Patent Publication Number: US-2016238427-A1

Title: Electronic level gauge having improved noise rejection and power transmission

Description:
FIELD 
     Disclosed embodiments relate to electronic level gauges (e.g., guided radar, free-space radar) for measuring the level of a material in a tank or in a container. 
     BACKGROUND 
     A radar level gauge is commonly used in industry as part of a guided wave radar (GWR) and/or non-contact radar (NCR) system to measure the amount (e.g., level) of material (liquid or bulk solid (e.g., powder)) in a tank or a storage container. A radar level gauge provides continuous level (volume) measurement 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 gauge for guided or free-space radar is mounted on top of the tank and measures the distance from a reference point, usually a mounting flange at the top of the antenna to the surface of the product material in the tank using reflection of the measuring signal from the surface of the product material. The product level value is obtained by subtracting the measured distance from a total height of the tank. 
     The NCR level gauge has a transmitter for generating electrical pulses at a carrier frequency and an antenna that conveys the electromagnetic pulses towards a surface of the material. A reflected electromagnetic signal originates from the surface of the material due to the electromagnetic pulses. A receiver receives the reflected electromagnetic signal from the antenna. 
     SUMMARY 
     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&#39;s scope. 
     Disclosed embodiments recognize because the transmitter and receiver of an electronic level gauge (ELG) for measuring a level of a material in a tank share a common antenna, power loss and attenuation can occur during transmission of the electrical pulses due to unwanted signal reflections and impedance mismatches. At the receiver, increased noise can occur due to unwanted signal reflections and impedance mismatches. 
     Disclosed embodiments include ELGs for measuring a level of a material in a tank that include two switches for terminating the undesired part of the signal from reaching the transmitter/receiver. An antenna is coupled to an output of the transmitter for receiving the electrical pulses from the transmitter and for conveying electromagnetic pulses towards a surface of the material and for receiving a reflected electromagnetic signal from the surface of the material responsive to the electromagnetic pulses. A receiver is coupled to the antenna for receiving the reflected electromagnetic signal from the surface of the material. A first switch is coupled between the transmitter and the antenna. In some embodiments a transceiver provides both the transmitter and receiver for the ELG, so that when the description refers to a transmitter and receiver it is understood the transmitter and receiver can be provided as a single transceiver, or be embodied as separate transmitter and receiver blocks. 
     The first switch is for coupling or decoupling (selectively coupling) the transmitter from the antenna. A second switch is coupled between the receiver and the antenna. The second switch is for coupling or decoupling (selectively coupling) the receiver from the antenna. A switch controller is coupled to the first switch and the second switch. The switch controller provides control signals for controlling the first switch to selectively couple the transmitter to the antenna when the electrical pulses are being transmitted and for controlling the second switch to selectively couple the receiver to the antenna when the reflected electromagnetic signal is being received from the surface. 
     One disclosed embodiment comprises a method of operating an ELG for measuring a level of a material in a tank. The method includes providing a transmitter for generating electrical pulses and an antenna coupled to an output of the transmitter for receiving the electrical pulses and for conveying electromagnetic pulses towards a surface of the material and for receiving a reflected electromagnetic signal from the surface of the material responsive to electromagnetic pulses. The method further includes providing a receiver coupled to the antenna for receiving the reflected electromagnetic signal from the surface of the material. A switch controller detects transmission of the electromagnetic pulses from the transmitter. A first switch is triggered to decouple the transmitter from the antenna and to couple the antenna to a first terminator. A second switch is triggered to couple the receiver to the antenna and to decouple the antenna from a second terminator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an example ELG system mounted to a tank for measuring the level of a material in the tank, according to an example embodiment. 
         FIG. 2  is a schematic diagram of an ELG circuit with the transmitter coupled to the antenna, according to an example embodiment. 
         FIG. 3  is a schematic diagram of the ELG circuit with the receiver coupled to the antenna, according to an example embodiment. 
