CA1102017A - Adjustable ionization chamber - Google Patents
Adjustable ionization chamberInfo
- Publication number
- CA1102017A CA1102017A CA361,337A CA361337A CA1102017A CA 1102017 A CA1102017 A CA 1102017A CA 361337 A CA361337 A CA 361337A CA 1102017 A CA1102017 A CA 1102017A
- Authority
- CA
- Canada
- Prior art keywords
- electrode
- ionization
- chamber
- ionization chamber
- adjusting mechanism
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 230000007246 mechanism Effects 0.000 claims abstract description 11
- 230000002285 radioactive effect Effects 0.000 claims abstract description 7
- 230000035939 shock Effects 0.000 abstract description 4
- 239000000779 smoke Substances 0.000 description 13
- 230000035945 sensitivity Effects 0.000 description 8
- 150000002500 ions Chemical class 0.000 description 6
- 230000009471 action Effects 0.000 description 3
- 206010069201 Smoke sensitivity Diseases 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 230000035515 penetration Effects 0.000 description 1
Landscapes
- Fire-Detection Mechanisms (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An ionization chamber with two electrodes having a variable spacing and with a radioactive source for the ionization of the electrode gap therebetween includes an adjusting mechanism for the positional adjustment of one of the electrodes relative to the other. The mechanism is such that a spring element presses the adjustable electrode against at least one point of the adjusting mechanism. Several arrangements are disclosed for adjustably mounting a cup-shaped electrode in the housing of the chamber in such a manner that it is readily adjustable and will not undergo spurious readjustment as a result of vibration of shock.
An ionization chamber with two electrodes having a variable spacing and with a radioactive source for the ionization of the electrode gap therebetween includes an adjusting mechanism for the positional adjustment of one of the electrodes relative to the other. The mechanism is such that a spring element presses the adjustable electrode against at least one point of the adjusting mechanism. Several arrangements are disclosed for adjustably mounting a cup-shaped electrode in the housing of the chamber in such a manner that it is readily adjustable and will not undergo spurious readjustment as a result of vibration of shock.
Description
The present invention relates to an ionization chamber having two electrodes with a variable spacing and with a radio-active source for the ionization of the electrode gap, particularly for use in an ionization smoke detector.
Examples of ionization smoke detectors of the type involved here are described, for example, in the U.S. Pats. 3,710,110,issued Jan. 9, 1973 and 3,767,917, issued Oct. 23, 1973, both to Lampart et al.
In general, known ionization smoke detectors have two series-connected ionization chambers with different smoke sensitivities.
For example, one of the chambers, normally called the measuring ionization chamber, is made extensiveIy accessible to air, while the other chamber, normally called the reference ionization chamber, is essentially sealed against the atmosphere or screened against air access. In such ionization smoke detectors, use is made of the fact that when heavier particles, e.g. of smoke, penetrate into the chamber, the stream of atmospheric ions formed by the radioactive source and which flows between the electrodes is reduced. As a result, the chamber resistance rises.
As the reference ionization chamber is not or only slightly in-fluenced by smoke, if at all,its stream of ions remains virtually constant, particularly when in the saturation range. Therefore, ,.
~1~2~17 when the voltage drop in the measuring ionization chamber increases upon penetration of smoke into the chamber, an evaluation circuit connected to the chamber gives an alarm signal after its voltage drop has exceeded a predetermined threshold value.
In practice, it is often necessary to be able to modify the threshold value, and consequently the sensitivity, of such an ionization smoke detector to adapt it to ambient conditions.
This can be brought about electrically on the one hand by modifying the evaluation circuit and on the other by varying the stream of ions or the resistance of one of the two ionization chambers.
Various ionization smoke detectors are already known in which the stream of ions or the resistance of either the measuring ionization chamber or the referenceionization chamber is modified by changing the spacing of the two electrodes.
For example, the British patent 1,446, 780 to Gacogne, published 18 Aug. 1976 and the Australian patent 402,078 to Ashwin published 26 Apr.1968 describe detectors with an ionization chamber in which the electrode spacing may be adjust~d by means of an adjusting screw. The British patent 1,088,976 published 25 Oct. 1967 discloses a detector with an ionization chamber in which the electrode spacing may be adjusted and fixed by means of a locking screw which, howcver, is not accessible from outside the detector.
3L1~2~17 When changing the sensitivity of an ionization smoke de-tector, preference is given to changing that of the reference ionization chamber, because in this case there is no need to influence the geometrical conditions, and consequently the smoke sensitivity, of the measuring ionization chamber.
