WO2006008642A2

WO2006008642A2 - Integrated system using time domain reflectometry for level measurements of liquids and complex systems phases

Info

Publication number: WO2006008642A2
Application number: PCT/IB2005/002154
Authority: WO
Inventors: Carlo Alberto De Carlo; Pasquale Cavaliere; Raffaella Di Sante
Original assignee: Carlo Alberto De Carlo; Pasquale Cavaliere; Raffaella Di Sante
Priority date: 2004-07-14
Filing date: 2005-06-24
Publication date: 2006-01-26
Also published as: ITBA20040032A1; WO2006008642A3

Abstract

Integrated system, based on Time Domain Reflectometry analysis, to measure liquid levels, with high repeatability and accuracy, and different phases of complex systems, comprising a TDR unit, a variety of guided-wave probes, a multiplexer to acquire simultaneously data from the different probes, a control software, a protection kit to use the system in critical conditions,whereby the high frequency pulses are guided by the probes, that are introduced directly into the product to be measured.

Description

Title: Integrated system for level measurements of liquids and complex systems phases

Applicant: Carlo Alberto De Carlo, Pasquale Cavaliere, Raffaella Di Sante.

Technical field

The present invention relates to an integrated system, based on

Time Domain Reflectometry (hereafter- "TDR") analysis, to measure liquid levels, with high repeatability and accuracy, and different phases of complex systems.

In the state of the technique, concerning the above mentioned applications, there are already some methods to measure and control liquid levels in a tank and container; the most common ones use motion, force and pressure transducer. Capacity variation can be also employed in the case of conductive fluids, or ultrasonic probes, based on waves reflection due to liquid/air interface. Lastly, radar transmitters are used to measure liquid levels, which offer all the advantages of contact-less technologies, wherever the measurement is complicated. Radar transmitters have no moving parts and are based on TDR. High frequency pulses are sent into a tank or container and part of the pulse is reflected back toward the transmitter some when the pulses reach the level substance; a receiver measures the exact duration of time between the transmitted and reflected signal —

CONFiRWlATlON COPY the "time of flight." In recent years, radar transmitters were considered the optimal choice to measure the level of in hard-to- measure environments, having many advantages with respect to mechanical devices, which do not perform properly in difficult environments. As far as liquid phases measurement is concerned, in the recent years, the chemical composition was determined by samples laboratory analysis, with suitable chemical tests, following standard procedures. The need for quick and automatic check of industrial processes and product quality led to the development of measurement systems able to determine the chemical composition. In this field, the state of art related to TDR techniques is also represented by radar which detect the interface between two different products or, more simply, the presence of different substances, as suspended or aggregated particles, or distinguishable phases.

However, one of the major problems of radar transmitters is the high probability of false echoes. In fact, part of transmitted waves bounce off the sides of the vessel, returning divergent signals, which interfere with the measurement. A similar problem also presents itself in ultrasonic measurements.

Disclosure of the invention

The invention solves the above mentioned problems being an integrated system, based on the principle of TDR, used to measure the level of liquids, with high repeatability and accuracy, and different phases of complex system, comprising a TDR unit, a variety of guided-wave probes, a multiplexer to simultaneously acquire data from different probes, a control software, a protection kit to use the system in critical conditions, - and characterized by the fact that the high frequency pulses, instead of through air, are driven by special probes, that is introduced directly into the product to be measured. The working principle is similar to the through-air radar transmitters one: the time of flight of the transmitted signal is measured and further analyzed to obtain the level of the product. But, differently by the known applications, the wave front enlargement is controlled by cables or bars, which are specifically designed to ensure high performances and reliability with respect to the drive-less propagation techniques. These and other advantages will be pointed out in the detailed description of the invention that will refer to the figures of the table 1/1 in which a preferred embodiment of the coaxial probe is shown, in a front view (Fig. 1) and in axonometric view (Fig. 2). Both are exemplifying and not restrictive.

Way of carrying out the invention

The integrated system comprises the following main parts: a

TDR unit, wave-guide probes, a control software, a multiplexer, and a protection kit. The TDR unit, generating a diagnostic step signal, acquires, digitalizes and analyzes the shape of the reflected wave. The main characteristics consist of a rising time less than 200 ps, an amplitude equal to 200 mV and a pulse duration of about 14 μs. The working temperature range is -30⁰C e +70⁰C. The modular wave-guide probes are made of stainless steel and are needed to transmit the signal through the mean and to detect discontinuities due to impedance changes and, therefore, to the dielectric constant variations of the product, in which the probe is introduced. The probes can also be coaxial and can be used in industrial tanks, with low viscosity products and low dielectric constant, and also with corrosive and difficult environments. The single modules can be serially connected (up to 7 units) to increase the probe total length. In this way, it is possible to monitor either industrial plants (specially containers and silos) or samples of small size. Several probes are commercially available, like flexible cables with counterbalance, single or coupled bars and coaxial probes. In the case of high viscosity liquids or light solids, cables and single bars are used; the length is up to 30 ÷ 45 m for cables and from 3 to 4 m for bars. Standard applications comprise gas, construction material aggregates, malt, powders and fermenting agents. To measure heavy solids, larger diameter cables and bars are used (cable diameters of about 6 mm and bar diameters of about 16 mm), for example, in catering, papery and pharmaceutical industry. In case of low viscosity liquids, coaxial probes are preferred, because of their better performance with low dielectrics (between 1,4 and 1,7). The probe lengths can reach 6 m. Examples are solvents, ammonia, alcohol and petrochemical products. The present invention also comprise the use of special coaxial probes (1), different from the most common commercial probes. The guide-bar (2), made of special steel, is bounded by an external trap (3) with holes (4) along it. This embodiment allows: • the advantages of the single bar probes, like a negligible measurement error due material adhesion on the probe (for example, paraffin wax in petrochemical processes);

• the advantages of the coaxial probes, as the capability to measure low dielectric constant products and to perform properly in case of strong turbulences in the tank. Thanks to this embodiment, coaxial probes can reach the best performance in case of low conductive materials (dielectric constant of about 1,3), like some petrochemical products.

