EP0501194B1 - Method of predetermining the time of maintenance of alarm detectors - Google Patents

Abstract

A method for predetermining the probable period of time to a no longer permissible change in sensitivity, i.e. the operating life of alarm detectors. In an alarm detector system with quiescent value correction, the probable operating life (tF) of the detector is determined from its change in quiescent value (RWx - RWb) over a certain past period (tV=tx-tb) and its predetermined operating threshold (FS), which can also be a maintenance or disturbance threshold (WS or ST), by extrapolation: tF = (tx-tb) x FS-RWx DIVIDED RWx-RWb , where tx = particular actual time tb = reference time RWx = quiescent value at actual time RWb = quiescent value at reference time. <IMAGE>

Description

The invention relates to a maintenance method according to the preamble of claim 1.

Hazard detectors, preferably smoke detectors, change their sensitivity over the course of their operating time due to environmental influences, especially pollution. In order to ensure that the susceptibility to false alarms does not increase sharply due to an increase in sensitivity, and that the expected scope of protection can no longer be guaranteed by reducing the sensitivity, such changes in sensitivity must be recognized in good time.

It is generally customary to generally replace such hazard detectors at certain time intervals based on experience, which depend on the operating conditions, and to clean and continue to use them as far as possible. It is usually not checked to what extent the detector sensitivity has actually changed. In this complex process, a large number of detectors are exchanged, which are still fully functional and could have remained in the alarm system for a long time, which causes unnecessarily high costs.

This general exchange procedure was and is justified for limit value detectors, the degree of contamination of which is not recognizable in the signaling system and for which the contamination significantly affects the sensitivity of the detector.

However, danger detection systems with limit detectors are also known, in which it can be determined during normal operation of the danger detection system whether the detector sensitivity has changed. For example, detector signals are changed by special tactile routines such that these detectors must trigger an alarm at one time and not trigger an alarm in the other. It is also possible to issue a warning by introducing additional monitoring thresholds if they are exceeded or not reached. Due to these measures, changes in sensitivity can be recognized and false alarms are reduced. However, significant changes in responsiveness are admittedly allowed up to this point. This measure is mainly based on economic considerations, because if the warning were given too early, the operating time of the detectors would be significantly shortened, which would result in higher costs for the detector replacement.

In hazard detection systems in which analog detector measurement values are transmitted to the control center and processed there. For example, in the known pulse detection system, operational monitoring is carried out today to determine whether the idle value derived from the current detector measurement values is still within the permissible working range. If the detector idle value leaves its working area, for example due to contamination, a maintenance threshold is exceeded first, and then a fault threshold is exceeded, which can be displayed in the control center for the detector in question. With the pulse detection system, the resting sensitivity and the sliding alarm calculation threshold keep the detector sensitivity constant over a very long period of time (EP-B1-0 70 449). With this signaling system, it would be possible to exchange only dirty detectors, i.e. those that are automatically displayed after one of the above-mentioned thresholds is exceeded. Such a thing however, there is generally no targeted exchange.

The length of time it takes to go through the detector's work area, i.e. its service life, however, depends heavily on the environmental conditions under which the detector is used. If the detectors displayed due to the maintenance threshold being exceeded are actually replaced, this method has the disadvantage that a short time after the exchange of the displayed, soiled detectors, one or more other detectors come into the maintenance or fault area and thus additional maintenance and travel costs are incurred can. For this reason, even in the case of hazard detection systems that work according to the principle of pulse detection technology, the regular exchange procedure introduced here by the limit value detection technology continues, albeit with extended intervals.

A prediction device for a maintenance and inspection time is known from the patent abstract of the Japanese patent publication JP 215 35 00. It can only be inferred from the abstract that the maintenance and inspection time can be derived with a permissible deviation by predicting how the work has been carried out from that time based on current results of a work in the past and a work model and by estimating the maintenance. and inspection time for the future. For this purpose, output data from a detection means are processed with several calculation devices. A precise way of working is not to be found in the abstract.

