RU2325632C1 - Method of oil product humidity measurement - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: method includes measurement of phase shift of cavity resonator resonance frequency signal Δφ, which corresponds to frequency shift, when its phase response characteristic frequencies are shifted along axis, at that oil product humidity is measured, which depends on inductive capacity.

EFFECT: improves sensitivity of measurements.

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Description

The invention relates to the field of measuring equipment and can be used in process control systems.

The known method, implemented by an automatic moisture meter, built on a bridge circuit and having one transceiver antenna (see V.A. Viktorov et al. "High-frequency method for measuring non-electric quantities", 1978, p. 254), in which the reflection coefficient from the controlled substance with taking into account the difference in the strengths of the waves reflected from the standard (a sample of medium with constant humidity) and the controlled substance serves as a measure of its humidity.

The disadvantage of this known method is the complexity of the humidity measurement procedure associated with the formation of a bridge circuit.

The closest technical solution to the proposed one is the method adopted by the author for determining the humidity in the substance flow (see V.A. Viktorov et al. "High-frequency method for measuring non-electric quantities", 1978, pp. 2553-254). According to a device that implements this method, electromagnetic waves are excited in the measuring and reference volume resonators, a flow of a controlled medium is branched off from the main line (the reference resonator is filled with completely dehydrated material), and the frequency signals of these signals are mismatched through the tube mounted in the center of the measuring resonator two resonators (the device is built on a bridge circuit) receive information about the humidity of the stream.

The disadvantage of this method should be considered low sensitivity due to the complexity of the conversion of an informative moisture signal of a frequency signal.

The objective of the proposed technical solution is to increase the sensitivity of the measurement.

The problem is achieved in that in a method for determining the moisture content of an oil product flowing through a dielectric pipe passing through a measuring volume resonator, in which electromagnetic waves are excited and an offset is recorded along the frequency axis of the frequency characteristics of the volume resonator, the phase shift Δφ of the resonant frequency signal f of the volume resonator is measured, corresponding to the frequency shift Δf, and the moisture content of the oil is determined from the measured phase shift.

The essence of the claimed invention, characterized by a combination of these features, is that they obtain information about the moisture content of the oil product by the phase shift of the resonant frequency signal of the volume resonator.

The presence in the inventive method of the combination of the above essential features allows us to solve the problem of determining the moisture content of the oil based on fixing the bias along the frequency axis of the phase-frequency characteristic of the cavity resonator and measuring the phase shift of the signal of its resonant frequency with the desired result, i.e. high sensitivity measurements.

The drawing shows a functional diagram of a device that implements the proposed method.

A device that implements the proposed method contains an electromagnetic oscillation generator 1, a measuring volume resonator 2, a device for observing the frequency characteristics 3. In the drawing, the number 4 indicates the pipeline passing through the measuring volume resonator through which the oil flows.

The proposed method is as follows.

As you know, in the radio wave moisture measurement of an oil product based on resonant systems, moisture information is obtained from the resonant frequency of the resonator. The dependence of this parameter on humidity through the dielectric constant of the controlled medium is determined by the shift along the frequency axis of the amplitude-frequency characteristic of the resonator, i.e. shift of the resonance frequency.

Practice shows that the determination of the moisture content of substances with a low content (up to 5%) of moisture does not always provide high measurement sensitivity.

According to the proposed method, when electromagnetic waves are excited in a volume resonator with a pipeline passing through it, through which a watered oil product flows, the phase shift Δφ of the resonant signal associated with a change in the moisture content of the oil product can be expressed as a dependence experimentally found

Q _r.ob - quality factor of the cavity resonator;

f ₀ - resonant frequency of the resonator (without disturbance of the resonator);

Δf is the shift of the resonance frequency due to a change in the moisture content of the oil product.

It follows from the presented formula that, when the phase-frequency characteristic (PFC) of the resonator is displaced along the frequency axis with a known dependence of Δf on humidity, the moisture of the oil product can be determined by measuring the Δφ parameter.

In the case under consideration, when measuring the low moisture content of an oil product flowing, for example, through a dielectric pipeline passing through a given resonator, the resonant frequency Δf (frequency shift) of the latter can be expressed by the following formula (see V.A. Viktorov et al. “Radio wave measurements of technological parameters processes. ”M .: Energoatomizdat, 1989, p.176).

