Versatile Microbridge Flow Control Sensor Structure and Applications

Availability of reliable and accurate sensors is a necessary first step in the design of control systems. This paper first describes the nature of a hot-thin-film microanemometer and then reviews its applications for Environmental Control and Life Support Systems (ECLSS). This Si sensor chip measures less than 2 mm x 2 mm x 0.3 mm, consumes less than 4 mW of power, and features a 10- to 20-ms response time. For applications requiring battery operation, the average power consumption can be further reduced by more than a factor of 100 using intermittent operation. The sensor output can be expressed in STP volumetric or mass flow units; however, changes in environmental temperature or fluid composition would cause errors if left uncorrected. Such corrections have been worked out and implemented with the help of an additional sensor, so that a fully compensated flow sensor package has been achieved, with an accuracy near ±1% over a major part of its 3000:1 dynamic range. The small mass of the 1-μm-thick sensing film makes it suitable for use in systems subject to vibration as well as for a wide range of gravitational environments, including zero-g.