Kozak Y. Substantiation of the impulse method for determining fire detectors' time parameters with a thermal resist sensitive element.

The dissertation is devoted to solving an urgent scientific problem – substantiation of the pulse method for determining fire detectors' time parameters – time constant and response time – with a thermal resist sensitive element. Failure to detect a fire promptly at the initial stage is accompanied by a significant spread of fire hazards, which can lead to threats to human life and health, significant material damage, and the spread of fire over large areas, which in turn leads to complications in its elimination. The primary element of fire detection is a fire detector, with certain technical characteristics and parameters, which is an integral part of any automatic fire alarm system and notification system. The fire detector, depending on the purpose, detects dangerous factors of fire and informs the control-receiving device, which in turn transmits a signal to the 24-hour monitoring panel with further notification of fire-rescue units and notifies people about the fire occurrence, which in turn facilitates the timely evacuation of people from the premises and the fire eliminating possibility at the initial stage before the fire-rescue units arrival, which significantly reduces material losses. Proper functioning of automatic fire alarm systems, in particular primary information sensors-fire detectors, determination of their main technical characteristics and their improvement is an indispensable component in ensuring fire safety of objects of various purposes. Therefore, the aim of the work is to improve the definition of fire detectors’ technical characteristics with a thermal resist sensitive element, which are focused on their implementation during object tests. In the course of the dissertation research, a comprehensive research method was used, which was based on the analysis and generalization of the currently existing fire detectors’ testing methods with a thermal resist sensitive element, their shortcomings, and the methods development for their improvement. The time parameters of thermal fire detectors are interrelated. The contribution of the fire detector’s time constant to its response time can be up to 20% at an ambient temperature change rate of 0.5 °C0с–1. To determine the fire detectors’ time parameters, tests are used, which are divided into stationary or autonomous and operational or object–based. The disadvantage of stationary tests using heat chambers is the asymmetry of airflow and temperature distribution, and the disadvantage of such tests using standard combustion cells is that the parameters of thermal impact on the fire detector sensitive element are not normalized. It is shown that in the first case, the fire detectors’ time constant value is not determined, and in the second case, only the control of the response time according to the tolerance criteria is carried out. During the object tests, the thermal effect on the fire detectors’ sensitive element is mainly realized using small thermal chambers, and the purpose of such tests is to check the fire detectors performance without obtaining estimates of their time parameters. It has been shown that the thermal effect on the sensitive element of fire detectors can be carried out using both external and internal heat sources. The second option is typical for fire detectors with a thermal resist sensitive element and is based on the Joule–Lenz effect use. In this case, new opportunities are opened to increase the fire detectors’ operation system efficiency of this type. Thermal processes in the thermal resist sensitive element of fire detectors when an electric current flows through it are described by a nonhomogeneous equation of mathematical physics with boundary conditions of the third kind. The Hankel integral transform is used to solve this differential equation. Using the reduction formula, a general expression for the temperature of the fire detectors’ thermal resist sensitive element was obtained, provided that an electric current flows through it without restrictions on its parameters. This expression is presented as a series of Bessel functions, which quickly converge and are the basis for the transition to other mathematical models of the thermal resist sensitive element. Using the integral Laplace transform, an expression for the transfer function of such a sensitive element is obtained and it is shown that with an error not exceeding 4.6%, it is described by the transfer function of the inertial link. The transfer coefficient of the fire detectors’ thermal resist sensitive element includes two multiplicative components, one of which is its time constant.