Where

ε is the dielectric constant of the watered oil product,

ε _T is the dielectric constant of the pipeline,

A is a coefficient depending on the type of oscillations in the cavity of the resonator, its dimensions and

etc. This coefficient can be considered approximately constant.

From the last formula, it can be seen that for known values of ε _T and the dependence of the dielectric constant of the watered oil product on moisture content (see Wiener’s formula. “Theory and practice of express control of moisture in solid and liquid materials.” Under the general editorship of ES Krichevsky, M. : Energy, 1980, p. 55) you can determine the moisture content of the oil.

Expression (1) taking into account expression (2) will take the form:

From the above reasoning, it follows that the shifts of the resonant frequency of the cavity resonator and the phase of the resonant signal can determine the moisture content of the oil product.

According to the proposed technical solution, it is necessary to evaluate the sensitivity of the conversion of moisture through the dielectric constant ε in this case into frequency and phase, compare these characteristics and show the prospects of converting moisture to phase.

If frequency and phase changes are denoted by f and φ, respectively, then expressions (2) and (3) in general form can be represented as

From the theory of measuring technology it is known that the sensitivity of the transducer must be understood as the ratio of the magnitude of the transducer to its input signal. In accordance with this sensitivity in frequency S _f and phase S _φ in this case can be defined as

where df and dφ are the increments of the frequency and phase (output values), respectively,

dε is the increment of the dielectric constant of the watered oil product (input signal). Here, the absence of the influence of side factors (temperature, pressure) on the transducer and the constancy of the parameters ε _T , Q _p.ob and A.

Differentiating equations (4) and (5) with respect to ε makes it possible to determine the absolute sensitivity (see V. Yu. Kneller. “Automatic measurement of the components of complex resistance.” Leningrad: Energia, 1967, p. 77) according to the frequency S _f and according to phase S _{φ by the} following formulas:

An analysis of the formulas obtained shows that due to the quality factor of the resonator, which determines the steepness of the phase response, the phase sensitivity may be greater than the frequency. It should be noted that the phase measurement must be carried out on a linear phase phase response with the possibility of ensuring the maximum dynamic range.

Calculations show that when using, for example, a rectangular resonator with a resonant frequency of 3000 MHz and a Q factor of ≈19600 (see L.D. Goldstein, N.V. Zernov. “Electromagnetic fields and waves.” - M .: Soviet Radio, 1971, p. 520) can provide an increase in phase sensitivity.

In the device that implements this technical solution, the electromagnetic oscillation generator 1 is driven by the output signal of electromagnetic oscillations in the volume resonator 2 with a dielectric pipe passing through it, through which a controlled watered oil product flows. After that, with resonance on the screen of the device for observing the frequency characteristics 3, the amplitude-frequency (AFC) and phase-frequency (PFC) characteristics of the resonator are recorded. In the absence of an oil product in pipeline 4, the intrinsic resonant frequency and quality factor are determined (see L. D. Goldstein, N. V. Zernov. Electromagnetic Fields and Waves, Moscow: Sovetskoe Radio, 1971, p. 512, formula 13.22). The shift along the frequency axis of the frequency response and phase response, indicating the presence of a watered oil product in the pipeline, is used to determine the shift of the resonant frequency and phase of the resonance signal. Moreover, in the frequency region near the inflection point, where the phase response can be approximated by a linear dependence, the frequency shift Δf associated with the moisture content of the oil through the dielectric constant of the watered oil product corresponds to a phase change (shift) Δφ of the resonant signal. As a result, with known values of f ₀ and quality factor Q _{r.o., the} measurement of Δf (transformation of the ratio Δf / f ₀ according to formula (2), for example) allows you to determine the moisture content of the oil when it changes.

Thus, according to the proposed method, based on measuring the phase shift of the resonant frequency signal corresponding to the shift of the resonant frequency of the resonator, it is possible to provide high sensitivity for measuring the moisture content of the oil product.

Claims (1)

A method for determining the moisture content of a petroleum product flowing through a dielectric pipe passing through a measuring volume resonator, in which electromagnetic waves are excited and an offset along the frequency axis of the frequency characteristics of the volume resonator is recorded, characterized in that the phase shift Δφ of the resonant frequency signal f _{0 of the} volume resonator is measured, which corresponds to the shift frequency Δf,

, where ε is the dielectric constant of the watered oil product; ε _t is the dielectric constant of the pipeline; A is a coefficient depending on the type of oscillations in the cavity of the resonator, its size, etc., and determine the moisture content of the oil, depending on the dielectric constant ε.