Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
  • G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F22/00—Methods or apparatus for measuring volume of fluids or fluent solid material, not otherwise provided for
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
  • G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
  • G01F23/28—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring the variations of parameters of electromagnetic or acoustic waves applied directly to the liquid or fluent solid material
  • G01F23/284—Electromagnetic waves
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
  • G01S13/88—Radar or analogous systems specially adapted for specific applications

Definitions

• process control industry employs process variable transmitters to monitor process variables associated with substances such as solids, slurries, liquids, vapors, and gasses in chemical, pulp, petroleum, pharmaceutical, food and other food processing plants.
• Process variables include pressure, temperature, flow, level, turbidity, density, concentration, chemical composition and other properties.
• a process variable transmitter can provide an output related to the sensed process variable over a process control loop to a control room, such that the process can be monitored and controlled.
• the process control loop can be a two-wire 4 -20mA process control loop.
• the energization levels are low enough that even under fault conditions the loop generally will not contain enough electrical energy to generate a spark. This is particularly advantageous in flammable environments.
• Process variable transmitters can sometimes operate on such low energy levels that they can receive all electrical power from the 4-20 mA loop.
• the control loop may also have digital signals superimposed on the two-wire loop according to a process industry standard protocol such as the HART ® digital protocol.
• LPTDRR Time Domain Reflectometry
• MIR Micropower Impulse Radar
• Low power radar circuits are generally capable of detecting the level of one product in a tank at a time.
• a storage tank contains multiple products layered on top of one another. This creates multiple interfaces between products having different dielectric constants at which the transmitted microwaves can be reflected. For example, in a tank having a water based material and an oil based material, there will typically be two interfaces, one between the air and the oil and one between the oil and the water based material.
• a dielectric constant of a first product is calculated in order to calculate levels of the first and second products in a tank.
• a termination extends into the first and second products in the tank.
• a transmit pulse generator transmits a pulse along the termination into the first and second products.
• a low power time domain reflectometry radar (LPTDRR) pulse receiver receives the first and second reflected wave pulses corresponding to reflection of a first portion of the transmit pulse at a first product interface and to reflection of a second portion of the transmit pulse at a second product interface, respectively.
• a threshold controller generates a first threshold for detection of the first reflected wave pulse and a second threshold for detection of the second reflected wave pulse.
• a dielectric constant calculator calculates a dielectric constant of a first product as a function of a first reflected wave pulse.
• a level computer computes levels of the first and second products .
• FIG. 1 is a diagram of a microwave level transmitter illustrating the environment of embodiments of the invention.
• FIG. 2 is a block diagram illustrating circuitry of an embodiment of the invention.
• FIGS. 3 is a block diagram illustrating circuitry of an alternate embodiment of the invention.
• FIGS. 4 and 5 are plots illustrating Low Power Time Domain Reflectometry Radar (LPTDRR) equivalent time waveform controllable thresholds.
• LPTDRR Low Power Time Domain Reflectometry Radar
• FIG. 6 is a schematic diagram of a controllable receive threshold circuit.
• FIG. 7 is a plot illustrating an LPTDRR equivalent time waveform.
• FIGS. 8 and 9 are flow diagrams illustrating methods implemented by a level transmitter in accordance with an embodiment of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• FIG. 1 is a diagram illustrating level transmitters 100 operating in the environment of being mounted to storage tanks 12, 13, 17, 24 containing process products positioned on top of one another. As illustrated, tank 12 contains first product 14 positioned on top of second product 15. Level transmitters 100 include housings 16 and terminations 110. Transmitters 100 are coupled to process control loops 20, and transmit information related to heights of the process products over loop 20 to control room 30 (which is modeled as voltage sources and resistances) or to other devices (not shown) coupled to process control loops 20. Loops 20 are sources of power for transmitters 100 and can use any industry standard communications protocol such as 4-20 mA, FoundationTM Fieldbus, or HART . As low power radar transmitters, transmitters 100 can be completely powered by energy received over a 4-20 mA process control loop.
• FIG. 1 illustrates various applications in which radar level transmitters are useful.
• process products 14 and 15 in tank 12 are fluids, while process products 18 and 19 in tank 13 are solids.
• Process products 21 and 22 in tank 17 are fluids the levels of which are communicated to tube 23 into which one of terminations 110 extends.
• tank 24 is shown containing products 25 and 26, and having a radiative-type termination mounted on top of thank 24.
• tanks 12, 13, 17 and 24 are shown in FIG. 1, the embodiments of the invention may be practiced without tank such as in a lake or reservoir.
• FIGS. 2 and 3 are block diagrams of a level transmitter 100.
• FIGS. 2 and 3 are block diagrams of a level transmitter 100.
• FIGS. 1 are block diagrams of a level transmitter 100.
• transmitter 100 includes transmit pulse generator 210, pulse receiver 220, threshold controller 230, dielectric constant calculator 240, and level computer 250.
• Transmitter 100 also includes termination 110.
