MXPA00008718A - Measurement of process product dielectric constant using a low power radar level transmitter - Google Patents

Abstract

Disclosed is a method of using a low power radar level transmitter to calculate a dielectric constant of a product in a tank. Low Power Time Domain Reflectometry Radar (LPTDRR) circuitry is controlled to calculate a time delay between transmission of microwave energy down a termination (110) extending into the product (26) in the tank and reflection of the microwave energy. In some embodiments, the dielectric constant of the product is calculated as a function of the time delay. In other embodiments, the dielectric constant is calculated by controlling the LPTDRR circuitry to calculate amplitudes of transmit and receive pulses. The dielectric of the product is calculated as a function of the amplitudes of the transmit and receive pulses.

Description

"MEASUREMENT OF THE DIELECTRIC CONSTANT OF THE DEVELOPING PRODUCT, USING A LOW-POWER RADAR LEVEL TRANSMITTER" BACKGROUND OF THE INVENTION The processing control industry employs variable processing transmitters to remotely monitor processing variables associated with substances such as solids, slurries, liquids, vapors and gases in chemical, pulp, petroleum, pharmaceutical, food and other plants food processing plants. Processing variables include pressure, temperature, flow, level, turbidity, density, concentration, chemical composition and other properties. A variable processing transmitter may provide an output related to the processing variable detected through a processing control loop to a control room, such that processing can be monitored and controlled. The processing control loop can be a two wire processing control loop, 4-20 mA. With this processing control loop, the energization levels are low enough that even under fault conditions, the loop will generally not contain enough electrical energy to generate a spark. This is particularly advantageous in flammable environments. The variable processing transmitters can sometimes operate at these low energy levels that can receive all the electrical power of the 4-20 mA loop. The control loop may also have digital signals superimposed on the two-wire loop in accordance with a normal manufacturing industry protocol such as the HART® digital protocol. Reflectometry radar instruments from Low Power Time Domain (LPTDRR) have been used to measure the level of processing products (either liquid or solid) in storage containers. In Time Domain Reflectometry, electromagnetic energy is transmitted from a source, and reflected to a discontinuity. The travel time of the received pulse is based on the medium through which it runs. One type of LPTDRR is known as the Micropotence Impulse Radar (MIR), which has been developed by Lawrence Livermore National Laboratory. Since the LPTDRR level of the transmitters typically determines the level as a function of the travel time of the microwave signals to and from an interface or surface of the product, and since the travel time depends on the dielectric constant of the material to through which the microwaves go, it may be necessary to know the dielectric constant (s) beforehand. This is particularly necessary when the storage tank contains multiple products placed in layers one on top of the other, thereby creating multiple interfaces between the products having different dielectric constants. Previous LPTDRR level transmitters have required that a transmitter operator admit a dielectric constant of the product in order to determine the level of the multiple interfaces. A method for determining the dielectric constant (s) of one or more of the products in a tank would be a significant improvement in the art.

COMPENDIUM OF THE INVENTION A method and level transmitter that calculates a dielectric constant of a product in a tank is disclosed. The Low Power Time Domain Reflectometry Radar circuit (LPTDRR) is controlled to calculate a time delay between the transmission of the microwave energy along a termination that extends to the product in the tank and the reflection of microwave energy. In some embodiments, the dielectric constant of the product is calculated as a function of the time delay. In other modalities, the dielectric constant is calculated by controlling the LPTDRR circuit to calculate the transit amplitudes and receive impulses. The dielectric constant of the product is calculated as a function of the amplitudes of the transmitter and receiver pulses.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram of a processing process system illustrating the environment of the embodiments of the invention. Figure 2 is a functional diagram illustrating the circuit of a radar level transmitter in accordance with one embodiment of the invention. Figure 3 is a functional diagram illustrating the circuit of a radar level transmitter in accordance with an alternative embodiment of the invention. Figures 4 and 5 are traces illustrating the controllable thresholds of equivalent time waveform of Low Power Time Domain Reflectometry (LPTDRR). Figure 6 is a schematic diagram of a controllable threshold threshold circuit according to an embodiment of the invention.

