Abstract: A mechanism for coupling a coaxial cable (108) to a planar circuit to provide galvanic isolation between the coaxial cable and the planar circuit while providing low transmission loss and reflections between the coaxial cable (108) and the circuit. The mechanism comprises a co-planar waveguide (211) coupled to the coaxial cable (108), a microstrip line (240) connected to the circuit, a galvanic isolation component (234) and a ground plane (222). The co-planar waveguide (211), the microstrip line (240) and the galvanic isolation component (234) are formed on one side (203) of a two-sided substrate (202). The ground plane (222) is formed on the other side (205) of the substrate (202) and underlies at least a portion of the co-planar waveguide (211) to form a grounded co-planar waveguide (221). The ground plane (222) includes a notch (224) underlying a portion of the co-planar waveguide (211) to provide a transition region (225) from the co-planar waveguide (211) to the grounded co-planar waveguide (221).

Abstract: An embedded calibration mechanism and method for a time-of-flight ranging system. The calibration mechanism (200) comprises a channel (202) having known characteristics. Periodically or as part of a calibration function, a pulse is transmitted through the calibration channel (202) and parameters such transmit pulse delay time and apparent velocity are determined. The calibration parameters or measurements are used to calibrate or compensate operation or measurements from the measurement channel.

Abstract: A protection circuit for a current loop powered level measurement or time of flight ranging apparatus. The protection circuit includes one or more Zener diodes, a leakage current detector circuit and a compensating current circuit. The leakage current detector circuit detects the leakage currents flowing from the Zener diodes and generates an output for the compensating current circuit. The compensating current circuit generates a compensating current so that the sum of the leakage currents and the compensating current remains a constant and the loop current is not affected by variations in the leakage currents for example as a result of variations in the voltage in the current loop or temperature of the device.

Abstract: A mechanism for coupling a coaxial waveguide to another waveguide. The mechanism includes a lower or matching waveguide and an impedance transformer. A coaxial port couples the coaxial waveguide to the matching waveguide. The matching waveguide has a waveguide impedance which is close to the impedance of the coaxial waveguide. This arrangement allows matching between the coaxial waveguide and the matching waveguide over a wider frequency band. The impedance transformer couples the matching waveguide to the other waveguide. The impedance transformer comprises a single-stage, double-stage, or multi-stage transformer. The mechanism is suitable for coupling an antenna to a coaxial cable interface in a radar or microwave based level measurement or time of flight ranging systems.

Abstract: In a method for processing an echo profile generated by a pulse-echo ranging system, the echo profile is compared with a time-varying threshold function to identify valid echoes in those portions of the echo profile which exceed the TVT function. Based on the amplitude and/or area above the TVT function, each echo is rated and attributed a level of confidence. The echo with the highest level of confidence is selected as the echo of interest, and the level of confidence is reported. To provide an improved echo processing with increased accuracy in determining the confidence level of the selected echo of interest, it is furthermore determined whether the portion of the threshold function which timely corresponds to the selected echo of interest is part of a hump-shaped section of the threshold function. If so, said section is reshaped to reduced hump amplitude, and the confidence level of the echo of interest is redetermined based on the amplitude and/or area above the reshaped TVT function.

Abstract: Pulse-echo ranging system are used in level measurement applications for determining the distance to a target object by measuring how long after transmission of a pulse an echo pulse is received. An echo profile (17) is generated and then processed to determine the temporal position of the echo pulse on a temporal axis. Based on the fact that the peak portion and the trailing edge of the echo profile are susceptible to be affected by the measurement environment and the target object itself, the accuracy in determining the echo arrival time is increased, by the steps of fitting a branch of a parabola (19) to a selected portion of the leading edge (18) of the echo profile (17) and determining the temporal position of the fitted parabola (19) on the temporal axis.

Abstract: A method and apparatus for controlling pulses in a pulse-echo level measurement or time-of-flight ranging system. The apparatus comprises a controller, a transducer, and an energy storage device. The energy storage device is operatively coupled to the transducer through a relay. The relay is enabled and disabled by the controller and in the disabled state the energy storage device is allowed to accumulate energy. The energy is stored in the energy storage at a variable voltage level. The controller includes a component for determining a voltage level corresponding to an acceptable confidence level for echo pulses. The controller includes another component for determining a voltage level an increased response time.

Abstract: An digital interface and receiver for time-of-flight level measurement and pulse-echo ranging systems. The level measurement device comprises a controller, a transducer, a transmitter stage, an interface, and a digital receive signal processing module. The transmitter is operatively coupled to the transducer and responsive to the controller for emitting energy pulses directed at the surface of a material contained in a vessel. The interface is operatively coupled to the transducer and includes an analog-to-digital converter for digitizing the energy pulses reflected by the surface. The digital receive signal processing module comprises a plurality of program components for processing the digitized echo pulses and determining a level measurement for the material contained in the vessel.

