US3717861A

US3717861A - Tornado alarm

Info

Publication number: US3717861A
Application number: US00070267A
Authority: US
Inventors: R Wright
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-09-08
Filing date: 1970-09-08
Publication date: 1973-02-20
Anticipated expiration: 1990-02-20

Abstract

A tornado alarm of the pressure responsive type which responds only to the particular barometric phenomena associated with a tornado while remaining insensitive to pressure fluctuations of different origin. The device comprises a housing divided into a sensing chamber and a buffer chamber by a flexible diaphragm. The buffer chamber communicates with the atmosphere through an orifice sized so that pressure in the buffer chamber is insensitive to atmospheric pressure variations at rates higher than those produced by the tornado and arising from such extraneous causes as door or window closing. The sensing chamber communicates with the atmosphere through another orifice, sized so that pressure in the sensing chamber can follow only slow atmospheric pressure variations, such as result from the progression of atmospheric highs and lows across the country. The diaphragm thus has a pressure differential across it only when the pressure conditions associated with a tornado are present. A switch, actuated by the diaphragm, controls an alarm to signal the presence of these conditions and permit safety measures to be taken before the tornado strikes.

Description

[58] Field of Search ..340/236, 421; 73/170 United States Patent [191 Wright, Jr.

[54] TORNADO ALARM [76] Inventor: Robert C. Wright, Jr., 5 North Street, Hingham, Mass. 02043 [22] Filed: Sept. 8, 1970 [21] Appl. No.: 70,267

[52] US. Cl ..340/236, 200/83 N [51] Int. Cl. ..G08b 21/00 200/83 R, 83 C, 83 N [5 6] Reierences Cited UNITED STATES PATENTS [451 Feb. 20, 1973 ABSTRACT A tornado alarm of the pressure responsive type which responds only to the particular barometric phenomena associated with a tornado while remaining insensitive to pressure fluctuations of different origin. The device comprises a housing divided into a sensing chamber and a buffer chamber by a flexible diaphragm. The buffer chamber communicates with the atmosphere through an orifice sized so that pressure in the buffer chamber is insensitive to atmospheric pressure variations at rates higher than those produced by the tornado and arising from such extraneous causes as door or window closing. The sensing chamber communicates with the atmosphere through another orifice, sized so that pressure in the sensing chamber can follow only slow atmospheric pressure variations, such as result from the progression of atmospheric highs and lows across the country. The diaphragm thus has a pressure differential across it only when the pressure conditions associated with a tornado are present. A switch, actuated by the diaphragm, controls an alarm to signal the presence of these conditions and permit safety measures to be taken before the tornado strikes.

10 Claims, 4 Drawing Figures (SENSING) (ACTUAITING) PATENTEDFEBZOW 3,717. 861

' SHEET 2 OF (AMBIENT) ,P (BUFFER) Ap ACTUATION LEVEL L PS pB 1 SWITCH CLOSED TORNADO ALARM BACKGROUND OF THE INVENTION The field of the present invention relates to pressure responsive signalling devices, and more particularly, to such devices specifically adapted. to signal the proximity of a tornado.

Tornadoes provide the most violent weather phenomena known. The characteristic tornado vortex has probable wind speeds up to 300 miles per hour and travels a path of destruction averaging 700 feet wide and 4 m5 miles long. Damage in the millions of dollars, with loss of many lives, takes place when tornadoes strike heavily populated areas. Because tornadoes move unpredictably, and often during thunderstorms whenvisibility is low, they are difficult to track reliably. Hence there is no way to determine with complete accuracy whether one is in the path of a tornado. However, it is possible to determine if one is near a tornado, and thus in heightened danger of being struck by it, through the use and analysis of certain barometric phenomena associated with the tornado. It is known that in the area immediately surrounding the tornado, e.g., within roughly a 1 mile radius of the vortex, there is a marked drop in barometric pressure which persists for as long as the tornado stays close. This adjacent pressure drop cannot be put in terms of any absolute barometric pressure, as it may occur as a deviation from widely varying ambient pressures.

Devices have been developed to detect the characteristic tornado pressure drop without being affected by ambient pressure variations. Examples of such devices are illustrated in Wilson, U.S. Pat. No.

