Flow Sensor With Adjustable Sensitivity

The present invention relates to flow sensors. More specifically, the present invention is directed to a flow sensor having an adjustable sensitivity.

The object of the present invention is to provide an improved flow sensor having an adjustable sensitivity.

In accomplishing this and other objects, there has been provided, in accordance with the present invention, a flow sensor having a differential pressure sensing means, a hollow container means having an internal compartment, a first fluid port on said container means communicating with said compartment, a second fluid port on said container means diametrically opposite to said first port and communicating with said compartment, differential pressure transducer means located in said compartment and responsive to a differential pressure between said first and second ports to produce an output signal representative of said differential pressure and a means for selectively rotating said container means on a fixed axis of rotation.

A better understanding of the present invention may be had when the following detailed description is read in connection with the accompanying drawings, in which:

FIG. 1 is a block diagram illustration of a flow measuring system utilizing an example of the present invention,

FIG. 2 is a cross-section of an example of a sensor suitable for use in the system shown in FIG. 1 and taken along a plane orthogonal to the axis of rotation of the sensor,

FIG. 3 is a cross-section of the sensor shown in FIG. 2 along a plane containing the axis of rotation of the sensor and

FIG. 4 is a cross-section of an example of an alternate embodiment of a sensor suitable for use in the system shown in FIG. 1 and taken along a plane orthogonal to the axis of rotation of the sensor.

Referring to FIG. 1 in more detail, there is shown an example of a fluid pressure measuring system utilizing a plurality of fluid flow lines 2, 4, 6 and 8 with each of the flow lines having a corresponding by-pass line and a flow restriction, e.g., flow line 2 has by-pass lines 2A and 2B and restriction 2C. Each of the by-pass lines 2-8 has a fluid pressure sensor, e.g., sensors 10, 12, 14 and 16 connected therein. For example, the fluid pressure sensor 10 is connected between the by-pass flow lines 2A and 2B to subject the sensor 10 to the fluid pressure differential existing between the flow lines 2A and 2B produced by the flow restriction 2C which, in turn, is representative of the fluid flow in flow line 2.

The output signals of each of the sensors 10-14 are applied to respective output signal lines 18, 20, 22 and 24. These signal lines 18-24 are connected to the respective inputs of a signal multiplexer 26. The signal on the single output of the multiplexer 26 is representative of a selected one of the signal lines 18, 20, 22 and 24 and is applied to a multiplexer output line 27. The output line 27 is connected to an input of a signal amplifier 28. An output from the amplifier 28 applied along amplifier output line 29 is connected to a signal converter 30 having an output line 31 connected to a display 32. Thus, the sensors 10, 12, 14, and 16 are each effective to produce an output signal representative of their respective sensed pressures which signals are selected by the multiplexer 26 and ultimately displayed on the display 32 as desired. It should be noted that while the plurality of sensors 10, 12, 14 and 16 are shown in a by-pass line configuration, the plurality of sensors 10, 12, 14 and 16 may be each arranged directly in the respective ones of the main flow lines without the use of a by-pass line without departing from the scope of the present invention.

In FIG. 2, there is shown a cross-section taken along a plane orthogonal to the plane of rotation of an example of one of the sensors 10, 12, 14 and 16, e.g., sensor 10, with similar reference numbers being used in FIG. 2 to identify elements used in common with FIG. 1. Thus, the by-pass lines 2A and 2B are arranged to direct a fluid flow from the main fluid flow line 2 into a housing 36 containing a rotatable hollow container in the form of a cylinder 40 having its axis of rotation positioned at right angles to the direction of flow of the fluid through the housing 36 between the lines 2A and 2B. The fluid flow is produced by the differential pressure between the bypass lines 2A, 2B produced by the restriction 2C. A pair of fluid flow passages 42, 43 are connected between respective ones of diametrically opposite ports 42A, 43A on the surface of the cylinder 40 and an internal compartment 44 located within the cylinder 40. The compartment 44 is divided by a diaphragm 46 supporting a fluid pressure transducer 48 thereon. Thus, the movement of the diaphragm 46 in response to a pressure differential applied to opposite sides thereof is effective to produce an output signal from the transducer 48, in a manner well-known in the art. For example, the sensor 48 may include piezoresistive bridge circuit elements affixed to the diaphragm 46 which change their dynamic characteristics when subject to bending stresses and, accordingly, produce corresponding output signals representative of the differential pressure producing the stress on the elements.

