Air-Gas Detection Circuits

Using an ionization chamber and a high-impedance (CA3130) op amp, the presence of smoke will cause the CA3130 ..

Views: 18 | Votes: 14 | Comments: 0 | Rating: 8 | Rank: 5 | Added: Mar 27, 2013 |

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 U4-b and U4-c to sense present caution and danger levels. ..

Views: 29 | Votes: 2 | Comments: 0 | Rating: 8.5 | Rank: 5 | Added: Mar 25, 2013 |

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 or smoke is introduced near the sensor, VA will quickly rise (rate and final.....

Views: 18 | Votes: 2 | Comments: 0 | Rating: 7 | Rank: 5 | Added: Mar 19, 2013 |

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..

Views: 2687 | Votes: 79 | Comments: 0 | Rating: 7 | Rank: 5 | Added: Feb 26, 2013 |

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 detector circuit are cahbrated via R3 and R4, and the inputs to each section are.....

Views: 16 | Votes: 96 | Comments: 0 | Rating: 2 | Rank: 5 | Added: Feb 19, 2013 |

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. ..

Views: 8 | Votes: 93 | Comments: 0 | Rating: 0 | Rank: 5 | Added: Jan 22, 2013 |

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. ..

Views: 9 | Votes: 52 | Comments: 0 | Rating: 4 | Rank: 5 | Added: Dec 16, 2012 |

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 output and ground reads 1.40V. ..

Views: 4607 | Votes: 78 | Comments: 0 | Rating: 4 | Rank: 10 | Added: Nov 28, 2012 |

The smoke alarm signal must be a continuous one rather than pulsating, then the slightly less expensive..

Views: 4216 | Votes: 69 | Comments: 0 | Rating: 3 | Rank: 5 | Added: Nov 28, 2012 |

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 sensor, a generalpurpose gas detector that is not sensitive to smoke or carbon.....

Views: 6 | Votes: 6 | Comments: 0 | Rating: 8 | Rank: 5 | Added: Nov 2, 2012 |

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 a variable resistor that varies Ql "s base current, hence its collector.....

Views: 28 | Votes: 103 | Comments: 0 | Rating: 3 | Rank: 5 | Added: Oct 17, 2012 |

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 output. Resistor R2 is used to adjust the level of the output voltage at pin 1. ..

Views: 11 | Votes: 33 | Comments: 0 | Rating: 7 | Rank: 5 | Added: Oct 13, 2012 |

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 is held at near zero bias to minimize leakage currents..

Views: 1064 | Votes: 10 | Comments: 0 | Rating: 0 | Rank: 5 | Added: Oct 11, 2012 |

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. ..

Views: 11 | Votes: 58 | Comments: 0 | Rating: 1 | Rank: 5 | Added: Oct 11, 2012 |

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)..

Views: 807 | Votes: 83 | Comments: 0 | Rating: 9 | Rank: 5 | Added: Sep 22, 2012 |

Using the thermistor-bridge circuit, you can detect system-cooling air losses caused by filter or inlet ..

Views: 11 | Votes: 86 | Comments: 0 | Rating: 7 | Rank: 5 | Added: Sep 6, 2012 |

A bar-graph LED driver is used to drive 10 LEDs to give a relative indication of moisture. The moisture probes are connec..

Views: 11 | Votes: 67 | Comments: 0 | Rating: 8 | Rank: 5 | Added: Aug 15, 2012 |

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 resistance, caused by detection of noxious gases, will unbalance the circuit and deflect.....

Views: 1554 | Votes: 34 | Comments: 0 | Rating: 3 | Rank: 4 | Added: Aug 7, 2012 |

This circuit can be used to measure exhaust gas temperature in a furnace. The 10-bit LTC1091A gives 0.5°C resolution over a ooc to 500°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. ..

Views: 5 | Votes: 12 | Comments: 0 | Rating: 7 | Rank: 5 | Added: Jul 27, 2012 |

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. ..

Views: 4 | Votes: 60 | Comments: 0 | Rating: 9 | Rank: 5 | Added: Jul 17, 2012 |