         FIG. 4  is a flow chart that shows steps in an example method of operating an ELG for measuring a level of a material in a tank, according to an example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     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. 
       FIG. 1  illustrates an example ELG system  100 . ELG system  100  can be used in a variety of manufacturing plants that handle and process a tangible material. In one embodiment, ELG system  100  can be used in a petroleum refinery. In another embodiment, ELG system  100  can be used in a grain processing and shipping facility. ELG system  100  includes a tank  110  that contains a liquid or other material  120  (liquid or bulk solid (e.g., powder)). The tank has an inlet  112  and an outlet  114 . The liquid or other material  120  fills the tank  110  to an upper level or surface  122 . An ELG  140  such as a radar gauge is mounted to the top  116  of tank  110 . 
     A radar gauge provides continuous level (volume) measurement for the liquid or other material  120  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 gauge for guided or free-space radar is mounted on the top  116  of the tank  110  and measures the distance from a reference point, usually a mounting flange at the top of the antenna to the surface of the product material in the tank using reflection of the measuring signal from the level or surface  122  of the liquid or other material  120 . 
     ELG  140  as shown includes coaxial connector  144 , feed-through  146 , and flange  148  that couple the ELG  140  to an antenna (or probe)  150  which is inserted over a tank aperture (not shown) in the top  116  of the tank  110 . As shown, antenna  150  extends well into the liquid or other material  120  in the tank  110 , such as to implemented guided wave radar (GWR). However, the antenna  150  may also be used in a non-contact manner. ELG  140  is shown coupled to processor  160  via an electrical cable  152 . Coupling between ELG  140  and processor  160  may also be accomplished wirelessly. 
     ELG  140  can transmit electrical signals representative of the distance from the top  116  of the tank  110  to the level of liquid or other material  120  in the tank  110  to the processor  160  (e.g., digital signal processor (DSP), microprocessor or microcontroller unit (MCU)). Memory  170  is coupled to processor  160 . Memory  170  stores instructions  172  and algorithms  174 . Processor  160  can execute instructions  172  and/or algorithms  174  causing processor  160  to perform any one or more of the methods, processes, operations, applications, or methodologies described herein. For example, after digital conversion processor  160  can receive electrical signals resulting from the reflected electromagnetic signals received by the antenna  150  of the ELG  140  representative of the measured distance from the top of tank to the level of liquid or other material  120 , and using a stored total height of the tank  110  calculate the level by subtracting the measured distance from the total height of the tank  110 . Processor  160  is further coupled to a display  180  for showing the calculated level to an operator. 
       FIG. 2  illustrates example electrical schematic diagrams of ELG  140  and an example front end circuit  205  positioned between the transmitter  210  and receiver  220  of the ELG  140  and the antenna  150 . Although not shown, a transceiver can provide both the transmitter  210  and receiver  220 . ELG  140  includes a transmitter  210  for generating electrical pulses and a receiver  220  for receiving a reflected electromagnetic signal from the surface of the liquid or other material  120  responsive to electromagnetic pulses. Transmitter  210  includes a digital-to-analog (D/A) converter  211 , signal generator  212  and an amplifier  214 . Signal generator  212  generates electrical pulses that are amplified by amplifier  214 . Transmitter  210  has an input coupled to an output of the processor  160 . 
     Front end circuit  205  includes switch  1   230  and switch  2   240 . Transmitter  210  is also coupled to switch  1   230 . In one embodiment, switch  1   230  is a microwave single pole double throw switch. The switches may also comprise metal-oxide-semiconductor field-effect transistor (MOSFET) switches, or other solid state switches provided they are fast enough for RF applications. Switch  1   230  has signal terminals  232 ,  233 ,  234  and a control terminal  235 . In one embodiment, front end circuit  205  is physically mounted to a printed circuit board with component interconnections accomplished by printed circuit lines as is known in the art. Transmitter  210  is coupled to signal terminal  232 . 
