| 摘要 |
<p>PURPOSE:To accurately measure a suction amount of air by eliminating the detection error caused by the back flow of an air stream generated at the time of pulsation, by providing heat generating resistors each composed of a temp.-sensitive resistance film to a substrate on the upstream and downstream sides thereof. CONSTITUTION:A Wheatstone bridge is constituted of the heat generating resistor 11a on the upstream side, the temp. compensating resistor 12a on the upstream side and fixed resistors 13a, 14a, 15a and the potential difference between the middle point of the resistors 13a, 15a and the middle point of the resistors 14a, 11a is detected by a differential amplifier 16a. The signal from said amplifier 16a is inputted to the base of a transistor (Tr) 17a and closed loop control is performed so as to make the potentials at the middle points of the bridge equal. The current allowed to flow to the bridge is controlled by the amplifier 16a and the Tr 17a so as to make the resistance value of the resistor 11a constant regardless of a flow rate. By detecting the current flowing to the resistor 11a as the voltage drop in the resistor 14a, a flow rate of air can be calculated.</p> |
