Showing posts with label fire. Show all posts
Showing posts with label fire. Show all posts
Saturday, March 30, 2013
Pyro Electric Fire Alarm
Here is an ultra-sensitive fire sensor that exploits the direct piezoelectric property of an ordinary piezo element to detect fire. The lead zirconate titanate crystals in the piezo element have the property to deform and generate an electric gate protected p-channel MOSFETs in the inputs. It has high speed of performance and low input current requirements.There are two inputs—the non-inverting input (pin 3) connected to the piezo element through diode D7 (OA71) that carries the voltage signal from the piezo element and the inverting input (pin 2) that gets a preset voltage momentarily changes the voltage level at pin 3 of IC1 and its output swings high.
Transistor T1 conducts taking the reset pin 12 of IC2 to ground. IC2 is now enabled and starts oscillating. With the shown values of the oscillating components C3 (0.22μ) and R6 potential when heated, thus converting the piezo element into a heat sensor. The circuit described here is very sensitive. It gives a warning alarm if the room temperature increases more than 10°C. The entire circuit has two sections—the sensor and the power supply section.
Fig. 1: Pyroelectric fire sensor Circuit diagram:
Sensor side circuit. Fig. 1 shows the fire sensor circuit. The front end of the circuit has a sensitive signal amplifier built around IC1 (CA3130). It gives a high output when temperature near the piezo element increases. IC CA3130 is a CMOS operational amplifier with gate protected p-channel MOSFETs in the inputs. It has high speed of performance and low input current requirements. There are two inputs—the non-inverting input (pin 3) connected to the piezo element through diode D7 (OA71) that carries the voltage signal from the piezo element and the inverting input (pin 2) that gets a preset voltage through VR1.
Fig. 2: Power supply with battery backup
By adjusting VR1,it is easy to set the reference voltage level at pin 2. In normal condition, IC1 gives a low output and the remaining circuitry is in a standby state. Capacitor C2 keeps the non-inverting input of IC1 stable,so that even a slight change in voltage level in the inputs can change the output to high. Normally, IC1 gives a low output, keeping transistor T1 non-conducting. Reseting pin 12 of IC2 (CD4060) connected to the collector of transistor T1 gets a high voltage through R5 and IC2 remains disabled. When the piezo element gets heat from fire, asymmetry in its crystals causes a potential change, enabling capacitor C2 to discharge.
It (1M), the first output (Q3) turns high after a few seconds and a red LED2 starts flashing. If heat near the piezo persists, Q7 (pin 14) output of IC2 becomes high after one minute, and the alarm starts beeping. If heat continues, Q9 (pin 15) turns high after four minutes and turns on the relay driver transistor T2. At the same time, diode D8 conducts and IC2 stops oscillating and toggles. The solenoid pump connected to the N/O (normally opened) contact of the relay starts spraying the fire-ceasing foam or water to the possible sites of fire. Power supply circuit. Powe supply section (Fig. 2) comprises a 0-12V, 1A step-down transformer with a standard full-wave rectifier formed by D1 through D4 and filter capacitor C1. A battery backup is provided if the mains supply is cut-offb due to short-circuit and fire. A 12V, 4.5Ah rechargeable battery is used for backup to give sufficient current to the solenoid pump. When mains power is available, diode D5 forward biases.
It provides power to the circuit and also charges the battery through resistor R2, and it limits the charging current to 120 mA. When power fails, diode D5 reverse biases and diode D6 forward biases, giving instant backup to the circuit. LED1 indicates the availability of mains power. Assemble the circuit on a generalpurpose PCB and enclose it in a suitable case. Connect the piezo element to the circuit using a thin insulated wire. Glue the flat side of the piezo element on a 30×30cm aluminium sheet to increase its sensitivity. Fix the sheet with the piezo sensor to the site where protection is needed. The remaining circuit can be fixed at a suitable place. If only the alarm generator is needed, omit the relay driver section.
Author :D. Mohan Kumar :Copyright: EFY
Thursday, March 28, 2013
Fire Alarm Circuit Based on Transistor
This is a design for circuit o f the fire alarm. This circuit is work based on 3 transistors. When there is a fire breakout in the room the temperature increases. This ultra compact and low cost fire alarm senses fire breakout based on this fact. This is the figure of the circuit.
The operation of the circuit will based on this explanation. The transistor BC177 (Q1) is used as the fire sensor here. When the temperature increases the leakage current of this transistor also increases. The circuit is designed so that when there is an increase in the leakage current of Q1, transistor Q2 will get biased. As a result when there is a fire breakout the transistor Q2 will be on. The emitter of Q2 (BC 108) is connected to the base of Q3 (AC 128).So when Q2 is ON Q3 will be also ON. The transistor Q3 drives the relay which is used to drive the load ie, light, bell, horn etc as an indication of the fire. The diode D1 is used as a free wheeling diode to protect it from back EMF generated when relay is switched. All capacitors are electrolytic and must be rated at least 10V.
The load can be connected through the C, NC, NO points of the relay according to your need. The calibration can be done using a soldering iron, and a thermo meter. Switch ON the power supply. Keep the tip of soldering iron near to the Q1.Same time also keep the thermometer close to it. When the temperature reaches your desired value adjust R1 so that relay gets ON. This is not a latching alarm, when the temperature in the vicinity of the sensor decreases below the set point the alarm stops. The circuit can be powered using a 9V battery or a 9V battery eliminator.
The operation of the circuit will based on this explanation. The transistor BC177 (Q1) is used as the fire sensor here. When the temperature increases the leakage current of this transistor also increases. The circuit is designed so that when there is an increase in the leakage current of Q1, transistor Q2 will get biased. As a result when there is a fire breakout the transistor Q2 will be on. The emitter of Q2 (BC 108) is connected to the base of Q3 (AC 128).So when Q2 is ON Q3 will be also ON. The transistor Q3 drives the relay which is used to drive the load ie, light, bell, horn etc as an indication of the fire. The diode D1 is used as a free wheeling diode to protect it from back EMF generated when relay is switched. All capacitors are electrolytic and must be rated at least 10V.
The load can be connected through the C, NC, NO points of the relay according to your need. The calibration can be done using a soldering iron, and a thermo meter. Switch ON the power supply. Keep the tip of soldering iron near to the Q1.Same time also keep the thermometer close to it. When the temperature reaches your desired value adjust R1 so that relay gets ON. This is not a latching alarm, when the temperature in the vicinity of the sensor decreases below the set point the alarm stops. The circuit can be powered using a 9V battery or a 9V battery eliminator.
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