Figures 7, 9 and 12 are flow charts illustrating the methods implemented by the microwave transmitter of Figure 2. Figures 8, 10 and 11 are traces illustrating time waveforms equivalent to LPTDRR.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Figure 1 is a diagram illustrating level 100 transmitters operating in an environment mounted on storage tanks 12, 13, 17, 24 containing at least one product. As illustrated, the tank 12 contains the first product 14 placed on top of the second product 15. The transmitters 100 include housings 16 and terminations 110. The transmitters 100 are coupled to the processing control loops 20, and transmit the related information. with the dielectric constants and / or the heights of the processing products through the loops 20 to the control room 30 (which is modeled as sources and voltage resistors) or to other devices (not shown) coupled with the loops 20 of processing control. The loops 20 are sources of energy for the transmitters 100 and can use any normal communications protocol of the processing industry such - - such as 4-20 mA, Foundation ™ Fielbus, or HART®. As low-power radar transmitters, the transmitters 100 can be fully energized by the energy received through a 4-20 mA processing control loop. Figure 1 illustrates the different applications in which it is useful to measure the dielectric constant of radar. For example, the processing products 14 and 15 in the tank 12 are fluid, while the processing products 18 (shown having a certain angle of repose) and 19 in the tank 13 are solid. The processing products 21 and 22 in the tank 17 are fluid, the levels of which are communicated to the tube 23 towards which one of the terminations 110 extends. In addition, the tank 24 is shown containing the products 25 and 26 and having a radiative type termination mounted on the top of the tank 24. Although tanks 12, 13, 17 and 24 are shown in Figure 1, the embodiments of the invention can be implemented without the tanks such as in a lake or deposit. Figures 2 and 3 are functional diagrams of a transmitter 100. Figures 4 and 5 are traces of transceiver / receiver waveforms of Time Lapse Reflectometry of Low Power Time Time Equivalent (LPTDRR) that illustrate aspects of the detector of controllable threshold of the invention. Within the housing 16, the transmitter 100 includes the LPTDRR circuit 205 (shown in Figure 3), the LPTDRR circuit controller 206 (shown in Figure 3) and the dielectric constant calculator 240. The controller 206 controls the LPTDRR circuit 205 through the connections 207, in order to determine a parameter that is proportional to the dielectric constant of the product 14 in the tank 12. The dielectric constant calculator 240 calculates the dielectric constant of the product 14 as a function of the determined parameter. The LPTDRR circuit 205 may include pulse generator transmitter and pulse receiver 220. Transmitter 100 also includes threshold controller 230 and optionally level calculation circuit 250 (shown in FIG. 3). The threshold controller 230 may be a component of the LPTDRR circuit 205. The threshold controller 230, the dielectric constant calculator 240, the level calculation circuit 250 and the LPTDRR 206 controller can be implemented in the microprocessor 255, as shown in Figure 3. However, the discrete circuit for any of these functions is You can use. In embodiments in which these functions are encompassed in a microprocessor 255, the transmitter 100 includes an analog-to-digital converter 270. The transmitter 100 may also include the power supply and input / output circuit 260 (as shown in FIG. Figure 3) to energize the transmitter 100 with the energy received through the loop 20, and to communicate through the loop 20. This communication may include transmitting the information related to the processing product through the loop 20. The circuit of The power supply can be adapted to provide the sole power source for the transmitter 100 from the energy received through the loop 20. The microwave termination 110 can be of the type known in the level transmitter art and can be any line of transmission, waveguide or appropriate antenna. A transmission line is a material limit system that forms a continuous path from one place to another and that is capable of directing the transmission of electromagnetic energy along this path. In some embodiments, termination 110 is a twin wire antenna having conductor wires 115 and 120 connected in lower region 125 and capable of extending to products 14 and 15 in tank 12, and optionally having a launch plate 155. Termination 110 may also be a monopoly, coaxial, twin line, single line, microtire, or radioactive termination and have any number of appropriate wires. The transmit pulse generator 210 is preferably a low power microwave source coupled with the termination 110. Under control of the controller 206, the generator 210 generates a pulse or microwave transmit signal that is transmitted along the termination 110. towards products 14, 15. The transmitter pulse may be on 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 approximately 2.0 GHz. The fiducial pulse 310 of the equivalent time waveform 300 (shown in FIGS. 4 and 5) can be created on the launch plate 155 or by other mechanisms to designate the beginning of a transmitter / receiver cycle. A first portion of the transmitting pulse microwave energy transmitted along the wires 115 and 120 is reflected in the first product interface 127 between the air and the product 14. A second portion of transmitting pulse microwave energy is reflected at the interface 128 between the product 14 and the product 15. If the tank 12 contains only the product 14, but not the product 15, the interface 128 is typically at the bottom of the termination or tank. In Figures 4 and 5, the pulse 320 of the equivalent time waveform 300 represents the microwave energy reflected at the interface 127 between the air and the product 14, while the pulse 330 represents the microwave energy reflected in the interface 128. Those skilled in the art will recognize that the waveforms shown in Figures 4 and 5 can be reversed without deviating from the spirit and scope of the invention. Generally, if the product 14 has a dielectric constant that is less than the dielectric constant of the product 15, the amplitude of the pulse 330 can be greater than the pulse 320. The pulse receiver 220 is a low power microwave receiver coupled. with the termination 110. The receiver 220 receives the first reflected wave pulse corresponding to the reflection of the first portion of the transmitting pulse in the first product interface 127 (represented by the pulse 320 in Figures 4 and 5). The receiver 220 also receives the second reflected wave pulse corresponding to the reflection of the second portion of the transmitter pulse in the second product interface 128 (represented by the pulse 330 in Figures 4 and 5). Using a known low power time domain reflectometry radar sampling technique, the pulse receiver 220 produces as an output, the LPTDRR waveform of equivalent time 300. The threshold controller 230 receives the waveform 300 as an input. In embodiments in which the threshold controller 230 and the dielectric constant calculator 240 are encompassed in a microprocessor 255, the analog-to-digital circuit 270 digitizes the waveform 300. The threshold controller 230 generates thresholds 315, 340 and 350 for detecting the fiducial pulse 310 and thus the time T] _ where the pulse 310 was received, the detection of the reflected wave pulse 320 and therefore the time T2 at which the pulse 320 was received, and the detection of the reflected wave pulse 330 and thus the time T3 at which the pulse 330 was received. The threshold value 315 used to detect the fiducial pulse 310 can be a predetermined constant voltage, or it can be automatically determined as a function of the Peak amplitude of the pulse 310 in a known manner. The threshold controller 230 provides the receiver pulse threshold 340 shown in Figure 4 at a level that is exceeded by the pulse 330. The threshold controller 230 provides the receiver pulse threshold 350 shown in Figure 5, at a level that is exceeded by the pulse 320. The threshold controller 230 provides as an output to the dielectric constant 240 computer and to the circuit 250, the output information of the receiver pulse based on the detection of the reflected wave pulses 320 and / or 330 Figure 6 illustrates a procion of the threshold controller 230, implemented in the discrete circuit that generates controllable thresholds such as thresholds 340 and 350. The threshold controller 230 includes the comparator 400, which has a first input of the waveform. 300 of the receiver 220 containing receiver pulses 320 and 330. As a second input, the comparator 400 receives the controllable analog threshold voltage that is provided from the output of the digital-to-analog converter 410. The converter 410 receives a digital input of the microprocessor 255 representative of the desired threshold. The output 420 of the comparator 400 is provided to the calculator of the dielectric constant 240 and the calculation circuit of the level 250 as an indication of the times in which the pulses 320 and 330 are received. During a first scan cycle in which the form wave 300 is generated, the converter 410 is controlled to provide the threshold 350 for the detection of the pulse 320. During a subsequent scan cycle, the converter 410 is controlled to provide the threshold 340 for the detection of the pulse 330. The thresholds are can use to detect the times of receipt of the impulse of the reflected wave. The thresholds can also be controlled to determine the amplitudes of the reflected wave impeller. The dielectric constant calculator 240 in Figure 2 is coupled to the threshold controller 230 and is adapted to calculate a dielectric constant of the first product 14 in the tank 12, as a function of the output information of the receiving pulse that is provided. by means of a threshold controller 230. The methods implemented by the circuit 240 for calculating the dielectric constant will be discussed in detail below with reference to Figures 7 to 12. The relationship between the distance traveled by the microwave signal and the travel time it is shown in Equation 1.

