Patent Description:
Electromagnetic flowmeters (which are sometimes referred to as magnetic flowmeters or "mag meters") measure the flow rate of an electrically conductive fluid through a flowtube. In a conventional electromagnetic flowmeter, electrical coils are mounted on opposite sides of the tube and energized to produce an electromagnetic field perpendicular to the direction of fluid flow in the flowtube. When a conductive fluid flows through the electromagnetic field, an electric field is generated in the fluid that can be measured to determine the flow rate. In a typical set up, a pair of electrodes extends through the wall of the flowtube and into the fluid for measuring the strength of the electric field to determine the flow rate. Sometimes additional electrodes extend through the wall of the flowtube into a conduit therein in order to provide empty pipe detection or to ground the liquid. Each point where an electrode extends through the flowtube wall into the conduit requires a so-called process penetration. As illustrated in <FIG>, a conventional electrode <NUM> includes a head <NUM> and a shank <NUM> extending away from the head. The shank <NUM> is inserted into an opening <NUM> forming the process penetration so the head <NUM> is in the conduit <NUM> formed by the flowtube <NUM> and so the shank extends through the flowtube wall <NUM>. A fastener <NUM> (e.g., a threaded nut) is used to hold the electrode is in this position.

The process penetrations should be sealed to keep the fluid from leaking into the process penetration as it flows through the flowmeter <NUM>. One way this is done is to provide serrations <NUM> on the back side of the head <NUM> of each electrode <NUM>. The inner surface of the flow tube <NUM> is commonly lined with an electrically insulating and chemically resistant liner <NUM> to prevent the conductive fluid from creating a short circuit between the electrode <NUM> and the flowtube wall <NUM>, which is commonly made of an electrically conductive material such as metal. Thus, when the nut or other fastener <NUM> is tightened, the serrations <NUM> on the back of the electrode head <NUM> dig into the liner <NUM> and form a seal between the head of the electrode <NUM> and the liner. This seal is known as the primary seal. The shank <NUM> of the electrode <NUM> is insulated from the electrically conductive part of the flowtube wall <NUM> by an insulating sheath <NUM> surrounding at least the segment of the shank that is adjacent the conductive flowtube wall. If fluid leaks past the primary seal, it will also have to flow past the insulating sheath <NUM> to completely escape through the process penetration. As a result, fluid can leak through the liner <NUM> and contact the flowtube <NUM> without any evidence of the leak being visible from outside the flowtube <NUM>.

The fluids metered by electromagnetic flowmeters can include very corrosive and/or caustic materials. In some processes the fluids can also be at a fairly high temperature when they flow through the electromagnetic meter, which can increase the rate at which the fluid causes damage to other materials (e.g., the flowtube wall <NUM>). The present inventors have noted that fluids may leak past the primary seal and cause extensive corrosion of the flowtube wall <NUM> before a leak is detected. This can present a significant hazard because damage to the flowtube wall <NUM> can impair the pressure containment capability of the flowtube. Thus, the leak may not be detected until the flowtube bursts and releases the corrosive fluid in a catastrophic failure.

<CIT> discloses a magnetic flow meter with a diagnostic circuit indicating leakages from flowtube electrodes.

The obj ect of the invention is achieved by an electromagnetic flowmeter according to claim <NUM> and a method of making an electromagnetic flowmeter according to claim <NUM>, respectively.

One aspect of the invention is an electromagnetic flowmeter. The flowmeter has a flowtube configured to carry a flowing conductive fluid. The flowtube has a flowtube wall including a conductive material. The flowtube wall has an inner surface surrounding a fluid flow path for the conductive fluid. A non-conductive liner is positioned to electrically insulate the flowtube wall from the conductive fluid. The flowtube and non-conductive liner define an electrode mounting hole. An electrode extends through the electrode mounting hole. The electrode and the non-conductive liner form a fluidic seal between the electrode mounting hole and the fluid flow path. At least a portion of the electrode is arranged in fluid communication with the flowtube within the electrode mounting hole.

Another aspect of the invention is a method of making an electromagnetic flowmeter. The method includes providing a flowtube including an axis along which fluid can flow through the flowtube. The flowtube also has an outer surface and an inner surface. The flowtube is electrically conductive and configured so that the inner surface is electrically insulated from fluid flow passing through the flowtube. The flowtube includes an electrode mounting hole extending radially with respect to the axis through a wall of the flowtube, including the outer surface and the inner surface. An electrode is installed in the electrode mounting hole so that at least a portion of the electrode in the mounting hole is in fluid communication with the flowtube wall within the electrode mounting hole. The electrode is operatively sealed with the outer and inner surfaces of the flowtube. A short circuit detector is connected to the flowtube and electrode, whereby should the seal between the electrode and the inner surface of the flowtube fail, fluid flowing through the flowtube and entering the electrode mounting hole has access to the electrode for creating a short circuit detectable by the short circuit detector.