As shown in FIG. 3, which is a cross-section of the sensor 10 taken along a plane containing the axis of the flow channels 42, 43., the rotor 40 is fluid-sealed to the interior walls of the housing 36 by suitable O-rings 50 located on the surface of the rotor 40. One side of the rotor 40 is provided with a first axial extension 51 which extends out of the housing 36 and is connected to an adjusting knob 52 external to the housing 36 while the extension 51 is fluid-sealed to the internal surface of the housing 36 by an O-ring 54 encircling the extension 51. A second axial extension 56 of the rotor 40 is provided on the other side of the rotor 40 from the first extension 51 and extends out the housing 36 while being sealed to the internal surface of the housing 36 by an O-ring 58 encircling the second extension 56. The electrical connecting lines 18 to the sensor 48 are guided through an axial bore 60 in the second extension 56 and are sealed therein by a suitable sealing compound to provide a fluid-tight seal between the lines 18 and the wall defining the bore 60.

In operation, the cylinder 40 is rotated by means of the knob 52 to a position which changes the orientation of the fluid ports 42A, 43A and fluid inlet passages 42, 43 with respect to the fluid flow around the outside of the cylinder 40. Such a rotation subjcts the ports 42A, 43A to differing fluid pressures existing in the fluid flowing around the cylinder 40. Specifically, when the fluid channels 42, 43 are aligned with the fluid flow, the fluid pressure differential applied to the diaphragm 46 is a maximum while when the rotor 40 is rotated to have the fluid passages 42 and 43 orthogonal to the fluid flow, the differential pressure across the diaphragm 46 would be zero. Varying amounts of differential fluid pressure would occur between these end positions of the rotor 40.

In FIG. 4, there is shown a cross-section taken along a plane orthogonal to the plane of rotation of an alternate embodiment of one of the 10, 12, 14 and 16, e.g., sensor 10, with similar reference numbers being used in FIG. 4 to identify elements used in common with FIGS. 1 and 2. Thus, the bypass lines 2A and 2B are arranged to direct a fluid from the main flow line 2 into a housing 36 containing a hollow container in the form of a cylinder 40 having its axis of rotation positioned at right angles to the direction of flow of the fluid through the housing 36 between the lines 2A and 2B. A pair of fluid flow passages 42, 43 are connected between respective ones of diametrically opposite ports 42A, 43A on the surface of the cylinder 40 and an internal compartment 44 located within the cylinder 40. A flow sensor 48A is positioned within the compartment 44 to detect a fluid flow between the ports 42A, 43A induced by the differential pressure therebetween. Thus, the flow of fluid around the cylinder 40 is induced by the differential pressure between the bypass lines 2A and 2B produced by restriction 2c. Similarly, the axial position of the cylinder 40 produces a flow through the compartment 44 in proportion to the differential pressure at the ports 42A, 43A. Thus, the flow through the compartment 44 sensed by the transducer 48A is proportional to the flow in the main flow line 2. The transducer 48A may be a flow sensor of the type which uses a matrix or bridge of resistive elements that are heated by an electrical current with a fluid flow across the surface of one or more of the elements serving to cool the elements to change its electrical resistance and unbalance the bridge circuit. Thus, the amount of unbalance of the bridge circuit, i.e., its output signal, is proportional to the fluid flow through the compartment 44 which, in turn, is proportional to the fluid flow in the main line 2 in a manner similar to that previously discussed with respect to the sensor shown in FIGS. 2 and 3.

The sensor of the present invention has particular utility in a flow measuring system utilizing a plurality of the sensors 10, 12, 14, 16 either in a single installation, e.g., an industrial process monitor, or in a plurality of separate installations, e.g., an individual sensor located on a fuel gas supply for each of a plurality of consumers. In the first application, the sensors would be multiplexed to a shared amplifier as shown in FIG. 1 while in the latter application, a shared amplifier and detector system would be transported to each sensor to obtain an output therefrom. Since in either such measuring circuits employing a plurality of the sensors 10, 12, 14, 16, the sensors would each have to be calibrated to match their individual sensitivity to the shared amplifier, the sensor calibration is achieved by simply rotating each sensor by means of the knob 52 until its measured transducer output signal is the same as the output signals from the other sensors when the same input fluid flow is applied to each flow line. Thus, all sensors will be calibrated to produce an accurate output signal for a single measuring circuit, independent of the electronic sensitivity variations of each sensor and any other extraneous factors affecting the transducer output signal. The calibrated position of the sensor, which may be determined during the manufacture of the sensor, is retained during the pressure measuring operation of the system to assure that the shared amplifier system will produce an accurate measurement of each sensed fluid pressure. As previously mentioned, the sensor shown in FIGS. 2 and 3 may be employed directly in respective ones of a plurality of the main flow lines without the use of a bypass line and with a sensor operation similar to that described above.

Accordingly, it may be seen that there has been provided, in accordance with the present invention, an improved flow sensor having an adjustable sensitivity.