Ultrasonic vortex flowmeter having clamp-on housing

IS 2 292 178 T3

DESCRIPTION

Ultrasonic vortex flowmeter which has fixing housing.

Background of the invention

The present invention relates to improvements in flow meters for fluid, and more particularly to vortex flow meters of the type that use an ultrasonic detection circuit in conjunction with a flattened body arranged in a flow conduit.

Ultrasonic vortex flowmeters are generally well known, and operate on the theory that an obstruction, such as a flattened body, placed in a linear flow of fluid produces a plurality of vortices scattered downstream of the obstruction. Vortices create localized oscillatory variations in observable flow parameters such as pressure or velocity. When the ultrasonic waves are transmitted through the vortices, the vortices produce a phase difference between the transmitted wave and the received wave that depends on the strength and speed of the vortices. These phase differences are subsequently detected and used to calculate the fluid flow rate.

However, phase differences can also be caused by other external phenomena, such as temperature changes in the fluid, which can cause phase deviations between the transmitted and received waves that exceed the optimal range of the phase detector. As a result, known ultrasonic vortex flowmeters have typically used complex and expensive phase detection circuits that attempt to force the phase difference to remain in an optimal detection range.

For example, a known arrangement uses a phase lock loop (PLL) to slowly adjust the frequency of the transmitted signal to maintain the optimum phase angle, or the frequency of the oscillator to match the received signal. In addition to cost and complexity, the disadvantages of PLL arrangements are their fallibility to handle large changes in transmitted frequency caused by large temperature changes in the fluid, and the potential loss of blocking and the corresponding re-acquisition time if the transmitted wave it is interrupted such as by encountering an air bubble in the fluid. The reacquisition time can be especially problematic for large flowmeters, because the phase lock time constant must be greater than the lowest vortex spread frequency, for example on the order of 1 Hz.

Other known ultrasonic vortex flowmeters have attempted to overcome the phase corruption problem described above by using multiple sets of transmitters and receivers. However, these arrangements only make the detection circuit more complex and expensive.

In addition to the problems with the phase sensing circuitry, known flowmeter arrangements have also suffered from the disadvantage that due to the housing designs, any overhaul of the flowmeter has necessitated disconnection of the unit from the fluid conduit. Such disconnection is highly undesirable because it typically requires a temporary shutdown of the manufacturing process that is dependent on fluid flow so that fluid flow can be stopped. Furthermore, decoupling the flowmeter from the conduit may allow external contaminants to enter the conduit, thus further disrupting the manufacturing process, or potentially compromising the quality of the manufactured goods.

For example, GB-A-2 165 937 refers to an air conditioning system comprising an air conditioning apparatus having an air blower, at least one room connected to the air conditioning apparatus via a duct of air, in which a fluid flow meter is arranged in the air duct, the fluid flow meter using an ultrasonic transmitter and receiver apparatus and a network to detect periodically generated Karman vortices as a phase period modulation of ultrasonic rays.

Document US-A-4 924 710 relates to a vortex flowmeter adapted to detect the phase modulation of ultrasonic waves propagated in a fluid caused by Karman vortices generated in the fluid by a vortex generator and to measure the flow rate of the fluid by detecting the generation of Karman vortices.

Summary of the invention

Therefore, an object of the present invention is to provide an ultrasonic vortex flowmeter that can use a simple, cheap and reliable phase detector.

Another object of the present invention is to provide an ultrasonic vortex flowmeter that can be serviced by a technician without disassembling the fluid distribution system, and without potentially exposing the fluid to external contaminants.

Yet another object of the present invention is to provide an ultrasonic vortex flowmeter that includes a housing arranged to allow removal of the flow sensing component without interrupting the flow of fluid in the fluid distribution system.

Yet another object of the present invention is to provide an ultrasonic vortex flowmeter having a housing made entirely of non-corrosive material, and which slides around a fluid flow conduit or pipe.

In accordance with these and other objects, the present invention provides an improved ultrasonic fluid vortex flowmeter having a housing comprising a slide yoke removably mating with a flattened body conduit connector permanently installed in a fluid conduit. to control. An ultrasonic transmitter and receiver are respectively positioned within the fork legs to pass an ultrasonic wave through the fluid-scattered vortices as it flows through the flattened body located within the flattened body conduit connector. The slide yoke eliminates the need to shut off fluid flow during meter check, and the potential for external contaminants entering the fluid. The flowmeter further utilizes a single phase detector formed from an exclusive-OR gate in combination with an optimal phase range sensing arrangement. The optimal phase gap detection arrangement operates a 90 degree phase shift means when the phase difference between the transmitted wave and the received wave approaches 0 or 180 degrees.

