Acoustic glass break detectors.
A new Russian standard establishing general technical requirements for acoustic glass break detectors (AIRS) came into force in July of this year.
The standard will help solve many problems associated with the selection of AIRS for use at domestic facilities.
Disadvantages of foreign models
Passive acoustic (or sound) detectors designed to monitor the integrity of glazed structures in closed spaces are among the most common on the international market of technical security equipment.
Their popularity is growing every year.
Having appeared just a few years ago, they have spread to all developed countries, creating worthy competition for detectors of similar purpose (vibration, electric and impact contact). But the path to success was not easy.
In the early 90s, foreign security equipment appeared in Russia, including a wide range of these new sensors. Many domestic consumers and specialists working in the field of security and safety of facilities immediately liked them.
However, the detectors had various shortcomings: some had poor resistance to interference, others did not record the destruction of glass manufactured in Russia.
This problem was felt especially acutely in the non-departmental security units of the Ministry of Internal Affairs of Russia, whose duties include the selection and installation of alarms, response to an alarm signal (detention of an offender), and client insurance (compensation for damage from theft).
In connection with this, in 1994, the Research Center «Security» of the Main Directorate of the Ministry of Internal Affairs of Russia and the State Standard of Russia began to actively develop a regulatory framework to ensure professional control over the quality of products of this type entering the Russian market.
More than ten interested and competent organizations, departments, research institutes and manufacturers of security equipment, including permanent members of the Technical Committee for Standardization TC 234 «Technical means of security, security and fire alarms» were involved in the work on the new state standard.
As a result of joint efforts, in 1998 GOST R 51186-98 «Passive sound security detectors for blocking glazed structures in closed spaces» appeared.
General technical requirements and methods of test» (Alarm sonic passive glass break detectors for use in buildings. General technical requirements and methods of test), which entered into force on 01.07.99.
The structure of the document is presented in Fig. 1.
TC 234 also sent proposals necessary for the development of the relevant international document to the IEC representative office in Russia (TC-79/IEC).
Fig. 1. Structure of GOST R 51186-98
However, the low noise immunity of the first AIRS samples worried not only Russian specialists.
Thus, as a result of the analysis of the causes of false alarms received from facilities where the alarms in question were used, in 1994, under the auspices of the Security Industry Association (SIA) in Washington, the «Standard for Acoustic Glass Break Detectors — Measures to Reduce the Number of False Responses» was developed, which is mainly an instruction manual for the operation of these sensors (its structure is shown in Fig. 2).
Fig. 2. The structure of the SIA standard
High level of Russian standards
As the analysis of the development of AIRS shows, not all developers and manufacturers have chosen the right direction in the fight for noise immunity.
For example, some foreign (mainly American) companies began to fight to reduce false alarms of their sensors even to the detriment of their detection ability.
This situation categorically did not suit the non-departmental security service and the State Standard of Russia, therefore, from a certain point, the choice of this type of detectors for use at domestic facilities began to be approached with increased attention.
Only a few manufacturers have managed to successfully overcome this selection (see the article “Acoustic Glass Breakage Detectors”, “Security, Communication and Telecommunication Systems”, 1998, No. 22).
At the same time, some companies that received a negative conclusion from Russian specialists, accordingly improved their products and subsequently successfully passed the selection, while others looked for excuses for their «failures», publicly accusing experts of not being able to read the instructions, and Russian glass — of emitting «unearthly» sounds at the moment of their deliberate destruction,
Technical features of AIRS
Let's consider the main characteristics of AIRS from the point of view of the above-mentioned standards, as well as regulatory documents from related areas with which they are interconnected.
The most significant requirements for detectors will be accompanied by excerpts from the relevant sections of the Russian standard test methods, comments and practical recommendations.
Functioning
In accordance with GOST R 51186-98, the main functional parameters of the AIRS are: sensitivity, operating frequency, range, detection probability, noise immunity during non-destructive impacts on the protected structure, resistance to acoustic interference, time of readiness for operation and restoration of the normal state, alarm notification parameters.
The sensitivity of the detectors under consideration at the operating frequency (frequencies) must correspond to the minimum required level (levels) of sound pressure to generate an alarm notification when a glass sheet is destroyed.
It is usually expressed in dB (relative to the standard zero level of 2×10-5 Pa) and acts primarily as a controlled parameter when conducting a series of tests.
Sensitivity control is carried out using standard generators (low frequency, white noise, discrete spectrum, etc.), amplifiers, acoustic emitters, measuring microphones, equalizers or normalized bandpass filters (octave, 1/3 octave, etc.), sound pressure level meters (noise meters) in accordance with the structural diagram shown in Fig. 3.
