WO2010078555A2

WO2010078555A2 - Capacitive and resistive conductivity engine oil analyzer

Info

Publication number: WO2010078555A2
Application number: PCT/US2010/020050
Authority: WO
Inventors: Charles S. Miller
Original assignee: Waveon Technologies, Inc.
Priority date: 2009-01-02
Filing date: 2010-01-04
Publication date: 2010-07-08
Also published as: WO2010078555A3

Abstract

A device is disclosed for detecting the degradation of or the presence of contaminants in materials of interest, particularly engine oil. The invention includes a sensor for sensing the dielectric value (or permittivity) and resistive conductivity of the material under test by applying a changing electric field to the material and sensing the resulting signal having a time signal proportional to the dielectric and resistive value of the fluid. This invention also includes a signal processing circuit, responsive to the sensing signal, for converting the signal received to a steady state analog voltage which voltage can be compared to known values representing the state of the material being analyzed.

Description

CAPACITIVE AND RESISTIVE CONDUCTIVITY ENGINE OIL ANALYZER

CROSS-REFERENCED TO RELATED APPLICATIONS

This application claims the benefit of, and incorporates in by reference in their entirety, US Provisional Applications Serial No. 61/203,990, filed January 2, 2009 and Serial No. 61/277,062 filed September 21, 2009.

BACKGROUND OF THE INVENTION

1. FIELD OF INVENTION

This invention relates to a device for determining the quality of a material of interest and more particularly to a device for sensing the measuring the dielectric or permittivity characteristics of a material of interest, particularly engine oil, to determine the quality of the material under test.

2. PRIOR ART

The measurement of engine oil quality is an important method of determining the health of the oil as a lubricant, as well as the health of a vehicle's engine system. It is well known in the engine oil testing industry that the use of spectroscopy analysis or capacitive (dielectric or permittivity) analysis of engine oils are reliable methods of determining the health of the oil as a lubricant. These methods determine the acidity level of the oil as well as the level of particulates or non-oil based fluids in the oil that degrade the performance of an engine. Engine oils are in the low dielectric constant range and will differ in value based on oil type and use over pressure, temperature, viscosity and moisture absorption. A typical dielectric constant range for regular and synthetic engine oil will be between two and six (2 and 6) at room temperature. As oil degrades, the dielectric value of the oil will increase. Measurement of this change in dielectric value is useable and determines the degradation level of the oil. Oil degradation is caused by an increase in acidity level, and is typically measured by a TBN (Total Base Number) or TAN (Total Acid Number). At a molecular level, oil molecules break down over time due to high temperatures, pressure, viscosity (frictional break down) and moisture absorption. Allowing the oil to degrade past a certain acidity level is detrimental to the health and performance of the engine because the oil is not longer capable of carrying out its lubricating function. Over time, engine wear sets in and results in a shorter engine life, excess engine oil burning, excess gasoline or diesel usage and significant devaluation of the vehicle. Ohmic (resistive) sensing of engine oil is another indicator of oil quality and in some systems makes up approximately five per cent (5%) of a combination capacitive and resistive test.

Industrial capacitive oil analyzers are used in specific applications such as military vehicle maintenance, transformer oil testing and automotive engine maintenance. However, the cost of the technology in its current state is considered prohibitive for consumer level products. The most common method capacitive sensing method for detecting the TAN (Total Acid Number) or TBN (Total Base Number) of an oil is to use a broad band sine wave modulated voltage signal. The phase difference for the permittivity test of oil relates to a mathematical Tangent (Tan) function of the current verses time difference between the original and the resultant signal between the original oil and the oil under test.

This technology requires digital signal processing of medium level or higher processing power with concomitant cost in addition to the need to use exotic substrate materials for low front end load capacitance. Many capacitive oil sensors do not utilize resistive (conductivity) measurements in combination with a capacitive sensor method.

A circuit design that attempts to accomplish the desired operating parameters of a reliable capacitive-resistive sensing device is US Patent No. 6583631 by Kyong. The invention disclosed by Kyong uses capacitive sensing means to detect oil dielectric in an internal combustion engine in situ. In a preferred embodiment, the invention uses a coplanar ceramic substrate with dual conductors that are interleaved but spaced independent of each conductor, with the electronic circuitry coplanar to the conductors, arranged at the opposite end of the substrate. In addition to the conductive sensors and the electronics substrate, a large volume housing is required to allow access of large amounts of oil to the conductors while isolating the electronics.

The Kyong invention is also designed to be inserted into the oil under test and as a result is subject to high temperatures and a harsh operating environment. The Kyong invention does not use a resistive conductivity sensing of the oil for additional qualitative results. In addition, the Kyong invention references US Patent No. 4,398,426 which uses dual square waves (one reference, the second phase shifted) as a method of detecting the dielectric difference of the oil. It is evident in the design that additional circuitry and cost is required to stabilize the reference signal to adjust for temperature changes. US Patent 6028433 by Cheiky-Zelina and Bush describes an invention using a capacitive sensing means to detect oil dielectric externally of an automobile engine. This invention uses a multi frequency sweeping sine wave to detect the Tan Delta of the oil under test. The invention uses the Tan Delta as a method of measuring impedance of the oil under test. Although it is a reliable method, it is by no means the only successful method allowing for both capacitive sensing and resistive. The method of using a multi- frequency sweeping sine wave for Tan Delta measurements requires expensive microcontroller components and front end sensing materials.

Therefore, the capacitive proximity sensors described above suffer from one or more of the following disadvantages:

(a) the need for a reference and relaxation oscillator circuit (needed to deal with parasitic oscillation);

(b) poor sensitivity of the active signal (relaxation oscillator) with single frequency designs; (c) inability to incorporate the resistive sensing component with the capacitive sensing component;

(d) required to be used internally in a combustion engine;

(e) requiring large samples of oil for testing;

(f) requiring broadband frequency sweeps to gather signal information for data processing;

(g) requiring substantial microcontroller or processing analysis and additional coding. In view of the foregoing, there is a need for a device or system for analyzing the quality of oil that avoids these disadvantages.

SUMMARY OF THE INVENTION

The present invention seeks to address the limits of the prior art and address the need for a low cost, easy to use, portable device that can lower consumer maintenance costs for vehicles, manage natural resources voluntarily and reduce un-recycled oil waste that finds its way into our ecosystem. It is then, an object of this invention to overcome the above-mentioned drawbacks and provide a capacitive-resistive oil sensor to be used to detect the quality of a material of interest, particularly engine oil, over use and time. The present invention is such an apparatus for detecting the aspect of a fluid, particularly oil.