rates. The alarm has housing means providing an internal compartment, and flexible diaphragm means dividing the compartment into first and second chambers. The first chamber communicates with the exterior of the housing, i.e., the ambient atmosphere, through first orifice means which are sized to permit pressure in the first chamber to vary in response to external pressure changes at a rate within or lower than the predetermined range of rates which are associated with a tornado. Thus, the first chamber has a pressure from which rapid pressure fluctuations with spurious origins have been eliminated. The second chamber communicates with the exterior of the housing, either directly or through the first chamber, through second orifice means sized to permit pressure in the second chamber to vary in response to external pressure changes at a rate lower than the predetermined range of rates. Thus pressure in the second chamber follows only large scale pressure fluctuation due to changing high and low progression. A differential pressure will exist across the diaphragm means whenever the external pressure change is within the predetermined range of rates to be detected. Switch means are closed by travel of the 3,029,422 and Jacobs,U.S. Pat. No. 2,723,388. Both of these devices provide a chamber whose pressure varies along with the ambient atmospheric pressure to thus provide a datum against which the tornado pressure drop can be detected, thus relieving the device of any dependence on ambient pressure variations. Such devices are far more reliable than the earlier detecting devices which could only respond to a specific low pressure value. Notwithstanding this gain in reliability, these devices are still unsatisfactory as they are subject to a substantial amount of false signalling. Unfortunately, a number of other barometric phenomena not associated with tornadoes can also actuate these devices. Typical examples are the closing of a door to a room in which the device is located, a sudden gust of wind against the device, the turning on or off of air conditioning equipment, and the like. These pressure fluctuations can be quite commonplace and can severely lower the reliability of the sensing devices, sometimes to the point where, like the boy who cried wolf, their indication is no longer believed and their warning value is lost.

SUMMARY OF THE INVENTION Objects of the present invention are to provide a pressure responsive tornado alarm which responds to the pressure drop associated with a tornado, but which is insensitive to spurious pressure fluctuations; which is inexpensively constructed; and which is reliable and durable in use.

According to the invention, the tornado alarm is of the pressure responsive signalling type and detects pressure changes within a range of predetermined diaphragm in response to the pressure differential thereacross, and alarm means respond to closure of the switch means to warn that tornado conditions are present. Typically, both orifice means are adjustable in size to permit the rates of flow therethrough to be adjusted, and the switch means is adjustable so that it will respond to varying pressure differentials across the diaphragm. Thus sensitivity of the device to a particular range and magnitude of pressure changes can be selected to give best results for a particular locality or set of common conditions.

These and other objects and novel aspects of the invention will be apparent from the following description of preferred embodiments.

DESCRIPTION OF THE DRAWING FIG. 1 is a side sectional view of an embodiment of the invention;

FIG. 2 is a partial elevation of the embodiment of FIG. 1;

FIG. 3 is an essentially schematic view, similar to FIG. 1; of a modification of the invention; and

FIG. 4 is a graph relating pressures occurring in the apparatus illustrated in FIGS. 1-3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 illustrate, largely in schematic form, a tornado alarm 10 according to the invention. The alarm device 10 comprises a rigid housing 12 divided into a sensing chamber S and a buffer chamber B by a flexible diaphragm 14. As illustrated, the housing 12 can be formed from a pair of mating circular dished members 128 and 128 which sandwich diaphragm 14 between their outwardly extending flanges 16S and 168. The housing 12 is typically to be mounted in a base 18 to which a cover 20 (dashed lines) is fitted. The cover 20 is not air tight, but freely permits the ambient atmosphere A to surround the housing 12.

The buffer chamber B communicates with the ambient atmosphere A through an orifice 22 provided in housing member 128, and there is intercommunication between buffer chamber B and sensing chamber S through an internal orifice 24 provided in diaphragm 14. The diaphragm carries an electrical contact 26, located in the position of greatest diaphragm distention, which aligns with another contact 28 adjustably secured to housing member 128 by means of a threaded support 30 attached thereto. Connected to the

contacts

26, 28 by means not shown are signal means 32 of conventional type, shown diagrammatically as occupying space within base 18. The signal means 32 are preferably of the, battery operated type, as electric lines are sometimes downed just when the need for the tornado alarm is greatest.

As indicated previously, one of the primary objects of the present invention is to produce an alarm signal only when pressure changes of the type produced by a tornado are encountered. Accordingly, orifice 22 and orifice 24 are dimensioned so that flow therethrough will be differently responsive to pressure changes. As is well known, when pressure on one side of an orifice changes, there will be fiow of air through the orifice tending to equalize the pressures. The pressure change on the other side of the orifice behaves in an exponential manner, the time constant being determined by the size of the orifice. Using these principles, orifice 22 between buffer chamber B and ambient atmosphere A is dimensioned so that the pressure in buffer chamber B, designated p varies at a rate which is within or lower than the range of rates of pressure change associated with tornado conditions. More rapidly occurring fluctuations, having extraneous origins whose detection is undesirable, and due to door closings, window closings, air conditioner startings, and the like, occur too rapidly for any response to be reflected in buffer chamber B. As an illustration, the time constant for pressure change in buffer chamber B should be on the order of several seconds, such as ten seconds.'This speed of response is sufficiently fast to give adequate warning of a tornado, and it is sufficiently slow so that the alarm will not be sensitive to pressure fluctuations caused by closing of doors and the like.

lntercommunicating orifice 24 between buffer chamber B and sensing chamber S, however, is dimensioned so that pressure in the sensing chamber varies at a rate which is lower than the range of rates of pressure change associated with the tornado. Thus the sensing chamber pressure, designated p excludes pressure changes both of the tornado condition origin and of the extraneous origin, and follows only the slowly varying component of pressure which forms the datum against which these pressure changes occur. Thus the pressure p is adapted to follow large scale atmospheric changes, such as the progression of atmospheric highs and lows across large geographic regions.