Other objects and features of the invention will be in a part apparent and in part pointed out hereinafter.

Corresponding reference characters represent corresponding features throughout the drawings.

Referring now to the drawings, first to <FIG>, one embodiment of an electromagnetic flowmeter is generally designated <NUM>. The flowmeter <NUM> includes a flowtube <NUM> configured to carry a flowing conductive fluid through the flowmeter <NUM>. For example, the flowtube <NUM> suitably includes a generally cylindrical or tubular wall <NUM> having an inner surface surrounding a flow path <NUM> extending between opposite ends of the flowtube for flow of fluid through the flowmeter <NUM>. The flowtube <NUM> is suitably made of an electrically conductive material, such as stainless steel or another suitable metal. A non-conductive liner <NUM> lines the inner surface of the flowtube wall <NUM> to electrically insulate the flowtube wall from the conductive fluid. The non-conductive liner <NUM> may have any of several suitable configurations, such as a coating, a separate liner attached to the inner surface of the flowtube <NUM>, a treatment of the material of the flowtube adjacent the inner surface to provide a few examples.

The flowmeter <NUM> has an electrode <NUM> extending through a process penetration formed by an electrode mounting hole <NUM> extending through the flowtube wall <NUM> and the non-conductive liner <NUM>. The electrode <NUM> includes a head <NUM> and a shank <NUM> extending away from the head. The shank <NUM> has a shank diameter D1 and the head <NUM> has a head diameter D2 larger than the shank diameter. As illustrated in <FIG>, the shank <NUM> extends through the electrode mounting hole <NUM> in the flowtube wall <NUM> and non-conductive liner <NUM>. Though not illustrated for clarity, the shank <NUM> is suitably threaded. The end of the shank <NUM> opposite the head <NUM> extends through the flowtube <NUM> to an exterior of the flowtube. A fastener <NUM> holds the electrode <NUM> so the head <NUM> of the electrode is in contact with the liner <NUM>. The fastener is suitably a threaded nut <NUM> on the threaded shank <NUM>. The fastener <NUM> is capable of applying tension to the shank <NUM> to draw the head <NUM> of the electrode <NUM> tightly against the liner <NUM>. In the illustrated embodiment, for example, the threaded nut <NUM> can be tightened against a non-conductive washer <NUM> adjacent the exterior of the flowtube <NUM> to pull the shank <NUM> farther out of the electrode mounting hole <NUM> and draw the head <NUM> tightly against the liner <NUM> to form a seal. The non-conductive washer <NUM> suitably prevents the fastener <NUM> from creating an unwanted electrical connection between the flowtube <NUM> and the electrode shank <NUM>. The head <NUM> suitably has a plurality of serrations or teeth <NUM> positioned to contact the liner <NUM> when the fastener <NUM> is tightened. However, the serrations can be omitted within the scope of the invention. Also, although in the illustrated embodiment the electrode <NUM> includes a threaded shank <NUM> and the fastener includes a threaded nut <NUM>, it is understood that other types of fastening devices may be used without departing from the scope of the invention.

The electrode shank <NUM> extends through the conductive flowtube wall <NUM> and is everywhere spaced apart from the flowtube wall. In the illustrated embodiment, a non-conductive spacer <NUM> is disposed around at least a portion of the shank <NUM> in the electrode mounting hole <NUM> between the shank and the flowtube wall <NUM>. The illustrated spacer <NUM> has at least one fluidic path <NUM> extending between the electrode shank <NUM> and the flowtube wall <NUM>. Under normal circumstances, the fluidic path <NUM> defined by the spacer <NUM> is substantially devoid of fluid or other conductive materials. For example, the fluidic path <NUM> can suitably be filled with air or another non-conductive gas. The spacer <NUM> is positioned to insulate the electrode <NUM>, and in particular the shank <NUM> of the electrode, from the conductive flowtube wall <NUM> at the process penetration under normal circumstances. However, in the event fluid flowing through the flowmeter <NUM> leaks through the primary seal formed between the head <NUM> of the electrode <NUM> and the non-conductive liner <NUM> and into the fluidic path <NUM>, the conductive fluid can establish a low-resistance electrical connection between the electrode <NUM> and the conductive flowtube wall <NUM>. Leaking fluid in the fluidic path <NUM> establishes a short circuit between the electrode <NUM> and ground (i.e., the flowtube <NUM>) that can be detected without any visual evidence of the leak.