In one embodiment of the invention, a device is disclosed for detecting the degradation of or the presence of contaminants in engine oil. In this embodiment, the invention includes a sensor for sensing the dielectric value (or permittivity) and resistive conductivity of the material under test by applying a changing electric field to the material and sensing the resulting signal having a time signal proportional to the dielectric and resistive value of the fluid. This invention also includes a signal processing circuit, responsive to the sensing signal, for converting the signal received to a steady state analog voltage which voltage can be compared to known values representing the state of the fluid being analyzed. In embodiments of the invention, the sensing electrodes are arranged longitudinally parallel to each other and coupled to the material under test.

In the invention, the results of the capacitive - resistive oil test aligns with the industry oil tests in common use today. A result based on the TBN (Total Base Number) of an oil sample is obtained by the present invention much more cost effectively than by the more costly means of spectroscopy and other methods currently used in the industry. The present invention senses the TBN of a fluid sample by use of a capacitive - resistive sensing method. The combination of sensing an oil sample based on its dielectric value plus resistive (conductivity) increases the probability of determining oil degradation as acidity in the oil increases, as well as the detection of foreign contaminants, and converts the results into a form understood by a user.

Another embodiment of the invention includes a sensor for sensing the dielectric value (permittivity) and resistive conductivity of a material under test through an object such as non-metallic pipe or tube, by use of a changing electric field versus time signal proportional to the dielectric value of the material. This invention includes a signal processing circuit, responsive to the sensing signal, for converting the signal received to a steady state analog voltage representative of the state of the fluid sample.

In a preferred embodiment of the present invention, the sensor has two sensing traces on a printed circuit board (PCB) and a repository for containing the engine oil under test. An oscillator circuit (exciter signal) is connected to a sensing antenna trace and has a square waveform, the frequency of which is fixed. The receiver sensing trace accepts the voltage induced through the oil, the voltage and time length of the signal is determined by the dielectric and resistive conductivity of the oil under test. The preferred embodiment of the invention also includes a signal processor circuit to convert the periodic voltage signal into a steady state analog voltage. The signal processing stage integrates a single stage amplifier, the resultant output is filtered and input into an Analog Digital Converter (ADC) and interpreted by use of a microcontroller. The results are displayed indicating the quality of the oil.

In the preferred embodiment, a changing electric field is generated by the sensing antenna trace and a receiving sensing trace is prepared to accept the resulting signal. As oil or other fluid of interest is positioned in the repository, the oil dielectrically couples the sensing traces resulting in a high band pass voltage filter signal. The dielectric of clean unused oil is significantly less than that of high-use old contaminated oil. The high band pass filtered voltage signal coupled to the receiving sensing trace increases as the oil under test becomes contaminated with acid build up, metal particles, water, alcohol based coolants, dirt, soot and carbon residue. The sensing voltage is changed into a steady state voltage by a filter, and applied to the ADC (analog digital circuit) of a microcontroller. The voltage is compared against a predetermined set of values and, in one embodiment, the output is applied to a set of LEDs or LCD (liquid crystal display) for visual determination of the quality of the oil. There are many objects of the present invention that may be addressed individually or in combinations and permutations in the various embodiments of the invention. Consequently, the embodiments of the invention address one or more of the following objectives: a) a reduction in the overall component part count; b) a reduction in the overall cost of the device; c) the use of a low voltage fixed frequency oscillator to generate an excitation electric field; d) the use of a receiving sensor that acts as a capacitive and resistive sensor; e) the use of a high band pass filter circuit responsive to the receiving sensing signal; f) the use of a single signal voltage reference signal; g) the use of a low impedance signal processing circuit to negate stray capacitance; h) the ability to operate at or below 50 KHz; i) the ability to resist high levels of electromagnetic radiation in close proximity to the sensor.

A primary object of the invention in one or more embodiments is to provide a sensing device to sense and measure the quality of automobile, marine and diesel engine oils.

Another object of the invention in one or more embodiments is to provide a sensing device with sensing electrodes in one plane, longitudinal and parallel to one another, for the purpose of non-contact material detection. Another object of the invention in one or more embodiments is to provide a sensing device with longitudinal electrodes arranged in three-dimensions including with a radius to conform to objects such as non-metallic pipes and tubes.

Another object of the invention in one or more embodiments is to provide a sensing device to sense and measure the quality of vegetable and animal based cooking oils.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described hereafter in detail with particular reference to the drawings. Throughout this description, like elements, in whatever embodiment described, refer to common elements, wherever referred to and referenced by the same reference number. The characteristics, attributes, functions, interrelations ascribed to a particular element in one location apply to that element when referred to by the same reference number in another location unless specifically stated otherwise. All Figures are drawn for ease of explanation of the basic teachings of the present invention only, the extensions of the Figures with respect to number, position, relationship, and dimensions of the parts to form the preferred embodiment will be explained or will be within the skill of the art after the following description has been read and understood. Further, the exact dimensions and dimensional proportions to conform to specific force, weight, strength and similar requirements will likewise be within the skill of the art after the following description has been read and understood.

FIG 1 is a schematic block diagram of an embodiment of this invention.

FIG 2 is an electronic circuit of the preferred embodiment of the invention showing the main elements of the invention in detail. FIG 3 is a frontal drawing of the preferred embodiment of the invention.

FIG 4 is an isometric drawing of the preferred embodiment of the invention.

FIG 5. is a schematic block diagram of one embodiment of the invention.

FIG 6 is an electronic circuit of one embodiment of the invention showing the main elements of the invention in detail. FIG 7a is a chart showing the output of the voltage signal after the high frequency band pass filter and first stage amplifier.

FIG 7b is a chart showing engine oil degradation over distance.

FIG 7c is a program flow chart for the microcontroller software code. FIG 7d is an isometric drawing of one embodiment of the invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The preferred invention, or capacitive - resistive oil analyzer device internal functions and electronics are shown in Figures 1 and 2 and are generally labeled 0. The capacitive - resistive oil analyzer 0 in the preferred embodiment shown in Figures 1 and 2, has high impedance resistive and capacitive - resistive load 1 (typically oil) under test, sensing antenna element 2, receiving sensor element 3, high band pass filter 4, single stage amplifier 5, signal filter 6, microcontroller 7, LEDs (Light Emitting Diodes) 12 and sensing area 100.