The object of the invention is for hazard detection systems with rest value tracking and sliding alarm calculation threshold to specify a procedure which allows the expected service life of the detector to be predetermined with regard to its functionality, taking current and past data into account.

This object is achieved in the method described at the outset with the characterizing features of claim 1.

With the method according to the invention, the expected detector life is extrapolated for each detector from its change in idle value over a specific, past time and from its predetermined functional threshold, which could be clearly identical, for example, to a threshold already present in the system (maintenance or fault threshold), rather, its probable duration of service is determined. The period of functional reliability is therefore predetermined, in general with constant environmental influences. This enables the maintenance technician to determine, for example, regular maintenance by entering the time interval until the next maintenance appointment, all detectors that are likely to reach the functional threshold by then, and then to replace them at the same time. The method according to the invention has the advantage that only soiled detectors can be replaced without causing additional maintenance costs and travel times. Since it is known from the current cleaning methods that only a very small part of the detectors currently exchanged at regular intervals is actually contaminated, considerable savings can be made with the method according to the invention if, due to this method, significantly fewer detectors have to be exchanged and possibly cleaned in the future, as before. A large number of clean and fully functional detectors can therefore remain in the alarm system for a significantly longer time.

According to the invention, the detector life, or better the function, is calculated by multiplying the difference between an actual point in time and a reference point in the past by a quotient, which is the difference between the function threshold and the detector idle value at the actual point in time and from the difference between the detector idle value at the actual time and the reference rest value. The functional threshold is formed by an upper or lower threshold value, above which the detector is no longer functional, as will be described later. This can be an upper or lower maintenance threshold or fault threshold.

In the method according to the invention, those detectors are therefore advantageously determined and displayed from the calculated expected functional duration of the individual detectors which reach or exceed the respectively predefined functional threshold by a certain later point in time, for example the period until the next maintenance. Depending on the determined duration of operation of the individual detectors, the time until the next maintenance appointment is derived.

• Fig.1 und 2 den Einfluß der Verschmutzung auf einen bekannten Grenzwertmelder mit größerwerdender Empfindlichkeit in Fig. 1 und mit kleiner werdender Empfindlichkeit in Fig. 2,
• Fig. 3 und 4 den Einfluß der Verschmutzung auf einen bekannten Pulsmelder mit konstant bleibender Empfindlichkeit, jedoch mit größer werdendem Melderruhewert in Fig. 3 und mit kleiner werdendem Melderruhewert in Fig.4 und
• Fig. 5 ein Diagramm zur Vorausbestimmung der voraussichtlichen Funktionsdauer.

The method according to the invention is briefly explained below using diagram drawings. Show

• 1 and 2 the influence of pollution on a known limit detector with increasing sensitivity in Fig. 1 and with decreasing sensitivity in Fig. 2,
• 3 and 4 the influence of contamination on a known pulse detector with constant sensitivity, but with increasing detector idle value in Fig. 3 and with decreasing detector idle value in Fig. 4 and
• Fig. 5 is a diagram for predicting the expected service life.

1 and 2, the detector measured value MW is recorded over the time t, which can be months or years depending on the operating conditions. In Fig.1 the detector measured value MW changes due to the contamination of the limit detector, whereby the sensitivity increases. The detector measured value MW increases from the initial measured value MWa over a certain period of time and then exceeds an upper monitoring threshold ÜSo, which is intended to indicate that the detector is no longer functional above this threshold. At a much later time tAL, it reaches the alarm threshold AS and thus emits a false alarm F-AL due to the increase in sensitivity.

2 shows the influence of contamination on the limit detector with detector measured value MW and decreasing sensitivity. Due to the contamination, the detector measured value MW changes from an initial measured value MWa below and at a time tK reaches a lower monitoring threshold USu, which generally does not lead to a message. This threshold should also indicate that the detector no longer functions properly below the threshold. If such a limit detector can not report that its sensitivity has exceeded a lower monitoring threshold ÜSu, then the detector remains in the system until the next exchange cycle, and an occurring danger can no longer be indicated, because the alarm threshold AS is also present Hazard event no longer reached and an alarm is therefore no longer displayed. The dirty detector could only be replaced in good time if these monitoring thresholds lead to a message.

