Patent Application
20160334262
Disclosed embodiments relate to coaxial probes for time-domain reflectometry-based guided wave level measurement.
Time-domain reflectometry (TDR) can be used as a level determination method involving analyzing reflection characteristics of electromagnetic waves and signals. There are many different types of TDR-based level measuring systems including contact radar such as guided wave radar (GWR), non-contact radar, ultrasonics, and laser. In a GWR TDR-based level measuring system, a microwave pulse is generated by level gauge electronics including a transceiver and processor which is coupled by a process connection into a waveguide (or probe) that is guided along the length of the probe that extends into the tank. The probe can be a coaxial waveguide, a metal rod or a steel cable. If the microwave pulse is incident on the surface of the medium to be measured, part of the pulse is reflected at the surface and returns along the probe to the gauge electronics, which then calculates the fill level from the time difference between the transmitted pulse and the received pulse.
The gauge can output the calculated fill level as a continuous analog signal (typically 4-20 mA) or as a digital signal. An advantage of this method is that the measurement result is only to a small extent influenced by the properties of the medium to be measured, for example density, conductivity and dielectric constant, or by the environmental conditions such as pressure and temperature, and that no interference-prone moving parts are required.
In GWR level measurement systems a coaxial probe (or coaxial waveguide) is commonly used when interfering obstacles or process conditions can adversely degrade the accuracy of the level measurements rather than a lower cost single wire or single rod probe design. Such coaxial probes typically comprise an inner rod in an outer tube design with spacers between the inner rod and outer tube that are placed periodically along the length of the coaxial probe. The spacers are used to ensure that the distance between the inner rod and outer tube is maintained within a certain tolerance so that the measurement is not degraded by deflection of the inner rod in vibrational or non-vertically mounted installations.
This Summary is provided to introduce a brief selection of disclosed concepts in a simplified form that are further described below in the Detailed Description including the drawings provided. This Summary is not intended to limit the claimed subject matter's scope.
Disclosed embodiments recognize the presence of conventional spacer(s) in coaxial probes (or waveguides) for level measurement by level gauges positioned between the inner electrically conductive rod (inner rod) and outer electrically conductive tube (outer tube) for ensuring the distance between the inner rod and outer tube is maintained within a certain tolerance for guided wave radar (GWR) level measurement systems can result in degraded measurement accuracy. By tensioning the inner rod, it has been found that the stiffness of the inner rod increases, which reduces the deformation or deflection of the inner rod under forces such as vibration, gravity, environmental influences such as temperature, or deformation or deflection over time (creep). Tensioning the inner rod enables a reduction in the number of spacers or in some cases (e.g., for probe lengths ≦2 m) removing the need for spacers altogether, while still maintaining a given spacing tolerance between the inner rod and outer tube.
Tension can be applied to the inner rod through a wide variety of different structures and methods. For example, using threads internal/external on the inner rod, or internal/external on the outer tube. The springs can be coil type or leaf type, and be retained either on the inner rod or on the outer tube.
For example, to tension the inner rod a tensioning device including a tensioner body can be positioned between the inner rod and the outer tube. The tensioner body has an aperture through which a threaded member is inserted through for screwing the threaded member into the inner threading of the inner rod which functions to stretch the inner rod in a length (height) direction relative to the outer tube, which can be provided at one or both ends of the coaxial probe. The tensioning device may also include a flexible member between the head of the screw and the tensioner body, such as a spring or a Bellville washer, designed to take up changes in coaxial probe's dimensions due to temperature or creep over time. The tensioning device can provide a tension load to the inner rod of 10 N to 10,000 N, such as about 100 N to 500 N in one embodiment.
Disclosed embodiments are described with reference to the attached figures, wherein like reference numerals, are used throughout the figures to designate similar or equivalent elements. The figures are not drawn to scale and they are provided merely to illustrate aspects disclosed herein. Several disclosed aspects are described below with reference to example applications for illustration. It should be understood that numerous specific details, relationships, and methods are set forth to provide a full understanding of the embodiments disclosed herein.
One having ordinary skill in the relevant art, however, will readily recognize that the disclosed embodiments can be practiced without one or more of the specific details or with other methods. In other instances, well-known structures or operations are not shown in detail to avoid obscuring aspects disclosed herein. Disclosed embodiments are not limited by the illustrated ordering of acts or events, as some acts may occur in different orders and/or concurrently with other acts or events. Furthermore, not all illustrated acts or events are required to implement a methodology in accordance with this Disclosure.
