Patent Description:
Magnetostrictive technology is usually sensitive to vibration. Vibrations can trigger unwanted electrical pulses from magnetostrictive sensors that can be misinterpreted by detection circuits. Most existing magnetostrictive instruments suffer from such vibration sensitivity, which is typically addressed by steadily securing the magnetostrictive transmitters during use, or even using vibration isolators.

Additionally, some configurations offered with magnetostrictive transmitters require interconnecting components between the magnetostrictive sensors and the detection circuits. Intrinsic capacitance coupling between these interconnecting components and power supplies or large rotating electrical machines located in the proximity of the magnetostrictive transmitter can generate significant electromagnetic noise in the small signal from the magnetostrictive sensor. <CIT> describes a method for monitoring tanks in an inventory management system. The method includes lowering a sensor unit in a tank, determining a first distance between the material and the sensor unit and determining a second distance between the sensor unit and a main unit that lowers the sensor unit. In addition, the method includes determining a level of the material in the tank using the first and second distances. The method could further include calibrating the sensor unit to compensate for variations in a medium within the tank, where the sensor unit transmits wireless signals through the medium to determine the first distance. <CIT> discloses a DAC compensation method for ultra-long-range magnetostrictive liquid level meter. <CIT> discloses a redundant level measuring system comprises a chamber for fluidic coupling to a process vessel whereby material level in the vessel equalizes with material level in the chamber. A measurement circuit measures time of flight of a through air signal representing level of the material in the chamber.

According to one aspect, a magnetostrictive transmitter and a method according to the attached claims are provided.

Other aspects and advantages of the present invention will become apparent upon consideration of the following detailed description and the attached drawings wherein like numerals designate like structures throughout the specification.

The detailed description below refers to the appended drawings, in which:.

In one or more implementations, not all of the depicted components in each figure may be required, and one or more implementations may include additional components not shown in a figure. Variations in the arrangement and type of the components may be made without departing from the scope of the subject disclosure. Additional components, different components, or fewer components may be utilized within the scope of the subject matter disclosed and defined by the appended claims.

The detailed description set forth below is intended as a description of various implementations and is not intended to represent the only implementations in which the subject technology may be practiced. As those skilled in the art would realize, the described implementations may be modified in various different ways, all without departing from the scope of the present disclosure as defined by the appended claims. Still further, modules and processes depicted may be combined, in whole or in part, and/or divided, into one or more different parts, as applicable to fit particular implementations without departing from the scope of the present disclosure as defined by the appended claims. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive.

Referring now to <FIG>, the principle of operation of a magnetostrictive level transmitter <NUM> is illustrated in a simplified diagram. At a high level, the magnetostrictive level transmitter operates by measuring a time of flight of a torsional wave between a magnetic float <NUM> and a sensing element <NUM>, which is then converted into a distance. The illustrative magnetostrictive level transmitter <NUM> shown in <FIG> includes two magnetic floats 12A and 12B. The magnetic float 12A is configured to float at an upper surface <NUM> of a liquid <NUM> held in a tank <NUM>, while the magnetic float 12B is configured to float at an interface <NUM> between the liquid <NUM> and a liquid <NUM> also held in the tank <NUM>. It is contemplated that other types of magnetic floats <NUM> can be used in other embodiments.

In operation, an electronic circuit in the transmitter <NUM> generates a current pulse <NUM> (e.g., at fixed intervals) which travels down a specialized wire <NUM> inside the sensor tube <NUM> at near the speed of light, creating a magnetic field around the wire <NUM>. The interaction of the magnetic field around the wire <NUM> and the magnetic float 12A or 12B causes a torsional stress wave to be induced in the wire <NUM>. This torsional stress wave propagates along the wire <NUM> at a known velocity, from the position of the magnetic float 12A or 12B toward the sensing element <NUM> in the transmitter <NUM>. The sensing element <NUM> converts the received mechanical torsion into an electrical return pulse that is used to measure the elapsed time between the start and return pulses (time of flight). The measured time of flight is then converted it into a value representing a level, an interface, an empty distance, a volume, a position or simply a distance, depending of the requirements of the application. Throughout the present disclosure, the term "distance" will be used to encompass any such value, including a level of fluid, an interface level, an empty distance, a volume, a position, or a distance.