The

orifices

22 and 24 must be carefully sized to produce the desired time constants if tornado detection is to be accurate. One technique permitting easily reproducible and precise time constants to be obtained fashions the orifices from fixed bore capillary tubing. In

' on the alarm apparatus, can be easily understood from the example given by the graph of FIG. 4. FIG. 4 is a graph having a common horizontal time axis for the pressures depicted. The example for atmospheric pressure p shows the pressure to change with very rapid variations in the form of spikes 40; a moderately fast variation in the form of prolonged drop 42, this being the condition associated with a tornado; and a gradual variation provided by the downwardly drifting portions 44 of the curve, this last variation having its origin in the progression of highs and lows over long periods of time. As described above, the buffer chamber B filters out the high frequency variations, and thus the buffer pressure p, comprises only the gradual drift 44 and the tornado associated drop 42. The sensing chamber S on the other hand reacts to neither the quickly varying spikes 40 nor to the tornado associated drop 42, and its pressure p; includes only the slowly varying drift 44, as illustrated. The action of diaphragm 14 is completely dependent upon the relative pressures in the buffer and sensing chambers B and S. The diaphragm 14 will be distended to the right, as shown in FIG. 1, to close

contacts

26 and 28, only if there is a differential pressure Ap p p which is greater than a prescribed value. As shown in FIG. 4, the differential pressure Ap rises above a low value only during the time when the tornado associated pressure change 42 is present. At other times, the slowly decreasing component 44 is present in both buffer and sensing chambers and cancels itself out.

The spacing of

contacts

26 and 28 determine how great a differential pressure is required for the contacts to be closed. The actuation level L shown in FIG. 4 corresponds to a particular spacing, and can be raised or lowered to decrease or increase the sensitivity of the device. Whenever the differential pressure is above this actuation level L, the switch contacts are closed.

FIG. 3 illustrates schematically an alarm device which has several modifications and omits base and cover members. The alarm device 100 comprises a rigid housing 112 divided by a diaphragm 114 into buffer chamber B and sensing chamber S, as before. Buffer chamber B communicates with ambient atmosphere A, however, through an orifice 122 whose size is controlled by means of a valve 122V. The valve 122V is adjustable, and thus permits the size of the orifree to be adjusted to precisely obtain the flow rate desired. Sensing chamber S, instead of communicating with the ambient atmosphere A through a path including a diaphragm orifice, the buffer chamber B, and its orifice, instead communicates directly with the atmosphere through the orifice 124 provided in housing 112 and having an orifice valve 124V to adjustably control rate of flow therethrough. By means of valves 122V and 124V, the

orifices

122 and 124 are adjusted so that buffer chamber B has its pressure vary at rates within or below the predetermined rates of pressure change associated with a tornado; and sensing chamber S hasits pressure vary only at rates below those associated with a tornado, as before. Accordingly, the graph of FIG. 4 applies to the structure shown in FIG. 3 as well as the structure shown in FIGS. 1 and 2. Instead of providing a movable contact on diaphragm 114 as in FIG. 1, the embodiment of FIG. 3 has a microswitch adjustably mounted adjacent the diaphragm. The

microswitch can be self-contained and covered,

thereby eliminating any problems arising from dirt preventing contact closing.

From the foregoing description several advantages of the tornado alarm of the present invention appear. First, the alarm effectively prevents false signalling by filtering out the sort of pressure perturbations which are most likely to generate a false signal. Second, the alarm device is able to provide this added reliability without complicated structural changes. Very little is needed in addition to that required for prior art devices. Third, the device can be adjustedto compensate for aging, and to provide the required degree of sensitivity, by means of simple adjustments. Fourth, the device can be made into a self-contained unit which can be conveniently located within a house or business building, without having to make a compromise with sensitivity to allow for extraneous pressure fluctuations, and without having to make any other allowances for such fluctuations. I

It should be understood that the present disclosure is for the purpose of illustration and that the present invention includes all modifications included within the scope of the appended claims.

