WO2019193453A1

WO2019193453A1 - A magnetostrictive level transmitter with orientation sensor

Info

Publication number: WO2019193453A1
Application number: PCT/IB2019/052435
Authority: WO
Inventors: Shanthala KAMATH
Original assignee: ABB Schweiz AG
Current assignee: ABB Schweiz AG
Priority date: 2018-04-02
Filing date: 2019-03-26
Publication date: 2019-10-10
Anticipated expiration: 2020-10-02

Abstract

The present invention relates to a magnetostrictive level transmitter with orientation sensing. The present invention provides a magnetostrictive level transmitter comprising: a sensor tube housing a magnetostrictive wire; a sensor electronics board with a processor having a circuitry for imparting an electrical start pulse in the magnetostrictive wire; a transmitter to communicate measurements; a magnetic float, the position of the magnetic float being indicative of the liquid level; an orientation sensor to detect the orientation of mounting; wherein the processor provides a measure of the level of liquid obtained by correcting a first measure of the level of liquid taking into account: (a) orientation of the magnetostrictive sensor to correctly account the position of the float with respect to the detected orientation of the mounting, (b) variations due to interaction between the magnetic field from the magnetic float with the magnetic field of the electrical start pulse.

Description

A MAGNETOSTRICTIVE LEVEL TRANSMITTER WITH ORIENTATION SENSOR

FIELD OF THE INVENTION

The present invention relates generally to magnetostrictive level transmitter for transmitting level of liquids and more particularly to a magnetostrictive level transmitter with orientation sensors.

BACKGROUND OF THE INVENTION

Magnetostrictive level transmitters/sensors are devices based on magnetostrictive phenomenon and are used in wide variety of industrial applications to measure the level of liquids in containers. Magnetostriction is a property exhibited by ferromagnetic materials wherein there is a change in dimension of the element on application of an external magnetic field. An effect observed in magnetostrictive materials is called the Wiedemann effect where twisting of these materials takes place on application of a helical magnetic field.

Magnetostrictive level transmitters/sensors use the Wiedemann effect to determine the level or position of liquids in containers. An initial electrical current pulse is generated and provided to a wire exhibiting Magnetostriction property. The wire is usually housed in a sensor tube. The initial electrical pulse creates a magnetic field which travels down the magnetostrictive wire inside the senor tube. A permanent magnet in the form of a float is used to mark a position along the sensor tube housing the Magnetostrictive wire. The interaction of the magnetic field around the wire and the magnetic float causes a torsional stress wave to be induced in the magnetostrictive wire. This torsion propagates along the wire at a known velocity, from the position of the magnetic float and toward both ends of the wire. A processor associated with the device electronics of the magnetostrictive level sensor/transmitter converts the received mechanical torsion into an electrical return pulse. Then the processor measures the elapsed time between the start and return pulses and converts it into a position (level) measurement which is proportional to the position (level) of the float along the sensor tube.

Magnetostrictive position sensors generally can be mounted in two orientations - top and bottom to allow for various measurement requirements. In some cases, the mounting orientation either straight or inverted needs to be manually fed into the device electronics via the Human Machine Interface (HMI)/faceplate or via a means of communication with the magnetostrictive level transmitter during configuration so that the measurement and calculations can be done based on the mounting orientation. Such a manual process is susceptible to errors. Also, in some other cases, the magnetic floats being used in the magnetostrictive position sensors can affect the measurement value owing to magnetic differences and dimension/orientation change in use or positioning of the magnetic float. Hence, in such cases, one may find differences in waveform characteristics of the return pulse, which may result in incorrect or less accurate assessment of elapsed time between the start and return pulse. Therefore, there is a need for a magnetostrictive level transmitter wherein orientation of the device or any differences in waveform characteristics arising from the use/change in the magnetic float are automatically accounted for during the operation of the magnetostrictive level transmitter and thereby provide level measurement that are accurate in spite of any variation in orientation of the sensor or use of magnetic float.

SUMMARY

The above-mentioned shortcomings, disadvantages and problems are addressed herein which will be understood by reading and understanding the following specification.