In Figures 3 and 4, the influence of contamination on a pulse detector, in which the detector sensitivity is known to remain constant, is considered. The detector idle value RW is plotted over time t (months or years), starting from an initial value RWa. The actual working area AB of the detector is limited by an upper and lower maintenance threshold WSo and WSu. Furthermore, a fault range SB is specified, which is limited by an upper fault threshold STo and a lower fault threshold STu. In between there is a maintenance area WB. As is known, these thresholds are specified in the alarm system in the control center for each detector.

Since in the known pulse signaling technology the detector idle value RW is tracked and the alarm calculation threshold ABS is also carried out in a "sliding" manner, the detector sensitivity remains constant over the entire working range.

In Fig. 4 the influence of pollution with decreasing detector idle value is very similar to that in Fig. 3 shown with increasing detector idle value. If the detector idle value RW exceeds its working range AB due to the soiling, the maintenance threshold WSu is exceeded first, which is displayed, and later the fault threshold Stu is exceeded, which is also displayed. At least at this point, the detector must be replaced.

In the method according to the invention, the expected service life is calculated according to the following relationship: $$\text{tF = (tx - tb)}\frac{\text{FS - RWx}}{\text{RWx - RWb}}$$

5 shows the rest value RW over time t. The working area AB of the pulse detector is limited by the upper and lower interference threshold STo and STu and identifies the interference area SB. The sliding alarm calculation threshold ABS is shown for the changing detector idle value RW. The change in the rest value in the past tV is determined from a specific reference time tb to a specific actual time tx. An actual idle value RWx results at the actual time tx, which can be, for example, the maintenance time. The function duration tF up to the function threshold FS can then be calculated by extrapolation according to the given equation. If the change in idle value increases, this is the upper function threshold SFo, as shown in FIG. 5, if the idle value change falls, this is the lower function threshold SFu. On the basis of this calculated expected duration of function of each detector, those detectors of the hazard alarm system are determined and displayed which reach or exceed the functional threshold within a certain period of time, which can be, for example, the interval between two maintenance intervals, or within this time.

5 shows the change in the rest value for an approximately linear course. If the change in the rest value is not linear due to the pollution, the method according to the invention can also be used. This course must then be approximated by a suitable mathematical function for the change in the rest value. From the intersection of this curve with the function threshold, the probable duration of the function of the detector is again determined.

Claims (2)

1. Maintenance method, the maintenance time for a hazard detection system being predicted taking into account current and previous data, which system operates with quiescent value tracking, the functional duration of hazard detectors, that is the probable time duration until a no longer admissible sensitivity change for each detector, being calculated, characterized in that the probable functional duration (tF) is determined by extrapolation from its quiescent value change (Rwx - Rwb) over a specific past time period (tV) and from its predetermined functional threshold (FS), the functional duration (tF) being calculated from the difference between the current time (tx) and the reference time (tb) multiplied by the quotient of the difference between the functional threshold (FS) and the detector quiescent value at the current time (Rwx) and the difference between the detector quiescent value at the current time (Rwx) and the reference quiescent value (Rwb), an upper functional threshold (FSo) being laid down in the case of a rising quiescent value change and a lower functional threshold (FSu) being laid down in the case of a falling quiescent value change, and the functional threshold (FS) being able to be defined by the operating range (AB) and a maintenance threshold or a fault threshold (ST) of the detector.
2. Method according to Claim 1, characterized in that, from the calculated anticipated functional duration of the individual detectors, those detectors of the hazard detection system which at a specific later time, for example the time interval until the next maintenance, will reach or exceed the predetermined functional threshold, are determined and indicated.

Images