I claim:

l. A pressure responsive signalling device for detecting pressure drop associated with the approach of a tornado; comprising housing means providing an internal compartment; flexible diaphragm means dividing said compartment into first and second chambers; said first chamber communicating with the exterior of said housing through first orifice means sized to exclude sudden, rapid pressure fluctuations from said first chamber and sufficient to permit pressure in said first chamber to vary in response to the pressure drop associated with the approach of a tornado; said second chamber communicating with the exterior of said housing through second orifice means sized to permit pressure in said second chamber to vary in response to pressure changes in said first chamber at a lower rate than said rate of change in said first chamber; whereby a differential pressure will exist across said diaphragm means whenever pressure drop occurs due to apprach of a tornado;

switch means adapted to be closed by travel of said diaphragm in response to a pressure differential thereacross; and

signalling means responsive to closure of said switch means.

2. A pressure responsive signalling device according to claim 1 wherein said first orifice means comprises an orifice provided in said housing sized to permit pressure in said first chamber to vary in response to external pressure changes that take place over a duration of at least several seconds and said second orifice means comprises an orifice provided in said diaphragm of smaller diameter then said first orifice means.

3. A pressure responsive signalling device according to claim 1 wherein said first and second orifice means are orifices provided in said housing means.

4. Pressure responsive signalling means according to claim 1 wherein said orifice means are adjustable in 5. Pressure responsive signalling means according to claim 1 wherein said switch means is adjustable to close said contacts at predetermined differential pressures across said diaphragm means.

6. Pressure responsive signalling means according to claim 1 wherein said switch means is adapted to close said contacts when said external pressure change is a pressure drop.

7. A tornado alarm device responsive to pressure drops associated with approach of a tornado, comprismg:

housing means providing an internal compartment;

flexible diaphragm means dividing said compartment into a buffer chamber and a sensing chamber; said buffer chamber communicating with the exterior of said housing through first orifice means sized to permit pressure in said buffer chamber to fluctuate at a rate within or lower than the range of pressure changes associated with approach of a tornado, thereby filtering out higher frequency, suddenly changing atmospheric disturbances; said sensing chamber communicating with the exterior of said housing through second orifice means sized to permit pressure in said sensing chamber to fluctuate at a rate lower than the range of rates associates with a tornado, thereby following slowly varying atmospheric changes; switch means adapted to be closed by travel of said diaphragm in response to a pressure differential thereacross due to greater pressure in the sensing chamber than in the buffer chamber; and

signalling means responsive to closure of said switch means.

8. Tornado alarm device according to claim 7 wherein said first orifice means is an orifice provides in said housing sized to permit pressure in said first chamber to vary in response to external pressure change that takes place over a duration of at least several seconds and said second orifice means is an orifice provided in said diaphragm of smaller diameter than said first orifice means.

9. Tornado alarm device according to claim 7 where both said first and second orifice means are orifices provided in said housing.

10. Tornado alarm device according to claim 7 wherein said switch means is adjustable to change the differential pressure at which said contacts close.

a m a e s

Claims

1. A pressure responsive signalling device for detecting pressure drop associated with the approach of a tornado; comprising housing means providing an internal compartment; flexible diaphragm means dividing said compartment into first and second chambers; said first chamber communicating with the exterior of said housing through first orifice means sized to exclude sudden, rapid pressure fluctuations from said first chamber and sufficient to permit pressure in said first chamber to vary in response to the pressure drop associated with the approach of a tornado; said second chamber communicating with the exterior of said housing through second orifice means sized to permit pressure in said second chamber to vary in response to pressure changes in said first chamber at a lower rate than said rate of change in said first chamber; whereby a differential pressure will exist across said diaphragm means whenever pressure drop occurs due to apprach of a tornado; switch means adapted to be closed by travel of said diaphragm in response to a pressure differential thereacross; and signalling means responsive to closure of said switch means.

4. Pressure responsive signalling means according to claim 1 wherein said orifice means are adjustable in size.

5. Pressure responsive signalling means according to claim 1 wherein said switch means is adjustable to close said contacts at predetermined differential pressures across said diaphragm means.

7. A tornado alarm device responsive to pressure drops associated with approach of a tornado, comprising: housing means providing an internal compartment; flexible diaphragm means dividing said compartment into a buffer chamber and a sensing chamber; said buffer chamber communicating with the exterior of said housing through first orifice means sized to permit pressure in said buffer chamber to fluctuate at a rate within or lower than the range of pressure changes associated with approach of a tornado, thereby filtering out higher frequency, suddenly changing atmospheric disturbances; said sensing chamber communicating with the exterior of said housing through second orifice means sized to permit pressure in said sensing chamber to fluctuate at a rate lower than the range of rates associates with a tornado, thereby following slowly varying atmospheric changes; switch means adapted to be closed by travel of said diaphragm in response to a pressure differential thereacross due to greater pressure in the sensing chamber than in the buffer chamber; and signalling means responsive to closure of said switch means.