초록 ▼

A sensing circuit of a thermal mass flow sensor provides enhanced precision control of heating and temperature sensing coils used for fast sensing responses. The sensing circuit includes a pair of coil servo loops achieving servo loop control of the sensing coils in each servo loop. The current path

A sensing circuit of a thermal mass flow sensor provides enhanced precision control of heating and temperature sensing coils used for fast sensing responses. The sensing circuit includes a pair of coil servo loops achieving servo loop control of the sensing coils in each servo loop. The current paths in the servo loop include a main current path carrying low levels of current and minor current paths carrying very small levels of current. These small levels of current have insignificant current levels compared to the levels of current in the main current path. The single main current path in the servo loop allows nearly all of the current from the primary servo amplifier to be used for driving the coils, thereby improving the efficiency of the coil servo loop. The heating and sensing coil in each servo loop is coupled to an integration network for measuring power provided to the coil. The coil is also coupled to a voltage follower network for providing a programmable voltage level to the integration network to compensate for any differing coil parameters between the sensing coils. Thus, the sensing circuit has the flexibility to accommodate coil parameter differences. Further, the heating and sensing coils of the servo loops are wrapped around a sensing tube of a mass flow sensing apparatus. The sensing tube is short and holds a low fluid mass, allowing for small sensing coils, a fast sensing response, and insensitivity of the sensing tube to the position of the heating and sensing coils.

대표청구항 ▼

[ What is claimed is:] [1.] A mass flow sensing circuit of a sensor adapted for improved sensing flexibility, comprising:at least one inductive heating and sensing coil for heating a fluid passing through the sensor to maintain a constant temperature for the fluid, the mass flow rate of the fluid de

[ What is claimed is:] [1.] A mass flow sensing circuit of a sensor adapted for improved sensing flexibility, comprising:at least one inductive heating and sensing coil for heating a fluid passing through the sensor to maintain a constant temperature for the fluid, the mass flow rate of the fluid derived from power necessary to maintain a constant temperature for the fluid;at least one integrator measuring the power provided to said coil; andat least one voltage follower network coupled to said coil and said integration network for providing a programmable voltage level to said integration network to adjust the coil parameters of said coil.