PULSE CANCELLING FOR FLOW MEASUREMENTS

Abstract

Apparatus and a method for sampling fluid flow quality. The apparatus includes a flow channel through which the fluid is flowing, a pressure sensor provided in said flow channel and adapted to detect a pressure in said flow channel, a membrane provided downstream or upstream said pressure sensor in said flow channel and adapted to induce a pressure modification, and a control unit connected to said pressure sensor and said membrane. The control unit is configured to activate said membrane so as to induce said pressure modification when said detected pressure deviates from a predetermined pressure interval, thereby neutralizing any pressure fluctuation in said flow channel.

Claims

1. Monitoring apparatus comprising: a flow channel configured for flow of a fluid therethrough, a pressure sensor disposed in said flow channel and adapted to detect a pressure in said flow channel, a membrane configured to induce a pressure modification to said fluid within said flow channel, and a control unit connected to said pressure sensor and said membrane wherein said control unit configured to activate said membrane so as to induce said pressure modification when said detected pressure deviates from a predetermined pressure interval, to reduce pressure fluctuations in said flow channel.

2. The monitoring apparatus of claim 1, wherein said predetermined pressure interval is based on an average pressure over a predetermined time period detected by said pressure sensor.

3. The monitoring apparatus of claim 1 wherein said pressure sensor is a differential thermal mass flow sensor.

4. The monitoring apparatus of claim 1 wherein said flow channel includes an inside wall and said flow channel has a flow direction from an upstream location to a downstream location within the flow channel, said differential thermal mass flow sensor comprising: a heating element disposed on the inside wall of said flow channel, at least one first thermal sensor positioned in the flow direction up-stream said heating element on the inside wall of said flow channel, and at least one second thermal sensor positioned in the flow direction downstream of said heating element on the inside wall of said flow channel.

5. The monitoring apparatus of claim 1 wherein said membrane ) is a flexible element adapted to be actuated by said control unit.

6. The monitoring apparatus of claim 1 wherein said membrane comprises one of: an electro-dynamically actuated membrane, comprising a coil attached to said membrane, wherein said membrane is adapted to move in a magnetic field; an electrostatically actuated membrane, wherein said membrane is adapted to be provided with an electrical charge and move in an electrostatic field according to a potential of said electrical charge; a magneto-statically actuated membrane, comprising a conductor or a coil integrated in said membrane and being adapted to move in a magnetic field; a piezo-electrically actuated membrane wherein said membrane comprises a piezoelectric crystalline material that changes its shape when subjected to an electrical current; a Heil's air motion actuated membrane wherein said membrane is pleated and mounted in a magnetic field and forced to close and open according to an electrical current; and a mechanically actuated membrane wherein said membrane is controlled by a mechanical motor, each revolution being synchronized to a measured periodic flow pulsation.

7. The monitoring apparatus of claim 1 further comprising a pump adapted to create said flow of the fluid in said flow channel.

8. A fluid flow monitoring method comprising the steps of: providing a flow of fluid in a flow channel, detecting a pressure in said flow channel with a pressure sensor disposed in said flow channel, and activating a membrane in communication with said fluid to induce a pressure modification in said fluid when said detected pressure deviates from a predetermined pressure interval, to reduce a pressure fluctuation in said flow channel

9. The monitoring apparatus of claim 1 wherein said membrane is disposed in said flow channel upstream of said pressure sensor.

10. The monitoring apparatus of claim 1 wherein said membrane is disposed in said flow channel downstream of said pressure sensor.

11. The monitoring apparatus of claim 1 wherein said membrane is disposed in a channel in fluid communication with said flow channel, wherein said channel in fluid communication with said flow channel is located upstream of said pressure sensor.

12. The monitoring apparatus of claim 1 wherein said membrane is disposed in a channel in fluid communication with said flow channel, wherein said channel in fluid communication with said flow channel is located downstream of said pressure sensor.

13. The fluid flow monitoring method of claim 8 wherein said membrane is disposed in said flow channel upstream of said pressure sensor.