In the illustrated embodiment, the spacer <NUM> is a cylindrically-shaped sleeve positioned so the electrode shank <NUM> extends through an axial hole in the sleeve for receiving the shank. In this embodiment, the fluidic path <NUM> includes a transverse hole extending laterally through the cylindrically-shaped sleeve <NUM>. In particular, the hole <NUM> extends laterally through the sleeve <NUM> from the shank <NUM> to the flowtube wall <NUM>. Though the illustrated embodiment uses the spacer <NUM>, it is also contemplated that the electrode shank <NUM> may be secured in spaced apart relationship with the flowtube wall <NUM> (and be electrically insulated therefrom) other ways without departing from the scope of the invention. For example, in some embodiments (not shown), a fastener secures the electrode to the wall in a position in which the shank extends through a process penetration but does not make electrical contact with the wall. Likewise, various differently sized and shaped spacers can be used within the broad scope of the invention. In these alternative embodiments, the flowmeter includes a fluidic path between an electrode (specifically, in some embodiments, an electrode shank) and a conductive flowtube wall. The fluidic path is configured so that, in the event conductive fluid leaks into the fluidic path, the conductive fluid that leaks into the fluidic path establishes an electrical connection between the electrode and the conductive flowtube wall. Likewise, in these embodiments the electrode is electrically insulated from the conductive flowtube wall as long as the conductive fluid does not leak into the fluidic path. In certain of these embodiments, at least a portion of the electrode (e.g., a portion of the shank) and a portion of the flowtube in the electrode mounting hole are in opposed relation, free of obstruction therebetween.

Referring again to the embodiment of <FIG>, the flowmeter <NUM> includes a system <NUM> that monitors for the presence of fluid in the fluid path <NUM> by assessing electrical impedance between the electrode <NUM> and the conductive flowtube wall <NUM>. For example, the flowmeter <NUM> suitably includes a short circuit detector <NUM> configured to detect whether or not conductive fluid is in the fluid path <NUM>. A suitable short circuit detector can be formed by any electrical components that can be configured to detect electric current passing through the fluidic path <NUM> between the electrode shank <NUM> and the flowtube wall <NUM>. Somewhat relatedly, a suitable short circuit detector can be formed by any electrical components that can be configured to detect a change in the overall electrical resistance in the electrical paths between the electrode <NUM> and the flowtube wall <NUM>. The electrical resistance in the fluidic path <NUM> will be relatively high when the fluidic path is substantially devoid of fluid and much lower if the fluidic path is filled with conductive fluid. Those skilled in the art will be familiar with many different ways to detect the formation of a short circuit between two nodes in an electrical system (e.g., the electrode and the flowtube wall).

Referring to <FIG>, in a suitable embodiment the monitoring system <NUM> includes a comparator <NUM> that compares the resistance between two nodes (the flowtube <NUM> and the electrode <NUM>) to a reference value. As discussed above, the flowtube <NUM> is made from conductive material, and the fluid flowing through the flowtube is likewise conductive. The non-conductive liner <NUM> extends only a certain length L1 (<FIG>) from the electrode <NUM>. The fluid in the flow path <NUM>, in normal, non-leaking conditions, electrically connects the electrode <NUM> to the flowtube <NUM> at the location where the non-conductive liner <NUM> ends. Thus, current passes between the electrode <NUM> and the flowtube <NUM> over a relatively long length L1 of fluid around the upstream and downstream ends of the liner <NUM> under normal, non-leaking conditions. For purposes of explanation, the illustrated liner <NUM> does not coat the entire inner surface of the flowtube <NUM>. However, it should be understood that, in some embodiments, a non-conductive liner will coat the full length of the flowtube. In certain of these embodiments, the flowmeter is fluidly connected to an electrically conductive pipeline. Fluid between the electrode head and the conductive pipeline will provide a normal connection between the electrode and ground. When the electrical resistance in the path <NUM> is relatively high (no leaks), the resistance between the electrode <NUM> and the flowtube wall <NUM> is approximately the same as the resistance to flow of this current through the conductive liquid. Still other connections between an electrode and ground may establish the normal electrical resistance between an electrode and a corresponding flowtube wall (ground) without departing from the scope of the invention. One skilled in the art will appreciate that techniques described with respect to the illustrated embodiment for detecting a deviation in the normal impedance between the electrode <NUM> and the flowtube <NUM> can be readily adapted to other normal connections between an electrode and ground.