In one aspect, the present invention provides a magnetostrictive level transmitter for liquid level measurement in a container containing liquid, the magnetostrictive level transmitter comprising: a sensor assembly having a: sensor tube housing a magnetostrictive wire; a sensor electronics board with a processor for the liquid level measurement and comprising an electronic circuitry for imparting an electrical start pulse current in the magnetostrictive wire; a transmitter having a communication module for communicating the liquid level measurement; at least one magnetic float comprising a permanent magnet, the magnetic float being movable along the length of the magnetostrictive wire, the position of the magnetic float being indicative of the liquid level ; an orientation sensor to detect the orientation of mounting of the sensor assembly; wherein the electric start pulse current in the magnetostrictive wire causes a torsional wave in the magnetostrictive wire upon interaction with a magnetic field caused by the magnetic float, the torsional wave detectable by the sensor electronics board for conversion to an electrical return pulse current and an elapsed time between the electrical start pulse current and electrical return pulse current is determined to provide a first measure representative of the level of the liquid based on detection of a pulse peak in the converted electrical return pulse current according to a preset polarity; and wherein the processor provides a corrected measure of the first measure by processing the electrical return pulse current wave shape to determine a significant pulse peak in the electrical return pulse current wave shape and provide correction in the case where the significant pulse peak is of a different polarity than that considered in the first measure, wherein the corrected measure of the first measure is a value obtained by a correction to account : at least one of (a) orientation of the magnetostrictive sensor based on detected orientation by the orientation sensor to correctly account the position of the float with respect to the detected orientation of the mounting of the sensor assembly, and b) variation in wave shape of the converted electrical return pulse observed due to the interaction between the magnetic field from the magnetic float with the magnetic field of the electrical start pulse.

In an embodiment of the magnetostrictive level transmitter the orientation sensor to detect the orientation of mounting of the sensor assembly is at least one of an accelerometer and a tilt switch.

In an embodiment of the magnetostrictive level transmitter two magnetic floats are provided for sensing the level of two immiscible liquids in the container, the two magnetic floats causing two torsional waves detectable by the sensor electronics board for conversion to two electrical return pulses, wherein the processor provides a corrected measure by processing the two electrical return pulses.

In an embodiment the magnetostrictive level transmitter is inserted in an orientation from at least one of top of the container and bottom of the container.

In an embodiment of the magnetostrictive level transmitter the measure of the level of the liquid in the container is communicated to a process control system.

In an embodiment of the magnetostrictive level transmitter the transmitter communicates the measure of the level of the liquid in the container to a remote control location for storage or processing of measurement.

BRIEF DESCRIPTION OF DRAWINGS The appended drawings illustrate exemplary embodiments as disclosed herein, and are not to be considered limiting in scope. In the drawings:

Figure 1 shows a magnetostrictive level sensor inserted in a container with a level of liquid to be measured.

Figure 2 shows the magnetostrictive level sensor being mounted from the bottom of the vessel. Figure 3 shows a magnetostrictive level sensor 300 with two floats.

Figure 4 shows a block diagram representing the blocks and components essentials for operation of the magnetostrictive level transmitter.

DETAILED DESCRIPTION

The present invention is related to magnetostrictive wire based position transmitter. The present invention provides for measurement of liquid levels using magnetostrictive wire based position transmitter with automated detection of mounting orientation of the magnetostrictive wire based position transmitter. As mentioned, magnetostrictive position sensors can be mounted in two orientations - top (straight) and bottom (inverted) and the mounting orientation either straight or inverted. The present invention discloses a magnetostrictive level transmitter wherein an automated detection of the orientation of the device is effectuated during the operation of the magnetostrictive level transmitter.

In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments, which may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments, and it is to be understood that other embodiments may be utilized. The following detailed description is, therefore, not to be taken in a limiting sense.

Figure 1 shows a magnetostrictive level sensor 100 inserted in a tank/container 110 with a level of liquid 120 to be measured. The operations of a magnetostrictive level sensors are well known in the art. The magnetostrictive level sensor 100 shown in Figure 1 is inserted in the tank to measure in a straight manner. The magnetostrictive level sensor 100 comprises a sensor assembly comprising a sensor tube 130. The sensor tube 130 contains a magnetostrictive wire 140, which is pulsed at fixed time intervals. The sensor assembly has a sensor electronics board 150 with a processor (not shown) for the liquid level measurement. The sensor electronics board 150 is equipped with an orientation sensor for the purpose of measurement and an electronic circuitry for imparting an electrical start pulse current in the magnetostrictive wire. A transmitter having a communication module for communicating the liquid level measurement is also provided. A display unit or Human Machine Interface (HMI) is also provided for displaying the measured level of the liquid.