Thus, according to a first aspect of the present invention, a vortex flowmeter2

ES 2 292 178 T3 ce comprises a housing connected around a fluid flow conduit, means arranged within the conduit to generate vortices in the fluid flow, a transmitter located within the housing to propagate an ultrasonic wave through the vortices , and an ultrasonic receiver located inside the housing to receive the propagated wave. A phase sensing means is connected to the transmitter and receiver to produce an output representative of any phase difference between the transmitted wave and the received wave, and a processing means is responsive to the output of the phase sensing means to determine the fluid flow rate. as a function of the phase difference caused by the vortices. An optimal phase range detector means is connected to the phase detector means to detect whether the phase difference is about 0 degrees or 180 degrees, and a phase change means is sensitive to the optimum phase range detector means to change the phase of the transmitter signal supplied to the phase detecting means by substantially 90 degrees as long as the phase difference is approximately 0 or 180 degrees.

In accordance with a second aspect of the present invention, a vortex flowmeter comprises a housing having a yoke sized to slide around a separate flattened body conduit connector coupled to a fluid flow conduit. The flattened body is arranged so as to produce vortices in the fluid flow. An ultrasonic transmitter and receiver are disposed within the yoke to respectively locate on opposite sides of the flattened body conduit connector. The transmitter is positioned to propagate an ultrasonic wave through the vortices to be received by the receiver. A phase sensing means is connected to the transmitter and receiver to produce an output representative of any phase difference between the transmitted wave and the received wave, and a processing means is responsive to the output of the phase sensing means to determine the fluid flow rate. as a function of the phase difference caused by the vortices.

The present invention will be better understood after reading the following detailed description of the preferred embodiment in conjunction with the accompanying drawings.

Brief description of the drawings

Figure 1 is a perspective view of an ultrasonic vortex flowmeter in accordance with the present invention;

Figure 2 is a front longitudinal view of the flowmeter of Figure 1;

Figure 3 is a cross-sectional view taken along line 3-3 of Figure 2;

Figure 4 is a cross-sectional view taken along line 4-4 of Figure 2;

Figure 5 is a schematic block diagram for a flowmeter processing circuit in accordance with the present invention; Y

Figures 6 (a) - (c) are representations illustrating the signals processed at various points in the circuit of Figure 5.

Detailed description of the preferred embodiment (s)

Referring to Figures 1-4, an ultrasonic vortex flowmeter 10 in accordance with the present invention is shown having a housing 12 formed from a metering head 14 rotatably mounted on a slide yoke 16. The yoke 16 It is arranged to slide into and engage with a separate flattened body conduit connector 18, and is held in place by a locking cam bolt 20. In addition, a pair of rubber bushings 21 are respectively located within cavities 23 and 25 formed on opposite sides of the interior of fork 16, and are arranged to extend slightly outward from the internal surface of the fork to provide a tight fit. friction between the yoke 16 and the flattened body conduit connector 18 once the yoke 16 has slid therein.

The flattened body conduit connector 18 is arranged to fit a desired fluid conduit or pipe during initial installation, after which the fluid whose flow rate is to be controlled passes through a first open end 22 into a flow passage 24 of the flattened body, and finally flows out through a second open end 26 located opposite the first end 22. At least one flattened body 28 is attached to conduit connector 18 to be positioned to extend internally within passageway 24.

The meter head 14 is arranged in accordance with the present invention to provide two isolated circuit compartments 30 and 32. The first compartment 30 houses the detector circuit (described hereinafter in connection with Figure 5) and is sealed closed. after installation using cover 36. The second compartment 32 is closed with a removable cover 38, and houses various field connections that are typically accessed after installation of the flowmeter to allow connection of the flowmeter outlet for external monitoring and control circuitry. All components of the flowmeter housing are made of non-corrosive materials, such as nylon, Teflon^®, PVC, PVDF, or other suitable plastic. The use of plastics allows the flowmeter of the present invention to be resistant to corrosion, acid, and most solvents, and is therefore well suited for use in harsh industrial manufacturing environments.