• Threshold controller 230, dielectric constant calculator 240 and level computer 250 can be implemented in microprocessor 255 as shown in FIG. 3. However, discrete circuitry for any of these functions can also be used.
• transmitter 100 includes analog-to-digital converter 270.
• Transmitter 100 can include power supply and input/output circuitry 260 (shown in FIG. 3) for powering transmitter 100 with power received over loop 20, and for communicating over loop 20. Such communication can include transmitting information related to product heights over loop 20.
• Circuitry 260 can be adapted to provide the sole source of power for transmitter 100 with power received over loop 20.
• Termination 110 can be of the type which is well known in the level transmitter art and can be any appropriate transmission line waveguide or antenna.
• a transmission line is a system of material boundaries forming a continuous path from one place to another and capable of directing transmission of electromagnetic energy along this path.
• termination 110 is a twin lead antenna having leads or conductors 115 and 120 connected at bottom region 125 and extendable into products 14 and 15 in tank 12, and optionally having launch plate 155.
• Termination 110 also be a monopole, coaxial, twin- line, single-line, microstrip, or radiative horn termination with any appropriate number of leads.
• Transmit pulse generator 210 can be a low power microwave source coupled to termination 110.
• the transmit pulse can be at any of a wide range of frequencies, for example between about 250 MHz and about 20 GHz or more. In one embodiment the frequency of the transmit pulse is about 2 GHz .
• pulse 320 of equivalent time waveform 300 represents microwave energy reflected at interface 127 between air and product 14, while pulse 330 represents microwave energy reflected at interface 128 between product 14 and product 15.
• pulse 330 represents microwave energy reflected at interface 128 between product 14 and product 15.
• Pulse receiver 220 can be a low power microwave receiver coupled to termination 110.
• Receiver 220 is adapted to receive the first reflected wave pulse corresponding to reflection of the first portion of the transmit pulse at product interface 127 (represented by pulse 320 in FIGS. 4 and 5) .
• Receiver 220 is also adapted to receive the second reflected wave pulse corresponding to reflection of the second portion of the transmit pulse at the second product interface 128 (represented by pulse 330 in FIGS. 4 and 5) .
• receiver 220 produces as an output equivalent time LPTDRR waveform 300.
• Threshold controller 230 receives waveform
• threshold controller 230 and dielectric constant calculator 240 are embodied in microprocessor 255
• analog-to-digital conversion circuitry 270 digitizes waveform 300.
• Threshold controller 230 generates thresholds 315, 340 and 350 for detection of fiducial pulse 310 and thus time T at which pulse 310 was received, detection of reflected wave pulse 320 and thus time T 2 at which pulse 320 was received, and detection of reflected wave pulse 330 and thus time T 3 at which pulse 330 was received.
• Threshold value 315 used to detect fiducial pulse 310 can be a predetermined constant voltage, or can be automatically determined as a function of the peak amplitude of pulse 310 in a known manner.
• Threshold values 340, 350 can be calculated as a function of user entered data.
• threshold controller 230 can be embodied in software as an algorithm that looks for multiple pulses. Threshold controller 230 provides receive pulse threshold 340 shown in FIG. 4 at a level which is surpassed by pulse 330. Threshold controller 230 provides receive pulse threshold 350 shown in FIG. 5 at a level which is surpassed by pulse 320. Threshold controller 230 provides as an output to dielectric constant calculator 240 and to level computer 250, receive pulse information based upon to detection of reflected wave pulses 320 and/or 330 based upon a comparison of the reflected wave pulses 320, 330 to the respective threshold values.
• FIG. 6 illustrates a portion of threshold controller 230, implemented in discrete circuitry, which generates controllable thresholds such as thresholds 340 and 350.
• Threshold controller 230 includes comparator 400, having a first input from receiver 220 waveform 300 containing receive pulses 320 and 330. As a second input, comparator 400 receives the controllable analog threshold voltage which is provided from the output of digital-to-analog converter 410. Digital-to-analog converter 410 receives a digital input from microprocessor 255 representative of the desired threshold. The output 420 of comparator 400 is provided to dielectric constant calculator 240 and level computer 250 as an indication of the times that pulses 320 and 330 are received.
• converter 410 is controlled to provide threshold 350 for detection of pulse 320.
• converter 410 is controlled to provide threshold 340 for detection of pulse 330.
• Dielectric constant calculator 240 in FIG. 2 is coupled to threshold controller 230 and is adapted to calculate a dielectric constant of first product 14 in tank 12 as a function of the receive pulse output information provided by threshold controller 230.
• a method implemented by dielectric constant calculator 240 in calculating the dielectric constant is discussed below in detail with reference to FIGS. 7-9.
• Level computer 250 is coupled to threshold controller 230 and to dielectric constant calculator 240 and is adapted to calculate a level of the first product 14 and of the second product 15 using known mathematical functions to derive data from the reflected pulses. Such mathematical functions can, for example, operate upon pulse amplitude, pulse flight time, pulse slope, and pulse area.
