| 摘要 |
<p>PURPOSE:To reduce the heating value of a power transistor by a method wherein the voltage impressed on a bridge is made to be of a pulsating waveform faster than the change in the flow velocity of suction air and thereby the power transistor is employed only for switching in a temperature control circuit of the hot wire for the hot-wire type current meter. CONSTITUTION:The output from the terminals (a) and (b) of the bridge of the current meter consisting of the temperature dependency type hot wire Hw, a temperature dependente resistor Rk set on the up-stream side of the former and reference resistors R1 and R2 is inputted in the minus terminal of the operational amplifier OP2 of a chopper-type voltage controlling part 7 through the intermediary of an amplifier 6. The input to the pulse terminal of OP2 comes through an intergration and delay circuit consisting of a coil L and is delayed to the minus-terminal input by a time required for integration. Therefore, the output of OP2 becomes high and low alternately owing to this difference in time and the difference in potential, thereby turning on and off the power transistor Tr. The output of TR is made to be of pulsating waveform through the intermediary of a flywheel diode D and the aforesaid integration circuit and impressed on the bridge. Since the power transistor Tr performs only switching operation in this way, the heat value thereof is small.</p> |
