The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
May. 12, 1998
Filed:
Dec. 21, 1995
Tapani Ryhanen, Helsinki, FI;
Vaisala, Oy, Helsinki, FI;
Abstract
The invention relates to a method and apparatus for linearizing a flow velocity sensor based on pressure difference measurement. According to the method, a difference of two pressure signals is measured from the flow under measurement and is proportional to the square of the flow velocity. The pressure difference is measured using a micromechanically manufactured symmetrical capacitive differential pressure sensor based on the force balance principle. The pressure-induced deviation from force balance is compensated for by inducing on the pressure-sensing diaphragm of the differential pressure sensor a force-balance-restoring electrostatic pressure. The amplitude of the force-balance-restoring electrical feedback control signal also acts as the system output signal and is directly proportional to the square root of the difference of the two pressure signals, and thus, a linear function of the flow velocity. According to the invention, the feedback control voltage is a function of the direction of the pressure difference and is applied only to one of the stationary electrodes so that the electrostatic force of attraction thus induced acts counter to the force generated by the pressure difference under measurement, whereby the polarity of the system output voltage signal is dependent on the direction of the flow.