The present disclosure provides a unique signal conditioning circuit for magnetostrictive transmitters. The presently disclosed signal conditioning circuit includes several hardware features configured to process the signal from the magnetostrictive sensor and to reduce noise at the same time. Furthermore, the present disclosure provides software (which may be embodied as firmware on the transmitter and/or software on a personal computer (PC) or control system, all referred to as "software" in the present disclosure) that is configured to readapt the hardware of the signal conditioning circuit to specific conditions. Additionally, the presently disclosed software can evaluate data received from the signal conditioning circuit to determine the value of the process variable being monitored by the magnetostrictive transmitter and can perform deep processing and analysis of system parameters to raise diagnostic messages if certain diagnostic criteria are met. The software may also display the waveform of the signal in a human-machine interface (HMI) display to assist with identification of any problem and adequate reconfiguration of the transmitter for optimal performance given the conditions of the application. Additionally, the systems and methods of the present disclosure provide flexibility to easily change a mounting configuration, a sensor type, and/or a sensor size of the magnetostrictive transmitter, while utilizing the same hardware.

Referring now to <FIG>, one illustrative embodiment of a signal conditioning circuit <NUM> according the present disclosure is shown as a simplified block diagram. This simplified block diagram illustrates the path of a return signal <NUM>, received from the magnetostrictive sensor, as it is processed by the signal conditioning circuit <NUM>. In operation, the return signal <NUM> from the magnetostrictive sensor is fed to an analog section <NUM> of the signal conditioning circuit <NUM>. This analog section <NUM> includes an instrumentation amplifier <NUM> with high-common noise rejection, an active high pass filter <NUM> with constant group delay, and an additional amplifier stage <NUM> with a wide range of variable gain.

After amplification in the analog section <NUM> of the signal conditioning circuit <NUM>, the signal is sampled with an analog-to-digital converter (ADC) <NUM> and then plotted in an HMI display <NUM>. The HMI display <NUM> may be part of the magnetostrictive transmitter <NUM>, or part of an associated the control system (in which case the data representing the sampled signal may be transmitted using the appropriate communication drivers).

In parallel to the sampling by the ADC <NUM>, the signal is processed by a distance detection module <NUM>. In the illustrative embodiment, the distance detection module includes programmable logic configured to implement a distance detection algorithm. The data output by the distance detection module <NUM> (e.g., from the distance detection algorithm) is then passed to a median filter <NUM> and a diagnostic algorithm <NUM>, both of which are illustratively embodiment in software. The median filter <NUM> is configured to remove spikes from the measurement.

The diagnostic algorithm <NUM> validates the resulting data and can send one or more diagnostic messages to the HMI display <NUM>, as needed. In particular, the diagnostic algorithm <NUM> evaluates both raw and filtered data for key parameters and diagnostic patterns, raising diagnostic messages or alarm conditions when certain diagnostic criteria are met (or not met). In the illustrative embodiment, the diagnostic messages that may be displayed on the HMI display <NUM> include: "Level Not Detected", "Level Sensor Stuck", "Level Sensor Out of Range", and "Level Out of Limits". In other words, if any problems are detected by the software (e.g., by the diagnostic algorithm <NUM>), the HMI display <NUM> presents the diagnostic message(s) to a user, while also allowing the user to review the signal waveform for identification of the root cause. Proper adjustments can then be made to the signal conditioning circuit <NUM> to improve the quality of the measurement. In some embodiments, once the software of the signal conditioning circuit <NUM> has processed the return signal <NUM> and determined the characteristics of the noise produced by vibration or electromagnetic sources, the software can apply the necessary adjustments to the signal conditioning circuit <NUM> to reduce the impact of those factors on the integrity of the measurement.

<FIG> shows a more detailed block diagram of one illustrative embodiment of the analog section <NUM> of the signal conditioning circuit <NUM>. As discussed above, the magnetostrictive sensor is usually fitted with one or more floats <NUM> with built-in magnets to measure distance inside a tank <NUM> (or other vessel). Those skilled in the art will appreciate that, in other embodiments, the magnetostrictive transmitter <NUM> can be used with standalone magnets secured to other moving objects to measure distance.

In operation, a programmable control circuit <NUM> (e.g., a microcontroller) sends an appropriate control signal <NUM> to cause a pulsing circuit <NUM> to send a current pulse <NUM> with a specified energy level to the magnetostrictive sensor. As described above with reference to <FIG>, application of the current pulse <NUM> results in a return signal <NUM>. The return signal <NUM> from the sensing element <NUM> is passed into the instrumentation amplifier <NUM>, which provides amplification of the signal with low direct current (DC) offset, low drift, and a high common mode rejection ratio (CMRR) and a high power supply rejection ratios (PSRR). Thus, the instrumentation amplifier <NUM> rejects much of the electrical noise injected to the return signal <NUM>.