Equation 1 where T / 2 = half the travel time of the microwave pulse to and from the interface; e = the dielectric constant of the material through R of which the microwave pulse (for air, e = 1); R C = the speed of light; and D = the distance traveled from the top of the termination to the interface. Using this relationship, the dielectric constant of a material being measured can be calculated. The travel time of a microwave depends on the dielectric constant of the medium through which it is traveling. The dielectric constant of the medium is proportional to the travel time according to the relationship shown in Equation 2. e oc (A 'Time) 2 Equation 2 R where: Time = microwave travel time through the medium; and A = a constant of proportionality. Also, the amplitude of the impeller reflected outside an interface with a material is proportional to the dielectric constant of the material according to the relationship shown in Eq. 3, where VR = the amplitude of the reflected impulse; and VR eR or c Equation 3 Vt Vt = the amplitude of the transmitted impulse. Using the relationships illustrated in Equations 2 and 3, independently or in combination, the dielectric constant (s) of one or more of the products or materials in a tank can be calculated. METHODS A method for calculating the dielectric constant of product 14 is illustrated in Figure 7. The method begins at block 500 with low power time domain reflectometry radar control (LPTDRR) to direct the energy of the microwave to the processing product. In block 503, the circuit LPTDRR is controlled to receive the reflected microwave energy. In block 505, the LPTDRR circuit is controlled to measure a parameter that is proportional to the dielectric constant of product 14. Then, in block 510, the dielectric constant of product 14 is calculated as a function of the parameter measured using the ratios of Equation 2 and / or Equation 3. A more specific first method for calculating the dielectric constant of the product 14 with the relationship of Equation 3, uses the threshold controller 230 to more accurately measure the transmitted and reflected pulse amplitudes . The method is shown in the trace of Figure 8, and is summarized in the flow diagram of Figure 9.