When conducting such measurements, the conditions of «free field» according to GOST R 16123-88 (IEC 268-4-72) must be observed.
Thus, the possibility of creating metrological equipment that meets the requirements of Russian standards, as well as the required level of reproducibility of test results, is realized.
Fig. 3. Structural diagram of the installation for testing the operating frequency of sensitivity and noise immunity of the AIRS with sound interference
In this regard, to ensure convenience and acceptable cost of tests related to measuring (controlling) the sensitivity of detectors, GOST R 51186-98 sets forth a requirement for their operating frequency (frequencies), which is recommended to be selected from the series (Table 1) according to GOST 12090-80 (IEC-1, ISO 266) in the range from 31.5 to 16,000 Hz.
Table 1. Preferred series for selecting the operating frequency of AIRS according to GOST 12090-80
The so-called acoustic noise immunity of the AIRS is tested when exposed to a sinusoidal signal (signals) with a carrier frequency corresponding to the operating frequency, as well as a broadband sound signal with a spectral characteristic of white noise (Fig. 4).
During an expert examination of the detectors, in addition to the specified requirements, their resistance to the impact of typical household noise, signals from sound fire alarms, life support systems, and others is analyzed.
Fig. 4. Examples of signals for checking the acoustic noise immunity of AIRS Discrete spectrum signal «white noise», spectral characteristics of signals.
The noise immunity of sensors during mechanical impact on the protected glass is checked by applying multiple non-destructive effects with an energy of 1.9 J.
For these purposes, a rubber ball weighing 0.39 kg and having a hardness of 60 international IRHD units is used during testing.
It should be noted that all requirements for the noise immunity of AIRS in accordance with GOST R 51186-98 are checked at their maximum sensitivity (if there is a corresponding adjustment).
Fig. 5. A number of values for selecting the maximum range of action of AIRS
To select the maximum range of detectors, the Russian standard recommends using a range of values from 3 to 15 m (Fig. 5), which allow you to set the nominal value of this parameter and the corresponding measurement error.
As the experience of operating AIRS shows, the most important functional characteristic, which largely determines the suitability of detectors for use at facilities, is the probability of detecting the destruction of protected glass. According to GOST R 51186-98 — not less than 0.9.
This is nothing more than the minimum permissible level, compliance with which allows us to consider the detector «professional».
Today, we remind you, only a very small number of serially produced sensors meet this requirement.
Tests of the probability of detection of AIRS are usually carried out together with a check of their maximum range and noise immunity during a non-destructive impact on the protected glass.
Fig. 6. Scheme of testing the range, probability of detection and noise immunity of AIRS
However, it should be borne in mind that when assessing the detection ability of detectors, Russian experts never limit themselves to data on the standard destruction of only one type and size of glass.
During the field tests, penetration through the glazed structure occurs in the same way as is most often the case in well-known criminal practice.
In this case, glass of various types and sizes is subject to destruction, starting from the minimum protected area. The thickness of the glass is selected from the range specified in the accompanying documentation for the device being tested. It is clear that the complexity and cost of such tests are quite high.
Table 2. Data for planning AIRS tests according to GOST R 51186-98
Table 2 provides the information necessary for planning functional tests of AIRS and evaluating their results in accordance with GOST R 51186-98.
Table 3 provides the main types of building glass used in Russia to fill translucent openings of closed spaces and subject to blocking against breakthrough.
Table 3. Construction glass used in Russia
It is worth noting that the accompanying documentation for most imported sensors either completely lacks information on the types and parameters of protected glass, or the data provided does not meet the requirements of Russian standards, and also uses dubious statements about the unlimited capabilities of a particular type of detector.
The SIA standard does not specify the functional requirements for the AIRS, it only states that the consumer should be able to buy a device for accurately measuring the range of the detectors when installed at the facility.
You must admit that it is not entirely clear what is meant. One can only assume that we are talking about electronic sound imitators of glass breakage (simulators).
But these devices are not quite suitable for such measurements, especially accurate ones.
The probability of error in this case can be quite significant, since there is no link to a specific object.
Electronic simulators can be effectively used only for partial testing of the operability of sensors already installed at the object.
The range of the AIRS or its adaptation to specific conditions of the protected object can be correctly assessed only by applying real imitation effects to the protected glass, as is done, for example, when installing most domestic devices.
It is not necessary to buy expensive simulators.
The difficulty in developing the considered functional requirements for this type of detectors lies mainly in the specificity of the acoustic signals that arise when the glass structure is destroyed and propagate in the air of a closed room.
The specificity of these signals is such that a priori they cannot be accurately described using specific parameters.