     Front end circuit  205  includes terminator  1   250  and terminator  2   252 . Terminator  1   250  is coupled to signal terminal  233 . Terminator  1   250  is a passive or active device that is coupled to an end of a circuit in order to absorb signals. Terminator  1   250  prevents unwanted signal reflections due to signals reflected by the splitter or impedance mismatches, which can produce interference that causes signal loss and noise. The impedance of terminator  1   250  is matched to the circuit it is connected with. In one embodiment, terminator  1   250  is a passive terminator that can include resistors, inductors, capacitors and transmission lines or a combination of resistors, inductors, capacitors and transmission lines. In one embodiment, terminator  1   250  is an active terminator. 
     Front end circuit  205  includes a power splitter  270  that has terminals  264 ,  266  and  272 . Terminal  264  of power splitter  270  is coupled to terminal  234  of switch  1   230  via a circuit line  290 . Terminal  272  of power splitter  270  is coupled to antenna  150 . Power splitter  270  couples both transmitter  210  and receiver  220  to antenna  150 . 
     Receiver  220  includes an amplifier  222  and an analog to digital (A/D) converter  224 . Amplifier  222  amplifies received reflected electromagnetic signals and A/D converter  224  converts the amplified reflected electromagnetic signals into a digital signal. Receiver  220  has an output coupled to an input of the processor  160  and an output coupled to signal terminal  242  of the switch  2   240 . In one embodiment, switch  2   240  is a microwave single pole double throw switch. Switch  2   240  has signal terminals  242 ,  243 ,  244  as well as a control terminal  245 . 
     A terminator  2   252  is coupled to signal terminal  243 . Terminator  2   252  is a passive or active device that prevents unwanted signal reflections due to impedance mismatches, which can produce interference that causes signal loss and noise. The impedance of terminator  2   252  is matched to the circuit it is connected with. In one embodiment, terminator  2   252  is a passive terminator that can include resistors, inductors, capacitors and transmission lines or a combination of resistors, inductors, capacitors and transmission lines. In one embodiment, terminator  2   252  is an active terminator. Terminal  266  of power splitter  270  is coupled to terminal  244  of switch  2   240  via a circuit line  292 . 
     Front end circuit  205  further includes a switch controller  256  that is coupled to transmitter  210  and to a node  261 . In one embodiment, switch controller  256  is a microcontroller. However, in another embodiment, processor  160  of ELG  140  may also provide the functions provided by switch controller  256 . Node  261  is coupled to terminal  245  of switch  2   240  and to an input of inverter  260 . The output of inverter  260  is coupled to terminal  235  of switch  1   230 . Switch controller  256  has a timer  258 . Timer  258  can be started to track a pre-determined time period for switch  1   230  to be coupled and decoupled from the transmitter  210  and for switch  2   240  to be coupled and decoupled from the receiver  220 . Switch controller  256  provides control signals typically to the control terminals (e.g., gates) of the switches for controlling switch  1   230  to selectively couple the transmitter  220  to the antenna  150  when the electrical pulses are being transmitted and for controlling the switch  2   240  to selectively couple the receiver  220  to the antenna  150  when the reflected electromagnetic signal is being received from the surface  122  of the liquid or other material  120  in tank  110 . 
     Antenna  150  is coupled to an output of the transmitter  210  for receiving the electrical pulses and for conveying electromagnetic pulses towards a surface  122  of the liquid or other material  120  and for receiving a reflected electromagnetic signal from the surface of the material responsive to electromagnetic pulses. The receiver  220  is coupled to the antenna  150  for receiving the reflected electromagnetic signal from the surface of the material. Switch  1   230  is coupled between the transmitter  210  and the antenna  150 . Switch  1   230  couples and decouples the transmitter  210  from the antenna  150 . 