Abstract: An antenna assembly suitable for use with a microwave-based level measurement system mounted on a vessel. The antenna assembly comprises a rod antenna having a mounting member with an integral sealing ring. The antenna is molded from a conductive polymer such as PTFE. The sealing ring is also formed from the same polymer as the antenna. The sealing ring may be formed as an integral component of the mounting member molded from a polymer material or as a separate ring element which is welded or otherwise affixed to the mounting member. The antenna assembly is coupled to the level measurement apparatus using a clamping mechanism. As the clamping mechanism is secured to the mounting member, the sealing ring is compressed and deflected and in the compressed state provides a seal between the level measurement apparatus and the section of antenna extending into the vessel. According to another embodiment, the antenna assembly is adapted for and mounted in a horn antenna.

Abstract: A method and apparatus for damping an ultrasonic transducer suitable for time of flight ranging and level measurement systems. The ultrasonic transducer comprises a damping component which absorbs vibrations in the transducer to reduce the ringing effect. The damping component is subjected to plasma etching to produce a surface which readily bonds to component(s) of the transducer. According to one aspect, the damping component is formed from an inert elastomer, such as silicone rubber, and the transducer component is made of stainless steel.

Abstract: Dynamic tuning of a tunable filter within the receiver of a pulse-echo ranging system. A filter tuning module compares a transmit signal and a filtered signal to obtain a phase difference indicative of any mis-match between the resonant frequency of the tunable filter and the transmit frequency. The filter tuning module outputs a phase correction signal corresponding to the phase difference and a controller uses the phase correction signal to determine any adjustments necessary to minimize the phase difference. Adjustments to the tunable filter may be made with each ‘shot’ or transmission.

Abstract: A current limiter circuit which exhibits a low dropout voltage. The current limiter circuit is suitable for protecting process control equipment operating on a current loop. The current limiter circuit includes an interface for coupling to the current loop, and a current source element coupled to the process control equipment. The current source element comprises a current limiter circuit to limit the current flowing to the process control equipment, and a voltage reference circuit coupled to the current limiter circuit provides a predetermined voltage reference during operation of the current source element.

Abstract: A method for processing echoes in a time-of-flight ranging system or level measurement system. The method comprises a recursive descent parser which is applied to an echo profile to process and identify potential echoes. In another aspect, the method provides for processing the ring down portion of the echo profile.

Abstract: A method and apparatus for calibrating and/or improving the accuracy of time of flight ranging or level measurement systems. A correction factor is determined and applied to the calculated receive times for echo pulses in response to a change in the amplitude of the echo pulses or in response to a change in the noise floor.

Abstract: A mounting mechanism for detachably coupling an antenna to a level measurement device. The mounting mechanism is coupled to the housing of the level measurement device and comprises an outer ring and an inner ring. The inner ring has a centred opening for receiving an end of the antenna. The inner ring is coupled to the outer ring and rotatable with respect to the outer ring between a locking or engaged position and an unlocking or release position. The inner ring includes one or more cams or pawls, which engage the end of the antenna when in the locked or engaged position. The cams or pawls may include a gripping surface for further securing the antenna end when in the locked position.

Abstract: A power decoupling circuit for a time-of-flight ranging or level measurement system coupled to a current loop. The level measurement system receives power from the current loop and includes a loop current regulator. The loop current regulator is responsive to signals from a controller for regulating the current in the loop to transmit level measurement data and other information. Power is also taken from the current loop to energize a transducer for generating pulses for performing level measurements. The power decoupling circuit comprises a feedback circuit and a step-up converter. The step-up converter provides charging current to an energy storage device for the transducer and may also generate a voltage gain. The feedback circuit controls the voltage drop across the loop current regulator to minimize losses on it and maximize power available for measurement.

Abstract: A loop powered level measurement and time of flight ranging system with power management. The level measurement system includes a controller, a transducer for distance ranging, a power supply, and a power management stage. The power management stage comprises a shunt current regulator and a circuit for charging a storage capacitor. The shunt current regulator shunts excess current from the current loop and the circuit charges the storage capacitor. The charging of the capacitor is monitored and stored energy is applied to the transducer to make a level measurement. During charging, the controller continues to operate a user interface and communication module.

Abstract: A method for processing echoes in a time-of-flight ranging system or level measurement system. The method comprises applying an entropy filter to the echo profile. The entropy filter comprises determining the information content in the echo profile. The entropy filter determines the occurrences of a pattern in the bit stream representing magnitudes in the echo profile. Repeated occurrences of the pattern are used to characterize the echo signal as having low randomness (i.e. higher information content) indicative of a potential echo pulse or as having high randomness (i.e. lower information content) indicative of noise.

Abstract: A current loop control circuit for a process variable transmitter coupled to a receiver at a remote location through a two-conductor current loop. The current loop control circuit efficiently utilizes the current in the loop to produce an optimal voltage and current for the operation of the process variable measurement transmitter.

Abstract: A dielectric rod antenna assembly for a level measurement system. The antenna assembly includes a transition structure housed within a coupling sleeve. The transition structure includes a short-circuited waveguide filled with a dielectric material and an exciter element projecting through the waveguide into the material. The transition structure directs electromagnetic energy through the bottom of the dielectric material into a rod antenna attached to the bottom of the coupling sleeve for propagation within the container. The dielectric material includes a longitudinal axial bore having a tapered tip to provide a dielectric-lined waveguide. The bottom end of the dielectric is encircled with a metal ring of a diameter larger than the dielectric to smooth the transition into the rod antenna.