As shown best in <FIG>, when no fluid leaks past the non-conductive liner <NUM>, the resistance between the electrode <NUM> and the flowtube <NUM> is substantially equal to the normal resistance RF, a relatively high value, which is directly related to the length L1 of fluid connecting the conductive flowtube <NUM> to the electrode <NUM> as well as the fluid's resistivity. However, as shown in <FIG>, when fluid leaks past the non-conductive liner <NUM>, a new, parallel current path is created in the fluidic path <NUM>. The length L2 of the fluidic path <NUM> is much shorter than the length L1 of fluid between the electrode head <NUM> and the end of the flowtube liner <NUM>. Thus, the short circuit electrical resistance RL between the flowtube <NUM> and the electrode <NUM> along the fluid path <NUM>, is much lower than the normal resistance RF. When fluid leaks past the non-conductive liner <NUM>, the total resistance RT between the flowtube <NUM> and the electrode <NUM> is equal to the combined resistances of RF and RL in parallel: <MAT>.

When fluid leaks past the non-conductive liner <NUM> and into the fluidic path <NUM>, the total resistance RT between the flowtube <NUM> and the electrode <NUM> is much lower than when there is no leak. The normal (e.g., when there is no leak) resistance RF between the flowtube <NUM> and the electrode <NUM> can be calculated based on the type of fluid flowing through the flow path <NUM> (e.g., the resistivity of the fluid) and the length L1 between the electrode head <NUM> and the end of the non-conductive liner <NUM>. Referring again to <FIG>, the short circuit detector <NUM> is configured to detect the presence of conductive fluid in the fluidic path <NUM>. An adjustable reference generator <NUM> supplies a reference resistance value Rref to the comparator <NUM>. Suitably, the reference resistance value Rref is set at a value slightly lower than the expected fluid resistance RF (e.g., between about <NUM>% and about <NUM>% of the expected fluid resistance RF) and higher than the expected total resistance RT in the event of a short circuit. The resistance between the flowtube <NUM> and the electrode <NUM> is measured, and the measured resistance Rmeas is supplied to another input of the comparator <NUM>. There are various ways the resistance can be measured. For example, a known amount of current can be driven between the flowtube <NUM> and the electrode <NUM> for a brief time and the induced voltage during this time can be used as a measure of the resistance and/or used to calculate the resistance. The resistance can be measured in other ways without departing from the scope of the invention. The comparator <NUM> receives the measured resistance and compares it with the reference value Rref. If the measured resistance Rmeas is less than the reference value Rref, the short circuit detector <NUM> is configured to output an alarm. For example, it may output a signal that causes a local display to indicate the detection of a leak. Likewise, it may output a signal that is transmitted to a distributed control system.

Although only one electrode is illustrated in <FIG>, <FIG>, and <FIG>, it is understood that the flowmeter will generally have at least two electrodes on opposite sides of the flowtube. It is also understood that more than two electrodes can be included in the flowmeter, such as to provide empty pipe detection or to ground the fluid flowing through the meter.

Referring to <FIG>, another embodiment of an electromagnetic flowmeter configured to detect a fluid leak is generally indicated at reference number <NUM>. The electromagnetic flowmeter <NUM> includes a conductive flowtube <NUM> and a non-conductive inner liner <NUM> that insulates the flowtube from a conductive fluid flowing in a flow path <NUM> extending axially through the flowtube. First and second electrodes 215A, 215B extend through respective process penetrations <NUM> in the wall <NUM> of the flowtube <NUM> at diametrically opposed positions. A pair of drive coils (broadly, an electromagnetic field source; not shown) are located adjacent the outside of the flowtube <NUM> at diametrically opposed positions angularly spaced from the positions of the electrodes 215A, 215B about a longitudinal axis of the flowtube <NUM>. The drive coils generate an electromagnetic field in the conductive fluid flowing through the flowtube <NUM>, and the electrodes 215A, 215B detect a voltage induced in the fluid as the fluid flows through the electromagnetic field. Suitably, the drive coils generate an electromagnetic field that has an electromagnetic field direction, and the electrodes 215A, 215B detect respective voltages induced in the fluid at diametrically opposed positions oriented perpendicular to the electromagnetic field direction.

In the illustrated embodiment, an insulating sheath <NUM> separates the shank <NUM> of each of the first and second electrodes 215A, 215B from the flowtube wall <NUM>, and a non-conductive washer <NUM> provides electrical insulation between the flowtube wall <NUM> and the fastener <NUM> that secures each electrode to the flowtube wall. Thus, as in the previous embodiment, under normal operating conditions, each electrode 215A, 215B is electrically insulated from the flowtube wall <NUM> at the process penetration <NUM>. When fluid leaks past the seal formed between the head <NUM> of either electrode 215A, 215B and the inner liner <NUM>, it creates an electrical connection between the respective electrode and the flowtube wall <NUM> that is not present under normal operating conditions. Though the illustrated insulating sheath <NUM> provides a transverse hole <NUM> for creating a direct fluid path between the flowtube wall <NUM> and the respective electrode 215A, 215B, it will be understood that, even in the absence of such a sheath, leaking fluid can penetrate the seams between the insulating and conductive components to create an undesired electrical connection between the electrode and flowtube wall. A leak detection system <NUM> detects when a leak in the flowtube creates an undesired electrical connection between one of the first and second electrodes 215A, 215B and the inner liner <NUM>.