A capacitive - resistive load 1 such as oil electrically consists of a capacitive and resistive characteristic; the resulting combination of the values of these components indicates the quality of the capacitive - resistive load 1 (e.g., oil) under test when compared to known values of the unused or perfectly clean material of the capacitive - resistive load 1 (oil). It is well known in the field that oil becomes more acidic (by becoming less alkaline in its chemical composition) by its use as a lubricant and coolant in a combustion engine. The physical aspects that the oil is subjected to in that environment that influence the chemical composition change in oil are pressure, temperature, friction, and contaminants such as water in liquid or moisture form, soot, dirt, metal particulate and so forth. Historically, it has been known in the oil test industry to obtain what is known as a TBN (Total Base Number) by use of spectroscopy and other technical or chemical based methods. As oil changes its chemical composition due to use, the dielectric value (permittivity or effective capacitance) will increase proportional to the amount of acid molecules or other contaminants suspended in the oil. The capacitive - resistive oil analyzer 0 of the present invention uses this changed dielectric value to determine the quality of the capacitive - resistive load 1 which will typically be oil.

In many capacitive sensing applications, the techniques used to detect a capacitive load are based on a time base function. For example, a simple 555 timer LC. (Integrated Circuit) arrangement can be used to detect the capacitive load by replacing a fixed value capacitor to the trigger and threshold of the 555 timer with two capacitive sensor plate elements (which will act as a capacitor with various capacitive values) and impose a capacitive change detected by the two capacitive sensor plates by introducing an object within the sensing proximity of the sensor plates. The output frequency of the timer LC. will change proportionally to the amount of capacitive load change.

Many capacitive sensors used for oil analysis use this technique, but suffer from deficiencies mentioned above due primarily to their inherent low sensitivity to low dielectric materials. This inherent low sensitivity is due to their relying on a time based mathematical solution T (T au) = 1/ R (Resistor) * Cl (Capacitive load) + CI (Capacitive Internal) to determine the quality of the oil. Unfortunately, the internal parasitic capacitance of an LC. (Capacitive Internal) will often be in the order of 1 to 10 picofarads which will often be an order of magnitude larger in value than the fempto farad range dielectric values of the oils (Capacitive load).

Some oil quality detections systems use sine wave generators. These systems use the sine wave function as a series of frequency points. The tangential loss of the signal is measured for each frequency and a result is obtained determining the dielectric loss of the material under test. The sine wave form as a single frequency is not able to singularly interpret the phase shifted loss of signal (tangential loss described) because of the mathematical limitations of the wave form used. A single frequency, pure sine wave exhibits a less responsive signal proportional to the dielectric value of a material under test, because of the dV/dT (differential Voltage over differential Time) component of the wave form. However, integrating the tangential current loss over a range of sine wave frequencies emulates the mathematical approach of a square wave form, and the sine wave sensing method becomes more responsive to changes in dielectric changes in materials such as oil.

The preferred embodiment of the capacitive - resistive oil analyzer 0 invention uses an excitation voltage composed of a fixed (single) frequency square wave form, the preferred duty cycle being fifty percent (50%) imposed on a sensing antenna element 2. It is important to understand that a square wave form is mathematically composed of an infinite series of sine waves having frequencies from one to infinite, and can be represented in Fourier transform mathematics. The excitation square wave form (i.e., the oscillation signal provided to the sensing antenna element 2) produces an electric field that carries the sine wave characteristics described across the medium of the capacitive - resistive load 1 (e.g. oil). The capacitive - resistive load 1 can be interpreted in electrical terms as a capacitor in parallel with a resistor. However, the characteristics of the excitation wave form are interpreted separately between the capacitive and resistive components of the capacitive - resistive load 1. The resulting signal detected by the receiving sensor element 3 and passed to the high band pass filter 4 is the combination signal of the capacitive aspect and the resistive aspect of the same excitation signal.

When considering the dielectric aspect of the signal (i.e., the aspect of the signal related to the capacitive characteristics of the capacitive -resistive load 1), the square wave form transmitted across the capacitive - resistive load l(oil medium) is reduced to an analog voltage signal composed of an amplitude and time base, depending on the dielectric value of the capacitive - resistive load 1. So, the electronic signal circuit in series with the capacitive - resistive load 1 behaves as a high band pass filter. Simultaneously, the resistive aspect of the square wave signal is conducted across the capacitive - resistive load 1 so that the square wave form at the positive voltage cycle behaves as a Direct Current (DC) signal across the capacitive - resistive load 1 (oil medium) and is directly imposed at the base of an amplifier circuit 5. As mentioned, and as can be seen referring to Fig 2, the resulting signals are combined at the base of transistor 14 and amplified as a combination of both the DC and AC (alternating current) signal wave forms resulting from the capacitive and resistive aspects of the capacitive - resistive load 1.

FIG 1, a schematic block diagram of a preferred embodiment of the invention, shows a high impedance resistive and capacitive - resistive load 1, such as an oil sample, that couples a sensing antenna element 2 and a receiving element 3. The function of the sensing antenna element 2 is to produce a three dimensional electric field, the size of which is a function of the surface area of the sensing antenna element 2, the magnitude of the electric field potential and frequency being generated by oscillator 11 under control of the microcontroller 7. In a preferred embodiment, the sensor antenna element 2 is made of a conductive material such as Printed Circuit Board (PCB) copper but may be made of any conductive material including, but not limited to, silver, gold, aluminum and stainless steel. The function of sensing receiving element 3 is to couple to the electric field produced by the sensing antenna element 2 as modified by the capacitive - resistive load 1. The voltage produced at the sensing receiving element 3 is proportional to the resistive -capacitive value of the capacitive - resistive load 1 (e.g. oil) under test. The coupled voltage is band pass filtered through high band pass filter 4 and applied to a single stage high gain and frequency amplifier 5. The output of the amplifier 5 is filtered to a steady state voltage at filter 6. The purpose of filtering the amplified voltage by filter 6 is to provide a steady state voltage for an ADC (Analog Digital Circuit) of the microcontroller 7 to accept the instantaneous voltage reading and produce a digital output representing such instantaneous voltage reading.

