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Air-Gas Detection Circuits
Air-Gas Detection Circuits
Line-Operated Smoke Detector
Using an ionization chamber and a high-impedance (CA3130) op amp, the presence of smoke will cause the CA3130
Explosive Gas Detector Circuit
A gas sensor (TGS823 from Allegro Electronics, Cornwall Bridge, CT 06754) conducts in the presence of explosive gases. U5 is a voltage-to- frequency converter that produces a frequency proportional to the sensor conductance. The output frequency ranges from 100 IIz in clean air to 8 kHz in a contaminated atmosphere. The dc voltage from the sensor also drives bar graph LED U7 and comparators...
The sensor is based on the selective absorption of hydrocarbons by an n-type metal-oxide surface. The heater in the device serves to burn off the hydrocarbons once smoke or gas is no longer present in the immediate area; hence, the device is reuseable. When initially turned on, a 15 minute warm-up period is required to reach equilibrium (V, = 0.6 V) in a hydrocarbon-free environment. When...
Gas and smoke detector
This circuit can detect smoke and a number of gases (CO, CO2, methane, coal gas and others) with a 10 ppm sensitivity. It uses a heated surface semiconductor sensor. Detection occurs when the gas concentration increase causes a decrease of the sensor element internal resistance
When power is applied to the circuit, the heater coil in the sensor is energized by the 5-V output of IC5, a 7805 voltage regulator. Breathing into the sensor with alcohol on your breath will lower the sensor"s resistance; consequently, the input voltage to the detector circuit, will change. The detector circuit consists of quad op amp, IC2 and its associated circuitry. All sections of the...
This circuit comes from U.S. Patent 3, 778,800, granted to BRK Electronics in Aurora, IL. The circuit provides a smoke detector with an alarm for both smoke and low batteries. The R6/R7 voltage divider monitors the battery and will turn Q2 and Ql off when the battery voltage falls too low. The smoke-detector chamber will also cut Ql off when it senses smoke.
This smoke detector uses a MEM 817 p-channel enhancement mode MOSFET as its buffer amplifier. Operation of the sensor is based on a decrease in the current when smoke enters the chamber, thereby causing a negative voltage excursion at the gate of the buffer MOSFET.
Humidity Sensor with the H14DL
A humidity sensor with temperature compensation built-in. Never apply a DC voltage to the sensor, even measuring the sensor with an ohmmeter will damage the device, always ensure that an AC voltage is applied. Avoid condensation, freezing, dust, mist, oil, alcohol, etc. To set up this circuit replace the H14DL with Min Res 22Kohm and Min Res 51Kohm as shown, Acjust RV1 until a voltmeter between...
Ionization chamber smoke detector II
The smoke alarm signal must be a continuous one rather than pulsating, then the slightly less expensive
In the presence of smoke or gas, the ac output voltage increases and becomes rectified, filtered and zener-diode coupled (D2 for thresholding) to sensitivity control R3. Under no gas condition, the output equals approximately 0 V (high). When gas is present, the output will be a negative value (low) sufficient to overcome the threshold of MeMOS gate 2 and D2. The circuit shown uses a TGS 308...
ICl, an Intersil ICL 7106, contains an aid converter, a 3,1/2-digit LCD driver, a clock, a voltage reference, seven segment decoders, and display drivers. A similar part, the ICL7107, can be used to drive seven segment LEDs. The probe body is a five-inch length of light-weight aluminum tubing. The leads from the circuit are connected to the body and tip of the probe. The sensor functions as...
When a current of air hits tbe piezo element, a small signal is generated and is fed through Cl and Rl to inverting input pin 2 of one section of the LM324. That causes output pin 1 to increase. Resistor R3 is used to adjust the sensitivity of the detector. The circuit can be set so high as to detect the wave of a hand or so low that blowing on the element as hard as you can will produce no...
Photoelectric smoke detector
The LED predriver output pulses an external transistor which in turn, switches on the infrared light emitting diode at a very low duty cycle. The desired IR LED pulse period is determined by the value of the external timing resistor. The Smoke Sensitivity is adjustable through a trimmer resistor which varies the IR LED pulse width. The light sensing element is a silicon photovoltaic cell which...
Air-Flow Detector Circuit
Two precision temperature sensors are used to detect a small temperature difference. When air flow occurs, self-heating of the LM335 is reduced, and the output of the two temperature sensors is unequal.
