CA1154118A - Rate of change responsive alarm system - Google Patents
Rate of change responsive alarm systemInfo
- Publication number
- CA1154118A CA1154118A CA000335872A CA335872A CA1154118A CA 1154118 A CA1154118 A CA 1154118A CA 000335872 A CA000335872 A CA 000335872A CA 335872 A CA335872 A CA 335872A CA 1154118 A CA1154118 A CA 1154118A
- Authority
- CA
- Canada
- Prior art keywords
- signal
- alarm
- analogue
- analogue signal
- tracking
- 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
Landscapes
- Alarm Systems (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
. .
An alarm system which includes at least one detecting device which provides an analogue output signal, means to monitor the rate of change of the analogue output signal by providing a periodic stepwise tracking signal and provide an alarm signal when the rate of change alters sharply so that the analogue signal will become coincident with the tracking signal. Upper and lower limit reference signals are provided such that when the analogue system becomes coincident with either of them a warning signal is given that the system is inoperative. The analogue signal may be compared to an alarm reference to additionally provide an alarm signal when the analogue signal becomes coincident with the alarm reference signal. A pre-maintenance warning signal may be provided when the analogue output signal reaches the level of a pre-maintenance reference signal. The invention also provides a method of processing an analogue output signal of a detecting device which includes the steps of generating an alarm signal if the rate of change of the analogue output signal alters sharply to become coincident with a step of a periodic step-wise tracking signal. -
. .
An alarm system which includes at least one detecting device which provides an analogue output signal, means to monitor the rate of change of the analogue output signal by providing a periodic stepwise tracking signal and provide an alarm signal when the rate of change alters sharply so that the analogue signal will become coincident with the tracking signal. Upper and lower limit reference signals are provided such that when the analogue system becomes coincident with either of them a warning signal is given that the system is inoperative. The analogue signal may be compared to an alarm reference to additionally provide an alarm signal when the analogue signal becomes coincident with the alarm reference signal. A pre-maintenance warning signal may be provided when the analogue output signal reaches the level of a pre-maintenance reference signal. The invention also provides a method of processing an analogue output signal of a detecting device which includes the steps of generating an alarm signal if the rate of change of the analogue output signal alters sharply to become coincident with a step of a periodic step-wise tracking signal. -
Description
5~1i8 -`.;: ' , This invention relates to an alarm system.
~ larm systems such as are employed for the purposes o~ fire detection or for security purpoes often include a plurality of detectors which are situated in remote locations or in locations which are not easily accessible. These de-tectors as is the case with all others employed in a particular system must be inspected regularly to assess their working con-dition. The operation of thejdetectors is usually subject to environmental conditions, the accumulation of dirt or moisture, and the ageing of certain components. These ~actors produce changes in the output signal of each detector which can induce --false alarms. To overcome these difficulties frequent preven-titive maintenance may be called for and this in turn presents obvious problems lf the detectors are situated in remote loca-~tions or locations which are not easlly accessible.
It is an object of the presentinvention to provide an alarm system which obviates or mitigates disadvantages of `
:
~ ~ prior systems. ~ ~
:
It has been a problem to distinguish between a genuine alarm condition and;at least some false alarm conditions.
An alarm system is desirable which generates a warning that preventitive~maintenance is called for on one or more of the detectors or other parts of the system.
The invention provides an alarm system to provide warning of alarm conditions which comprises at least one detector to emit an analogue output signal responsive to fluctuations in conditions! monitor means to monitor the analogue signal by providing a tracking signal therefor stepped over a plurality of similar periods, first comparator means to compare the analogue signal with the tracking signal ,~
., .
., .. ~, 11~4~
whereby an alarm signal is generated when the analogue signal c~anges at a .rate that coincidence occurs between the analogue signal and a step of the tracking signal, and limit com-parator means to compare the ~nalogue signal with upper and lower preset reference limit signals and to generate a signal indicative that the system is inoperative on coincidence of the analogue signal with either of the upper and lower reference signals.
Further according to the invention is a method of providing warning of alarm conditions which comprises providing an analogue signal responsive to fluctuation ln conditions, monitoring the analogue signal by pro-: viding a tracking signal stepped over a plurality of similarperiods, comparing the analogue signal and the tracking signal .
: and generating an alarm signal when the rate of change of the analogue signal is such that there is coincldence of the analogue slgnal~with a step oE the tracklng signal; and comparing the analogue signal with upper and lower reference limit signals and generating a signal that the system is inoperative on :coincidence o~ the analogue signal with either of the upper and lower limit signals.