In the preferred embodiment of the sensor antenna element 2 and receiving sensor element 3 shown in Figure 1 , the sensor antenna element 2 and receiving sensor element 3 is a simple two dimensional geometric shape, in this case, a circular pattern formed by the sensor antenna element 2 and receiving sensor element 3 being parallel. Although this configuration of the sensor antenna element 2 and receiving sensor element 3 has been found to be particularly useful in the design of the capacitive - resistive oil analyzer 0, other shapes and configurations of sensor elements 2 and 3 may be used including, but not limited to, geometrically simple and complex shapes of two or three dimensions such as two-dimensional ovals, rectangles and other geometric shapes with the sensor antenna element 2 and receiving sensor element 3 being parallel and also non-parallel as well as curving or bending the respective sensor elements 2 and 3 into three-dimensional configurations. The capacitive - resistive oil analyzer 0 also contains a sensing element 100 where the capacitive - resistive load 1 material of interest (e.g., oil) is placed so that the capacitive - resistive load 1 will be located between the sensor antenna element 2 and receiving sensor element 3 or in a position so that the material of the capacitive - resistive load 1 acts as a dielectric between the sensor antenna element 2 and receiving sensor element 3. In a preferred embodiment of the capacitive - resistive oil analyzer 0 shown in FIGS 3 and 4, the sensing element 100 is a cup-shaped depression located on the front of the capacitive - resistive oil analyzer 0. By gravity, the capacitive - resistive load 1 (oil) placed in the sensing element 100 by the user accumulates at the bottom of the sensing element 100. The sensor antenna element 2 and receiving sensor element 3 are wrapped around or formed in the walls of the sensing element 100 so that the capacitive - resistive load 1 material becomes the dielectric between and is thus coupled to the sensor antenna element 2 and receiving sensor element 3. Particularly in embodiments of the capacitive - resistive oil analyzer 0 where the capacitive - resistive oil analyzer 0 is reusable, having a cup-shaped sensing element 100 allows the user easy access to the sensing element 100 to easily add and remove the material of the capacitive - resistive load 1 (e.g., oil), as well as clean the sensing element 100, for each test.

Although the sensing element 100 has been described as preferably being cup- shaped, sensing element 100 may be any shape where the material of the capacitive - resistive load 1 is centrally located with the sensor antenna element 2 and receiving sensor element 3 surrounding this centrally located material either in two or three dimensions. For example, instead of the sensing element 100 being cup-shaped, the sensing element 100 could be cylindrical so that the material of the capacitive - resistive load 1 is placed on the inside of the cylinder and the sensor antenna element 2 and receiving sensor element 3 are formed around or in the walls of the cylinder. This cylinder could be modified to have any geometric cross-section and have a flat or curved base. Further, the capacitive - resistive oil analyzer 0 could have a sensing element 100 that is essentially flat so that the material of the capacitive - resistive load 1 is placed on the flat surface of the sensing element 100. In this variant, the sensor antenna element 2 and receiving sensor element 3 are formed in the material making up the flat surface.

As mentioned above, the capacitive - resistive oil analyzer 0 preferably contains a microcontroller 7. In a preferred embodiment of the microcontroller 7, the microcontroller 7 is a member of the Microchip family of programmable integrated circuits (LC. 's) and also preferably contains an ADC (Analog Digital Circuit). The function of the microcontroller 7 is to produce an RF signal that will be applied to the sensor antenna element 2, ultimately process and analyze the signal received by the receiving sensor element 3 and produce an output indicative of the determined quality of the oil being analyzed. Although use of a microcontroller is preferred, the present invention is not limited to the use of a particular type or brand of electronic components such as TTL (Transistor-Transistor Logic) or ASIC's (Application Specific Integrated Circuits). Instead, all types of electronic components capable of making a microcontroller, including but not limited to a microprocessor, can be used. Further, the function of the microcontroller 7 may be performed by discrete components so long as the functions of producing an RF signal that will be applied to the sensor antenna element 2, ultimately processing and analyzing the signal received by the receiving sensor element 3 and producing an output indicative of the determined quality of the oil being analyzed is performed.

The preferred embodiment of FIG 7b shows the combined impedance change of the oil as a capacitive - resistive load 1 over distance. It is an important feature of engine oils that they can have different impedance values, but are common to each oil family type in value as is between standard oil types and synthetic oil types. To facilitate the analysis of the correct type of oil, the capacitive - resistive oil analyzer 0 of the present invention, in one embodiment, uses a switch 8 to determine the oil type under test. FIG's 1 and 2 disclose an oil type selector switch 8. When in an open state, switch 8 sets code in the microcontroller 7 to accept standard oil values. When switch 8 is closed, it sets the code in the microcontroller 7 to accept synthetic oil values. Oil type switch 8 is preset by the user before normal operating functions are started. Of course, switch 8 may be an actual switch or a "virtual" switch that is software controlled and which may be changed in value through the graphical user interface of the microcontroller 7. In addition, more than two values can be set by the switch 8 to reflect many types of capacitive - resistive load l.

Although the preferred embodiment of the capacitive - resistive oil analyzer 0 uses a switch 8 that is manually set by the user to the type of oil that is to be analyzed as described above, in another embodiment of the capacitive - resistive oil analyzer 0, the capacitive - resistive oil analyzer 0 automatically determines the type of oil. In this embodiment, the air base value calibration step is replaced with a fresh (unused) oil sample, and the fresh oil is used to measure against the used oil value. In this embodiment, it is necessary to have the same oil type as the oil reference to ensure a quality measurement. However, a drawback of this embodiment is that this embodiment requires that an original oil sample to be available for calibration.

Power switch 9 activates the microcontroller 7. In a preferred embodiment of the capacitive - resistive oil analyzer 0, a preset switch for oil type 8 would already be in the correct position to indicate the type of capacitive - resistive load 1 to be analyzed before the power switch 9 is initiated. As can be seen in FIG 2, when the power switch 9 is closed, current flows from the power source (battery or power supply) into the voltage regulator circuit 455 and microcontroller 7 which initiates the microcontroller 7 code at start up. This allows the calibration sequence to commence. Resistor 40 is current biased to the base of transistor 23. The bias current is amplified through the collector and emitter of transistor 23 and applied to precision zener 24, where it is voltage regulated to a set voltage, in this case three volts (3VDC), by voltage compensating resistors 38 and 39. Capacitor 26 is used to smooth transitional voltages as microcontroller 7 is activated and when it generates a fixed frequency oscillation signal 11 to sensor antenna 2. Referring to FIG 7a, the oscillator signal produced by the microcontroller 7 and sent to the sensor antenna element 2 is shown at 150, the signal voltage detected at receiving sensing element 3 for air as the dielectric at the sensing element 100 is shown at 151, the voltage signal detected at receiving sensing element 3 for a capacitive - resistive load 1 (e.g., oil) at the sensing element 100 is shown at 152, the negative swing voltage signal is shown at 153 and the conditioned voltage signal after filtering by filter 6 is shown at 154. The function of the oscillator signal at 150, is to impose a fixed frequency changing voltage signal (excitation of the electric field at, for example, 50 KHz with 50% duration) at sensor antenna element 2. This will induce an instantaneous voltage at receiving sensing element 3, through a capacitive - resistive load 1 medium such as oil which will change the induced voltage at sensing element 3 in response to the condition of the oil.

