流量傳感器：計算體積流量和質(zhì)量流量

　　流量傳感器用來測量液體、氣體的流速、體積流量或質(zhì)量流量。氣體質(zhì)量流量在標(biāo)準(zhǔn)升每分鐘單位指定（SLM）或每分鐘標(biāo)準(zhǔn)立方厘米（SCCM）。通過將體積流量參考標(biāo)準(zhǔn)溫度和壓力，可以從體積流量中計算出精確的質(zhì)量流量（G／min）。圖1顯示了氣體/液體流量開關(guān)和控制的一些例子。

　　To design with and properly use gas/liquid sensors， we must first take some preliminary steps and also understand some terms and equations in order to get our desired design results. First， let’s look at any external support circuitry that may be needed for the sensor. Airflow sensors without an internal sensor amplifier and other circuitry sometimes require external heater control circuitry （Fig. 2）， power to bias an internal sensing bridge （Fig. 3）， and amplification and conditioning of the sensor output signal （Fig. 4）。 STMicroelectronics LM2902 op amps may be used to construct this circuit.