Also, the terms “coupled to” or “couples with” (and the like) as used herein without further qualification are intended to describe either an indirect or direct electrical connection. Thus, if a first device “couples” to a second device, that connection can be through a direct electrical connection where there are only parasitics in the pathway, or through an indirect electrical connection via intervening items including other devices and connections. For indirect coupling, the intervening item generally does not modify the information of a signal but may adjust its current level, voltage level, and/or power level.
Tension as known in physics is the act of stretching or straining, where a tensioning force produces an elongation of a body or structure such as a rod. Tension is the force that can be exerted by a rope, string, cable, or similar object on one or more objects, such as rods in the case of disclosed embodiments.
The ELG 140 is shown adapted to be mounted onto the top of a tank through an electronics housing 149, feed-through (or process connection) 146, and a flange 148 that couples the ELG 140 to the coaxial probe 100 which is inserted over a tank aperture (not shown) generally in the top of the tank (see tank 310 in
The ELG 140 generally includes a transceiver (which as used herein can include a separate transmitter and receiver), a computing device such as a processor 341 (e.g., digital signal processor (DSP), microprocessor or microcontroller unit (MCU)) having an associated memory 342 that stores a radar level determination algorithm (radar level algorithm) 343 as firmware. Other electronics, such as signal amplifiers, filters, an analog-to-digital converter (ADC, in the receive circuitry) and digital-to-analog converter (DAC, in the transmit circuitry) are generally part of ELG 140, but are not shown to provide simplicity.
ELG 140 provides continuous level (volume) measurement for the liquid or other product material 320 of high reliability at a generally reasonable price. The reliability is obtained due to lack of moving parts and insensitivity of the measurements to changes in process pressure, temperature, and density of measured material. The radar level algorithm 343 measures the distance from a reference point, usually a fixed internal reflection at the top of the antenna (or waveguide) to the surface of the product material in the tank using reflection of the measuring signal from the level or surface 322 of the liquid or other product material 320 in the tank 310.
ELG 140 as shown is mounted to the top 316 of the tank 310 by a process connection comprising a coaxial connector 144, feed-through 146, and flange 148 that couple the transceiver 345 of the ELG 140 to the coaxial probe 100 which is inserted over a tank aperture (not shown) in the top 316 of the tank 310. As shown, coaxial probe 100 extends well into the liquid or other product material 320 in the tank 310 to create physical contact, such as to implement GWR.
ELG 140 is shown coupled to a remote computer 360 having a local display 380 (such as being a control room of a plant) via a cable (e.g., electrical cable) 352. Coupling between ELG 140 and computer 360 may also be accomplished wirelessly. For GWR applications, coaxial probe 100 extends to essentially the bottom of the tank 310 or to a portion of the tank (if only a portion of the tank needs to be measured). The measurement signal propagates along coaxial probe 100 to the product material 320 and is then reflected back to ELG 140.
ELG 140 can transmit electrical signals representative of the distance from the top 316 of tank 310 to the level 322 of liquid or other product material 320 in the tank 310 to the processor 341. Processor 341 can perform any one or more of the methods, processes, operations, applications, or methodologies described herein. For example, processor 341 can implement the radar level algorithm 343 from digitized versions of received electrical signals resulting from the reflected electromagnetic signals (echo signals) received by the transceiver 345 representative of the measured distance from the top of tank to the level of liquid or other material, and using a stored total height of the tank 310 can calculate the material level by subtracting the measured distance from the total height of the tank 310.
Disclosed embodiments of the invention are further illustrated by the following specific Examples, which should not be construed as limiting the scope or content of this Disclosure in any way.
While various disclosed embodiments have been described above, it should be understood that they have been presented by way of example only, and not as a limitation. For example, besides tension as disclosed above, applying compression to the inner rod may also reduce its deflection. Numerous changes to the disclosed embodiments can be made in accordance with the Disclosure herein without departing from the spirit or scope of this Disclosure. Thus, the breadth and scope of this Disclosure should not be limited by any of the above-described embodiments. Rather, the scope of this Disclosure should be defined in accordance with the following claims and their equivalents.
Although disclosed embodiments have been illustrated and described with respect to one or more implementations, equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. While a particular feature may have been disclosed with respect to only one of several implementations, such a feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application.
This application claims the benefit of Provisional Application Ser. No. 62/159,706 entitled “TENSIONED COAXIAL PROBE FOR LEVEL MEASUREMENT”, filed on May 11, 2015, which is herein incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62159706 | May 2015 | US |