In known ionization chambers such a modification to the electrode spacing is generally brought about by fixing one electrode to a screw which is passed through the rigid chamber casing and which can be turned from the rear wall of the chamber.
However, such an adjustment by means of a simple screw thread has the disadvantage that over a period of time, and particularly under the action of vibrations or shocks, the setting changes by itself.
Thus, a smoke detector equipped with such an io~zation chamber is not operationally reliable over a period of time, unless the adjusting screw is locked, e.g. with a thread setting compound.
As a result, once it is locked, the sensitivity cannot be readily adapted to otherkonditions. In other known ionization chambers with spacing adjustment, only a small electrode plate is placed on the adjusting screw, obviously for stability reasons. Thus, the change to the stream of ions which can be broughtabout by varying the electrode gap is much smaller than in the case of larger electrode dimensions and can in no way be considered optimum.
A further disadvantage is that such adjustment mechanismsrequire a large amount of space outside the ionization chambers and can therefore undesirably increase the overall dimensions of an ionization smoke detector.
~02~17 The present invention eliminates the above-indicated disadvantages and provides an ionization chamber in which the stream of ions can be changed by modifying the electrode spac ng in a simple reliable and extremely efficient manner without there being any danger of a spurious readjustment over a period of time under the influence of vibrations and shocks, whereby the space requirements are reduced and the stability and operational reliability are increased.
According to the present invention there is provided an ionization chamber with two electrodes having a variable spacing, with a radioactive source for the ionization of the electrode gap therebetween, and with an adjusting mechanism for the positional adjustment of one of the electrodes relative to the other being constructed and positioned in such a way that a spring element presses the adjustable electrode against at least one point of the adjusting mechanism, wherein the adjustable electrode comprises a plate-shaped part to which are fixed a plurality of spiral arms secured in elastically resilient manner by their ends to the bottom of a chamber housing.
The present invention will be further illustrated by way of the accompanying drawings in which:
Fig. la is a radial section through an ionziation chamber in accordance with a thi~d embodiment of the present invention and having an inclined slit adjustment;
Fig. lb is a side section of the chamber of Fig. la;
Fig. lc is an exploded view of a portion of the chamber of Figs. la and lb with the top removed;
Fig. ld is a side section of an internal element of the chamber of Figs. la, lb and lc;
Fig. 2a is a radial section through an ionization chamber in accordance with a fourth embodiment of the present ~lV2~17 invention and having a cam adjustment;
Fig. 2b is a partial side section of the chamber of Fig. 2a;
Fig. 2c is an elevational view of an internal component of the chamber of Fig. 2a;
Fig. 2d is an elevational view of another internal component of the chamber of Fig. 2a;
Fig. 2e is a side view of a third internal component of the chamber of Fig. 2a.
. .
In the case of the embodiment shown in Figs. la and lb, the ionization chamber is enclosed by a cup 2, made from plastic or preferably metal, mounted on a plastic mounting plate 1. A
central electrode carrying a radioactive source 4 i5 inserted in mounting plate 1. The radioactive source can also be located at another point in the chamber in such a way that the inside of the chamber is adequately ionized.
~n electrode 12 is provided in cup 2 which over its entire length can be adjusted uniformly as regards height, and therefore spacing, relative to counterelectrode 3. To this end, electrode 12 is constructed in cup-shaped manner with a flat bottom and cylirdrical side wall in such a way that it can slide up and down in cup 2. The movement of electrode 12 is limited by slots 13 in the cylindrical part and by pins 14 engaging through the slots on the cup wall. On the bottom of electrode 12, a slot 17 is provided into which can pass a screw-driver through a hole 18 in the bottom of cup 2. The turning of electrode 12 by means of a screw-driver leads to the adjustment of its height, and consequently the electrode gap, by means of the guide slots 13. Leaf springs 15 are fitted to the bottom of cup 2 by means of rivets 16 in such a way that by means of their spring tension they force electrode 12 upwards and consequently force pins 14 against the lower edge of guide slots 13. The compression springs 15 can be replaced by tension springs, so that pins 14 press against the upper edge of guide slots 13. The spring action in all cases prevents the spurious adjustment of the electrode gap.Since in this embodiment the friction of the adjusting mechanism is smaller, at least as compared with a screw thread, it is advantageous to provide an additional securing means. This comprises a pin 19 which, by means of a spring 20, is pressed through cup 2 and into holes 21 in the cylindrical part of electrode 12. On turning electrode 12, llOZ~7 pin 19 automatically engages in specified positions with a clearly defined electrode gap. This provides the additional advantage that the sensitivity can be adjusted in clearly defined stages.
