DEVICE TO DETECT HEATING LEVELS IN EXCESS IN L.H.D CABLES

Abstract: The object of the invention is to provide the distance length of a digital linear heat detector cable in alarm and to display it on a panel or a PC screen, independently from its electrical parameters, when it is exposed to temperatures in excess of the selected sensor minimum temperature alarm level. The instrument is capable to discriminate the short-circuit on the electrical junction cable from the sensing cable short circuit. The precision, for up to 5 Km length, is better than 1 %, and the instrument is able to transmit the signal as an analogue output, and an RS 485/232 output.

Description: Device to detect heating levels in excess in L.H.D cables. TECHNICAL FIELD This invention concerns a device for the detection of the alarm position of an alarm generated in a special cable defined as "linear heat detector " ' ("L.H.D. " ' from now on ) The L.H.D. 's are cable used for fire alarm signalisation when exposed to temperatures in excess of the selected minimum alarm level produced in the environment or in a plant, as for an example, but not exclusively, in highway-railways-underground tunnels, belt conveyors, electrical cabinets and power lines cable trays, transformers, flammable storage tanks, cooling towers, in warehouses and in any case in all those installations where, caused by attrition, by chemical reactions or by short-circuit there could be the conditions for the development of a fire and in which it's useful to identify as soon as possible the exact location of the danger, above all in case of great plants or of long length runs. BACKGROUND ART An L.H.D. is an electrical twisted pair of stainless steel conductors cable provided with a special thermoplastic sensitive insulation which melts at selected temperature levels. When exposed to temperature in excess of the selected minimum alarm level the specific sensitive insulation melts allowing the conductors to short-circuit. It's, therefore, an on-off digital device. The alarm condition is monitored through a fire control panel which monitors the status ( fire or fault) checking the current output from the control panel The main problem in plants with linear heat detectors installed is that the fire control panels management system can identify the status of alarm of the "zone" in which the cable is installed, but can't identify precisely the location in that zone, i.e. the distance from a conventional reference distance, problem is particularly serious when , as in tunnels or in cable trays, the cable lengths are relevant. A solution to this problem has been offered by Protectowire Co.- U.S.A, see patent N°3701 141 deposited the 29 th of April 1971 and edited the 24 th of October 1972. The solution proposed by Protectowire even if it was a new method for the location identification ,is such that it is applicable only for the cables having the features ( in terms of electrical parameters as Resistance =R(ohm), Capacity =C(farad) and Inductance =L ( Henry) of the Protectowire cables produced by the same company. It's not applicable to other's manufacturers of digital linear heat cables. It's necessary to take into consideration that so many plants are provided with L.H.D. cables of more than one manufacturer ( i.e. at least two, Protectowire-U.S.A. and Bicc-Kidde Fire Protection) and that visualisation, archiving and data storage, events memory, are a must for a modern security management system. Further, since the identification of the alarm point is dependent from the above mentioned parameters, and given the fact that these parameters value change with environmental temperature, it's necessary to provide for a temperature compensation in order to guarantee the precision required. The solution proposed by Protectowire does not help in solving all the above problems. DISCLOSURE OF INVENTION The solution according this invention is able to identify the distance of alarm in any digital cable, no matter which is the manufacturer, or in other terms no matter which are the electrical parameters of the digital cable electrical features. The device, object of this invention, is capable to display the location of alarm in meters or feet or any other measuring unit, and the display can be local in alphanumeric display or remotely on a PC screen with a digital map or a drawing of the site indicating the exact location of the fire. The precision claimed is superior in the range of 1 % to 3%max for length of cable over 4.000mt, with environmental temperature variation ranging from +/-20°. The instrument is realized in portable or fixed version , the portable one for maintenance purposes , the fixed one to be installed in electrical cabinet or control rooms. The electronic unit features a microprocessor for measuring the voltage drop on L.H.D, comparing it with physical parameters stored in a memory as reference and displaying it locally or remotely via PC. Lastly the control unit is capable of discriminating short-circuit on L.H.D from a short-circuit on electrical junction cable or for its opening status ( as for example for interruption of its continuity ) There's the possibility to join the electronic board with other boards for the management of other types of fire detectors . Circuitry description of the device for cabinet version The electronic board, microprocessor based, is powered via a 24VDC charger through a connector .The power block generates a 15VDC - 10V- 12,5V supply reference voltages .Terminals are provided for L.H.D input, which is connected to a reference relay and in stand-by terminates on proper terminals ; Two steady current generators which supply a reference resistor and the L.H.D to be measured ; A suitable trimmer to zero the electrical junction cable resistance up to the beginning or the end of L.H.D. A trimmer for the circuit amplification control; And two analogue outputs 0-10V and 4-20mA,not usable simultaneously. Circuitry description of the portable unit. This version of the circuit capable of detecting the voltage drop on a L. H.D. cable is powered through 9Vdc battery and is provided with : voltmelric module capable of generating a reference voltage dependent from the L.H.D manufacturer ( its electrical parameters, R-L-C) proper terminals to connect the L.H.D cable; Control buttons for proper operation; Display. BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a diagram block of the electronic board showing the operating principle of the voltage drop; Fig.2 shows the block diagram of inputs; Fig.3 shows the block diagram function of the charger-comparator ; Fig.4 shows the block diagram of outputs; Fig.5 shows the electronic board capability of discriminating fault conditions; Fig.6,6a,6b show the portable version of the device. With reference the herewith included drawings the device, according this invention, is constituted by an electronic board capable of measuring the voltage drop on L.H.D. cable digital type of any manufacturer and to compare it to reference parameters and displaying it with a precision in the range 1-3% max, in function of the environment temperature of the L.H.D. in alarm, as described in the following examples. Example 1 (electronic board, fixed version) The circuit is powered at 24 V dc through a proper connector (variable with the control unite). The circuit generates a 15 V dc voltage and 10 V dc-12.5 V dc reference voltages . The input line from the L.H.D. in the field passes through a relay and in stand-by terminates on terminals. On the electronic board two steady current generators power a reference resistor and the line to be measured. When an alarm is generated, via terminal , or via manual pressure , the relay changes over an amplifier circuit . A trimmer zeroes the junction electrical cables resistence up to the beginning or the end of the L.H.D. A resistor regulates the amplification of the circuit. Between terminals there are : a 0 - 10 V output and a 0 -20 mA output; the two analogue outputs cannot be used simultaneously. Example 2 (electronic port for the portable version) The electronic board is powered through a 9 V battery. Pressing the pushbutton, the voltmeter module is capable to produce a reference voltage proportional to the resistance calibration value, to set in function of the L.H.D. type ,which. has to be connected on provided terminals; two diodes are provided for a protection function. The device according invention provides means to reset the system, to store the data , to acknowledge the alarm until problem resolution, and to sequentially investigate many zones of L.H.D. The control unit is capable to control external devices for fire extinguishing. Operation As above mentioned the device operation is based on the current variation between a reference value and the alarm value. This variation r in turn depends from the distance of the alarm point (i.e. of the L.H.D. resistance). The circuitry sends continuously a signal into the cable and if the cable is whole the signal turns back unchanged. If on the contrary there is a short circuit the circuit measures the voltage drop and transduces it in a reference value which is properly displayed. , r. The dimension and the shape of the device according this invention can change according the request and the same is valid for some components. Some details could be changed with equivalent ones without changing the present patent comprehensive field.