14. The fluid flow monitoring method of claim 8 wherein said membrane is disposed in said flow channel downstream of said pressure sensor.

15. The fluid flow monitoring method of claim 8 wherein said membrane is disposed in a channel in fluid communication with said flow channel and said channel in fluid communication with said flow channel is located upstream of said pressure sensor.

16. The fluid flow monitoring method of claim 8 wherein said membrane is disposed in a channel in fluid communication with said flow channel and said channel in fluid communication with said flow channel is located downstream of said pressure sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The above objects, as well as additional objects, features and advantages of the present invention, will be more fully appreciated by reference to the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, when taken in conjunction with the accompanying drawings, wherein:

[0025] FIG. 1 is a schematic drawing of the sampling device according to the invention.

[0026] FIG. 2 is a diagram showing the principle of the cancellation of flow deviations.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0027] FIG. 1 is a schematic drawing of the sampling device 1 for sampling fluid quality according to the invention. The sampling device comprises a flow channel 2, through which the fluid is flowing 7, PF. A pressure sensor 3 is provided in the flow channel 2 adapted to detect a pressure in the flow channel 2. A membrane 4 is provided downstream the pressure sensor 3 in the flow channel 2 adapted to induce a pressure modification as shown by the arrow 5. The membrane can move so as to induce pressure modification sin the flow channel 2 by moving the fluid in the flow channel 2 with the membrane 4. When the membrane moves away from the flow channel the pressure is decreased in the flow channel 2 and when the membrane is moved towards the flow channel centre the pressure is increased in the flow channel 2. A control unit 6 is connected to the pressure sensor 3 and the membrane 4. The control unit 6 is further adapted to activate the membrane 4 so as to induce the pressure modification when the detected pressure deviates from a predetermined pressure interval, thereby neutralizing any pressure fluctuation in said flow channel, thus providing pulse cancellation. This may be made by having the membrane induce a pressure modification that is the inverse of the measured pressure deviations/fluctuations as shown in FIG. 2.

[0028] In FIG. 2 the pulsating flow (PF) is shown in a diagram where the y-axis is the flow rate and the x-axis is time. Pressure modifications (PM) are induced by the membrane 4 creating a pulse-canceling effect resulting in a resulting flow (RF) that is free from fluctuations. The net flow from the pressure modifications (PM) is zero, thus not contributing or affecting the mean flow flowing through the flow channel 2.

[0029] The pressure sensor 3 may preferably be a differential thermal mass flow sensor comprising a heating element 11 arranged in on the inside wall 8 of the flow channel 2, at least one up-stream thermal sensor 10 arranged in the flow direction up-stream the heating element 11 on the inside wall 8 of the flow channel, and at least one down-stream thermal sensor 12 arranged in the flow direction 7 down-stream the heating element 11 on the inside wall of the flow channel.

[0030] The membrane 4 is a flexible element adapted to be actuated by the control unit 6. The membrane 4 is preferably of a load speaker type, i.e. it is electro-dynamic with a coil (not shown) attached to said membrane 4 wherein the coil is adapted move in a magnetic field created by a magnet (not shown), the magnet being either a permanent magnet or an electro-magnetic magnet. The control unit 6 inverts the pressure signal received from the pressure sensor 3 and sends it to the coil of the membrane membrane so that the membrane will induce the inverted pulsation to that measured by the pressure sensor.

[0031] The sampling device preferably further comprises sampling equipment (not shown) for collecting pollutants in the fluid, as membranes, adsorptions surfaces, and/or impactor surfaces. The sampling equipment is preferably placed down-stream the membrane so that the laminar flow created by the sampling device is used where the laminar flow is important to have. A pump (not shown) adapted to create the flow 7, PF of fluid in said flow channel 2. May in turn be placed down-stream the sampling equipment.

[0032] It is understood that other variations in the present invention are contemplated and in some instances, some features of the invention can be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly in a manner consistent with the scope of the invention.