A magnetic float 160 that floats in the liquid is provided and it comprises a permanent magnet. The float is movable along the length of the magnetostrictive wire on the sensor tube and the position of the magnetic float 160 is determined as indicative of the liquid level. The interaction of the magnetic field from the electrical current pulse with the magnetic field created by the permanent magnet(s) in the magnetic float 160 causes a torsional stress wave to be induced in the magnetostrictive wire 140. This torsion wave propagates along the wire 140 at a known velocity, starting from the position of the magnetic float 160. A piezo-magnetic sensing element located in the sensor electronics board 150 detects and converts the received mechanical torsion into an electrical return pulse. Sensor electronics measure the elapsed time 180 between the start 185 and return pulses 190 (a time instant generally associated with the time instant of detection of a peak in the return pulse waveform), which is proportional to the liquid level (position of float) being measured. Sensor electronics includes the piezo-magnetic sensing element, the current pulsing equipment, the return pulse detection equipment and the various electronic components used for signal conditioning, determination of return pulse peak and elapsed time between the start and return pulses, excluding the magnetostrictive wire. The time between the electrical start pulse current and electrical return pulse current is processed by the sensor electronics board having an electronics and digital signal processing unit with a processor to provide a measure representative of the level of the liquid.

The magnetic float 160 is generally of stainless steel construction, or some other material inert to the environmental conditions and material within the tank. The magnetic float 160 has a center bore and is slidable on the sensor tube 130, floating or moving with the height or level of a liquid in the tank 110. In some installations, two or more magnetic float can be used to determine liquid levels when multiple liquid separable by density are used in the same container. It can be understood for the person skilled in the art that the number of return pulse detected will correspond to the number of floats used in the magnetostrictive level sensor i.e. there will be one return pulse when one float is used to measure level of a single liquid and two return pulses when two floats are used to measure level of two liquids in a container. For dual float configurations where two immiscible liquids or a liquid or gas level is being measured, more than one float may be used for sensing the level of each type of fluid. The torsion wave from each float is represented by one large peak and a trailing smaller peak in the opposite direction. The measurement is accurate when the measurement is made at the largest peak.

The magnetostrictive level sensor also comprises an orientation sensor 170 (accelerometer or tilt sensor) to detect the orientation of mounting of the sensor assembly. The orientation sensor 170 as shown in the Figure 1 is provided in the neck region of the magnetostrictive level sensor as a part of the sensor board electronics.

At the time of installation or maintenance of the magnetostrictive level sensors, the magnetic float may be inserted in a specific orientation for sliding along the sensor tube. If the magnetic float is not inserted in the specific orientation as that during the time of calibration/commissioning or changed during a maintenance activity, there can be a difference in the nature of interaction between the magnetic field by the electric start pulse travelling in the sensor tube and the magnetic field from the magnetic float from that observed initially. This can cause variation in the measurement as the nature of the torsion wave/ electric return pulse characteristic (e.g. pulse wave shape) can differ t Hence there is a need that the signal conditioning unit automatically detects such variations in the pulse shape and properly determine the elapsed time to obtain a correct value of liquid level measurement. The signal processing unit in the sensor electronics board thus additionally provides for any correction that is required to correct the measurement (first value of measurement) resulting from the orientation of the magnetostrictive level sensor and also account the resultant variations in the torsional wave arising out of the interaction of the magnetic field from the magnetic float and the electrical start pulse i.e. for any change in the measured pulse wave shape.

In the exemplary case, the processor picks up the positive going peak (independent of whether it is the largest peak or the trailing smaller peak) and makes the level calculation. In a prior art method, after installing a sensor an user views the signal waveform and sets the signal polarity so that the large peak is in the positive orientation. This ensures that the positive peak is picked for accurate measurement in the prior art method. The present invention provides for an automated detection of the largest peak and adjusting the signal polarity automatically whilst eliminating a manual step and improve accuracy.

In an embodiment, the present invention provides for an orientation sensor, such as a tilt switch or an accelerometer in the neck region to automatically detect the mounting orientation and automatically accounting for the orientation in device operation while processing of the detected signal corresponding to the level(s) of the liquid(s).

