriters Laboratory requirements for widespread (including residential) applications.

A need has therefore been felt for apparatus and an associated method which simulate the introduction of an appropriate gas into the smoke sensor to determine if the test circuits, including an associated alarm device, are functional.

FEATURES OF THE INVENTION It is an object of the present invention to provide an improved detection unit for detecting the products of including smoke (i.e., carbon monoxide).

It is a feature of the present invention to provide an improved detection unit for detecting smoke (carbon monoxide) .

It is another feature of the present invention to provide a smoke detector with a test circuit, the test

circuit determining when the smoke detector and an associated alarm are operational.

SUMMARY OF THE INVENTION The aforementioned and other features are attained, according to the present invention, by providing the smoke detector unit with circuits that affect the smoke detector unit sensor element in a manner similar to the introduction of smoke into the detector chamber of the sensor element. In this manner, the smoke detector unit will be considered functional when conditions simulating the introduction of smoke into the detector chamber result in activation of the alarm. In particular, the introduction of smoke into the detector chamber lowers the resistance across the sensor element and results in a change in voltage across the sensor element. The present invention permits an operator by throwing of a switch or by pressing a button to cause a voltage change in the smoke detector that is similar to the change when smoke is introduced into the detector chamber of the sensor element.

These and other features of the invention will be understood upon reading of the following description along with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram of the smoke detector without the test circuits.

Figure 2 is a schematic diagram of a smoke detector unit of the present invention including the smoke detector and the test circuits according to a first embodiment.

Figure 3 is a schematic diagram of the smoke detector unit of the present invention including the smoke detector and the test circuits according to a second embodiment.

Figure 4 is a schematic diagram of the smoke detector unit according to a third embodiment of the present invention.

Figure 5 is a schematic diagram of the smoke detector unit according to a fourth embodiment of the present invention.

Figure 6 is a schematic diagram of the smoke detector unit according to a fifth embodiment of the present invention. Figure 7 is a schematic diagram of the smoke detector unit according to a sixth embodiment of the present invention.

Figure 8 is a schematic diagram of the smoke detector unit according to a seventh embodiment of the present invention.

Figure 9 is a schematic diagram of the smoke detector unit according to an eighth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

1. Detailed Description of the Figures

Referring now to Fig. 1, the schematic diagram of the smoke detector unit without the test circuits is shown. The input terminals of transformer Tl are coupled to the power lines while a first output terminal of the transformer Tl is coupled to an input terminal of voltage regulator U4. The output terminal of voltage regulator U4 is coupled through resistor R19 to the reference terminal of voltage regulator U4. The reference terminal of voltage regulator U4 is coupled through resistor R20 to the common terminal. The output terminal of voltage regulator U4 is coupled through resistor R3 to a first input terminal of comparator Ul. A second output terminal of transformer Tl, which is also the common terminal, is coupled to a first terminal of the heater element of sensor element SI, to a first terminal of

rheostat Rl, through capacitor Cl to a second input terminal of comparator Ul, and through resistor R4 to the first terminal of comparator Ul. A second terminal of rheostat Rl is coupled to first sensing terminal of sensor element SI, while the variable terminal of rheostat Rl is coupled through resistor R2 to the second input terminal of comparator Ul. A second sensing terminal of sensor element SI and a second heating terminal of sensor element SI are coupled to an output terminal of voltage regulator U2. The input terminal of voltage regulator U2 is coupled to a third output terminal of transformer Tl. The output terminal of voltage regulator U2 is coupled through resistor R17 to a reference terminal of voltage regulator U2. The reference terminal of voltage regulator is coupled through resistor R18 to the common terminal. The output terminal of comparator Ul provides the alarm signal.

Referring now to Fig. 2, the smoke detector unit shown in Fig. 1 is repeated with the addition of test circuit elements. The test circuit elements include a resistor R5 coupled in series with normally open switch SW1, the series circuit of the resistor R5 and the switch SW1 being coupled in parallel with resistor R4.

Referring now to Fig. 3, the smoke detector unit of Fig. 1 is shown with a second embodiment of the test circuit elements of the present invention. The test circuit elements include resistor R7 coupled in series with normally closed switch SW2, the series combination of resistor R7 and switch SW2 being coupled in parallel with rheostat Rl.

Referring next to Fig. 4, the smoke detector unit of Fig. 1 is shown with a third embodiment of the test circuit elements according to the present invention. A resistor R8 and a normally open switch SW3 are coupled in parallel, the parallel combination of switch SW3 and resistor R8 being coupled between the second sensing terminal of sensor element SI and the output terminal of voltage regulator U2.

