Patent ID: 9360357
Filing Date: 2016-06-07
CPC Classification: G01F

Claim Text:
1. A micromachined mass flow sensor with condensation prevention capability comprising: a suspending thermally isolated membrane structure on a silicon substrate with a cavity underneath; a first heater thermistor is disposed on top of the suspending thermally isolated membrane structure as a membrane heating source which elevates membrane temperature to a certain level; a first temperature sensing thermistor surrounding and adjacent to the first heater thermistor is disposed on top of the suspending thermally isolated membrane structure and provides a feedback signal for membrane temperature control; and wherein the first heater thermistor and the temperature sensing thermistor are covered by a layer of dielectric film as an electrical insulation layer; a second heater thermistor, an upstream temperature sensing thermistor, and a downstream temperature sensing thermistor being disposed on top surface of the electrical insulation layer; wherein the second heater thermistor is located between, and equidistant from each of, the upstream temperature sensing thermistor and the downstream temperature sensing thermistor and wherein the second heater thermistor serves as a flow medium heating source; and a second temperature sensing thermistor being disposed on a non-suspending-membrane region of the silicon substrate; wherein the second temperature sensing thermistor is serving as an ambient temperature sensing thermistor for the flow medium; wherein the first heater thermistor and the first temperature sensing thermistor are connected to a control circuit, wherein a feedback signal from the first temperature sensing thermistor is utilized to control and elevate the suspending thermally isolated membrane to a setting temperature, which is above the flow medium's vaporization temperature, to prevent a condensation of the flow medium or a moisture deposition on the suspending membrane's surface; wherein the second heater thermistor and the ambient temperature sensing thermistor are connected to a second control circuit, wherein a feedback signal from the ambient temperature sensing thermistor is utilized, to control and elevate the second heater thermistor's temperature to be above the temperature setting of the second heater thermistor; and wherein a temperature difference measured between the upstream temperature sensing thermistor and the downstream temperature sensing thermistor is utilized to calculate a mass flow rate.