As shown in Fig. ld this result can also be brought about by a corresponding construction of the guide slots 13 in place of en-gagement holes. In this case, the edges of the guide slots are not linear but instead have a plurality of locking points 22 into which the pins 14 can engage.
If springs 20 have an adequate spring tension, it may be possible to eliminate springs 15.
A further advantage of the embodiment of Figs. la and 1 is that the adjusting mechanism is located entirely within the ionization chamber, i.e. requires no additional space. As a result, the overall dimensions of the ionization chamber can be kept particularly small.
, ' In the embodiment of Figs. 2a to 2e the adjustable electrode comprises a central plate 23, which is not, however, fixed to the base of the chamber at only one point, but is instead fixed thereto at several points 25 by means of several spiral arms 24. Thus, the spring tension is smaller than when fixing a circular disc to several points of its periphery. In addition, the elasticity ilC92g~1~
constant can be adjusted in accordance with requirements by a corresponding choice of the width and length of the spiral arms.
It is also advantageous that in the case of electrode adjustment, the central plate 23 which forms the preponderant part of the effective electrode surface is no-t inclined, and consequently during e]ectrode adjustment the sensitivity change remains largely linear.
In this embodiment the adjusting mechanism comprises a plurality of cam plates 26, located on a cylindrical surface and whose number corresponds to the number of spiral arms 24. The diameter of the cylindrical surface is selected in such a way that the cams engage between electrode plate 23 and spiral arms 24 in such a way that the inclined cams 26 displace upwardly from the inoperative position the attachment points of spiral arms 24 on plate 23. Here again, the spring tension of spiral arms 24 acts against any adjustment, so that a spurious adjustment through . friction between the cam and the electrode is prevented. Since cams 26 are fitted to a base plate 27, whlch is rotateable through the bottom of the chamber by means of a slot 28, it is once again possible to adjust the height of electrode plate 23 in a continuous and reliable manner by turning from the back of the chamber a screw-driver which passes through slot 28.
Instead of having a linear edge, the cams 26 can also be constructed in such a way that there are a plurality of locking points 29 in which engage the extension pieces of spiral arms 24.
This once again leads to a reliable and accurate stepwise ~ L02~17 sensitivity adjustment, and spurious adjustment under the action . of vibrations, and shocks can be even more reliably prevented.
- An ionization smoke detector equipped with such an ionization chamber can be easily and reliably adjusted to several sensitivity stages by untrained personnel, so that the selected sensitivity setting is reliably maintained even over long periods.
Examples of ionization smoke detectors of the type involved here are described, for example, in the U.S. Pats. 3,710,110,issued Jan. 9, 1973 and 3,767,917, issued Oct. 23, 1973, both to Lampart et al.
In general, known ionization smoke detectors have two series-connected ionization chambers with different smoke sensitivities.
For example, one of the chambers, normally called the measuring ionization chamber, is made extensiveIy accessible to air, while the other chamber, normally called the reference ionization chamber, is essentially sealed against the atmosphere or screened against air access. In such ionization smoke detectors, use is made of the fact that when heavier particles, e.g. of smoke, penetrate into the chamber, the stream of atmospheric ions formed by the radioactive source and which flows between the electrodes is reduced. As a result, the chamber resistance rises.
As the reference ionization chamber is not or only slightly in-fluenced by smoke, if at all,its stream of ions remains virtually constant, particularly when in the saturation range. Therefore, ,.
~1~2~17 when the voltage drop in the measuring ionization chamber increases upon penetration of smoke into the chamber, an evaluation circuit connected to the chamber gives an alarm signal after its voltage drop has exceeded a predetermined threshold value.
In practice, it is often necessary to be able to modify the threshold value, and consequently the sensitivity, of such an ionization smoke detector to adapt it to ambient conditions.
This can be brought about electrically on the one hand by modifying the evaluation circuit and on the other by varying the stream of ions or the resistance of one of the two ionization chambers.
Various ionization smoke detectors are already known in which the stream of ions or the resistance of either the measuring ionization chamber or the referenceionization chamber is modified by changing the spacing of the two electrodes.
For example, the British patent 1,446, 780 to Gacogne, published 18 Aug. 1976 and the Australian patent 402,078 to Ashwin published 26 Apr.1968 describe detectors with an ionization chamber in which the electrode spacing may be adjust~d by means of an adjusting screw. The British patent 1,088,976 published 25 Oct. 1967 discloses a detector with an ionization chamber in which the electrode spacing may be adjusted and fixed by means of a locking screw which, howcver, is not accessible from outside the detector.
