This invention relates to a pneumatic device which is subject to positive feedback and, more particularly, to a sloped nozzle within the device designed for reducing the positive feedback.
As disclosed hereinafter, the present invention is particularly useful in conjunction with reversing pneumatic amplifiers which are designed to reverse the action of sensors with respect to the branch line output of the sensing system although the present invention may have applications wider than in the described reversing relay.
As described herein, the present invention is useful in connection with the Velocitrol CP980 manufactured by Honeywell Inc. and described in U.S. Pat. No. 4,182,486. The Velocitrol includes a velocity sensor which comprises a pair of nozzles mounted generally transversely to the air moving through a duct. One of the nozzles, the primary nozzle, is designed to be connected to a source of pressure and the other of the nozzles, the secondary nozzle, is designed to receive air issuing from the primary nozzle dependent upon the velocity of air moving through the duct. As the velocity of the air moving through the duct increases, the amount of air received by the secondary nozzle decreases and as the velocity of the air moving through the duct decreases the amount of air received by the secondary nozzle increases. This Velocitrol controller thus is a reverse acting device.
A pneumatic device is necessary, therefore, to reverse the action of the velocity sensor to make it direct acting. However, it was found that the reversing pneumatic device selected for converting the Velocitrol to a direct acting controller was subject to positive feedback. This problem of positive feedback gave rise to the present invention for eliminating positive feedback in pneumatic devices.