Those skilled in the art will recognize that the waveform shown in Figure 8 can be reversed without deviating from the spirit and scope of the invention. The method starts at block 705 with the generation of a transmitter pulse. The transmitter pulse is transmitted along the termination to products in the tank, and is reflected off surfaces 127 and 128. In block 710, the first reflected wave pulse 540 is received. The first reflected wave pulse corresponds to the reflection of the first portion of the transmit pulse in the first product interface 127. After controlling the LPTDRR circuit 205 to receive the reflected wave pulse, the amplitude of the first reflected wave pulse is calculated in block 715. The amplitude of the first reflected wave pulse is a parameter that is proportional to the dielectric constant of the product 14. In block 720, the dielectric constant of the first product is calculated as a function of the first reflected wave pulse. As shown in waveform 520 LPTDRR of equivalent time of Figure 8, the transmit pulse (represented by fiducial pulse 530) has a transmit amplitude V ^, while receiver pulse 540 has a receiver amplitude VR. Either digitizing the waveform 520 LPTDRR of equivalent time with the analog-to-digital converter 270 and analyzing the digitized signal with the microprocessor 255, or using the digital-to-analog converter 410 to adjust the comparator thresholds, the amplitude of the first The reflected wave impulse is calculated and the dielectric constant of the first product 14 is calculated using equation 3. In this way, the calculated parameter that is proportional to the dielectric constant of the product 14 is typically a ratio between the amplitude of the first reflected wave pulse and the amplitude of the transmitted pulse. Controlling the circuit LPTDRR includes controlling the threshold controller 230 to adjust a threshold in order to calculate the amplitude of the reflected wave pulse 540. A second more specific method for calculating the dielectric constant of the product 14, with the relationship of Equation 2, it uses the threshold controller 230 to calculate a time delay between transmitting the transmitting pulse and the reflection of the pulse from the surface 128. More particularly, the method calculates a travel time of the microwaves through a known distance from the product. The method is shown in the lines of Figures 10 and 11 and is summarized in the flow chart of Figure 12. Those skilled in the art will recognize that the waveforms shown in Figures 10 and 11 can be reversed without deviating of the spirit and scope of the invention. The method begins at block 805 with the generation of the transmitter pulse. The transmit pulse is transmitted along the termination to products 14 and 15. In block 810, the first reflected wave pulse is received and detected in the threshold controller. The receipt of the first reflected wave pulse begins to operate a clock or designates the beginning of a period of time as shown in block 815. Then, the second reflected wave pulse is received and detected in block 820. The receipt of the second reflected wave pulse designates the end of the time period as shown in block 825 where the time period is recorded. In block 830, the dielectric constant of the product 14 is calculated as a function of the recorded time period which is indicative of a time of travel of the microwaves along the termination of a known distance through the product 14. The Figures 10 and 11 illustrate the method of Figure 12. Figures 10 and 11 illustrate waveforms 850 and 880 of equivalent time LPTDRR corresponding to the representations of the first and second different product filling tanks with the first and second products having first and second dielectric constants respectively. In both strokes, the product either essentially completely covers the wires of termination 110, or covers them by a known distance. As can be seen in Figures 10 and 11, the time delay between the transmitted pulses (represented by the fiducial pulses 860 and 890) and the reflected pulses 870 and 895 (corresponding for example to the reflections outside the lower part of the tank 32 or termination 110 or reflections in the product-to-product interface) varies from one material to the next. This variation is due to the different dielectric constants of the materials. This is further illustrated by the time differences representing the time required for the microwaves to run through the same sample distance in each of the two materials. In the material that has the first dielectric constant, the required time that the sample distance had to travel was 3.08 ms, while in the material that has the second dielectric constant, the time required to travel the same sample was a distance of 3.48 ms. In this way, the time delay between the transmission of the microwave signal and the reflection off of a known remote interface to the termination can be used to calculate the dielectric constant. Although the present invention has been described with reference to preferred embodiments, those workers skilled in the art will recognize that changes in form and detail can be made without departing from the spirit and scope of the invention. For example, the previously described methods for calculating the dielectric constants can be combined to help calculate the multiple dielectric constants or to provide a more accurate calculation of the dielectric constants.