: Each detecting device may be connected directly to the monitoring and comparison means by hardware lin~s. Alter- .
natively if each detecting device is remote from the monitoring and comparison means, connection may be established via a tele-metering link.
The invention is further described by way of example with reference to the accompanying drawings in which~
Figure 1 illustrates an alarm system accordin~ to the invention, ~ ~, ~ :' ' ` . , 1 . . : ` ., ' ;;, . ' ~ .
l~S~
.
Figure 2 schematically illustrates one way in which the system of Figuxe 1 can be modified, and Figuxe 3 illustrates in graphical form the operation of the system of Figure 1. ::
; Figure 1 illustrates an alarm system which includes a detector 10 which produces an analogue output signal 12 (see Figure 3). The slgnal 12 is applied by means of cabling 14 to a rate of change detector 18 and comparators 20, 22, 24 and 26. The detector may be any sultable detector, for example 10 a fire detector, which produces an electrical output signal `~
12.
A rate change monitor 18 for signal 12 consists of j a sampling circuit 40, a subtractor 42, and a comparator 44. ~`
The inverting input of the subtractor 42 is connected to a .
variable voltage source 46. ~
The sampling circuit 40 is designed to sample the ~ .
signal 12 periodically and to generate a tracking signal 18A, ::~
in stepwlse fashion, which has an amplitude for each period ~ : :
T, between samplin~ instants, which diEfers from the sampled ;amplitude of~the slgnal 12, at the beginning of the period, :by a gap voltage 48 (see Figure 3).
The output voltage of the subtractor 42 equals the signal 12 sampled and held over the period T minus the gap volt-age. This voltage is the signal 18A and is aompared in the :~ comparator 44 with the signal 12. The sampling period T of the circuit 40 and~the gap voltage 48 are chosen so that the signal 18A can ha~e~a maximum rate of change, or slope, of gap voltage/T. When the rate of change of the signal 12 exceeds :
this maximum slope, the signals 12 and 18A momentarily become coincidçnt as they cross one another and, the comparator ~ ~ 3 ~
il generates an alarm signal 50 at its output.
The comparators 20 to 26 have adjustable reference levels 20~ to 26A, respecti~ely, and are re~erred to as a pre-maintenance detector, an upper limit detector, a lower limit detector and an absolute alarm device, respectively.
Figure 3 is a graphical representation of the manner in which the system of Figure 1 operates. In Figure 3 the vertical axis represents the amplitude of the various signals encountered in the system while the horizontal axis represents time. The analogue output signal 12 of the detector 10 is shown as drifting naturally with time. until at time P a genuine alarm condition occurs. The rate of change monitor 18 produces the tracking signal lBA which closely follows the analogue slgnal 12 and compensates for variations in the signal which are at-tributable for example to temperature variations. However when :: a geniune alarm conditlon occurs as at time P and the analogue signal changes rate rapidly in response the tracking signal ~.
.. ls~unable to follow the analogue slgnal sufficiently rapidly -~ and the two signals cross and the alarm warning 50 is generated.
In this example the acceptable working range of the analogue signal 12 is located between the comparator levels.
20A and 22A of the pre-maintenance detector 20 and the upper ~ limit detector 22 respectively. Should the signal 12 reach the upper limit signal 22A this will indicate that the .system is inoperative. On the other hand if the signal 12 reaches khe signal 20A of the pre-maintenance detector this will be indicative that maintenance is called for. The operating level of the signal 12 can then be adjusted to an acceptable amplitude.
: In the lower limit.detector 24 the reference signal 24A is co~tinuously compared to the signal 12. Should the ampli-.
~ : - 4 -1 .
3LiS~
tude of the signal 12 drop to the amplitude of the signal 24A
a warning sig~al is generated indicating that the system is inoperative, The signals gen~rated by the comparators 20 and 26 and the signal from the comparator 24 should preferably be distinguishable to enable one to distinguish a failure of the system signals, maintenance signals and alarm signals.
Should the signal 12 proceed beyond pre-maintenance signal 20 it may reach reference signal 26A produced from ab-solute alarm detection means 26. Reference signal 26A is also compared to the analogue signal 12. An alarm signal will be generated by the comparator 26 if for example the analogue signal 12 falls below the level of the pre-maintenance signal 20A at a rate which is not sufficiently high to cause it to cross the reference signal 18A of the rate of change monitor 18.
The alarm system of Figure 1 thus provides an alarm signal on sudden change of rate of the analogue signal 12 on the occurrence of a geniune alarm condition. In addition a backup is provided by the alarm comparator 26 to provide an alarm signal if the level of the analogue signal actually reaches that of signal 26A. Comparators 20, 22 and 24 are used to analyze the analogue signal 12 and enable one to discriminate between false and geniune alarm conditions.