• Computer 250 calculates the level of product 14 as a function of time T 2 of detection of first reflected wave pulse 320. Computer 250 can further calculate the level of product 15 as a function of time T 3 of detection of second reflected wave pulse 330 and of the calculated dielectric constant of product 14.
• dielectric constant calculator 240 can calculate the dielectric constants of products, and combining this information with the multiple product interface timing information, the level of multiple products can be computed by level computer 250.
• the dielectric of the upper medium is calculated by computer 250, for example using the following method.
• Equation 1 The amplitude of the pulse reflected off of an interface with a material is proportional to the dielectric constant of the material according to the relationship shown in Equation 1.
• V R the amplitude of the reflected pulse
• V ⁇ the amplitude of the transmitted pulse
• METHODS A method of calculating the dielectric constant of product 14 with the relationship of Equation 1 uses threshold controller 230 to more precisely determine the transmitted and reflected pulse amplitudes. This method is used to calculate the levels of first product 14 and second product 15 within tank 12. The method is shown in the plot of FIG. 7, and is summarized in the flow diagram of FIG. 8. Those skilled in the art will appreciate that the plot of FIG. 7 may be inverted and still fall within the scope of the invention.
• the method begins at block 560 with generating a transmit pulse.
• the transmit pulse is transmitted along the termination into the first and second products in the tank.
• the first reflected wave pulse is received.
• the first reflected wave pulse corresponds to reflection of the first portion of the transmit pulse at the first product interface 127.
• the second reflected wave pulse is received.
• the second reflected wave pulse corresponds to reflection of a second portion of the transmit pulse at the second product interface 128 formed between first product 14 and second product 15.
• the dielectric constant of the first product is calculated as a function of the first reflected wave pulse.
• the transmit pulse (represented by fiducial pulse 530) has a transmit amplitude V ⁇
• the receive pulse 540 has a receive amplitude V R .
• the amplitude of the first reflected wave pulse is calculated, and the dielectric constant of first product 14 is calculated using Equation 1.
• the level of first product 14 is computed.
• the level of first product 14 is computed as a function of the first reflected wave pulse.
• the level of product 14 is typically computed as a function of a time of receipt of the first reflected wave pulse, and ultimately as a function of a first time period between transmission of the transmit pulse and receipt of the first reflected wave pulse.
• the level of second product 15 is computed.
• the level of second product 15 is computed as a function of the first and second reflected wave pulses and as a function of the calculated dielectric constant of first product 14. More specifically, the level of product 15 can be computed as a function of the calculated dielectric constant of first product 14 and as a function of a second time period between receipt of the first reflected wave pulse and receipt of the second reflected wave pulse. Ultimately, computation of the level of product 15 is also a function of the level of product 14.
• FIG. 9 illustrates a more particular method of computing the level of products 14 and 15 in tank 12.
• the transmit pulse is generated and transmitted along the termination into products 14 and 15.
• generation and/or transmission of the transmit pulse starts a clock or designates the beginning of one or more time periods.
• the first reflected wave pulse is received, and at block 720 the first time period between transmission of the transmit pulse and receipt of the first reflected wave pulse is recorded.
• the level of first product 14 is computed as a function of the first time period.
• an amplitude of the first reflected wave pulse is calculated.
• the dielectric constant of first product 14 is calculated as a function of a comparison of the amplitude of the first reflected wave pulse to a reference amplitude. The reference amplitude is based upon the amplitude of the transmit pulse.
• the second reflected wave pulse is received, and at block 745 the second time period between receipt of the first reflected wave pulse and receipt of the second reflected wave pulse is recorded.
• the level of second product 15 is computed. Computation of the level of second product 15 is performed as a function of the second time period, as a function of the calculated dielectric constant of the first product, and as a function of the computed level of the first product.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• General Physics & Mathematics (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Electromagnetism (AREA)
• Computer Networks & Wireless Communication (AREA)
• Fluid Mechanics (AREA)
• Thermal Sciences (AREA)
• Measurement Of Levels Of Liquids Or Fluent Solid Materials (AREA)
• Radar Systems Or Details Thereof (AREA)
• Arrangements For Transmission Of Measured Signals (AREA)

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• 1999
  • 1999-01-21 US US09/234,999 patent/US6198424B1/en not_active Expired - Lifetime
• 2000
  • 2000-01-18 BR BR0004311-7A patent/BR0004311A/pt not_active Application Discontinuation
  • 2000-01-18 JP JP2000595114A patent/JP2002535641A/ja active Pending
  • 2000-01-18 EP EP00904382A patent/EP1066500B1/en not_active Expired - Lifetime
  • 2000-01-18 CN CNB008000107A patent/CN1213284C/zh not_active Expired - Lifetime
  • 2000-01-18 CA CA002323558A patent/CA2323558A1/en not_active Abandoned
  • 2000-01-18 AU AU26149/00A patent/AU2614900A/en not_active Abandoned
  • 2000-01-18 DE DE60034631T patent/DE60034631T2/de not_active Expired - Lifetime
  • 2000-01-18 WO PCT/US2000/001076 patent/WO2000043739A1/en not_active Ceased

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