In FIG 7a, the voltage signal 152 is shown with oil present as the capacitive - resistive load 1. As can be seen however, signal voltage 151 shows less voltage due to a "no presence" signal of air as the medium. It should be understood that the combined capacitive (based on dielectric value of the capacitive - resistive load 1 (e.g., oil)) and resistive impedance of the capacitive - resistive load 1 will increase as the oil acidity and other contaminants are integrated in to the oil. The differential voltage over time aspect of the receiving voltage signal is accepted by the receiving sensor element 3 and accepted by electronic circuit node 13 shown in FIG 2. The signal received at node 13 is high band pass filtered by means of arrangement of the bias resistors 28, 29 and the base of transistor 13. The increasing of the capacitive - resistive impedance of the oil under test is proportional to the increasing of the high band pass voltage signal accepted at node 13. This means that as the impedance of the oil increases, the signal voltage increases at node 13 and is added to the DC (direct current) bias voltage preset by resistors 28 and 29.

Referring to FIG 7a, at node 13 signal 151 or 152, depending on whether oil or air is present as the capacitive - resistive load 1, is presented to the collector of transistor 14, a high gain switching component, to be amplified which amplified signal is presented at node 15 where it is current biased across resistor 30. The transistor characteristics of transistor 14 being able to operate at high frequency and high gain are critical for the performance of the signal. One transistor particularly well suited for this application is sold under the part number MBBT6429 manufactured by ON Semiconductor. Although this transistor is particularly suited to be used in this invention, any transistor having the high frequency-high gain characteristics described above can be used as will be clear to those skilled in the art. The switching speed and high frequency gain (hfe) qualities of the transistor 14 permit the resulting signal to be single stage amplified, thus, allowing the high frequency band pass signal to be amplified adequately for further signal processing. The voltage signal at node 15 is opposite in phase and amplified significantly as compared to the input signal at node 13.

Referring to Fig 7a, the negative swing voltage signal 153 at node 15 (Fig 2) pulls biased diode 44 and pull up resistor 31 and voltage signal storage capacitor 32 at node 16 to produce a filtered steady state voltage signal 154 (FIG 7a) as will be described hereafter. The unfiltered steady state voltage signal is stored near the peak negative swing voltage of node 15 minus the voltage drop across diode 40. The unfiltered steady state voltage signal which is at a high impedance state is injected into the base of transistor 17 to decrease the impedance further, and the resulting voltage is further filtered at node 18 by resistor 33 and capacitor 34 to produce the conditioned voltage signal 154 after filtering. Signal 154 will only be active in steady state voltage level for the duration the oscillator 11 signal is present during the testing sequence. The components used at node 18 are designed to filter and store the low impedance steady state voltage for further signal processing by the ADC 19 (Analog Digital Converter) at microcontroller 7. Referring to FIG 2, microcontroller 7 is coded to accept the steady state voltage value at node 18 into the ADC port 19. It is the function of ADC 19 to accept and store the steady state signal voltage at node 18, convert the value into a binary value and store it in the memory associated with the microcontroller 7 for further calculation. A further description of the microcontroller processes will be given hereafter.

Referring to FIG 2, resistors 41 and 42 create a voltage divider network at node 21 which resulting voltage is presented to an ADC 43 at microcontroller 7. This voltage divider network circuit determines the battery supply voltage level. When a low voltage condition (e.g., less than 4.5 Vdc) is presented to the ADC 43, the microcontroller 7 will acknowledge this condition. A further description of this process will be addressed hereafter.

Test switch 10 is used to activate the sensing sequence of microcontroller 7. Resistor 35 and capacitor 36 are used as a de-bouncing filter for spurious electrical contact noise generated by switch 10. Resistor 37 current limits any spurious electrical contact noise that may be generated into the port of microcontroller 7.

LEDs 12 are preferably located on the face of the capacitive - resistive oil analyzer 0 (FIGS 3 and 4) and are controlled by microcontroller 7 to display the condition of the capacitive - resistive load 1 (e.g., oil) as ascertained by the microcontroller 7. LEDs 12 are current limited by resistors 45 and are independently activated by the microcontroller 7 in response to the ascertained impedance value of the capacitive - resistive load 1 (oil). Although LEDs 12 are preferably used to communicate the state of the capacitive - resistive load 1 of interest, it will be clear to those skilled in the art that any means of communicating the state may be used. Such methods include, but are not limited to, presentation to a monitor or other visual display device, printing via a printer and the production of an aural signal indicating the status of the capacitive - resistive load 1 including a spoken or simulated spoken message. Referring to FIG 7c, the sequence of operation describing the calibration and testing steps will be explained in detail. Prior to initiating the method shown in FIG 7c, the user determines if the oil of the capacitive - resistive load 1 is standard or synthetic and presets oil type switch 8 to the correct state. Oil or other capacitive - resistive load 1 of interest is NOT present at this stage. It is important for the user to clean the sensing element 100 (FIG 3 and 4) prior to each testing and to ensure no unnecessary residue is present on sensor elements 2 and 3.

A user activates power switch 9 at "Start" and, as a result, the microcontroller 7 powers up. The program then passes to step 500 where the initial settings sub routine is loaded and oscillator 11 is activated, preferably for a short time (e.g., less than 20 ms). The reason for activating the oscillator 11 for a short time, particularly in the battery operated version of the invention, is that the oscillator needs to be operated for enough time to charge the capacitor created by the sensing antenna element 2 and receiving sensor element 3 and allow the microcontroller 7 to read the signal captured by the receiving sensor element 3 but not operated much longer than this and thereby unnecessarily drain the battery. The program then passes to step 501.