Claims (23)

CLAIMS:

1. A low power radar level transmitter for measuring a dielectric constant of a processing product having first and second product interfaces, the transmitter comprising: a termination capable of extending into the processing product; a pulse generator coupled with the termination, the pulse generator is adapted to generate a microwave transmitter pulse that is transmitted along the termination to the product, a first portion of the transmitter pulse is reflected to a first product interface and a second portion of the transmitter pulse being reflected in a second product interface; a pulse receiver coupled with the termination and adapted to receive a first reflected wave pulse corresponding to the reflection of the first portion of the transmitting pulse in the first product interface, and to receive a second reflected wave pulse corresponding to the reflection of the second portion of the transmitter pulse in the second product interface; a threshold controller coupled to the pulse receiver and adapted to detect whether the first reflected wave pulse fills at least a first threshold value and to provide the output information of the receiving pulse based on the detection of the first reflected wave pulse; and a calculator of the dielectric constant coupled with the threshold controller.

The transmitter of claim 1, wherein the dielectric constant calculator is adapted to calculate the dielectric constant of the product as a function of a magnitude of the first reflected wave pulse relative to a magnitude of the transmitting pulse.

3. The transmitter of claim 1, wherein the threshold controller is further adapted to detect if the second reflected wave pulse fills at least a second threshold value, the threshold controller provides the output information of the receiver pulse based on in the detection of the first and second reflected wave pulses.

The transmitter of claim 3, wherein the second product interface is placed at a known distance along a length of the termination, the output information of the receiving pulse being indicative of a travel time of the transmitting pulse to a known distance through the product.