Located adjacent to the rubber bearings 21 within each respective cavity 23 and 25 is an ultrasonic transmitter 40 and a receiver 42. As best seen in Figure 3, when the yoke is properly mounted to the flattened body conduit connector 18, the transmitter and receiver will be positioned so that an ultrasonic signal passes through the scattered vortices 43 as fluid flows within. of the passageway of the flattened body 24 impacts the flattened body 28, as is well understood by one of ordinary skill in the art. The vortices 43 create a phase difference between the transmitted wave and the received wave that is detected by a phase detector circuit, such as an exclusive-OR gate 44, which is more fully described below in this document in context with a flowmeter 100 processing circuit shown in Figure

5.

More specifically, as shown in Figure 5, the processing circuit 100 includes an oscillator 102 to produce a reference wave, which has a frequency of 2 MHz. The reference wave is then divided, such as by a divider 103 that divided by 2, and supplied to transmitter 40 to generate the transmitted wave. The output of oscillator 102 is also supplied to one of the inputs of

ES 2 292 178 T3 the exclusive-OR gate 44 by means of a second divider (shown as a divider 105 that divides by 2), while the output of receiver 42 is supplied to the other input of exclusive-OR gate 44. As shown shown in Figure 6 (b), exclusive-OR gate 44 subsequently produces an output 46 composed of a series of pulses having a width that is a function of the phase difference between the transmitted wave and the received wave shown as " a ”in Figure 6 (a).

The output of the exclusive-OR gate 44 is filtered by a low pass filter 104 that has a cutoff frequency less than the frequency of the carrier wave, but greater than the frequency of the vortex spread. The low pass filter 104 effectively removes the carrier wave from the phase detector output. Thus, by means of an exemplary embodiment shown in Figure 6 (c), if a conventional CMOS-type exclusive-OR gate is used, the output of the low-pass filter 104 will comprise a DC voltage component that varies between 0 and 5 V DC corresponding to the variable phase difference, and a small AC voltage component whose frequency is a function of the flow rate of the fluid. A high-pass filter 106 separates the AC voltage component for input to a control processor 108. The control processor 108 processes the AC component for output to a digital-to-analog converter (DAC) 110. The output of the DAC 110 is supplies to a suitable fluid flow screen 112 or other external monitoring equipment.

In accordance with the present invention, to compensate for the inability of the exclusive-OR gate 44 to produce an output when the phase difference between the transmitted wave and the received wave is substantially 0 or 180 degrees, the control processor 108 controls the amplitude. of the DC component of the exclusive-OR gate output using an analog-to-digital (A / D) converter 114 to determine when the phase difference is essentially 0 or 180 degrees. For example, in the exemplary arrangement noted above, when the phase difference is in an optimal range, the amplitude of the DC component will be 2.5 V DC, and when the phase difference is substantially 0 or 180 degrees, the amplitude of the DC component will be respectively 0 or 5 V DC. When processor 108 detects the phase difference at or near 0 or 180 degrees, processor 108 activates a switch 116 to cause the oscillator / transmitter input to the exclusive-OR gate to be inverted by an inverter 118. Due to the divider 105, this switch arrangement effectively produces a 90 degree shift in the transmitter input to the exclusive-OR gate 44, which in turn maintains the phase difference between the transmitted and received waveform in the detection range. optimal phase.

Thus, the ultrasonic vortex flowmeter 10 of the present invention achieves significant advantages over conventional flowmeters for fluid. Specifically, the slide yoke can be opened to allow quick removal, replacement, and inspection of the flowmeter without even opening the fluid passage, thus eliminating the possibility of external contaminants entering the fluid when the flowmeter needs to be checked. Additionally, the monitoring of any deviation from an optimal phase difference detection range and the subsequent compensation arrangement for the 90 degree phase shift of the present invention enables the present invention to utilize a simple, reliable, exclusive-OR gate, and cheap as a phase detector. And finally, as the flowmeter head is arranged to isolate individual compartments for the flowmeter circuit and field connections, the need for field personnel to directly access and expose the flowmeter circuit after installation is eliminated simply to connect. external monitoring or other control equipment.

It will be understood that the foregoing description of the preferred embodiment of the present invention is for illustrative purposes only, and that the various structural and operational features described herein are susceptible of numerous modifications, none of which depart from the present invention as stated. defined in the appended claims.