3L1~2~17 When changing the sensitivity of an ionization smoke de-tector, preference is given to changing that of the reference ionization chamber, because in this case there is no need to influence the geometrical conditions, and consequently the smoke sensitivity, of the measuring ionization chamber.
In known ionization chambers such a modification to the electrode spacing is generally brought about by fixing one electrode to a screw which is passed through the rigid chamber casing and which can be turned from the rear wall of the chamber.
However, such an adjustment by means of a simple screw thread has the disadvantage that over a period of time, and particularly under the action of vibrations or shocks, the setting changes by itself.
Thus, a smoke detector equipped with such an io~zation chamber is not operationally reliable over a period of time, unless the adjusting screw is locked, e.g. with a thread setting compound.
As a result, once it is locked, the sensitivity cannot be readily adapted to otherkonditions. In other known ionization chambers with spacing adjustment, only a small electrode plate is placed on the adjusting screw, obviously for stability reasons. Thus, the change to the stream of ions which can be broughtabout by varying the electrode gap is much smaller than in the case of larger electrode dimensions and can in no way be considered optimum.
A further disadvantage is that such adjustment mechanismsrequire a large amount of space outside the ionization chambers and can therefore undesirably increase the overall dimensions of an ionization smoke detector.
~02~17 The present invention eliminates the above-indicated disadvantages and provides an ionization chamber in which the stream of ions can be changed by modifying the electrode spac ng in a simple reliable and extremely efficient manner without there being any danger of a spurious readjustment over a period of time under the influence of vibrations and shocks, whereby the space requirements are reduced and the stability and operational reliability are increased.
According to the present invention there is provided an ionization chamber with two electrodes having a variable spacing, with a radioactive source for the ionization of the electrode gap therebetween, and with an adjusting mechanism for the positional adjustment of one of the electrodes relative to the other being constructed and positioned in such a way that a spring element presses the adjustable electrode against at least one point of the adjusting mechanism, wherein the adjustable electrode comprises a plate-shaped part to which are fixed a plurality of spiral arms secured in elastically resilient manner by their ends to the bottom of a chamber housing.
The present invention will be further illustrated by way of the accompanying drawings in which:
Fig. la is a radial section through an ionziation chamber in accordance with a thi~d embodiment of the present invention and having an inclined slit adjustment;
Fig. lb is a side section of the chamber of Fig. la;
Fig. lc is an exploded view of a portion of the chamber of Figs. la and lb with the top removed;
Fig. ld is a side section of an internal element of the chamber of Figs. la, lb and lc;
Fig. 2a is a radial section through an ionization chamber in accordance with a fourth embodiment of the present ~lV2~17 invention and having a cam adjustment;
Fig. 2b is a partial side section of the chamber of Fig. 2a;
Fig. 2c is an elevational view of an internal component of the chamber of Fig. 2a;
Fig. 2d is an elevational view of another internal component of the chamber of Fig. 2a;
Fig. 2e is a side view of a third internal component of the chamber of Fig. 2a.
. .
In the case of the embodiment shown in Figs. la and lb, the ionization chamber is enclosed by a cup 2, made from plastic or preferably metal, mounted on a plastic mounting plate 1. A
central electrode carrying a radioactive source 4 i5 inserted in mounting plate 1. The radioactive source can also be located at another point in the chamber in such a way that the inside of the chamber is adequately ionized.
~n electrode 12 is provided in cup 2 which over its entire length can be adjusted uniformly as regards height, and therefore spacing, relative to counterelectrode 3. To this end, electrode 12 is constructed in cup-shaped manner with a flat bottom and cylirdrical side wall in such a way that it can slide up and down in cup 2. The movement of electrode 12 is limited by slots 13 in the cylindrical part and by pins 14 engaging through the slots on the cup wall. On the bottom of electrode 12, a slot 17 is provided into which can pass a screw-driver through a hole 18 in the bottom of cup 2. The turning of electrode 12 by means of a screw-driver leads to the adjustment of its height, and consequently the electrode gap, by means of the guide slots 13. Leaf springs 15 are fitted to the bottom of cup 2 by means of rivets 16 in such a way that by means of their spring tension they force electrode 12 upwards and consequently force pins 14 against the lower edge of guide slots 13. The compression springs 15 can be replaced by tension springs, so that pins 14 press against the upper edge of guide slots 13. The spring action in all cases prevents the spurious adjustment of the electrode gap.Since in this embodiment the friction of the adjusting mechanism is smaller, at least as compared with a screw thread, it is advantageous to provide an additional securing means. This comprises a pin 19 which, by means of a spring 20, is pressed through cup 2 and into holes 21 in the cylindrical part of electrode 12. On turning electrode 12, llOZ~7 pin 19 automatically engages in specified positions with a clearly defined electrode gap. This provides the additional advantage that the sensitivity can be adjusted in clearly defined stages.