The transmitter of claim 1, and further comprising an analog-to-digital converter coupled to the pulse receiver and adapted to digitize the first and second reflected wave pulses, wherein the threshold controller and the dielectric constant calculator they comprise a microprocessor coupled with the analog to digital converter that is adapted to detect the first digitized pulse and the second reflected wave pulse that determines the dielectric constant of the product.

The transmitter of claim 1, wherein the threshold controller comprises: a comparator having first and second inputs, the first input is coupled to the pulse receiver and receives the first and second reflected wave pulses; a microprocessor that generates a digital output representative of a desired threshold; and a digital-to-analog converter coupled with the microprocessor and receiving the digital output, the digital-to-analog converter converts the digital output to an analog threshold voltage and provides the threshold voltage at the input of the second comparator.

7. The transmitter of claim 1, wherein the termination is a twin wire antenna.

The transmitter of claim 1, wherein the transmitter is capable of being coupled with a two-wire processing control loop, the transmitter further comprising an output circuit that is capable of coupling with the two-stage control loop. wires to transmit information related to the product through the loop.

9. The transmitter of claim 8, wherein the transmitter further comprises a power supply circuit coupled to the two wire processing control loop to receive the power of the loop to provide the sole power source for the transmitter.

The transmitter of claim 9, wherein the processing control loop is a 4-20 mA processing control loop operating in accordance with a normal manufacturing industry communications protocol.

11. A power level radar transmitter adapted to measure a dielectric constant of a processing product, the transmitter comprises: a low power time domain reflectometry radar circuit (LPTDRR); a means to control the LPTDRR circuit in order to calculate the parameter that is proportional to the dielectric constant of the product; and a means for calculating the dielectric constant of the product as a function of the calculated parameter.

The transmitter of claim 11, wherein the calculated parameter is an amplitude of a received pulse.

The transmitter of claim 11, wherein the calculated parameter is a travel time of the microwaves through a known distance of the product.

14. A method for using a low power radar level transmitter to measure the dielectric constant of a processing product, the method comprising: controlling the low power time domain reflectometry radar circuit (LPTDRR) in the transmitter to direct the microwave energy towards the processing product; control the LPTDRR circuit to receive microwave energy reflected from the processing product; control the LPTDRR circuit to calculate a parameter based on the reception of the microwave energy whose parameter is proportional to the dielectric constant of the product; and calculate the dielectric constant of the product as a function of the calculated parameter.

15. The method of claim 14, wherein the parameter is an amplitude of the microwave energy reflected in an interface with the product.

The method of claim 14, wherein the parameter is a ratio between the amplitude of the microwave energy reflected in an interface and an amplitude of the microwave energy directed toward the processing product.

The method of claim 16, wherein the control of the LPTDRR circuit in the transmitter to calculate the parameter 'further includes controlling a threshold controller to adjust a threshold of the receiving pulse to calculate the amplitude of the microwave energy reflected in the interface with the product.

18. The method of claim 14 wherein the parameter is a time delay between the transmission of the microwave energy down a termination extending to the product and the reflection of the microwave energy.

The method of claim 18, wherein controlling the LPTDRR circuit to calculate the parameter further includes calculating the time delay between the transmission of the microwave energy along the termination and reflection of the microwave energy from a surface .

The method of claim 19, wherein the surface is the bottom of a tank containing the processing product.

The method of claim 19, wherein the surface is a surface of the product at a known distance along a length of the termination.

The method of claim 19, wherein calculating the dielectric constant of the product as a function of the calculated time delay comprises calculating the dielectric constant of the product as a function of the square of the calculated time delay. - 2 -

23. A medium capable of being read on a machine containing a readable program on a machine that configures a processor to carry out the following: control the low power time domain reflectometry radar circuit (LPTDRR) to direct the microwave energy towards a processing product; control the LPTDRR circuit to receive the microwave energy reflected from the processing product; controlling the LPTDRR circuit to calculate a parameter that is proportional to a dielectric constant of the product based on the received reflected microwave energy; and calculate the dielectric constant of the product as a function of the calculated parameter.