A special multiplexer allows the simultaneous data acquisition from several probes (up to 512) by means of a single TDR unit.

The proper functioning is controlled by the system software, which manages the measurements, analysis, data registration and transmission. The protection kits will be used in case of critical conditions, like high humidity and powder rate, to protect the TDR unit and the multiplexer. The system working principle is the following. The TDR unit transmits a step signal in a short rising time (about 200 ps), then registers the time to flight and the amplitude of the reflected signal. Any impedance change causes a discontinuity, which can be localized and registered by means of the reflected signal analysis. For example, in case of liquids monitoring, the discontinuities are due to variations of the dielectric constant in the propagation mean. The signal is guided by special coaxial probes, suitable for different products and different operating conditions, including corrosive liquids and aggressive products. The advantages of this system consist in the fact that the high frequency pulses, instead of being transmitted through air, are driven by special probes, directly introduced into the product. The wave fronts enlargement is controlled by specifically designed cables or bars, ensuring higher performances and reliability than the ones of the drive-less propagation techniques. Moreover, being the radar transported energy concentrated in the guide probe (and not dispersed in the measurement environment), it needs less power and ensure a better signal/noise ratio. The response time is also better, since that the propagation speed is higher and response is almost instantaneous. Higher length can be measured by guide waves radar, since the energy is focalized along a determined direction. The guide waves radar provide reliable measurements, in hostile chemical conditions and wide temperature and pressure ranges, and do not require calibration in case of specific products, as required by capacitive sensors.

This system also overcomes the main problem of the guide waves radar: inaccuracy in the case of low dielectric constant products, causing low intensity reflects signals. In fact, being the guide bars of the coaxial probes protected by an external pipe, which acts as a screen canalizing the energy, the use of such coaxial probe allows the electrical resistance to be constant along the radius propagation length, avoiding consistent signal losses. Moreover, the external coaxial shield act as a trap, improving the device performances in case of turbulence. For example, the system can be utilized in the chemical industry (distillation columns, solvent containers), catering (beer production, milk), papery and pharmaceutical industry and water tanks. Concerning phases detection in complex systems, the invention is able to detect small Diesel oil quantities (around 10%) in the gasoline; such alteration represents one of the most known contamination of transportation fuels. Similarly, the system can determine other contaminants, if they are not completely soluble or miscible in the main substance. Even food fraud can be revealed analyzing, for example, the contaminants added to olive oil, wine or milk. Moreover, the system can detect variations in specific chemical characteristics, like alcohol percentage or olive-oil acidity. Finally, the system is able to manage remote data, transmitted via modem or GMS and GPRS modules, thanks to a suitable interface.

Claims

1) Integrated system, based on Time Domain Reflectometry (hereafter - "TDR") analysis, to measure liquid levels, with high repeatability and accuracy, and different phases of complex systems, comprising a TDR unit, .a variety of guided- wave probes, a multiplexer to acquire simultaneously data from different probes, a control software, a protection kit to use the system in critical conditions, and characterized by the fact that the high frequency pulses, instead of through air, are driven by special probes, that is introduced directly into the product to be measured.

2) Probe for an integrated system according to claim 1, characterized in that it is made of stainless steel, has a wide modularity to obtain different lengths, and can be used with large containers or small samples, with products having low viscosity and/or low dielectric constant, in corrosive or critical environments.

3) Probe according to claim 2, shaped as flexible cable or single bar, suitable for high viscosity liquids or solids. 4) Probe according to claim 2, coaxially shaped, suitable for low viscosity liquids.

5) Coaxial probe (1), according to claim 4, characterized by a guide-bar (2), made of special steel, bounded by an external trap (3) with holes (4) along it. 6) Integrated system according to claim 1, characterized by the fact that said TDR unit is able to generate a diagnostic step signal, to acquire, digitalize and analyze the reflected wave shape. 7) Integrated system according to claim 6, wherein the main characteristics of said TDR unit consists of a rising time less than 200 ps, an amplitude equal to 200 mV, a pulse duration of about 14 μs and a working temperature range between - 30⁰C e +70⁰C. 8) Integrated system according to one of the previous claims, wherein said multiplexer allows the simultaneous data acquisition from several probes by means of a single TDR unit.

9) Integrated system according to one of the previous claims, wherein said protection kits are used in case of critical conditions, like high humidity and powder rate, to protect the TDR unit and the multiplexer as well.

10) Integrated system according to one of the previous claims, characterized by the following working principle: transmission of a step signal in a short rising time (about

200 ps), registration of the "time-of-flight" and the amplitude of the reflected signal, localization of any discontinuity, by means of the reflected signal analysis.

11) Integrated system according to one of the previous claims, characterized by its application in many manufacturing processes: chemical industry (distillation columns, solvent containers, fuel contamination analysis), catering (beer production, milk, olive oil and wine contamination), papery and pharmaceutical industry.