As described earlier, the signal processing stages at nodes 13, 15 and 18 produce a steady state filtered voltage with air as the capacitive - resistive load 1 which is presented at ADC 19. At step 501, the "base" signal voltage value with air as the capacitive - resistive load 1 is stored. The program then passes to step 502.

At step 502, the voltage detected at ADC 43 is accepted by microcontroller 7 which determines whether the battery condition is adequate to proceed (i.e., the battery voltage is sufficiently high to allow the capacitive - resistive oil analyzer 0 to operate). In versions of the capacitive - resistive oil analyzer 0 not running on battery power, this step would be omitted. At step 502, if the battery voltage is less than a predetermined amount (e.g., 4.5 Vdc), a low flash indicator sub routine activates one or more LEDs 12 (101) to alert the user of this condition. If the capacitive - resistive oil analyzer 0 invention experiences this low battery condition, the microcontroller 7 prevents the program from passing to the testing step 504 and, as a result, the user will be unable to continue the test.

However, if the battery voltage is greater than the predetermined level (e.g., 4.5Vdc), the program passes to step 504 where the test oil sub routine is permitted to run when the test switch 10 is activated by the user. At this stage of the process, the "no presence" of oil or other capacitive - resistive load 1 of interest, or more specifically, the "base" value of the calibration step has been completed, and the user is required to add oil to sensing element 100 to complete the test. The amount of oil placed in the sensing element 100 to be tested depends to some degree on the size and shape of the sensing element 100 but is typically greater than about one hundred and sixty micro liters (160 uL). The sensing element 100 preferably has a convenient level line to show the user the minimum amount of oil to add to the sensing element 100.

When oil (or other capacitive - resistive load 1 of interest) has been introduced in sensor repository 100, the user depresses test switch 10 to activate sub routine at step 504. The sub routine of step 504 activates oscillator 11 and the program passes to step 505. At step 505, the signal received by receiving sensor element 3 is signal processed according to the signal processing steps described earlier. The resulting new "sense" value (the value determined with oil or other material of interest as the capacitive - resistive load 1) is stored and the program passes to step 506.

As step 506, the new "sense" value is compared to the "base" value described earlier. This is done by subtracting the "sense" value from the "base" value. In the embodiment of the capacitive - resistive oil analyzer 0 shown in FIG 7c, the program then passes to step 507 where it is determined whether the oil as the capacitive - resistive load 1 is synthetic. If it is, the program passes to step 508 where the determined difference value between the "sense" and "base" values are matched against table values stored for synthetic oil types. If the oil is not synthetic, the program passes to step 509 where the determined difference value between the "sense" and "base" values are matched against table values stored for standard oil types. Both step 508 and step 509 pass to step 510.

In step 510, the oil indicator sub routine activates the output (e.g., LEDs 12) corresponding to the quality determined for the tested oil as the capacitive - resistive load 1. For example, fresh oil would not change in voltage level when compared to the "base" value. A preferred way to representing this is for the LEDs 12 to flash or light up only the 1^st LED. On the other end of the spectrum, if the oil is past its performance level as a lubricant, then the last LED (e.g., 10^th LED) would flash or light up indicating the need to change the oil. For values between these two levels of oil quality, appropriate LEDS 12 between the 1^st and last LED would light corresponding to the determined oil quality. In addition, the LEDs 12 indicating the various conditions of the capacitive - resistive load 1 (e.g., oil) are preferably color coded corresponding to the condition of the material of the capacitive - resistive load 1. For example, the LED indicating the base value could be colored green indicating that the material of the capacitive - resistive load 1 is in the fresh range. The LED corresponding to the capacitive - resistive load 1 being in an unacceptable range, for example where oil is past its performance level as a lubricant, is preferably a color different from the other LEDs 12, for example red, to indicate that use of such oil is dangerous. The LEDs 12 between these two extreme ranges could be a third color, for example orange, to indicate that the material of the capacitive - resistive load 1 is in the acceptable range. Alternately, one of more LEDs 12 between the LEDs 12 representing the extreme values of the material of the capacitive - resistive load 1 could be used to produce degrees of "goodness" or "badness" of the material. For example, if the 1^st LED 12 representing the fresh state is green and the last LED 12 representing the unacceptable state is red, the LEDs between these two extremes could have more green if they are nearer the 1^st LED and gradually lose the green and acquire more red as the LEDs move toward the last red LED.

In a preferred embodiment of the capacitive - resistive oil analyzer 0 shown in FIGs 3 and 4, the LEDs 12 are arranged in a line around the circumference of the sensing element 100 so that the 1^st LED 12 representing the fresh condition of the capacitive - resistive load 1 is at a first position and LEDs 12 sequentially representing diminished condition of the material of the capacitive - resistive load 1 are located clockwise from the 1^st LED 12. Powering off the device by activating switch 9 resets the microcontroller 7 and the user is able to clean the sensor element 100 for the next test. Of course, in embodiments of the capacitive - resistive oil analyzer 0 where the capacitive - resistive oil analyzer 0 is disposable, there is no need to clean the sensor element 100 preparatory for another test.

DETAILED DESCRIPTION OF ANOTHER EMBODIMENT OF THE

INVENTION

In another embodiment of the capacitive - resistive oil analyzer 0 invention shown in FIGS 5, 6 and 7d, the capacitive - resistive oil analyzer 0 is shown as a tube sensor device generally labeled 199. The embodiment of the invention shown in Figures 5, 6 and 7d differs from the previously described embodiment of the capacitive - resistive oil analyzer 0 invention in that the capacitive load passes through a tube "T" as it is sensed by the capacitive - resistive oil analyzer 0 instead of being in the sensing element 100. In addition, this embodiment of the capacitive - resistive oil analyzer 0 may not have a microprocessor 7. The tube sensor device in this embodiment has low impedance front end circuit with a sensing antenna element 200, and receiving sensor element 201, a high band pass filter 250, single stage amplifier 252, signal filter 256, oscillation stage 250, comparator stages 257 and output driver stage 258. The sensing antenna element 200 is located in a sensing antenna element housing 239 located on one side of the tube T and the receiving sensor element 201 is located in a receiving sensor element housing 240 located on the opposite side of the tube T. The sensing antenna element housing 239 and the receiving sensor element housing 240 are connected together, for example by straps 241, snap-fit or friction- fit connection, screws, bolts, adhesives or other means well understood in the are, to precisely locate the sensing antenna element 200 and the receiving sensor element 201 with respect to the tube T FIG 5, a schematic block diagram of this embodiment of the invention, shows a capacitive load 299, sensing antenna element 200 and a receiving element 201. The function of the sensing antenna element 200 is to produce a three dimensional electric field, the size of which is a function of the surface area of the element, the magnitude of the electric field potential and frequency being generated by oscillator 250. In this embodiment, the sensor antenna element 200 is made of a conductive material such as copper, silver, gold, aluminum or steel. The function of sensing receiving element 201 is to accept the coupled induced voltage from an intermediary material such as a non- metallic tube. The sensing antenna element 200 and a receiving element 20 lean have the shape of the sensing antenna element 2 and receiving sensor element 3, respectively.

The coupled voltage is band pass filtered and applied to a single stage high gain and frequency amplifier 252. The output of the amplifier 252 is filtered to a steady state voltage at node 253. The purpose of filtering the amplified voltage is to provide a steady state voltage for the comparator stage 257. Capacitive load 299 in this embodiment of the invention may also consist of any material of measurable dielectric constant such as motor or lubricating oil, vegetable and animal based cooking oils and hydraulic oil, to name a few possible types of capacitive loads 99.

Referring to Fig 6, when the capacitive - resistive oil analyzer 0 device in this embodiment is powered on, current flows from the power source (battery or power supply) through diode 229. This diode is used for reverse diode protection only of the power supply. In variants of this embodiment having battery power, this diode 229 may not be necessary as will be well understood by those skilled in the art. Resistor 230 is current biased to the base of transistor 232 and sets the maximum regulated voltage at the base of transistor 232 by clamping to the zener 231 voltage. The bias current at the base of transistor 232 is amplified through the collector, emitter path of transistor 232 and applied to precision zener 235, where it is voltage regulated to a predetermined value (e.g., eight volts (8 VDC)) by voltage compensating resistors 236 and 238. Capacitor 234 is used only as a first pass voltage smoothing device and resistor 233 is used as a current limiter for supply current going into the precision zener circuit. Capacitor 238 is used to smooth transitional voltages as the device generates a fixed frequency oscillation signal to sensor antenna 200. The oscillator circuit is a fixed frequency square wave oscillator set to a determined value (e.g., one hundred kilo-hertz (100 KHz)). The oscillator uses a Schmitt trigger digital inverter 204 and is clocked by inputs to an RC (resistive, capacitive) input by resistor 202 and capacitor 203. The output generated is a fixed frequency square wave oscillator with a fifty percent duty cycle (50%). The square wave form is imposed upon sensing antenna element 200, and the excitation signal (square waveform) is coupled to sensing receiver 201 by a dielectric medium represented by capacitive load 299. The signal received by sensing receiver 201 is shown in Fig 7a as signal 151 where the capacitive load 299 is air and 152 where the capacitive load 299 is a material of interest (e.g., oil). As the excitation signal is received at receiving sensing element 201 , it is filtered by circuit components consisting of diode 207 and resistors 206 and 205. Diode 207 is also used as a temperature compensating diode which matches the base diode thermal characteristics of transistor 209. As the ambient temperature changes, the diode bias voltages of diode 207 and transistor 208 also change near the same rate. This allows for a low deviation amplified signal change over a range of temperatures. The transistor 209 characteristic is critical for the performance of the signal and, as described above, can be transistor sold under the part number MBBT6429 manufactured by ON Semiconductor. The switching speed and gain (hfe) qualities of the transistor 209n permit the resulting signal to be single stage amplified, thus, allowing the high frequency band pass signal to be amplified adequate for further signal processing.

The amplified voltage signal supplied to diode 211 and resistor 210 is opposite in phase and amplified significantly compared to the input signal at the transistor 209 base voltage. Referring to Fig 7a, the negative swing voltage signal 153 at transistor 209 collector pulls biased diode 211 and pull up resistor 212 and voltage signal storage capacitor 213 to produce a filtered steady state voltage signal 154 (FIG 7a). The steady state voltage signal is stored near the peak negative swing voltage minus the voltage drop across diode 211. In Fig 7a, signal 154 shows the conditioned voltage signal after filtering. Capacitor 214 is used to subtract any alternating current (AC) noise caused by external electromagnetic interference. Diode 218 is used to temperature compensate match diode 211 temperature changes.

Comparator 216 accepts a biased voltage into the inverting pin of the comparator 216. The bias set point is determined by resistor 219, potentiometer 220 and resistor 221. Potentiometer 220 is a multi turn component used to be set point calibrated by the user in the field at the time of operation. "Set point calibrated" in this context means the bias point is set to a predetermined level between the state where the capacitive load 299 is air and the state where the capacitive load 299 is material of interest (e.g., oil). The output of comparator 216 is joined to resistor 221 and resistor 217. Resistor 221 is a pull up resistor to the voltage supply rail. The bias voltage is fed back to the inverting pin of comparator 216 through resistor 217. The purpose of this design is to minimize chatter during switch over as well introduce hysteresis in the switching of the signal. The output signal is fed to the input of comparator 222 and the output from the switched signal is output to a driver stage. Pull up resistor 223 supplies a switched voltage to the gate of mosfet 224. The output stage at the drain of mosfet 224 goes to the ground plane when a voltage is present at the gate. LED 226 and current limiting resistor 225 (part of the output stage 258) is switched and becomes a visual indicator of the state of the output of the sensing device (an indication that the capacitive load 299 is not of acceptable quality). Diode 228 is used to accept an output switching component which is external to the invention, such as a resistive or inductive load such as a relay, solenoid or PLC (programmable logic control) input.

Alternately, output stage 258 could be the series of LEDs 12 as described above. In this variant, the output signal from the comparator 222 would be fed to either a microprocessor 7 that controls the operation of the LEDs 12 in response to the output signal from the comparator 222 or to discrete circuitry (e.g., a series of mosfets 224 with corresponding pull up resistors 223 corresponding to states of the material of the capacitive load 299) to indicate the condition of the material of the capacitive load 299. In any of the embodiments of the capacitive - resistive oil analyzer 0 described herein, the oscillator signal is most preferably a square wave since square waves are comprised of the superposition of bits of an infinite frequency spectrum of signals. These various frequency bits interact with the capacitive - resistive load 1 , 299 differently but are needed to produce a desired signal at the receiving element 3, 201, respectively. The exemplary frequency of 50 or 100 KHz is not limited to this particular frequency and can be increased accordingly for higher resolution or decreased as desired.