Referring to <FIG>, the drive coils are configured to generate an electromagnetic field <NUM> that changes periodically at a drive frequency f. The drive frequency can be constant or variable. In the illustrated embodiment, the electromagnetic field <NUM> is reversed at a constant drive frequency f. However, other changes in the electromagnetic field <NUM> can also be made periodically without departing from the scope of the invention. The first electrode 215A produces a first voltage signal 253A representative of an induced voltage in the fluid at the head <NUM> of the first electrode. Likewise, the second electrode 215B produces a second voltage signal 253B representative of an induced voltage in the fluid at the head <NUM> of the second electrode. Respective flow-induced portions of the first and second voltage signals 253A, 253B accurately represent the induced voltages and are related to the flow rate of the fluid in the flowtube <NUM>. However, respective noise portions of the voltage signals 253A, 253B are attributable to sources of noise (e.g., a DC potential between the first and second electrodes 215A, 215B) and detract from the accuracy of the voltage signals. One skilled in the art will appreciate that the flow rate of the fluid flowing through the flow path <NUM> is related to the difference between the flow-induced portions of the first and second voltage signals 253A, 253B under normal operating conditions.

Under normal operating conditions each of the first and second voltage signal 253A, 253B changes periodically with the periodic changes in electromagnetic field strength (i.e., at the drive frequency f). The flow-induced portion of the first voltage signal 253A is equal in magnitude and opposite in sign (i.e., <NUM>° out of phase) with respect to the flow-induced portion of the second voltage signal 253B under normal operating conditions. However, if the flowmeter <NUM> has a fluid leak, a short circuit can be created between either of the first and second electrodes 215A, 215B and the flowtube sidewall <NUM>. For example, when a fluid path forms between one the second electrode 215B and the flowtube wall <NUM>, the fluid path electrically connects the electrode and the flowtube wall <NUM>, creating a short circuit at the electrode. As a result, the second voltage signal 253B produced by the second electrode 215B is substantially constant (i.e., does not vary significantly in response to variations in the electromagnetic field induced in the fluid by periodic changes in the drive signal <NUM>), as illustrated in <FIG>.

Referring to <FIG> and <FIG>, the leak detection system <NUM> is operatively connected to the first and second electrodes 215A, 215B to receive the first and second voltage signals 253A, 253B produced by the electrodes. The leak detection system <NUM> is configured to analyze a content of the at least one of the voltage signals 253A, 253B at the drive frequency f to determine whether the signal is affected by a leak. For example, the leak detection system <NUM> can use the drive frequency content of one or both of the signals 253A, 253B to determine whether either or both of the signals vary periodically at the drive frequency f or whether the amount of variation in either of the signals at the drive frequency is suppressed below a normal (i.e., significant) amount of variation. When the leak detection system <NUM> determines that one or more of the signals produced by the electrodes <NUM> are affected by a leak in the flowmeter, it provides an output indicative of a detected leak.

The leak detection system <NUM> illustrated in <FIG> includes a summing amplifier <NUM> operatively connected to the first and second electrodes 215A, 215B to receive the first and second voltage signals 253A, 253B. The summing amplifier <NUM> is configured to add the voltage signals 253A, 253B to generate a summation signal. As discussed in further detail below, the leak detection system <NUM> analyzes a content of the summation signal at the drive frequency to determine whether either of the first and second voltage signals 253A, 253B is affected by a leak. A primary source of noise in the summation signal is caused by an inherent DC potential between the first and second electrodes 215A, 215B. The DC potential can be a differential mode potential, a common mode potential, or combination differential and common mode potential. Under normal operating conditions, the flow-induced portion of the first voltage signal 253A is equal in magnitude and opposite in sign (i.e., <NUM>° out of phase) with respect to the second voltage signal 253B. Thus when no noise is present, the output of the summing amplifier <NUM> should be a substantially constant zero signal. However, the inherent DC potential and other noise can cause the sum of the first and second electrode signals 253A, 253B under normal operating conditions to be non-zero. To mitigate the effects of the DC potential between the two electrodes, a high pass filter <NUM> with a cutoff frequency set lower than the drive frequency receives the output of the summing amplifier <NUM>. The high pass filter <NUM> suppresses at least a portion of the summation signal attributable to the DC potential between the first and second electrodes 215A, 215B.

