RU2385449C2 - Method and device for determining flow pressure using density information - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: flow metre processor (508) is configured to determine pressure of fluid material based on measuring density and temperature of the fluid material flowing through a channel (502). Density of the fluid material is determined based on measuring movement of a the channel (508) which vibrates under the effect of an exciter (504) using sensors (506).

EFFECT: easy measurement of flow pressure with no requirement for a pressure transducer and additional electronic circuits.

8 cl, 9 dwg

Description

Technical field

The invention relates to the field of flowmeters, in particular Coriolis flowmeters.

State of the art

Coriolis flowmeters determine specific mass flow rates by determining the Coriolis forces acting on the vibrating channel. A channel consists of one or more tubes and performs forced oscillations at a resonant frequency. The resonant frequency of the tube (s) is proportional to the density of the fluid in the venturi (s). Sensors located on the inlet and outlet sections of the tube (s) measure the relative vibration between the ends of the tube (s). During the flow, the vibrating tube (s) and the mass of the flow are connected due to Coriolis forces causing a phase shift in vibration between the ends of the tube (tubes). The phase shift is directly proportional to the mass flow rate.

There is a secondary effect of pressure on the venturi tube (s) of the Coriolis sensor. Changing the pressure without changing the specific mass flow rate will lead to a change in the action of bending forces acting on the tube. An increase in pressure will increase the stiffness of the Venturi tube (s), and the same value of Coriolis forces, due to the constant specific mass flow rate, will create a smaller value of the tube bend (s). If the pressure decreases, the venturi becomes more flexible, and the same value of Coriolis forces, due to the constant specific mass flow rate, will cause a large amount of bending of the tubes. The effect of flow pressure is linear and is typically defined as a percentage of the flow rate per unit pressure change. Correction for the effect of pressure requires either the use of an average pressure value or the measurement of current pressure. Using an average pressure value can cause unacceptable errors if there are large variations in operating pressure in the system. Measuring current pressure typically requires a pressure measuring port, a pressure transmitter, electronic circuits for monitoring the pressure transmitter, and some means for transmitting the measured pressure to the Coriolis flowmeter.

Therefore, there is a need for an improved system and method for determining pressure in a Coriolis flowmeter.

Japanese Patent JP 7083721, entitled “Vibration Type Measurement Device”, discloses the following solution. This device is made of tubes 2 and 3 of the sensor through which fluid flows, vibrators 5 and 6 for vibration of the tubes 2 and 3 of the sensor and controller 14 connected to the excitation coil of vibrators 5 and 6. The controller 14 contains a circuit 17 for determining the time difference, section 18, a flow calculation, a display section 19, a frequency measurement circuit 20, a density calculation section 21, a density to pressure conversion circuit 22, and a pressure correction input circuit 23. The density calculation section 21 determines the density of the measured fluid from the vibration frequency of the sensor tubes 2 and 3 and the pressure of the measured fluid from its density. Then, the pressure correction input circuitry performs a zero point correction for the measured flow rate from the flow calculation section 18 based on the pressure value from the density to pressure conversion circuit 22.

US Pat. No. 5,497,665, entitled "Coriolis Venturi-based Flowmeter with Adjustable Pressure and Density Sensitivity," discloses the following solution. Several geometries and electronic circuits of a Coriolis flowmeter based on a venturi are presented, which can be made sensitive to changes in pressure or density. In one embodiment, the meter comprises: (1) a fluid channel for filling with a fluid having physical characteristics, wherein the fluid can flow through a channel with an unknown fluid flow rate, (2) an excitation circuit for generating vibration in the fluid channel, the fluid changing vibration depending on physical characteristics and flow rate, (3) a detection circuit for measuring the altered vibration at the operating point and generating a signal representing the uncompensated specific mass flow rate of the fluid, and (4) a computing circuit for calculating the compensated specific mass flow rate of the fluid proportional to the uncompensated flow rate according to the expression 1 / .OMEGA.1.sup.n, where OMEGA.1 is the natural frequency of the excitation of the flow channel and n is the number selected as a function of the operating point in the compensated flow rate, effects of physical characteristics. A uniquely defined mathematical algorithm is also described that allows a much wider variety of design geometries while maintaining pressure or density insensitivity without requiring measurement or compensation of any of these characteristics. In addition, a method is described that provides accurate measurement and compensation of effects of both pressure and density.

