MOIRAGHI GUIDO (IT)
POZZI TANIA (IT)
MOIRAGHI LUCA (IT)
REDAELLI ALBERTO (IT)
MOIRAGHI GUIDO (IT)
POZZI TANIA (IT)
MOIRAGHI LUCA (IT)
WO2003031924A1 | 2003-04-17 | |||
WO2004008407A1 | 2004-01-22 |
US5726610A | 1998-03-10 |
reciprocal distances substantially equal to each other within a territory T to be controlled in relation to forest fires or other events. The distance between the alarm stations can vary in function of the orographic diversities, the vegetation diversities and the degree of protection required. A variable distance between 30 and 150 metres is foreseen. At least one intermediate detection unit CIR is located at the edges of the territory T with the task of detecting alarm signals emitted by the stations SA and transmitting relative information to a central control station SC by means of suitable earth and/or satellite communication systems. An example of alarm station SA is shown in Figure 2 and comprises at least one sensor, in the present case three, more precisely a temperature sensor Sl, an infrared ray sensor S2 and a CO sensor S3. The sensors are activated by and communicate with a microcontroller MC with time base set by an extremely low consumption internal clock controlled by a quartz oscillator XT. The microcontroller MC communicates in turn with a low power radiofrequency transceiver TRX, fitted with antenna A. A battery B provides the electrical powering of the various components of the alarm station. The microcontroller controls the functioning of the alarm station, that is it controls the absorption of energy from the battery B, the system of sensors S1-S3, the sending and receiving of alarm signals through the transceiver TRX and, periodically, a system of supervision, control and maintenance of the alarm station. An example of transceiver TRX is shown in Figure 3 and comprises a transmitting part ASK fitted with an oscillator OSC with a resonator SAW (Surface Acoustic Wave) Xl at high stability with a transistor Tl for the amplitude modulation and a transistor T2 for the frequency modulation, a receiving part DT fitted with a detection stage RIV, a low-pass filter LPFl and a filter SAW XFl, a selector TR between transmission and reception, and a further low-pass filter LPF2 placed between the selector TR and the antenna A. The transceiver TRX receives from the microcontroller MC transmission enabling signals TXE, transmitted data signals TXD, frequency variation signals TXF and reception enabling signals RXE and sends received data signals RXD to the microcontroller. In the functioning, by means of its internal clock, the microcontroller MC activates the sensors Sl -S3 and the transceiver TRX for short activity periods (for example, 250 msec) alternated to longer rest periods tl (for example, 10 sec) (Figure 5). During the activity periods the alarm station is capable of acquiring any signals indicative of fire (high temperature gradient, presence of flame, high presence of CO), of sending alarm messages to the adjacent stations, of receiving alarm signals and reĀ¬ transmitting them to the adjoining stations. The alarm messages are of the type illustrated in Figure 4, that is comprising a preamble P, whose task is to introduce the communication and establish the connection, a synchronism S, an address I, codified information IC relating to the alarm state and to the state of the battery B and finally an error control trailer CE. Each alarm station is fitted with a univocal recognition or address number, that can be programmed when positioning the station itself and that is automatically associated to the emission of each alarm. In case of alarm the station irradiates a message like that of Figure 4 on a radio and low power channel for a time exceeding tl, so as to have the certainty that it overlays one of the times of activity t2 of all the adjacent stations and thus to have the certainty that they receive it, they verify its address as belonging to their network and they retransmit it, complete with the original address indicating the point of alarm, to those adjoining. The message thus is spread in all directions starting from the "alarmed" station (indicated with SA' in Figure 1) until it reaches one or more intermediate units CIR, which in turn transmit it (by means of telephone, radio, GSM or other) to the central control station. The average time for broadcasting an alarm will be statistically equal to tl/2 x N, in which "N" is the number of stations situated between that detecting the fire and the unit CIR. It is important to note that the alarm message is transmitted by radio frequency and low power. This enables operation in ISM bands where the norm of "free use" ("License Exempt") is in force in accordance with the current norms RTT&E on the free use of short-range units. The transmission is carried out with pulse amplitude modulation technique thanks to the transmitting part ASK. The messages, both the original alarm and those retransmitted, are absolutely identical, both in contents of the message and time and duration of the pulses. At the same time as the IC information relating to the alarm state, the signal of time synchronism S is also transmitted, that forces all the stations SA to retransmit the message in exactly coinciding times. Any collisions of signals (two or more) in a generic receiver are thus not a problem, but on the contrary are an advantage given that the single pulses constituting the messages are summed coherently. This synchrony does not lead to big difficulties in production because it must be kept only for the time needed for the broadcasting of the alarm. A time base made with a quartz oscillator of modest precision is adequate. The problem of avoiding frequency beat between the radio frequency carriers of the various transmitters of the network is different. In fact they are "UHF" frequencies in the order of 900 MHz that do not permit (practically) the control of the frequency and the phase of the signal. If two carriers received by a receiver have a difference of frequency in the order of kHz between them, the beat generated in the detecting stage of the receiver can destroy the message. As it is foreseen to transmit the alarm messages at a speed of around 1 kbaud, the problem is resolved by generating in transmission the frequency of the carrier with the resonator SAW Xl, that has a frequency accuracy of +/- 150 kHz, and placing in the receiving part, after the detecting stage RIV, a low-pass filter LPFl with cut-off frequency of about 5 kHz. The probability of frequency coincidence of two transceivers within 5kHz is thus in the order of 3%. To eliminate also this possibility the signal transmitted, in addition to being amplitude modulated by the alarm signal, is frequency modulated casually (with variation of about +/- 10 kHz) by the signal TXF supplied by the microcontroller MC at the input of the transistor T. Figures 6 and 7 finally show a possible mechanical structure illustrative of the alarm station SA, which inside an air-tight mechanically- sealed casing fitted with a fixing ring AF provides for the microcontroller MC, the quartz clock XT, the battery B (for example, a lithium battery), and the antenna A (for example, a helical antenna). In an end cavity of the container C, opposite the fixing ring AF, one or more sensors Sl -S3 are positioned.