As shown in Fig. ld this result can also be brought about by a corresponding construction of the guide slots 13 in place of en-gagement holes. In this case, the edges of the guide slots are not linear but instead have a plurality of locking points 22 into which the pins 14 can engage.
If springs 20 have an adequate spring tension, it may be possible to eliminate springs 15.
A further advantage of the embodiment of Figs. la and 1 is that the adjusting mechanism is located entirely within the ionization chamber, i.e. requires no additional space. As a result, the overall dimensions of the ionization chamber can be kept particularly small.
, ' In the embodiment of Figs. 2a to 2e the adjustable electrode comprises a central plate 23, which is not, however, fixed to the base of the chamber at only one point, but is instead fixed thereto at several points 25 by means of several spiral arms 24. Thus, the spring tension is smaller than when fixing a circular disc to several points of its periphery. In addition, the elasticity ilC92g~1~
constant can be adjusted in accordance with requirements by a corresponding choice of the width and length of the spiral arms.
It is also advantageous that in the case of electrode adjustment, the central plate 23 which forms the preponderant part of the effective electrode surface is no-t inclined, and consequently during e]ectrode adjustment the sensitivity change remains largely linear.
In this embodiment the adjusting mechanism comprises a plurality of cam plates 26, located on a cylindrical surface and whose number corresponds to the number of spiral arms 24. The diameter of the cylindrical surface is selected in such a way that the cams engage between electrode plate 23 and spiral arms 24 in such a way that the inclined cams 26 displace upwardly from the inoperative position the attachment points of spiral arms 24 on plate 23. Here again, the spring tension of spiral arms 24 acts against any adjustment, so that a spurious adjustment through . friction between the cam and the electrode is prevented. Since cams 26 are fitted to a base plate 27, whlch is rotateable through the bottom of the chamber by means of a slot 28, it is once again possible to adjust the height of electrode plate 23 in a continuous and reliable manner by turning from the back of the chamber a screw-driver which passes through slot 28.
Instead of having a linear edge, the cams 26 can also be constructed in such a way that there are a plurality of locking points 29 in which engage the extension pieces of spiral arms 24.
This once again leads to a reliable and accurate stepwise ~ L02~17 sensitivity adjustment, and spurious adjustment under the action . of vibrations, and shocks can be even more reliably prevented.
- An ionization smoke detector equipped with such an ionization chamber can be easily and reliably adjusted to several sensitivity stages by untrained personnel, so that the selected sensitivity setting is reliably maintained even over long periods.
Claims (4)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An ionization chamber with two electrodes having a veriable spacing, with a radioactive source for the ionization of the electrode gap therebetween, and with an adjusting mechanism for the positional adjustment of one of the electrodes relative to the other being constructed and positioned in such a way that a spring element presses the adjustable electrode against at least one point of the adjusting mechanism, wherein the adjust-able electrode comprises a plate-shaped part to which are fixed a plurality of spiral arms secured in elastically resilient manner by their ends to the bottom of a chamber housing.
2. An ionization chamber according to claim 1, wherein the adjusting mechanism comprises cams arranged in a cylindrical surface, whose number corresponds to the number of spiral arms and which engage in the spaces between extension pieces of the spiral arms on the electrode plate.
3. An ionization chamber according to claim 2, wherein the cams are fitted to a base plate which through the bottom of the housing can be rotated about the cylindrical axis.
4. An ionization chamber according to claim 2, wherein the cams have locking points in which can engage the extension pieces of the spiral arms.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA361,337A CA1102017A (en) | 1976-11-29 | 1980-10-01 | Adjustable ionization chamber |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CH15'006/76 | 1976-11-29 | ||
| CH1500676A CH600563A5 (en) | 1976-11-29 | 1976-11-29 | |
| CA291,465A CA1102016A (en) | 1976-11-29 | 1977-11-22 | Adjustable ionization chamber |
| CA361,337A CA1102017A (en) | 1976-11-29 | 1980-10-01 | Adjustable ionization chamber |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1102017A true CA1102017A (en) | 1981-05-26 |
Family
ID=27165388
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA361,337A Expired CA1102017A (en) | 1976-11-29 | 1980-10-01 | Adjustable ionization chamber |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1102017A (en) |
-
1980
- 1980-10-01 CA CA361,337A patent/CA1102017A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |