Patent Description:
There are many applications that require measurement of the quantity of oil and/or the identification of oil or other contaminants present in a liquid. For example, in pipes leading from oil production or refining facilities or the like it may be required to measure the amount of oil and/or the identity of oil present in the liquid (mainly water) flowing in the pipes. Oil in water analysers or probes are used for this purpose, either in side stream passages or as insertion probes. Oil has a natural fluorescence. Therefore oil in water analysers typically measure the quantity of oil present in water by the detection of fluorescence. Devices that detect and/or measure fluorescence are commonly referred to as fluorometers. A fluorometer usually includes a light source for causing fluorescence in a target substance and a detector for measuring the resultant fluorescence.

A typical oil in water analyser has a measurement window located at a distal end of an elongate probe body through which the excitation light source is transmitted into the measurement region and through which the resultant fluorescent and/or reflected light is received to be analysed in order to determine the quantity and/or identify of oil and/or other contaminants present. Fouling of the measurement window by oil and other substances will occur without means for cleaning the measurement window. This problem may be addressed by using an ultrasonic transducer, typically located an inner end of the probe body, opposite said distal end, whereby the measurement window can be cleaned by ultrasonic cavitation created by the ultrasonic energy transmitted to the measurement window from the ultrasonic transducer through the probe body.

A known optical probe of an oil in water analyser, as illustrated in <FIG>, comprises an elongate hollow probe shaft <NUM> (known as a sonitrode) having a sapphire window <NUM> (defining the measurement window) at a distal end thereof. An ultrasonic transducer <NUM> having ceramic transducer discs is mounted on an opposite end of the probe shaft <NUM> for transmitting ultrasonic energy <NUM> to the window <NUM> via the probe shaft <NUM>.

Optical fibres and electrical leads are typically passed through a central channel <NUM> of the hollow probe shaft <NUM>, typically via an entry slot cut through side of the probe shaft or through a hollow bolt securing a back mass of the ultrasonic transducer <NUM> to the transducer discs.

The central channel <NUM> through the hollowed probe in itself introduces large inefficiencies in the transmission of ultrasonic energy. The probe is typically provided with a mounting flange <NUM> welded to the outer periphery of the probe shaft <NUM> adjacent a rear end of the probe shaft <NUM>. On a conventional ultrasonic probe the position of the ultrasonic transducer <NUM> at the rear of the probe, transmitting ultrasonic waves down the full length of the probe shaft <NUM>, applies physical stress directly to the mounting flange welds. This can result in fracture of the welded joint. To try and mitigate this problem the mounting flange may be positioned at a low ultrasonic energy point. However, the flange position is primarily dictated by the probe penetration depth. If the mounting flange is not positioned at a low energy point on the body of the probe, it will not only cause stress to the flange weld, it may greatly impact the efficient transmission of ultrasonic energy to the front of the probe and the optical window. The loss of transmission energy in this arrangement limits the effective cleaning capability to applications where the medium pressure is low, typically less than 10Bar.

<CIT> and <CIT> disclose an endoscope for use in the human body and <CIT> discloses an optical measuring device for measuring turbidity in waste water.

According to the present invention there is provided an optical probe for use in a high pressure medium comprising an elongate hollow probe body, an optical window mounted at a distal end of said probe body for transmitting light therethrough, an ultrasonic transducer mounted within said probe body for applying ultrasonic vibrations to said optical window for cleaning said optical window, and one or more light guides located within said probe body for transmitting light through said optical window to a measurement region and/or for receiving light transmitted through said optical window from said measurement region, wherein said ultrasonic transducer is located within said distal end of the probe body adjacent said optical window to transmit ultrasonic vibrations directly from said ultrasonic transducer to said window, wherein said ultrasonic transducer is located within the probe body via a mounting flange extending between the body of the ultrasonic transducer and an inner wall of the probe body, said mounting flange being located at a zero point of the ultrasonic transducer. The optical window may be mounted on a distal end of said ultrasonic transducer within an opening in said distal end of said probe body. A resilient seal may be provided between said optical window and said opening in the distal end of the probe body.

Preferably said one or more light guides are provided within said probe body to cooperate with the optical window, said one or more light guides extending between said ultrasonic transducer and an inner wall of said probe body. The one or more light guides may extend through said mounting flange.