A magnetostrictive level sensor can be mounted with the sensor tube inserted from the top of the vessel or from the bottom of the vessel, based on the application. Figure 2 shows the magnetostrictive level sensor 200 being mounted from the bottom of the vessel. The measurement electronics in a magnetostrictive level sensor needs to be aware of the mounting orientation in order to convert the measurement to the actual level height of the liquid in physical units. When the mount orientation is wrongly set in the device, a vessel full can be interpreted as level empty and thereby lead to overflow or empty vessel. In summary, mount orientation is essential to calculate the correct level value reading in the device, and the processor in the sensor electronics board is configured to make a correction according to the detected orientation of the magnetostrictive level sensor.

Figure 3 shows a magnetostrictive level sensor 300 with two floats. As mentioned earlier, a single float type sensor is capable of measuring one level and a dual float sensor can measure two levels, one between two immiscible liquids and one between the liquid and gas. The floats are selected based on the density of liquids whose level is being measured. Figure 3 shows a first liquid 310 being measured with a first float 320 and a second liquid 330 being measured with a second float 340. The first float 320 gives the first peak 350 in the waveform for level measurement of the first liquid and the second float 320 gives the second peak 360 in the waveform for the level measurement of the second liquid. As explained in Figure 1, the sensor electronics measure the elapsed time between the start 370 and return pulses from first peak 350 and second peak 360, which are proportional to the liquid levels being measured.

In an embodiment, the first measurement is being made with an electronic circuitry (first measure) and the correction is being done through signal processing with the processor. Figure 4 shows a block diagram representing the electronic/signal processing blocks/modules and components essentials for operation of the magnetostrictive level transmitter. Figure 4 represents the magnetostrictive level transmitter comprising a sensor assembly 400. The sensor assembly 400 comprises a sensor tube 410 which houses the magnetostrictive wire. The sensor assembly 400 has a sensor electronics board 420 with a processor 430 for the liquid level measurement. The sensor electronics board 420 is equipped with an orientation sensor 440 as well. And the sensor electronics board 420 is also equipped with an electronic circuitry for imparting an electrical start pulse current in the magnetostrictive wire. A transmitter unit 450 is attached to the sensor electronics board 420 having a communication module for communicating the liquid level measurement. A display unit or Human Machine Interface (HMI) 460 is also provided for displaying the measured level of the liquid. The magnetic float 470 comprising a permanent magnet is provided which is movable along the length of the magnetostrictive wire and the position of the magnetic float 470 is indicative of the liquid level.

The working of the signal processing unit is explained with an exemplary case. In the exemplary case, the magnetostrictive sensor measurement of level is processed with the electrical return pulse waveform extracted from the torsional wave and the waveform is said to have multiple peak (damped oscillating signal) with one large positive peak for single level measurement carried out with a single magnetic float and two large positive peaks i.e. two damped oscillating signal for two-level measurement carried out with two magnetic floats. For the purpose of measurement and determination of level(s) accurately, it is required to accurately determine the time difference between the electrical start pulse and the peak of the electrical return pulse. The measurement circuitry i.e. the sensor electronics board (with its hardware, software/firmware for processing of detected signal) are accordingly designed to detect the correct peak of the electrical return pulse and determine the liquid level(s).

In the exemplary case, the electrical return pulse waveform is processed/conditioned by the measurement circuitry and is configured to perform processing/conditioning for the positive polarity of the waveform. Initially, the processor uses peak detection techniques to process the number of peaks and then determine peak (here in the example, positive peak as the waveform characteristics has positive peak). If the pulse has a negative peak as the largest peak, the processing/conditioning is configured suitably (automatically) to process the waveform and detect the negative peak by the processor. In case the peaks are positive oriented and the default signal processing e.g. that performed by an electronic signal processing detects a positive peak, no change or correction in further signal processing by the processor or any further configuration is needed/performed. However, such further signal processing (corrections) is required in case the wave shape of the return pulse is found to be differently shaped (e.g. having a significant negative peak instead of positive peak) compared to any preset/default mode of peak detection (e.g. preset to positive peak detection expecting a positive peak as the significant peak in the detected return pulse wave shape) and requires a correction to be made to ensure accurate and sensitive level detection,

In a scenario where significant peaks are undetected then a missing float or any other miscalibration can be indicated and measurement is no longer carried out.