Ionization chamber smoke detector
Battery-operated, ionization chamber smoke detector includes a circuit to generate a unique alarm when the battery reaches the end of its useful life. The circuit uses the MCMOS MC14572 for two alarm oscillators (smoke and low battery)
Air-Flow Sensing Thermistor Bridge
Using the thermistor-bridge circuit, you can detect system-cooling air losses caused by filter or inlet
A bar-graph LED driver is used to drive 10 LEDs to give a relative indication of moisture. The moisture probes are connec
Gas and vapor detector
The power drain is approximately 150 mA. IC1 provides a regulated 5-volt supply for the filament heater of the sensor. The gas sensitive element is connected as one arm of a resistance bridge consisting of R4, R7, R8 and the meter Ml with its associated resistors R5 and R6. The bridge can be balanced by adjusting R8 so that no current flows through the meter. A change in the sensor's...
This circuit can be used to measure exhaust gas temperature in a furnace. The 10-bit LTC1091A gives 0.5Â°C resolution over a ooc to 500Â°C range. The LTC1050 amplifies and filters the thermocouple signal, the LT1025A provides cold junction compensation and the LT1019A provides an accurate reference. The ]-type thermocouple characteristic is linearized digitally inside the MCU.
Use CA3164A BiMOS detector/alarm system. For operation as smoke detector with electromechanical hom (Fig. 40-la), the output of driver at terminal 8 is used. Large npn transistor Q3,-with an active pull-up and transistor Q2 provide over 300 mA of drive current.
Air-Pressure Change Detector
A piezoelectric detector (BZ1) is used in this circuit to detect a change in air pressure. BZ1 produces a volt
Gas analyzer circuit
The circuit shows a simple yes/no gas detector. Three 1.5-V D cells are used as a power supply, with SI acting as an on/off switch. The heater is energized directly from the battery, while the electrodes are in series with a 10 k resistor. The voltage across this resistor is monitored by a pnp transistor. When the sensor is in clean air, the resistance between the electrodes is about 40 k, so...
Sensing circuit detects either steady or fluctuating air flows. The heart of the circuit is a Radio Shack piezo buzzer (P/N 273-060) and an LM324 quad op amp. (Red wire from the piezo element connects to capacitor CI, and the black wire to ground) When a current of air hits the piezo element, a small signal is generated and is fed through CI and R1 to the inverting input (pin 2) of one section...
Toxic gas detector
The major device in the circuit is SRI (a TGS812 toxic-gas sensor manufactured by Figaro Engineering Inc.) The gas-sensitive semiconductor (acting like a variable resistor in the presence of toxic gas) decreases in electrical resistance when gaseous toxins are absorbed from the sensor surface. A 25,000 ohm potentiometer (R5) connected to the sensor serves as a load, voltage-dividing network,...
Moisture Detector Circuit
The moisture detector uses two transistors and a piezoelectric transducer to sound an alarm tone when water is present. Transistor Ql forms a crystal-controlled oscillator, using a portion of piezoelectric transducer XDCwhich contains two piezoelectric crystal regionsas the crystal. The transducer has three separate leads. One lead goes to each of the crystals, and the third lead is common to...
Combustible Gas Detector Circuit
THE GAS SENSOR is mainly composed of tin dioxide on a ceramic base; the resistance of the sensor varies depending on the concentration of reducing gases in the air. The circuit shown is useful for the detection of dangerous levels of combustible fumes or gases. It uses a comparator circuit to trigger an alarm buzzer. The sensor`s resistant element is connected in series with resistor R1 to...
Transformer T1 supplies power to the heater of the sensor. Since the sensor is fairly sensitive to heater voltage, diodes Da, D4, and D5 regulate the heater voltage. Tl, together with D1 and CZ, forms a de power supply, whose current is regulated by Q1 and adjusted by Rl. The constant current from Ql feeds a variable resistance, consisting of thermistor R7 and the parallel combination of R5...
Gas Sensor Leakage Detector
the design of the gas detector of LPC221
Gas Leakage Sensor Alarm Circuit Engineering Project using 555 Timer and MQ6 SEN 1327 Gas Sensor Module
In this article we will be discussing about a home security alarm circuit. This is a LPG gas leakage sensor circuit that detects the outflow of LPG gas and alerts the user via audio and visual indications. The heart of this simple engineering project is a gas sensor module SEN 1327. QM 6 gas sensor is used in this SEN 1327 module. The output sign
Detecting liquified petroleum gas (LPG)
Figaro manufactures sensors that can sniff out various kinds of gases (e. g. hydrogen, methane, carbon monoxide, etc. ). I`ve designed a simple circuit built around the Figaro LPM2610 module which will sound an alarm if and when the level of liquified petroleum gas (LPG) in the kitchen rises above a certain predetermined level. I knew the dimensions
The tidal influence on oil and gas emissions from an abandoned oil well: Nearshore Summerland California
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