This is due to the influence of many objective factors on the formation of signals, which vary from case to case — from the conditions at the place of signal emission (glass parameters, methods of its fastening and destruction, features of the supporting structure, etc.) to the conditions of signal propagation and reception (features of the interior, acoustic properties of the room, design of the detector).
The main of these factors are shown in Fig. 7.
Fig. 7. Factors influencing the formation of an acoustic signal
When operating as part of a security alarm system, the AIRS must meet all the necessary requirements for docking with its other parts.
According to the Russian standard, the detectors must be ready for operation after no more than 60 s.
After their activation, as a result of glass destruction, an alarm signal is generated with subsequent restoration of normal activity or with fixation of the moment.
In this case, the duration of the alarm (without fixation) should be at least 2 s, and the time to return to normal operation ~ no more than 30 s.
Power supply, EMC, resistance to external factors
GOST R 51186-98 establishes three methods of power supply for AIRS:
— from a DC source:
— from an AC network;
— from an alarm loop (AL).
Table 4. Power supply requirements for AIRS according to GOST R 51186-98
The main power supply parameters are given in Table 4.
The Russian standard also presents the electromagnetic compatibility (EMC) standards for detectors, indicating specific degrees of severity according to GOST R 50009-92, as well as the field strength of radio interference generated by the devices during operation.
Some EMC requirements are also given in the SIA standard (section «Design requirements», subsection «External factors»). Generalized data on EMC standards are given in Table. 5.
Table 5. List of standard impacts for checking AIRS for EMC
The requirements for the resistance of AIRS to the impact of external factors (according to GOST R 51186-98) are given in Table 6.
Table 6. Treatment of external factors to check the resistance of AIRS according to GOST R51186-98
Safety
The detectors must comply with the general safety requirements of GOST R 5077595 (IEC 839-1-1-88); the class of protection of a person from electric shock according to GOST 12.2.007.0-75; the electrical strength of insulation and the electrical resistance of insulation of their circuits according to GOST 12997-84.
Design
In accordance with GOST R 51186-98, the AIRS must consist of a sensitive element (one or more microphones) and a processor located in one or different housings.
When placing the sensitive element in a separate housing, the electrical lines connecting the sensitive element to the processor should be considered as part of the alarm. If these lines are damaged (broken, short-circuited), preventing the signal from passing, the processor must provide an alarm notification no later than 10 seconds after the detection of the said damage.
For the convenience of consumers, as well as to improve the quality of installation and operation at the protected facility, the design of the alarms must provide for:
— sensitivity (range) regulator(s), for their adaptation to specific operating conditions (distance from the protected structure, parameters of the monitored glass, dimensions and acoustic properties of the room);
— alarm notification indicator and auxiliary indicators, for example, for visual monitoring of the interference level at the facility or modes (test/operation) of the detectors.
To protect against tampering, the AIRS must have a built-in device (usually a microswitch or microbutton) that provides an alarm notification (malfunction, tampering, etc.) in the event of an attempt at unauthorized access to the controls, terminals for connecting external electrical circuits and fixing elements.
The body of the detectors is checked for compliance with the degree of protection according to GOST R 14254-96 (IEC 529-89), selected from the series: 1РЗО, 1РЗЗ, 1Р34, 1Р40, 1Р41, 1Р44, and must ensure their reliable fastening during installation.
The requirements for the AIRS interface are that they must have an electronic key at the output, open in the normal state (standby mode) and closed at the time of an alarm, or relay contacts closed in the normal state and opening in the alarm state.
For alarm devices with power supply from the control panel loop, the interface parameters are set in their specifications.
Reliability
In accordance with GOST R 51186-98, the average failure time of detectors in the normal state is not less than 60,000 43.
Accompanying documentation In addition to the general requirements (according to GOST R 5077595) for technical documentation attached to the AIRS, in accordance with GOST R 51186-98, information is required on the range of thicknesses, minimum dimensions (area) and brand of the controlled glass sheet, types of protected glazed structures and features of fixing glass in them (if any).
The SIA standard recommends that the installation instructions for detectors additionally specify: types of glass to be monitored, procedures for checking (setting) the range and the required model of the measuring device, a list of known sources of interference, recommendations for periodic testing of the operability of the sensors, instructions for their installation, use, etc.
Recommendations for use
The SIA standard contains general recommendations for the use and installation of the AIRS, the implementation of which can help to increase the reliability of detector detection (reduce the number of false alarms and increase the probability of registering glass breakage).
The main of these recommendations are given in Table. 7.
Table 7. Operational measures to improve the reliability of AIRS detection
In addition, all the necessary data on the placement and maintenance of modern domestic devices are contained in their operating manuals.