From the instrumentation amplifier <NUM> the signal is routed into active high pass filter <NUM> with constant group delay. In the illustrative embodiment, the filter <NUM> is embodied as a constant group delay Bessel filter optimized to have a normalized transfer function of up to -<NUM> dB at <NUM> and -<NUM> dB at <NUM>. This enables the signal conditioning circuit <NUM> to effectively reject electromagnetic noise produced by electrical machines and most of the vibration noise produced in the low frequency range below <NUM>.

While the instrumentation amplifier <NUM> and the filter <NUM> are able to reject low frequency noise well, they do not eliminate noise in the same frequency range as the return signal <NUM>. To reduce such noise, and thereby increase the signal to noise ratio, the programmable control circuit <NUM> configures and controls components of the analog section <NUM> of the signal conditioning circuit <NUM>, including the pulsing circuit <NUM>, a polarity selection circuit <NUM>, and the additional amplifier stage <NUM> in accordance with a noise reduction algorithm.

From the output of the filter <NUM>, the signal is transferred to the polarity selection circuit <NUM>, which includes a plurality of analog switches controllable by the programmable control circuit <NUM> (via one or more control signals <NUM>) to switch a polarity of the received signal, as necessary, into the required polarity for proper operation of the signal conditioning circuit <NUM>. The ability of the polarity selection circuit <NUM> to adjust signal polarity allows the magnetostrictive transmitter <NUM> to be installed and used in both a top to bottom orientation and a bottom to top orientation, as well as using any type of magnetic float <NUM>. This feature provides flexible field configurability, which can result in significant shipping, service, and commissioning costs.

From the output of the polarity selection circuit <NUM>, the signal is transferred to the additional amplifier stage <NUM> with a wide range of variable gain. The variable gain of the additional amplifier stage <NUM> is controllable by the programmable control circuit <NUM> (via one or more control signals <NUM>). In the illustrative embodiment, the additional amplifier stage <NUM> provides up to <NUM> dB of dynamic range. Furthermore, in the illustrative embodiment, the maximum total gain of the analog section <NUM> of the signal conditioning circuit <NUM> is approximately <NUM> dB for frequencies between <NUM> and <NUM>, allowing amplification of very small signals but also, importantly, attenuation down to -<NUM> db on signals or noise produced in the <NUM> - <NUM> range. The signal <NUM> output by the analog section <NUM> is the provide, in parallel, to both the ADC <NUM> and the distance detection module <NUM>, as described above with reference to <FIG>.

<FIG> shows a more detailed block diagram of one illustrative embodiment of the distance detection module <NUM> of the signal conditioning circuit <NUM>. As shown in <FIG>, the programmable control circuit <NUM> sends a control signal <NUM> to a threshold circuit <NUM> to configure the threshold circuit <NUM> with the signal level desired to be ignored as noise. In response, the threshold circuit <NUM> generates a threshold voltage <NUM> that is fed to a threshold crossing detector <NUM> for comparison to the signal <NUM> output by analog section <NUM> of the signal conditioning circuit <NUM>. The signal <NUM> is simultaneously fed to a zero crossing detector <NUM>. The outputs of both the threshold crossing detector <NUM> and the zero crossing detector <NUM> are passed to a distance detecting circuit <NUM>, which validates the correct event and timing sequences and then determines the measured time of flight (representative of a measured distance, as discussed above). The adjustable threshold voltage <NUM>, generated by the threshold circuit <NUM> (under control of the programmable control circuit <NUM>) and fed to the threshold crossing detector <NUM>, provide an efficient mechanism for ignoring noise below the threshold voltage <NUM>, independently of the source of the noise.

Referring now to <FIG>, an illustrative configuration procedure <NUM> for the signal conditioning circuit <NUM> of the magnetostrictive level transmitter <NUM> is shown as a simplified block diagram. The configuration procedure <NUM> can be performed by the programmable control circuit <NUM> by configuring and controlling various aspects of the signal conditioning circuit <NUM> and by observing the resulting noise and signal information from the circuit <NUM> (including, for example, the signal <NUM> output by the analog section <NUM> of the signal conditioning circuit <NUM>).

The configuration procedure <NUM> begins by determining an appropriate energy level for the current pulse <NUM> to be sent down the wire <NUM> inside the sensor tube <NUM> of the transmitter <NUM>. To do so, the programmable control circuit <NUM> sends a first control signal <NUM> that causes the pulsing circuit <NUM> to apply a current pulse <NUM> and then observes the resulting signal <NUM> output by the analog section <NUM>. Next, the programmable control circuit <NUM> sends a second control signal <NUM> that causes the pulsing circuit <NUM> to apply a current pulse <NUM> with increased energy and then observes the resulting signal <NUM>. If the signal <NUM> has increased amplitude as a result of the increased energy current pulse <NUM> and has not saturated, this cycle is repeated (i.e., a third current pulse <NUM> of even greater energy is applied and the resulting signal <NUM> is observed, and so on). Once the signal <NUM> saturates, the energy of the current pulse <NUM> is reduced to the amount from the previous cycle (i.e., the last cycle without saturation of the signal <NUM>), and the configuration procedure <NUM> moves to the next step.