Referring next to Fig. 5, the smoke detector unit of Fig. 1 is shown with test circuit elements according to the fourth embodiment of the present invention. The test circuit elements, resistor R9 and normally open switch SW4, are coupled in parallel, the parallel combination of resistor R9 and switch SW4 being coupled between the second heater terminal of sensor element SI and the output terminal of voltage regulator U2.

Referring next to Fig. 6, the smoke detector unit of Fig. 1 is shown along the test circuit elements comprising a fifth embodiment of the present invention. Voltage regulator U2 has resistor RIO coupled between the output terminal the voltage regulator U2 and the reference terminal of voltage regulator U2. The reference terminal of voltage regulator U2 is coupled through resistors Rll and R12, resistors Rll and R12 being coupled in series, to the common terminal. Normally open switch SW5 is coupled in parallel with resistor R12. Referring next to Fig. 7, the smoke detector of Fig. 1 is shown along with test circuit elements according to the sixth embodiment of the present invention. The test circuit elements include resistor R9 coupled in parallel with normally open switch SW6, the parallel combination of resistor R9 and switch SW6 coupled between the output terminal of voltage regulator U2 and the second terminal of the heater element of sensor element SI and the second sensing terminal of sensor element SI, the second terminal of the heating element of sensor element SI and the second terminal of the second sensing element of sensor element SI being coupled together.

Referring to Fig. 8, the smoke detector of Fig. 1 is shown along with the test circuit elements according to the seventh embodiment of the present invention. The test circuit elements include: a second comparator U3 ; a resistor R14 coupled between an output terminal of voltage regulator U2 and a first terminal of second comparator U3 ; resistor R15 coupled between the first

terminal of comparator U3 and the second output terminal of transformer Tl; capacitor C2 coupled between a second terminal of second comparator U3 and the second output terminal of transformer Tl; and resistor R13 coupled between the variable terminal of rheostat Rl and the second input terminal of second comparator U3. The output terminal of second comparator U3 is coupled to one terminal of normally open switch SW7.

Referring to Fig. 9, the smoke detector of Fig. 1 is shown along with the test circuit elements of the eighth embodiment of the present invention. The voltage regulator U2, along with associated resistors R17 and R18 of Fig. 1 has been replaced by a two position switch SW8. The second terminal of the heating element and the second sensing terminal of the sensor element SI are coupled to one terminal of switch SW8. The second and third terminals of switch SW8 select one of two output terminals of transformer Tl.

2. Operation of the Preferred Embodiment

Referring again to Fig. 1, the operation of the smoke detector can be understood in the following manner. The voltage regulator U4 applies a voltage level to the first input terminal of comparator Ul. The output voltage of voltage regulator U4 is determined by the voltage between the first and second output terminals of transformer Tl and the ratio of resistor R19 to resistor R20. The resistors R3 and R4 provide a resistor dividing network that applies a predetermined ratio of the output voltage of voltage regulator U4 to the first input terminal of comparator Ul. The output voltage of voltage regulator U2 is determined by the voltage of the transformer Tl between the second and third terminals and the ratio of resistor R17 and resistor R18. The sensor element SI has a resistance RS. The voltage applied to the second input terminal of comparator Ul is determined by the resistor RS, the rheostat resistor Rl, and the

position of the variable terminal of the rheostat Rl. The voltage at the second terminal of comparator Ul is chosen to be less than the voltage applied to the first terminal of comparator Ul, the difference in voltage between the two terminals determining the sensitivity of the smoke detector and being controlled by the position of the variable terminal of rheostat Rl. The voltage applied to said second terminal is less than the reference voltage when no products of combustion are detected by the sensor element SI. The voltage applied to said second terminal is greater than the reference voltage when products of combustion detected by the sensor element SI exceed a predetermined amount. The resistor R2 and the capacitor Cl form a high frequency filter to minimize the effects of the signal pick-up and signal spikes.

When the carbon monoxide gas enters the sensor SI, the resistance RS of the sensor element SI decreases. Because the voltage at the output terminal of voltage regulator U2 is constant, then, the decrease in the resistance RS causes the voltage at the second input terminal of comparator Ul to increase. When the voltage of the second input terminal of comparator Ul becomes larger than the voltage applied to the first terminal of comparator Ul, then the output voltage of the comparator Ul changes state and an alarm signal is generated.