The modification of the alarm system shown in Figure
~ larm systems such as are employed for the purposes o~ fire detection or for security purpoes often include a plurality of detectors which are situated in remote locations or in locations which are not easily accessible. These de-tectors as is the case with all others employed in a particular system must be inspected regularly to assess their working con-dition. The operation of thejdetectors is usually subject to environmental conditions, the accumulation of dirt or moisture, and the ageing of certain components. These ~actors produce changes in the output signal of each detector which can induce --false alarms. To overcome these difficulties frequent preven-titive maintenance may be called for and this in turn presents obvious problems lf the detectors are situated in remote loca-~tions or locations which are not easlly accessible.
It is an object of the presentinvention to provide an alarm system which obviates or mitigates disadvantages of `
:
~ ~ prior systems. ~ ~
:
It has been a problem to distinguish between a genuine alarm condition and;at least some false alarm conditions.
An alarm system is desirable which generates a warning that preventitive~maintenance is called for on one or more of the detectors or other parts of the system.
The invention provides an alarm system to provide warning of alarm conditions which comprises at least one detector to emit an analogue output signal responsive to fluctuations in conditions! monitor means to monitor the analogue signal by providing a tracking signal therefor stepped over a plurality of similar periods, first comparator means to compare the analogue signal with the tracking signal ,~
., .
., .. ~, 11~4~
whereby an alarm signal is generated when the analogue signal c~anges at a .rate that coincidence occurs between the analogue signal and a step of the tracking signal, and limit com-parator means to compare the ~nalogue signal with upper and lower preset reference limit signals and to generate a signal indicative that the system is inoperative on coincidence of the analogue signal with either of the upper and lower reference signals.
Further according to the invention is a method of providing warning of alarm conditions which comprises providing an analogue signal responsive to fluctuation ln conditions, monitoring the analogue signal by pro-: viding a tracking signal stepped over a plurality of similarperiods, comparing the analogue signal and the tracking signal .
: and generating an alarm signal when the rate of change of the analogue signal is such that there is coincldence of the analogue slgnal~with a step oE the tracklng signal; and comparing the analogue signal with upper and lower reference limit signals and generating a signal that the system is inoperative on :coincidence o~ the analogue signal with either of the upper and lower limit signals.
: Each detecting device may be connected directly to the monitoring and comparison means by hardware lin~s. Alter- .
natively if each detecting device is remote from the monitoring and comparison means, connection may be established via a tele-metering link.
The invention is further described by way of example with reference to the accompanying drawings in which~
Figure 1 illustrates an alarm system accordin~ to the invention, ~ ~, ~ :' ' ` . , 1 . . : ` ., ' ;;, . ' ~ .
l~S~
.
Figure 2 schematically illustrates one way in which the system of Figuxe 1 can be modified, and Figuxe 3 illustrates in graphical form the operation of the system of Figure 1. ::
; Figure 1 illustrates an alarm system which includes a detector 10 which produces an analogue output signal 12 (see Figure 3). The slgnal 12 is applied by means of cabling 14 to a rate of change detector 18 and comparators 20, 22, 24 and 26. The detector may be any sultable detector, for example 10 a fire detector, which produces an electrical output signal `~
12.
A rate change monitor 18 for signal 12 consists of j a sampling circuit 40, a subtractor 42, and a comparator 44. ~`
The inverting input of the subtractor 42 is connected to a .
variable voltage source 46. ~
The sampling circuit 40 is designed to sample the ~ .
signal 12 periodically and to generate a tracking signal 18A, ::~
in stepwlse fashion, which has an amplitude for each period ~ : :
T, between samplin~ instants, which diEfers from the sampled ;amplitude of~the slgnal 12, at the beginning of the period, :by a gap voltage 48 (see Figure 3).
The output voltage of the subtractor 42 equals the signal 12 sampled and held over the period T minus the gap volt-age. This voltage is the signal 18A and is aompared in the :~ comparator 44 with the signal 12. The sampling period T of the circuit 40 and~the gap voltage 48 are chosen so that the signal 18A can ha~e~a maximum rate of change, or slope, of gap voltage/T. When the rate of change of the signal 12 exceeds :
this maximum slope, the signals 12 and 18A momentarily become coincidçnt as they cross one another and, the comparator ~ ~ 3 ~
il generates an alarm signal 50 at its output.