In any of the embodiments of the capacitive - resistive oil analyzer 0 described herein the capacitive - resistive oil analyzer 0 may be an entirely reusable device, a partially reusable device or a completely disposable device. Where the capacitive - resistive oil analyzer 0 is an entirely reusable device, the part of the capacitive - resistive oil analyzer 0 that comes into contact with the capacitive - resistive load 1 (e.g., oil) is either cleaned after each use or the capacitive - resistive load 1 passes through the device, for example through a tube (FIG 7c), so that the capacitive load is positioned between the sensor antenna element 2 and receiving sensor element 3.

Where the capacitive - resistive oil analyzer 0 is a completely disposable device, the capacitive - resistive oil analyzer 0 is disposed of after each use. Consequently, the capacitive - resistive oil analyzer 0 in this embodiment does not require, but may have, a robust battery or structural elements. In the embodiment of the capacitive - resistive oil analyzer 0 where part of the capacitive - resistive oil analyzer 0 is disposable, the sensing area 100 is designed to be removable from the body of the capacitive - resistive oil analyzer 0 to be disposable. In this embodiment, the electronics (microcontroller 7, a high band pass filter 4, single stage amplifier 5 and signal filter 6) are reused and the sensing area 100 is disposed of after each sample is analyzed. In this embodiment, the sensing element 100 part of the capacitive - resistive oil analyzer 0 that comes into contact with the capacitive - resistive load 1 (e.g., oil) is disposed of while retaining the other parts of the capacitive - resistive oil analyzer 0. The disposable sensing area 100 allows the user to replace sensing area 100 without the need for repetitive cleaning of the sensing area 100.

Also, in embodiments of the capacitive - resistive oil analyzer 0 described above, a switch 8 is moved into positions reflecting the type of capacitive - resistive load 1 (e.g., synthetic or standard oil). In a variant of this, the capacitive - resistive oil analyzer 0 can itself determine the type of capacitive - resistive load 1 and use this information to correctly characterize the condition of the material making up the capacitive - resistive load 1. In this embodiment, the user first places a small amount of a clean sample of the material of the capacitive - resistive load 1 in the sensing area 100. The clean sample is analyzed and the dielectric value determined is compared, for example through a look-up table, to determine the material composing the clean sample. Once the material of the clean sample has been identified, a sample of the material to be analyzed is placed on the sensing area 100. This sample is then analyzed as described above to determine the condition of the sample. Oil represents the preferred capacitive - resistive load 1 material to be analyzed by the capacitive - resistive oil analyzer 0 of the present invention and consists typically of automotive engine, heavy machinery, diesel and marine based oil types. Although the present invention has been described as being used to describe engine oil as described, the invention is not limited to specific to oil types described, but may encompass oil types in food processing, hydraulics and so forth. In addition, the capacitive - resistive oil analyzer 0 of the present invention has been described as used to determine the quality of fluids, particularly oils. However, the capacitive - resistive load 1, 299 is not limited to being an oil or even a fluid. Other materials, including but not limited to, solids and gels may also be the capacitive - resistive load 1, 299.

The capacitive - resistive oil analyzer 0 described herein, in one or more embodiments, uses a single oscillation circuit and thereby eliminates the need in many prior art devices for multiple oscillation circuits (e.g., one oscillation circuit to produce a reference electric field and another oscillation circuit to produce a sensing electric field).

In addition, the of the present invention improves on the poor sensitivity of the sensing signal in prior art designs having single frequency designs. In addition, the capacitive - resistive oil analyzer 0 incorporates the resistive sensing component and the capacitive sensing component together so that the capacitive - resistive oil analyzer 0 of the present invention takes advantage of both of these components to give an accurate reading for the state of the material of the capacitive - resistive load 1.

Also, because the capacitive - resistive oil analyzer 0 of the present invention uses only a single oscillator circuit and because the oscillator circuit operates at only a single frequency (as opposed to many prior art systems that operate in a broadband or swept frequency mode), the circuitry of the capacitive - resistive oil analyzer 0 of the present invention is simple. In addition, in the embodiments of the capacitive - resistive oil analyzer 0 using a microprocessor 7, the level of processing needed to be performed by the microprocessor 7 is relative modest. As a result, the cost and complexity of the required microprocessor 7 is greatly reduced compared to many prior art designs.

Further, the capacitive - resistive oil analyzer 0 may be used internally in a combustion engine or externally; the only requirement is that the material of interest (e.g., oil) may be brought into contact with the sensing element 100. Another advantage of the capacitive - resistive oil analyzer 0 of the present invention over many prior art devices is that only a small amount of the material of interest (e.g., oil) is needed to ascertain the quality of the material of interest.

There are many materials and configurations that can be used in constructing the capacitive - resistive oil analyzer 0 of the present invention that will be clear to those skilled in the art including, but not limited to, combining discrete components into a single integrated circuit or replacing an integrated circuit with discrete components. In addition, it is clear that an almost infinite number of minor variations to the form and function of the disclosed invention could be made and also still be within the scope of the invention. Consequently, it is not intended that the invention be limited to the specific embodiments and variants of the invention disclosed. It is to be further understood that changes and modifications to the descriptions given herein will occur to those skilled the art. Therefore, the scope of the invention should be limited only by the scope of the claims.

Claims

1. A device for determining the quality of a material of interest comprising: a source of oscillating electric current at a first frequency; a sensing antenna element attached to the source of oscillating electric current to produce an oscillating electric field; a receiving sensor element coupled to the sensing antenna element through the material of interest; signal processing means attached to the receiving sensor element to produce an electronic indicator of capacitive and resistive composition of the material of interest; means for comparing the electronic indicator to known values representing corresponding conditions of the material of interest to determine the condition of the material of interest; and means for communicating the condition of the material of interest.

2. A method for determining the quality of a material of interest comprising the steps of: providing an oscillating electric field at a first frequency; sensing an electric field coupled to the material of interest; processing the sensed electric field to produce an electronic indicator of capacitive and resistive composition of the material of interest; comparing the electronic indicator to known values representing corresponding conditions of the material of interest to determine the condition of the material of interest; and communicating the condition of the material of interest.