Claims: CLAIMS 1) Device to detect the location of an alarm for heating levels in excess in L.H.D. cables to be used either mounting in electrical cabinet or as a portable instrument, characterized by an electronic board measuring the voltage drop on a digital L.H.D. cable and comparing it to reference values stored in memory displaying the exact location with a precision ranging from 1 to 3% max in function of the environmental temperature. 2) Device to detect the location of an alarm for heating levels in excess in L.H.D. cables to be used either for mounting in electrical cabinet or as a portable instrument, according claim number 1, characterized in the fixed version by the following: current generation at 15-10-12,5 Vdc . input line of L.H.D. cables with passes through a reference relay and in stand by terminates on terminals of a proper connect; an electronic board including two steady current generators which supply a reference resistor and the line to be measured; one trimmer of suitable power to zero the junction electrical cable resistance up to the beginning or the end of L.H.D. cable; one trimmer for the circuit amplification control; one 0 to 10 V analogue output between the two first terminals of the electronic board and one to 20 n A analogue output between the second two terminals, not usable simultaneously. 3) Device characterized to detect the location of a heat alarm in L.H.D. cables to be used either for fixed mounting or for portable, used according previous claims, characterized for the portable version by: 9 V dc battery power; voltmetric module to generate a voltage reference equal to the value previously determined in function of the L.H.D. type; two terminals for the L.H.D. cable to be monitored; two diodes for input protection. 4) Device to detect the location of a thermal alarm in L.H.D. cables to be used either for fixed mounting or for portable, according previous claims, characterized by the fact that the reading of the location points can be displayed using any measuring units: feet, meters etc. 5) Device to detect the location of a heat alarm in L.H.D. cables to be used either for fixed mounting or for portable, according previous claims, characterized by relays for the system reset . 6) Device to detect the location of a thermal alarm in L.H.D. cables to be used either for fixed mounting or for portable version, according previous claims, characterized by means to store alarms data and memory events. 7) Device to detect the location of a thermal alarm in L.H.D. cables to be used either for fixed mounting or for portable version, according claims 1-2-4-5-6, characterized by the possibility of sequential scanning of many zones with L.H.D. cables . 8) Device to detect the location of a thermal alarm in L.H.D. cables to be used either for fixed mounting or for portable, according previous claims 1 -3-4-5-6, characterized by housing in a suitable box, complete with display terminals and a control main switch and the batteries further to the electronic board . 9) Device to detect the location of a thermal alarm in L.H.D. cables to be used either for fixed mounting or for portable ,according previous claims 1 -2-4-5-6, characterized by its possibility to provide the manual end/or automatic control of fire extinguishing systems . 10) Device to detect the location of a thermal alarm in L.H.D. cables to be used either for fixed mounting or for portable version, according previous claims 1-2-4-5-6-7-9, characterized by discrimination of fire alarm due to short circuit in L.H.D. from fault up or down the L.H.D connection line or in the electrical continuity.

Inventors: VILLANO ANTONIO, VILLANO, ANTONIO
Applicants: THERMOSTICK ELETTROTECNICA S R, VILLANO ANTONIO, THERMOSTICK ELETTROTECNICA S.R.L., VILLANO, ANTONIO
Application year: 2001
Main classification: G08B17
IPC codes: G08B17, G08B25