     There are some differences in the design of the antenna  150  depending upon the type of ELG. In the case of free-space (non-contact) radar transmitters, the antenna  150  extends into the tank  110  by only a relatively short distance so as to not contact the material in the tank  110 . The measuring signal is propagated from the antenna towards the measured material through free-space (air or other gas in the tank). In the case of guided waver radar (GWR), the antenna  150  (waveguide) extends essentially all the way to the bottom of the tank  110 , or a portion of the tank (if only a portion of the tank  110  needs to be measured). The measurement signal propagates along the antenna  150  (waveguide) to the liquid or other material  120  and then back to the ELG. 
     Switch  2   240  is coupled between the receiver  220  and the antenna  150 . Switch  2   240  couples and decouples the receiver  220  from the antenna  150 . Switch controller  256  is coupled to switch  1   230  and to switch  2   240 . Switch controller  256  provides control signals or trigger signals for controlling switch  1   230  to selectively couple the transmitter  210  to the antenna  150  when the electrical pulses are being transmitted and for controlling switch  2   240  to selectively couple the receiver  220  to the antenna  150  when the reflected electromagnetic signal is being received from the surface  122 . Inverter  260  causes switch  1   230  and switch  2   240  to be switched oppositely. 
     In  FIG. 2 , switch  1   230  is shown coupling the transmitter  210  to the antenna  150  and switch  2   240  is shown coupling the antenna  150  to terminator  2   252 . Terminator  2   252  reduces reflected signals on circuit line  292 . The connection of terminator  2   252  results in a lower insertion loss by power splitter  270  and increased power transmission from transmitter  210  to antenna  150 . 
     Referring to  FIG. 3 , front end circuit  205  is shown with switch  1   230  and switch  2   240  switched such that switch  1   230  couples the receiver  220  to the antenna  150  and switch  2   240  couples the antenna  150  to terminator  1   250 . Terminator  1   250  reduces reflected signals on circuit line  290 . The connection of terminator  1   250  results in lower noise for signals received by receiver  220 . 
       FIG. 4  is a flow chart showing steps in an example method  400  of operating an ELG system  100  for measuring a level of a liquid or other material  120  in a tank  110 . Method  400  can be implemented via a processor executing instructions and/or algorithms (I/A)  259  by switch controller  256 . Method  400  begins at the start block and proceeds to block  402  where switch controller  256  detects if transmitter  210  is transmitting electromagnetic pulses. At decision block  404 , switch controller  256  determines if any electromagnetic pulses from the transmitter  210  have been detected. In one embodiment, switch  1   230  and switch  2   240  can be synchronized with the trigger signals generated by switch controller  256  by delaying the transmission trigger signal. In response to no electromagnetic pulses being detected, switch controller  256  continues to detect electromagnetic pulses at block  402 . In response to electromagnetic pulses being detected, switch controller  256  triggers switch  1   230  via inverter  260  and control terminal  235  to decouple the transmitter  210  from the antenna  150  and to couple the antenna  150  to terminator  1   250  (block  406 ). Switch controller  256  triggers switch  2   240  via control terminal  245  to couple the receiver  220  to the antenna  150  and to decouple the antenna  150  from terminator  2   252  (block  408 ). 
     Switch controller  256  generates two different trigger signals with very low jitter and at two different but close frequencies. One trigger signal is used when electrical pulses are being transmitted from transmitter  210  and the other trigger signal is used when receiver  220  is receiving the reflected electromagnetic signal. In one particular embodiment, the transmitting trigger signal can be at 4 MHZ and the receiving trigger signal at 3.999993 MHZ. In this particular embodiment the trigger signals are approximately 7 Hz apart. 
     Switch controller  256  triggers switch  1   230  via inverter  260  and control terminal  235  to couple the transmitter  210  to the antenna  150  and to decouple the antenna  150  from terminator  1   250  (block  410 ). Switch controller  256  triggers switch  2   240  via control terminal  245  to decouple the receiver  220  from the antenna  150  and to couple the antenna  150  to terminator  2   252  (block  412 ). Method  400  then ends. 
     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. 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.