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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