The comparators 20 to 26 have adjustable reference levels 20~ to 26A, respecti~ely, and are re~erred to as a pre-maintenance detector, an upper limit detector, a lower limit detector and an absolute alarm device, respectively.
Figure 3 is a graphical representation of the manner in which the system of Figure 1 operates. In Figure 3 the vertical axis represents the amplitude of the various signals encountered in the system while the horizontal axis represents time. The analogue output signal 12 of the detector 10 is shown as drifting naturally with time. until at time P a genuine alarm condition occurs. The rate of change monitor 18 produces the tracking signal lBA which closely follows the analogue slgnal 12 and compensates for variations in the signal which are at-tributable for example to temperature variations. However when :: a geniune alarm conditlon occurs as at time P and the analogue signal changes rate rapidly in response the tracking signal ~.
.. ls~unable to follow the analogue slgnal sufficiently rapidly -~ and the two signals cross and the alarm warning 50 is generated.
In this example the acceptable working range of the analogue signal 12 is located between the comparator levels.
20A and 22A of the pre-maintenance detector 20 and the upper ~ limit detector 22 respectively. Should the signal 12 reach the upper limit signal 22A this will indicate that the .system is inoperative. On the other hand if the signal 12 reaches khe signal 20A of the pre-maintenance detector this will be indicative that maintenance is called for. The operating level of the signal 12 can then be adjusted to an acceptable amplitude.
: In the lower limit.detector 24 the reference signal 24A is co~tinuously compared to the signal 12. Should the ampli-.
~ : - 4 -1 .
3LiS~
tude of the signal 12 drop to the amplitude of the signal 24A
a warning sig~al is generated indicating that the system is inoperative, The signals gen~rated by the comparators 20 and 26 and the signal from the comparator 24 should preferably be distinguishable to enable one to distinguish a failure of the system signals, maintenance signals and alarm signals.
Should the signal 12 proceed beyond pre-maintenance signal 20 it may reach reference signal 26A produced from ab-solute alarm detection means 26. Reference signal 26A is also compared to the analogue signal 12. An alarm signal will be generated by the comparator 26 if for example the analogue signal 12 falls below the level of the pre-maintenance signal 20A at a rate which is not sufficiently high to cause it to cross the reference signal 18A of the rate of change monitor 18.
The alarm system of Figure 1 thus provides an alarm signal on sudden change of rate of the analogue signal 12 on the occurrence of a geniune alarm condition. In addition a backup is provided by the alarm comparator 26 to provide an alarm signal if the level of the analogue signal actually reaches that of signal 26A. Comparators 20, 22 and 24 are used to analyze the analogue signal 12 and enable one to discriminate between false and geniune alarm conditions.
The modification of the alarm system shown in Figure
2 enables the detectors emitting analogue signals 12 to be located at positions remote from the monitor 18 and comparators 20 to 26. This figure illustrates a number of detectors 28 whose output signals are fed to telemetering transmitters 30 which are capable of transmitting analogue information. The ;
outputs of the transmitters are fed via a suitable conventional telemetering link 31 to corresponding telemetering receivers ~ - 5 -, ~lS~
32. The output signals o~ the receivers 32 are analogue signals which correspond ~nd are proportional to the analogue output signals of the various detectors 28. These output signals are applied at a control point to the monitor 18 and comparators 20 to 26 which monitor the analogue signals in the manner al- -ready described in connection with Figure 1.
The alarm system of the invention has particular relevance to fire detection systems and security systems but clearly the principles of the invention are applicable to any othér system in which use is made of monitoring, warning or detecting devices.
:
'5 , ` : ` :
outputs of the transmitters are fed via a suitable conventional telemetering link 31 to corresponding telemetering receivers ~ - 5 -, ~lS~
32. The output signals o~ the receivers 32 are analogue signals which correspond ~nd are proportional to the analogue output signals of the various detectors 28. These output signals are applied at a control point to the monitor 18 and comparators 20 to 26 which monitor the analogue signals in the manner al- -ready described in connection with Figure 1.
The alarm system of the invention has particular relevance to fire detection systems and security systems but clearly the principles of the invention are applicable to any othér system in which use is made of monitoring, warning or detecting devices.
:
'5 , ` : ` :
Claims (7)
1. An alarm system to provide warning of alarm con-ditions comprising:-at least one detector to emit an analogue output signal responsive to fluctuations in conditions, monitor means to monitor the analogue signal by providing a tracking signal therefor stepped over a plurality of similar periods, first comparator means to compare the analogue signal with the tracking signal whereby an alarm signal is generated when the analogue signal changes at a rate that coincidence occurs between the analogue signal and a step of the tracking signal, and limiting comparator means to compare the analogue signal with upper and lower preset reference limit signals and to generate a signal indicative that the system is inoperative on coincidence of the analogue signal with either of the upper and lower reference signals.