US Pat. No. 5,734,112, entitled “Method and apparatus for measuring pressure in Coriolis mass flowmeters,” describes the following. A method for determining the pressure in a working mass flow meter based on the Coriolis effect is presented. Venturi tubes of a Coriolis flowmeter vibrate both in the bending mode (as is usually the case for measuring the specific mass flow rate) and in the twisting mode. The ratio of the fundamental frequencies at which the venturi tubes vibrate at each of the two modes of oscillation is proportional to the pressure inside the venturi tubes. In a preferred embodiment, the sum-difference method initially isolates a superposition of sinusoids representing the fundamental frequencies of the two vibrational modes. Digital filters based on the fast conjugate gradient method (FCG) are then used to quickly estimate the fundamental frequencies at each of the two vibrational modes. The estimated frequencies are then used by filter chains including a digital notch filter and a bandpass filter, and recursive digital maximum likelihood filtering (MLR) methods are applied to improve estimates of the fundamental frequency of the bending mode and twisting mode. Improved estimates of the fundamental frequency of the bending mode and the twisting mode are used to determine the pressure in the venturi depending on the ratio of the two frequencies, as well as to center the filter chains, including a digital notch filter and a band-pass filter, used to amplify the frequency of the bending mode of the two channels of the vibration sensor for calculating the specific mass flow rate. The pressure thus determined can then be used to correct the calculation of the specific mass flow rate or for other purposes of measuring pressure as such.

SUMMARY OF THE INVENTION

A method and apparatus for determining the density of a material flowing through a Coriolis flowmeter are disclosed. Density is used to output the pressure of a fluid material. The withdrawn pressure can then be used to correct the secondary effect of pressure in the Coriolis flowmeter or can be communicated to an external device.

Aspects

One aspect of the present invention includes a method comprising:

measuring the density of material flowing through a Coriolis flowmeter;

determination of the pressure of a fluid material from the measured density, characterized by the following steps:

и вычисление значения для давления Р, где Т - температура, М - молярный вес материала, протекающего в кориолисовом расходомере, ρ - плотность и R - постоянная,(a) setting the compressibility value z to 1 in the equation

and calculating the value for pressure P, where T is the temperature, M is the molar weight of the material flowing in the Coriolis flowmeter, ρ is the density and R is a constant,

(b) using the calculated pressure value P to determine a more accurate value for compressibility z;

(c) using a new, more accurate value for compressibility z to recalculate the value for pressure P;

(d) repeating steps (b) and (c) until, as a result of convergence, the pressure value is within predetermined limits.

Preferably, the method further comprises determining compressibility using the American Gas Association (AGA) Report No. 8.

Preferably, the method further comprises prompting the user to enter the molar weight (M) of the material flowing through the flow meter.

Preferably, the method further comprises prompting the user to enter the type of gas, while the Coriolis flowmeter determines the molar weight of the material flowing through the flowmeter based on the type of gas.

In a preferred manner, the Coriolis flowmeter configured to perform the method comprises:

a channel made to accommodate a fluid material;

at least one pathogen configured for channel vibration;

first and second sensors configured to measure the movement of the vibrating channel;

a processor configured to determine the density of the fluid material based on the movement of the vibrating channel;

wherein the processor is configured to determine the pressure of the flowing material based on the determination of density by performing steps (a) to (d).

Preferably, the method further comprises:

transferring a certain flow pressure to an external device.

Another aspect of the invention provides:

(a) calibrating the ratio of density to pressure of a Coriolis flowmeter for a material at a low pressure point;

(b) calibrating the ratio of density to pressure of a Coriolis flowmeter for a material at a high pressure point;

(c) maintaining two calibrated relationships for the material;

(d) determining the current pressure for the material based on the measured current density and two stored calibrated ratios, characterized by the following steps:

(e) determination of compressibility Z for high and low pressure points;

(f) determining the average molar weight M for the high and low pressure points;

, где Т - температура, М - средний молярный вес материала, протекающего в кориолисовом расходомере, ρ - плотность и R - постоянная,(g) the definition of "the latest assessment of P pressure" using the equation

where T is the temperature, M is the average molar weight of the material flowing in the Coriolis flowmeter, ρ is the density and R is the constant,

(h) determining the new compressibility Z using the “latest pressure rating P”;

(i) calculating a “new pressure estimate”;

(j) repeating steps (g) to (i) until, as a result of convergence, the value of the “new pressure estimate” is within predetermined limits.

Another aspect of the invention includes a Coriolis flowmeter configured to perform a method, comprising:

a channel made to accommodate a fluid material;

at least one pathogen configured for channel vibration;

first and second sensors configured to measure the movement of the vibrating channel;

a processor configured to determine the density of the fluid material based on the movement of the vibrating channel, wherein the processor is configured to determine the pressure of the fluid material based on the determination of density by performing steps (a) to (j).