Next, the configuration procedure <NUM> configures the gain settings of the analog section <NUM> of the signal conditioning circuit <NUM>. To do so, the programmable control circuit <NUM> repeatedly applies the control signal <NUM> (determined above) to cause the pulsing circuit <NUM> to apply the current pulse <NUM>, while adjusting the variable gain of the additional amplifier stage <NUM> via one or more control signals <NUM> and observing the resulting signals <NUM> output by the analog section <NUM>. The programmable control circuit <NUM> increases the variable gain of the additional amplifier stage <NUM> until saturation is observed and then sets the variable gain of the additional amplifier stage <NUM> as high as possible without saturation.

Finally, the configuration procedure <NUM> configures the distance detection module <NUM> of the signal conditioning circuit <NUM>. To do so, the programmable control circuit <NUM> determines the highest amplitude peaks in both the observed signals <NUM> and any noise present and calculates a value that is midway (<NUM>%) between those peaks. The programmable control circuit <NUM> then sends an appropriate control signal <NUM> to the threshold circuit <NUM> to cause the threshold circuit <NUM> to generate a threshold voltage <NUM> with the calculated value (i.e., midway between the highest amplitude peaks of signal and noise). As discussed above with reference to <FIG>, this threshold voltage <NUM> is the fed to the threshold crossing detector <NUM> for comparison to the signal <NUM>, and the output of the threshold crossing detector <NUM> is used by the distance detecting circuit <NUM> to ignore unwanted noise, regardless of source. As such, the configuration procedure <NUM> can effectively reduce the noise generated by vibration harmonics or other low frequency noise, because increasing the energy of current pulse <NUM> increases the amplitude of the signal without increasing the amplitude of the noise.

The above disclosure represents an improvement in the art by providing an advanced analog circuit highly integrated with programmable devices and software to provide effective analog and digital processing of signals from magnetostrictive sensors. The above disclosure further represents an improvement in the art by providing a configuration procedure to achieve the optimal performance of the foregoing system in noisy environments, especially targeting electrical and vibration noise.

While some implementations have been illustrated and described, numerous modifications come to mind, while the scope of protection is only limited by the scope of the accompanying claims.

To the extent that the terms include, have, or the like is used, such terms are intended to be inclusive in a manner similar to the term comprise as comprise is interpreted when employed as a transitional word in a claim.

The disclosed systems and methods are well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular implementations disclosed above are illustrative only, as the teachings of the present disclosure may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative implementations disclosed above may be altered, combined, or modified and all such variations are considered within the scope of the present disclosure. The systems and methods illustratively disclosed herein may suitably be practiced in the absence of any element that is not specifically disclosed herein and/or any optional element disclosed herein.

It should be understood that the described instructions, operations, and systems can generally be integrated together in a single software/hardware product or packaged into multiple software/hardware products.

Claim 1:
A magnetostrictive transmitter (<NUM>) comprising a magnetic float (<NUM>), a sensing element (<NUM>), a wire (<NUM>) connecting the magnetic float (<NUM>) and the sensing element (<NUM>), and a signal conditioning circuit (<NUM>), the signal conditioning circuit comprising:
an instrumentation amplifier (<NUM>) configured to receive and amplify an analog measurement signal from the sensing element (<NUM>) in response to a torsional stress wave in the wire (<NUM>) induced by the magnetic float (<NUM>) in response to a current pulse transmitted along the wire (<NUM>);
an active high pass filter (<NUM>) configured to reduce noise in a signal output by the instrumentation amplifier;
a variable gain amplifier stage (<NUM>) configured to further amplify a signal output by the active high pass filter;
a distance detection module (<NUM>) configured to process a signal output by the variable gain amplifier stage to determine a distance measurement associated with the analog measurement signal received by the instrumentation amplifier; and
a programmable control circuit (<NUM>) configured to control an energy level of the current pulse a gain level of the variable gain amplifier stage and to receive data concerning the signal output by the variable gain amplifier stage, including the distance measurement, from the distance detection module, wherein the programmable control circuit is further configured to iteratively set the energy level of the current pulse and subsequently the gain level of the variable gain amplifier stage to be as high as possible without causing saturation in the signal output by the variable gain amplifier stage.