In an exemplary scenario, the corrected measure of the first measure is obtained by a correction to take into account the orientation of the magnetostrictive sensor which is based on detected orientation by the orientation sensor. Such that, the position of the float with respect to the detected orientation of the mounting of the sensor assembly is correctly accounted for. In another exemplary scenario, the corrected measure of the first measure is obtained by a correction to take into account the variation in wave shape of the converted electrical return pulse observed due to the interaction between the magnetic field from the magnetic float and the magnetic field of the electrical start pulse. In yet another exemplary scenario, the corrected measure of the first measure is obtained by a correction to take into account both the orientation of the magnetostrictive sensor which is based on detected orientation by the orientation sensor and the variation in wave shape of the converted electrical return pulse observed due to the interaction between the magnetic field from the magnetic float and the magnetic field of the electrical start pulse.

In an embodiment, the magnetostrictive level transmitter transmits the measure of the level of the liquid in to a remote control location for storage or analysis.

In an embodiment, the magnetostrictive level transmitter is internet enabled for communication with any other remote location or remotely located devices and the various blocks and components in the magnetostrictive level transmitter are connected via wired or wireless communication. This written description uses examples to describe the subject matter herein, including the best mode, and also to enable any person skilled in the art to make and use the subject matter. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.

Claims

We claim,

1. A magnetostrictive level transmitter (100) for liquid level measurement in a container (110) containing liquid (120), the magnetostrictive level transmitter (100) comprising: a sensor assembly having a: a) sensor tube (130) housing a magnetostrictive wire (140); b) a sensor electronics board (150) with a processor for the liquid level measurement and comprising an electronic circuitry for imparting an electrical start pulse current in the magnetostrictive wire (140); c) a transmitter having a communication module for communicating the liquid level measurement;

at least one magnetic float ( 160) comprising a permanent magnet, the magnetic float being movable along the length of the magnetostrictive wire, the position of the magnetic float being indicative of the liquid level; an orientation sensor (170) to detect the orientation of mounting of the sensor assembly; wherein an electric start pulse current (185) in the magnetostrictive wire (140) causes a torsional wave in the magnetostrictive wire (140) upon interaction with a magnetic field caused by the magnetic float (160), the torsional wave detectable by the sensor electronics board (150) for conversion to an electrical return pulse current (190) and an elapsed time (180) between the electrical start pulse current (185) and electrical return pulse current (190) is determined to provide a first measure representative of the level of the liquid (120) based on detection of a pulse peak in the converted electrical return pulse current (190) according to a preset polarity; and wherein the processor provides a corrected measure of the first measure by processing the electrical return pulse current wave shape to determine a significant pulse peak in the electrical return pulse current wave shape and provide correction in the case where the significant pulse peak is of a different polarity than that considered in the first measure. wherein the corrected measure of the first measure is a value obtained by a correction to account at least one of:

(a) orientation of the magnetostrictive sensor based on detected orientation by the orientation sensor to correctly account the position of the magnetic float ( 160) with respect to the detected orientation of the mounting of the sensor assembly, and b) variation in wave shape of the converted electrical return pulse (190) observed due to the interaction between the magnetic field from the magnetic float (160) with the magnetic field of the electrical start pulse (185).

2. The magnetostrictive level transmitter as claimed in claim 1 , wherein the orientation sensor to detect the orientation of mounting of the sensor assembly is at least one of an accelerometer and a tilt switch.

3. The magnetostrictive level transmitter as claimed in claim 1, wherein two magnetic floats are provided for sensing the level of two immiscible liquids in the container, the two magnetic floats causing two torsional waves detectable by the sensor electronics board for conversion to two electrical return pulses, wherein the processor provides a corrected measure by processing the two electrical return pulses.

4. The magnetostrictive level transmitter as claimed in claim 1 , wherein the magnetostrictive wire based position transmitter is inserted in an orientation from at least one of top of the container and bottom of the container.

5. The magnetostrictive level transmitter, wherein the measure of the level of the liquid in the container is communicated to a process control system.

6. The magnetostrictive level transmitter as claimed in claim 1, wherein the transmitter communicates the measure of the level of the liquid in the container to a remote control location for storage or processing of measurement.