With further reference to <FIG> and <FIG>, under normal operating conditions the high pass filter <NUM> outputs a filtered summation signal <NUM> that is substantially constant and substantially close to zero. However, when, for example, fluid leaks through the seal formed between the head <NUM> of the second electrode 215B and the liner <NUM>, a short circuit is created. As illustrated in <FIG>, when a short circuit is formed between the second electrode 215B and the flowtube wall <NUM>, the second voltage signal 253B becomes substantially constant. As a result, the second voltage signal 253B is not equal in magnitude and opposite in sign with respect to the first voltage signal 253A, and the summation signal <NUM> becomes periodic in nature. Accordingly, the leak detection system <NUM> can determine whether either of the first and second voltage signals 253A, 253B is affected by a leak in the flowmeter <NUM> by detecting the presence of significant periodic changes in the summation signal <NUM>.

The leak detection system <NUM> in <FIG> includes an analog-to-digital converter <NUM> that samples the summation signal <NUM> and generates a digital output signal (i.e., a digital summation signal) representative of the summation signal. A digital leak detection processor <NUM> receives the digital summation signal and analyzes a content of the summation signal <NUM> at the drive frequency f to determine whether either of the voltage signals 253A, 253B is affected by a leak in the flowmeter. Though the high pass filter <NUM> can eliminate some of the DC offset from the output of the summing amplifier <NUM> (including both common and differential DC offset), a portion of the summation signal <NUM> can still be attributable to the DC potential between the first and second electrodes 215A, 215B. Moreover, the energy content of the summation signal <NUM> still includes frequencies above the cutoff frequency of the high pass filter <NUM>.

To minimize the effect of this noise on the leak determination, the leak detection processor <NUM> performs a Fourier analysis (e.g., a digital Fourier transform) on the summation signal <NUM> to analyze the energy content of the summation signal <NUM> at the drive frequency f. In a suitable embodiment, the leak detection processor <NUM> uses a Fourier transform to calculate a spectral number F(bin) for the summation signal <NUM> at the drive frequency f and converts the spectral number into an amplitude Vf of the summation signal at the drive frequency (i.e., a representation of the energy of the summation signal at the drive frequency). Under normal operating conditions, the drive frequency amplitude Vf should be close to zero. When the leak detection processor determines the amplitude Vf has strayed too far from zero (e.g., by comparing the amplitude to a threshold), it determines that one of the first and second voltage signals 253A, 253B is affected by a leak in the flowmeter <NUM> and provides an output indicative of a detected leak.

Referring to <FIG>, in one method <NUM> of detecting a leak in the flowmeter <NUM>, the analog-to-digital converter <NUM> samples the summation signal <NUM> (step <NUM>) during a sampling interval corresponding in time with one or more complete cycles of the drive signal <NUM> (i.e., an integral number of drive cycles). At step <NUM> the leak detection processor <NUM> stores N samples of the summation signal <NUM> taken during the sampling interval in a buffer. Thus, the buffer stores a digital representation of the summation signal <NUM> over one or more complete drive cycles. For example, in one embodiment, the drive frequency f is a constant low frequency (e.g., <NUM>) and the analog-to-digital converter <NUM> samples the summation signal <NUM> at a high frequency (e.g., <NUM>). The buffer preferably stores a large number of samples (e.g., <NUM> samples), which represents several complete drive cycles (e.g., <NUM> drive cycles).

At step <NUM>, the leak detection processor <NUM> uses Fourier analysis (e.g., the discrete Fourier transform) and the N samples stored in the buffer to calculate a spectral number F(bin) for the summation signal <NUM> at the drive frequency f. For example, the leak detection processor <NUM> can use the discrete Fourier transform to calculate a frequency spectrum for the summation signal <NUM> and determine the spectral number F(bin) from the frequency spectrum, where bin corresponds with the spectral array index for the drive frequency f. The bin index for the drive frequency f can, in a suitable embodiment, be calculated by dividing the sampling frequency by the number of samples N, plus <NUM>. As an alternative to calculating a frequency spectrum, the leak detection processor <NUM> can use Fourier analysis to calculate the drive frequency spectral number F(bin) directly using techniques such as cross-correlation or autocorrelation. At step <NUM> the leak detection processor <NUM> determines the amplitude Vf of the summation signal <NUM> at the drive frequency f using equation <NUM>. <MAT> The amplitude Vf is representative of the energy in the summation signal <NUM> at the drive frequency f. The number of samples N suitably corresponds with an integral number of drive cycles. If the number of samples N does not corresponds to an integral number of drive cycles, the drive frequency will fall between two points in the frequency domain. The calculation would be less accurate due to spectral leakage. However, a gross measurement can be sufficient to detect a leak. Thus, it is understood the number of samples N does not need to be limited to the number of samples in an integral number of drive cycles to practice the invention.

At step <NUM> the leak detection processor <NUM> receives a difference signal VΔ representative of magnitude of a difference between the first and second voltage signals 253A, 253B from a flow rate measurement system (not shown) of the flowmeter <NUM>. The leak detection processor <NUM> dynamically determines a threshold P as a percentage (e.g., from about <NUM> percent to about <NUM> percent) of the voltage difference VΔ at step <NUM>. At decision block <NUM>, the leak detection processor <NUM> compares the threshold P to the amplitude Vf of the summation signal <NUM> at the drive frequency f. If the amplitude Vf is greater than the threshold P, the leak detection processor <NUM> provides an indication that one of the first and second voltage signals 253A, 253B is affected by a leak in the flowmeter <NUM> (step <NUM>). If the amplitude Vf is not greater than the threshold P, the leak detection method <NUM> restarts at step <NUM>. Though the illustrated embodiment dynamically calculates the threshold P as a percentage of the voltage difference VΔ, it will be understood that other embodiments can compare the amplitude Vf of the summation signal <NUM> at the drive frequency f to a constant threshold to determine whether a leak in the flowmeter <NUM> affects either of the voltage signals 253A, 253B.

Referring to <FIG>, another embodiment of a leak detection system suitable for use with the flowmeter <NUM> is generally indicated at reference number <NUM>. The leak detection system <NUM> includes a multiplexer <NUM> that is operatively connected to the first and second electrodes 215A, 215B to receive the first and second voltage signals 253A, 253B from the electrodes. The multiplexer <NUM> is configured to generate a multiplexed signal, which includes alternating sequences of the voltage signals 253A, 253B spliced together serially in the time domain. A high pass filter <NUM> receives the multiplexed signal from the multiplexer <NUM> and suppresses a portion of the multiplexed signal attributable to a DC potential between each of the first and second electrodes 215A, 215B and ground. An analog-to-digital converter <NUM> samples the output of the high pass filter <NUM> and generates a digital output representative of the filtered multiplexed signal. As discussed in further detail below, a leak detection processor <NUM> receives the digital filtered multiplexed signal and uses it to analyze a content of the first voltage signal 253A at the drive frequency f and a content of the second voltage signal 253B at the drive frequency. The leak detection processor <NUM> compares the drive frequency contents of the first and second voltage signals 253A, 253B to determine whether either of the first and second voltage signals is affected by a leak. Though the illustrated leak detection processor <NUM> receives the first and second voltage signals 253A, 253B from a single input using a multiplexed signal, it is also contemplated that another leak detection processor could perform a similar processor by receiving the first and second voltage signals on two separate inputs.

Referring to <FIG>, in one method <NUM> of detecting a leak in the flowmeter <NUM> using the leak detection system <NUM>, the analog-to-digital converter <NUM> samples the digital multiplexed signal during first and second sampling intervals (steps <NUM>, <NUM>). Suitably, the samples from the first sampling interval define a first sample set representing the first voltage signal 253A and corresponding in time with one or more complete drive cycles (step <NUM>). Likewise the samples from the second sampling interval suitably define a second sample set representing the second voltage signal 253B and corresponding in time with one or more complete drive cycles (step <NUM>). The leak detection processor <NUM> stores NA samples from the first sample set in a first buffer (step <NUM>), which collectively form a digital representation of the first voltage signal 253A during the first sampling interval. The leak detection processor <NUM> likewise stores NB samples from the second sample set in a second buffer (step <NUM>), which collectively form a digital representation of the second voltage signal 253B during the second sampling interval.

To minimize the effect of noise on the leak determination, the leak detection processor <NUM> uses Fourier analysis to calculate a frequency spectrum for each of the first and second voltage signals 253A, 253B from the first and second sample sets stored in the first and second buffers (steps <NUM>, <NUM>). Additionally or in the alternative, the leak detection processor <NUM> calculates a spectral number F(bin)A, F(bin)B for each of the first and second voltage signals 253A, 253B from the stored first and second sample sets. Using equation <NUM> and the spectral numbers F(bin)A and F(bin)B, the leak detection processor <NUM> calculates respective amplitudes Vf,A, Vf,B of the first and second voltage signals 253A, 253B at the drive frequency f(steps <NUM>, <NUM>).

As discussed above, under normal operating conditions, the flow-induced portions of the first and second voltage signals 253A, 253B will be substantially equal in magnitude. Thus, one skilled in the art will appreciate that the amplitudes Vf,A, Vf,B of the first and second voltage signals 253A, 253B, which represent the amount of energy in the respective signals at the drive frequency f, will be substantially equal under normal operating conditions. However, when a leak creates a short circuit at, for example, the electrode 215B as shown in <FIG>, the amplitude Vf,B of the voltage signal 253B at the drive frequency f will be significantly lower than the amplitude value Vf,A of the voltage signal 253A at the drive frequency. Thus, at step <NUM>, the leak detection processor <NUM> compares the amplitude Vf,A of the first voltage signal 253A to the amplitude Vf,B of the second voltage signal 253B. If the leak detection processor <NUM> determines that the amplitude Vf,A of the first voltage signal 253A is significantly different than the amplitude Vf,B of the second voltage signal 253B, it provides an indication of a detected leak at step <NUM>. If the leak detection processor <NUM> determines the amplitudes Vf,A, Vf,B of the first and second voltage signals 253A, 253B are substantially equal, it returns to steps <NUM> and <NUM> at step <NUM>. In one or more embodiments, the leak detection processor <NUM> compares the amplitude Vf,A of the first voltage signal 253A to the amplitude Vf,B of the second voltage signal 253B by calculating a difference between the first and second voltage signals and comparing the calculated difference to a threshold (e.g., a constant threshold or a variable threshold determined dynamically, for example, as a percentage of either of the amplitudes Vf,A, Vf,B). When the leak detection processor <NUM> determines the difference between the amplitudes Vf,A, Vf,B of the first and second voltage signals 253A, 253B exceed the threshold, it provides an output indicative of a detected leak.

The leak detection systems <NUM>, <NUM> and the methods <NUM>, <NUM> for detecting a leak in a flowmeter <NUM> advantageously eliminate the effects of the DC potential between the first and second electrodes 215A, 215B and other sources of noise by using Fourier analysis to isolate the content of the voltage signals 253A, 253B at the drive frequency f from portions of the signal. The amplitude(s) of the voltage signals 253A, 253B at the drive frequency f represent the flow-induced portion of the voltage signals and suppress other portions of the voltage signals. Thus, only those portions of the voltage signals 253A, 253B that accurately reflect whether the voltage signals properly vary with periodic changes in the electromagnetic field are used to determine whether a leak affects either of the voltage signals. It is believed that isolating the flow-induced portions of the voltage-signals 253A, 253B from other portions of the signals inhibits noise, such as DC potentials inherent in the voltage signals, from significantly influencing the leak determination results. In addition, the construction of the insulating sleeves <NUM>, <NUM> creates a direct fluid path between the electrodes <NUM>, 215A, 215B and the respective flowtube walls <NUM>, <NUM>, which creates an intentional short circuit when a leak is present that is readily detectable using the leak detection systems <NUM>, <NUM>, <NUM>.

Having described the invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.

Claim 1:
Electromagnetic flowmeter (<NUM>) comprising:
a flowtube (<NUM>) configured to carry a flowing conductive fluid, the flowtube (<NUM>) having a flowtube wall (<NUM>) comprising a conductive material, the flowtube wall (<NUM>) having an inner surface surrounding a fluid flow path (<NUM>) for the conductive fluid;
a non-conductive liner (<NUM>) positioned to electrically insulate the flowtube wall (<NUM>) from the conductive fluid, the flowtube (<NUM>) and non-conductive liner (<NUM>) defining an electrode mounting hole (<NUM>);
an electrode (<NUM>) extending through the electrode mounting hole (<NUM>), the electrode (<NUM>) and the non-conductive liner (<NUM>) forming a fluidic seal between the electrode mounting hole (<NUM>) and the fluid flow path (<NUM>),
a non-conductive spacer (<NUM>) disposed around at least a portion of the electrode (<NUM>) in the electrode mounting hole (<NUM>) between the electrode (<NUM>) and the flowtube wall (<NUM>), wherein the non-conductive spacer (<NUM>) comprises a cylindrically-shaped sleeve,
wherein at least a portion of the electrode (<NUM>) is arranged in fluid communication with the flowtube (<NUM>) within the electrode mounting hole (<NUM>),
characterised in that
the non-conductive spacer (<NUM>) has at least one fluidic path (<NUM>) extending between the electrode (<NUM>) and the flowtube wall (<NUM>) so the conductive fluid can establish an electrical connection between the electrode (<NUM>) and the flowtube wall (<NUM>) in the event the conductive fluid leaks into the fluidic path (<NUM>),
wherein the fluidic path (<NUM>) is a transverse hole in the cylindrically-shaped sleeve.