Posts Tagged ‘Airflow sensitive’

Car Exhaust Meter

Bridge circuit contains two resistors lOO-ohm (R3 and R4), and two thermistors (Tl and T2). At room temperature, the resistance of T1 and 1’2 is about 2000 ohms. When they are each heated to 150 °C by an RNA 10 current, the resistance value decreases to 100 ohms. So. the four elements include a bridge circuit. CO is a characteristic that conducts heat from a thermistor at a rate different from that of air. A thermistor, TI, is exposed to automobile exhaust, while the other, 1’2, is isolated in an environment of clean air. Unlike thermal conduction bridge imbalance. A voltage difference is caused between points A and C. A differential amplifier. VI, amplifies this difference and leads to the counter with a current sufficient to read the percentage of CO and air-fuel ratio. A control panel before the balance, R5, balances the bridge and calibrates the instrument. The calibration is performed when both thermistors are exposed to outside air.
Cl O-1 uF. Electrolytic capacitor 25 vall diode Dl-silicon, general purpose, or equivalent IN2069 Ml-0.1 RNA ammeter Rl. R3, R4, IS-ohm Lao Si 10%. watt resistor Tor! All resistors are 10%, though. SO0 watll H2-ohm potentiometer, PC mounting potentiometer R5-la-ohm, mounting panel Tront H7, R8-22, OOO ohms resistance R9-570, OOO-resistance Ohrn TAB BOOKS, INC. Fig. 7-3 RL0 S-0.900-ohm resistance thermistor sensor-SR1, num ¬ ber 100 • Part 1648 of the heat mode hKit HERE) 080. Heath Company Benton Harbor, MI, 49022 lM309H Ul-S-volt regulator integrated cir- cooked U2-lM741TC op amp circuit intergraled Misc.-PC board, screws, cabinet, welding, hard sections, plastic tubing 10 feet, etc.

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Air Flow Detector

Air Flow Detector

This simple circuit uses an incandescent lamp to detect airflow. With the filament exposed to air, a constant current source is used to slightly heat the filament. As it is heated, the resistance increases. As air flows over the filament it cools down, thus lowering it’s resistance. A comparator is used to detect this difference and light an LED. With a few changes, the circuit can be connected to a meter or ADC to provide an estimation on the amount of air flow.

Read more original source:

http://www.aaroncake.net/circuits/airflow.htm

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Self-heated transistor digitizes airflow

A sensitive and reliable way to measure airflow is to exploit the predictable relationship between airspeed and the heat dissipated by a sensor exposed to the flow while being held at a constant temperature differential above ambient. The power required to maintain the elevated sensor temperature is proportional to the square root of the airspeed (King’s law). The popular hot-wire anemometer uses this principle, but suffers from the disadvantage of using a relatively fragile airflow sensor, a thin metallic filament.

Read more original source:http://www.edn.com/archives/1996/031496/06di3.htm