Said ultrasonic transducer may comprise one or more ceramic transducer elements and a reaction mass mounted against said one or more ceramic transducer elements at a rear end of the transducer, and a transducer shaft extending between said one or more ceramic transducer elements and said optical window. The transducer elements and reaction mass may be secured to the transducer shaft by means of a fastener passing therethrough. A distal end of said transducer shaft preferably has a diameter less than the diameter of said optical window such that said transducer shaft cooperates with a central region of said optical window to transmit ultrasonic vibrations thereto. Said one or more light guides preferably cooperate with a peripheral region of said optical window outside of said central region of said optical window.

The transducer shaft of the ultrasonic transducer preferably comprises a solid shaft whereby ultrasonic energy is transmitted therethrough with minimum energy loss.

Said one or more light guides may comprise one or more optical fibres.

An embodiment of the present invention will now be illustrated, by way of example, with reference to the accompanying drawing, in which:-.

As illustrated in <FIG> and <FIG>, an optical probe in accordance with an embodiment of the present invention comprises a measurement window <NUM>, defining a distal end of an insertion probe, said measurement window being mounted in an opening <NUM> in a distal end of a hollow elongate probe body <NUM>. A resilient seal <NUM> is provided in said opening in the probe body <NUM> around the periphery of the measurement window <NUM>.

As best shown in <FIG>, an ultrasonic transducer <NUM> is provided within the hollow probe body <NUM> adjacent the measurement window <NUM> for transmitting ultrasonic energy <NUM> to the measurement window <NUM> in order to clean the window <NUM>. The ultrasonic transducer <NUM> may comprise one or more ceramic transducer discs <NUM> located between a back mass <NUM> and a transducer shaft <NUM>. A bolt <NUM> preferably passes through the rear of the back mass <NUM> and through the ceramic transducer discs <NUM> into the rear end of the transducer shaft <NUM> to secure the ceramic discs <NUM> and back mass <NUM> to the transducer shaft <NUM>.

A distal end of the transducer shaft <NUM> of the ultrasonic transducer <NUM> is mechanically coupled to the measurement window <NUM> to directly transit ultrasonic energy from the transducer shaft <NUM> to the measurement window <NUM>. As such, the measurement window <NUM> receives ultrasonic energy directly from the transducer <NUM> without the losses inherent in prior art arrangements wherein a hollow probe body <NUM> is disposed between the ultrasonic transducer <NUM> and the measurement window <NUM>. Furthermore, the location of the measurement window <NUM> within the opening <NUM> in a distal end of the probe body <NUM>, without direct mechanical coupling between the probe body <NUM> and the measurement window <NUM> further avoids the losses of ultrasonic energy inherent in prior art arrangements wherein the measurement window is mechanically coupled to the probe body <NUM>. The resilient seal <NUM> seals the distal end of the probe body <NUM> while mechanically isolating the measurement window <NUM> from the probe body <NUM>.

Light guides <NUM> (only one shown in <FIG>), preferably in the form of optical fibres, extend alongside the transducer shaft <NUM>, distal ends of light guides <NUM> being mounted in an intermediate plate <NUM>, secured between the transducer shaft <NUM> and measurement window <NUM>, whereby the light guides <NUM> are located adjacent and alongside a distal end of the transducer shaft <NUM> to transmit and received light through the measurement window <NUM>.

The measurement window <NUM> is secured to the intermediate plate <NUM> via a cap <NUM> extending over the measurement window <NUM> and having an opening for the passage of light into and out of the window <NUM>, the seal acting between the opening <NUM> in the distal end of the probe body <NUM> and the outer sides of the cap <NUM>.

The solid cylindrical transducer shaft <NUM> extending between the ceramic transducer discs <NUM> and the measurement window <NUM> and the location of the ultrasonic transducer <NUM> within the front end of the probe body <NUM> directly adjacent and in contact with the measurement window <NUM> minimises any loss of energy between the two and therefore greatly reduces the energy consumption of the ultrasonic transducer <NUM> required for the creation of cavitation and efficient cleaning of the measurement window <NUM>.

Furthermore, the location of the light guides <NUM> to the side of the transducer shaft <NUM>, and therefore to a side region of the window <NUM> advantageously increases the useful life of the measurement window <NUM>. This is because ultrasonic energy from the ultrasonic transducer <NUM> is highest in a central region of the measurement window <NUM> (i.e. along the central axis of the transducer shaft <NUM>), reducing towards the outer edges of the window <NUM>. Therefore cavitation is greatest in this central region, leading to erosion and etching of this central region of the window <NUM>.

The transducer shaft <NUM> of the ultrasonic transducer <NUM> is located within the hollow probe body <NUM> by means of a transducer mounting flange <NUM> affixed (for example by welds) to the transducer shaft <NUM> and extending between the transducer shaft <NUM> of the ultrasonic transducer <NUM> and the probe body <NUM>. As shown in <FIG>, the probe body <NUM> comprises a distal portion <NUM> having said opening <NUM> at a distal end thereof within which the measurement window <NUM> is located, the mounting flange <NUM> of the ultrasonic transducer abutting a stepped seat <NUM> within the distal portion <NUM> of the probe body <NUM>, the remainder of the probe body <NUM> comprising a tubular portion <NUM> having a distal end inserted within the distal end of the distal portion <NUM> and engaging the mounting flange <NUM> of the ultrasonic transducer <NUM> to secure the ultrasonic transducer <NUM> (and the window <NUM>) within the probe body <NUM>. The distal end of the tubular portion <NUM> of the probe body <NUM> may be threadedly engaged within the distal portion <NUM> of the probe body <NUM>.

The transducer mounting flange <NUM> is located at a zero point of the ultrasonic transducer <NUM> (i.e. minimum point of ultrasonic energy) such that the probe body <NUM> is isolated from the ultrasonic vibrations generated by the ultrasonic transducer <NUM>, preventing ultrasonic energy from being absorbed by the probe body <NUM>.

The isolation of the probe body <NUM> from the ultrasonic transducer <NUM> and the direct coupling between the ultrasonic transducer <NUM> and the measurement window <NUM> avoids the losses in ultrasonic energy inherent in prior art optical probes. Furthermore, it allows the length of the probe body <NUM> and the position of a probe mounting flange <NUM> (see <FIG>) on the probe body <NUM> to be readily varied without requiring calibration of the position of the mounting flange <NUM> and length of the probe body <NUM>, unlike prior art examples wherein the mounting flange location needs to be aligned with a zero point of the ultrasonic vibrations to try and avoid losses of ultrasonic energy and fracture of the mounting flange welds.

Because the ultrasonic transducer <NUM> is located at the front end of the probe body <NUM>, isolating the ultrasonic waves from the probe body, the prior art problem of stressing of welds along the probe body, particularly at the mounting flange <NUM>, is avoided and the location of a mounting flange on the probe body (see <FIG>) is not critical. In turn, vast improvement in transmission efficiency is achieved, reducing the power required (by as much as <NUM>%) to achieve the desired effect of cleaning the optical window and allowing effective cleaning of the window in high pressure mediums (for example in excess of 80Bar. Furthermore, because the probe body <NUM> does not have to transmit ultrasonic energy it can be made of lighter construction, allowing a significant reduction in the overall weight of the probe, further reducing stress on the welds of the mounting flange.

Claim 1:
An optical probe for use in a high pressure medium comprising an elongate hollow probe body, an optical window (<NUM>) mounted at a distal end of said probe body (<NUM>) for transmitting light therethrough, an ultrasonic transducer (<NUM>) mounted within said probe body (<NUM>) for applying ultrasonic vibrations to said optical window (<NUM>) for cleaning said optical window (<NUM>), and one or more light guides (<NUM>) located within said probe body (<NUM>) for transmitting light through said optical window (<NUM>) to a measurement region and/or for receiving light transmitted through said optical window (<NUM>) from said measurement region, wherein said ultrasonic transducer (<NUM>) is located within said distal end of the probe body (<NUM>) adjacent said optical window (<NUM>) to transmit ultrasonic vibrations directly from said ultrasonic transducer (<NUM>) to said optical window (<NUM>)characterised in that said ultrasonic transducer (<NUM>) is located within the probe body (<NUM>) via a mounting flange (<NUM>) extending between a body of the ultrasonic transducer (<NUM>) and an inner wall of the probe body (<NUM>), said mounting flange (<NUM>) being located at a zero point of the ultrasonic transducer.