2. A system as claimed in claim 1, in which the track-ing signal is spaced from the analogue signal at the beginning of each time period.
3. An alarm system as claimed in claim 1, which in-cludes pre-maintenance comparator means to compare the analogue signal with a substantially constant pre-maintenance reference signal having a level chosen to define a maintenance requirement condition and being within the upper and lower limit signals to generate a signal indicative of a maintenance requirement when the analogue signal is coincident with the pre-maintenance reference signal.
4. An alarm system as claimed in claim 1 or 2, which includes alarm comparator means to compare the analogue signal with a substantially constant alarm reference signal having a level chosen to define an alarm condition and being within inside the upper and lower limit signals to generate an alarm signal when the analogue signal is coincident with the alarm reference signal.
5. An alarm system as claimed in claim 1 or 2, in which the or each detector is connected to the monitor means and the various comparator means by hardware links.
6. An alarm system as claimed in claim 1 or 2, in which the or each detector is remote from the monitor means and the various comparator means and is connected thereto through at least one telemetering link.
7. A method of providing warning of alarm conditions comprising:-providing an analogue signal responsive to fluctuation in conditions, monitoring the analogue signal by providing a tracking signal stepped over a plurality of similar periods, comparing the analogue signal and the tracking signal and generating an alarm signal when the rate of change of the analogue signal is such that there is coincidence of the analogue signal with a step of the tracking signal; and comparing the analogue signal with upper and lower reference limit signals and generating a signal that the system is inoperative on coincidence of the analogue signal with either of the upper and lower limit signals.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000335872A CA1154118A (en) | 1979-09-18 | 1979-09-18 | Rate of change responsive alarm system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000335872A CA1154118A (en) | 1979-09-18 | 1979-09-18 | Rate of change responsive alarm system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1154118A true CA1154118A (en) | 1983-09-20 |
Family
ID=4115165
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000335872A Expired CA1154118A (en) | 1979-09-18 | 1979-09-18 | Rate of change responsive alarm system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1154118A (en) |
-
1979
- 1979-09-18 CA CA000335872A patent/CA1154118A/en not_active Expired
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| EP0009901A1 (en) | Alarm system | |
| US6222456B1 (en) | Detector with variable sample rate | |
| CN116246407B (en) | Agriculture and forestry area fire early warning supervisory systems based on artificial intelligence | |
| NO170957B (en) | FIRE ALARMSYSTEM | |
| US4962368A (en) | Reliability and workability test apparatus for an environmental monitoring system | |
| BR112021013786A2 (en) | METHOD AND SYSTEM TO DETECT ANOMALIES OR PREMATURE INDICATIONS OF EQUIPMENT FAILURE | |
| US4757303A (en) | Alarm system | |
| US7843324B2 (en) | Detection arrangements | |
| US4831361A (en) | Environmental abnormality alarm apparatus | |
| US5864286A (en) | Distributed intelligence alarm system having a two- tier monitoring process for detecting alarm conditions | |
| CN205428085U (en) | Indoor security protection system based on fiber grating | |
| US4598271A (en) | Circuit arrangement for monitoring noise levels of detectors arranged in an alarm installation | |
| US6642846B1 (en) | Infrared intrusion detector and method | |
| KR20200041515A (en) | Early warning system and method of power plants using multiple prediction model | |
| ATE261164T1 (en) | METHOD AND DEVICE FOR DETECTING DRIFTS, JUMPS AND/OR OUTREAVIES OF MEASUREMENT VALUES | |
| CN114492629A (en) | Abnormality detection method, abnormality detection device, electronic apparatus, and storage medium | |
| CA1154118A (en) | Rate of change responsive alarm system | |
| CN116937818B (en) | High-voltage direct-current power distribution cabinet monitoring system for monitoring inside in real time | |
| US5237512A (en) | Signal recognition and classification for identifying a fire | |
| CN210667129U (en) | Intelligent access control management system based on distributed optical fiber temperature measurement and grating sensing system | |
| US4208627A (en) | Alarm circuit to detect shorting of periodic signal source | |
| JP2847597B2 (en) | Infrared monitoring system | |
| KR101214494B1 (en) | System and method for monitoring multistage self rack using heat/smoke detector | |
| CN1127394A (en) | Fire-alarm system for the early detection of fires | |
| CN113295255A (en) | Anti-cheating method and system for truck scale |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |