| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a thermal type flowmeter capable of showing high accu racy and high control responsiveness without complicating a circuit configura tion. SOLUTION: The flow rate of fluid is measured based on an applied voltage to a heater 112, the applied voltage being controlled based on the output of a sensor circuit 104 containing a temperature sensing element affected by the heater 112. The applied voltage to the heater is the sum of a fixed base voltage in a predetermined period and added voltage during variable applying period. A two-level signal consisting of an L level representing insufficient heating of the temperature sensing element and an H level excluding the L level outputted from a comparator 108 is sampled at predetermined intervals. When the L level count is for every predetermined period within a prescribed range, the base voltage is not changed. When it is lager than an upper limit, the base voltage is increased by one step value, and when it is lower than a lower limit, the base voltage is decreased by one step value. The added voltage is applied to a heater control circuit applies during only a period when the two-level signal outputted from the comparator is the L level.</p> |