Referring again to Fig. 2, when the switch SW1 is closed, resistor R5 is placed in parallel with resistor R4. The new combination has a lowered resistance between the first input terminal of comparator Ul, lowering the voltage with respect to the second input terminal. When the circuit and voltage values are correctly chosen, the voltage applied to the first input terminal of the comparator Ul will fall below the voltage level of the second input terminal of the comparator Ul, causing the comparator Ul to change state and providing an alarm signal for as long as the resistor R5 is coupled into the circuit.

Referring to Fig. 3, the resistor R7 is normally in the smoke detector circuit. When switch SW2 is activated, the resistor R7 is removed from the circuit. Therefore, the resistance between the sensor element and the common terminal is increased, causing the voltage across resistor Rl to increase and raising the voltage level applied to the second input terminal of comparator Ul. When the circuit components and voltages are properly selected, the voltage level applied to the first input terminal will rise above the voltage level applied to the second input terminal of comparator Ul resulting in an alarm signal until resistor R7 is reinserted in the circuit.

Referring again to Fig. 4, when switch SW3 is closed, the resistor R8 is shorted out, i.e., removed from the circuit. The current through rheostat Rl will increase, causing the voltage level applied to the second input terminal of comparator Ul to be increased. When the increase in voltage is sufficiently large, the comparator Ul will change state and an alarm signal will be generator until switch SW3 is opened and the resistor R8 reintroduced in the circuit.

Referring again to Fig. 5, the resistor R9 is typically included in series with the heater element(s) of the sensor element SI. When switch SW4 is closed, the resistor R9 is shorted out, i.e., is removed from the circuit. When the resistor R9 is no longer in series with the heater element of sensor element SI, the voltage across the heater will increase. The increased heat from the sensor heating element will cause the voltage across the sensor element SI to decrease, the voltage across rheostat Rl to rise, and the voltage applied to the second input terminal of comparator Ul to rise. When the circuit component values and voltage levels are selected properly, the output terminal of the comparator Ul will provide an alarm signal.

Referring again to Fig. 6, the ratio of resistor RIO to resistors Rll and R12 determine the voltage at the

output terminal of voltage regulator U2. When the resistor R12 is removed from the circuit by closing switch SW5 and providing a short circuit across resistor R12, the current through the sensor element SI will increase, both because of the increase voltage across sensor element SI and because the increased heater current will lower the resistance of sensor element SI. The increase in current, when the circuit parameters are correctly chosen, will activate the alarm signal at the output terminal of comparator Ul.

Referring again to Fig. 7, the resistor R9 is normally in the circuit in series with the sensor element SI. When switch SW6 is closed, the resistor R9 is removed from the circuit by providing a short circuit across resistor R9. The voltage will increase across the sensor element SI and the rheostat Rl. For the reasons described with reference to Fig. 6, correctly chosen circuit parameters will provide an alarm signal at the output terminals of comparator Ul as long as the resistor R9 is removed from the circuit.

Referring again to Fig. 8, the comparator U3 has a reference voltage set as a ratio of the voltage applied across the sensor element SI and the rheostat Rl. The voltage applied to the first terminal of comparator U3 is selected to be less than the voltage typically applied to the second input terminal of comparator U3. When the voltage applied to the second input terminal of U2 falls below the voltage applied to the first input terminal of comparator U3, an alarm signal will sound. This condition will occur when the heater elements have an open circuit (and the resistance across the sensor SI increases) , or when the sensing elements of the sensor element SI have a short circuit condition. The switch SW7 permits these parameters to be tested during a manual test, however, it will be clear that this test could be performed continuously to identify the undesired condition in the sensor element SI. The circuit of Fig.

8 can be used in conjunction with the other test circuit herein described.

Referring once again to Fig. 9, the voltage level applied to the first input terminal of comparator Ul is larger than the value of the peak alternating voltage when switch SW8 coupled the sensor element SI in the position shown. When switch SW8 is coupled to the higher voltage position (relative to the common terminal) , the voltage across the resistor and rheostat Rl will increase. When the parameters are selected properly, then the second input terminal will be higher than the first input terminal for a period during each cycle, resulting in the generation of an alarm signal.

The foregoing description is included to illustrate the operation of the preferred embodiment and is not meant to limit the scope of the invention. The scope of the invention is to be limited only by the following claims. From the foregoing description, many variations will be apparent to those skilled in the art that would yet be encompassed by the spirit and scope of the invention.