Preferably, the method further comprises:

a memory area containing pressure to density ratios for the flowing material at two different pressure points, wherein the pressure of the flowing material is determined using the density of the flowing material and the pressure to density ratio at the two pressure points.

Brief Description of the Drawings

1 is a table of gas compressibility for pressures varying from 14 lb / ⁱⁿ² (9.84 g / ^mm2) to 1464 lb / ⁱⁿ² (1029.3 g / mm ²⁾ at a constant temperature of 70 degrees Fahrenheit for a number of different gases.

Figure 2 presents a graph illustrating the information from the table in figure 1.

3 is a graph illustrating the relationship between pressure and compressibility for a theoretically linear compressibility and the real compressibility of the gas mixture from the area of the northern Gulf Coast (Gulf Coast) in the pressure range from 14 lb / ⁱⁿ² (9.84 g / mm ² ) up to 1464 lb / in ² (1029.3 g / mm ² ).

4 is a table showing the maximum difference between the theoretical linear compressibility and the actual compressibility of a number of other gases in the pressure range from 14 lb / ⁱⁿ² (9.84 g / ^mm2) to 1464 lb / ⁱⁿ² (1029.3 g / mm ² ).

5 is a block diagram of a Coriolis flowmeter according to an exemplary embodiment of the present invention.

6 is a flowchart for iteratively determining flow pressure from flow density in an exemplary embodiment of the present invention.

7 is a flowchart showing a method for calibrating a flow meter at two pressure points in one exemplary embodiment of the present invention.

8 is a graph showing the density ratio for Ekofish pressure in the pressure range from 314 lb / ⁱⁿ² (220.8 g / mm ²⁾ to 1014 lb / ⁱⁿ² (712.9 g / mm ^2).

FIG. 9 is a flowchart of a method for determining a current temperature-adjusted flow pressure using high and low pressure calibration points in an exemplary embodiment of the invention.

Detailed Description of a Preferred Embodiment

1-9 and the following description are specific examples for explaining to those skilled in the art how the best mode for carrying out the invention can be implemented and used. In order to disclose the principles corresponding to the invention, some traditional aspects are simplified or omitted. Variants of these examples that fall within the scope of the invention will be apparent to those skilled in the art. Those skilled in the art will appreciate that the features described below can be combined in various ways to provide various variants of the invention. As a result, the invention is not limited to the specific examples described below, but is determined only by the claims and their equivalents.

The gas flow pressure is expressed by law for non-ideal gas as follows:

where ρ is the density of the flowing gas, P is the pressure of the flowing gas, M is the molar weight of the gas, Z is the compressibility of the gas, R is the gas constant, and T is the temperature of the flowing gas. In many cases, the temperature and molar weight of the gas flowing through the Coriolis flowmeter remain relatively constant. In cases where there is a wide range of temperature of the fluid gas, the temperature of the fluid gas can be measured. If the flow temperature and molar weight are considered constant, then equation (1) can be written as follows:

where ρ is the density of the flowing gas, P is the pressure of the flowing gas, N is a constant, Z is the compressibility of the gas. Equation (2) shows that the variability of the flow density is mainly affected by the flow pressure and compressibility. Equation (2) also shows that the flow density is directly proportional to the flow pressure, in addition to compressibility effects. Flow pressure range in most applications related to measurements in gases varies from atmospheric pressure, approximately 14 lb / ⁱⁿ² (9.84 g / ^mm2) to 1464 lb / ⁱⁿ² (1029.3 g / mm ²⁾ that is, the variability is defined as 105 to 1. Figure 1 is a table of gas compressibility for pressures varying from 14 lb / ⁱⁿ² (9.84 g / ^mm2) to 1464 lb / ⁱⁿ² (1029.3 g / mm ² ) at a constant temperature of 70 degrees Fahrenheit for a number of different gases. The compressibility of these gases is well known in the art, and one of the sources for obtaining this information is the American Gas Association (AGA) Report No. 8, “Compressibility Factor of Natural Gas and related Hydrocarbon Gases” (second edition 1994), which is included in the present description by reference. Figure 2 presents a graph illustrating the information from the table in figure 1. As can be seen from Figures 1 and 2, compressibility has a maximum variation of roughly 1.3 to 1 in the range of 14 lb / ⁱⁿ² (9.84 g / ^mm2) to 1464 lb / ⁱⁿ² (1029.3 g / mm ² ).

3 is a graph illustrating the relationship between pressure and compressibility for a theoretically linear compressibility and the real compressibility of Gulf Coast gas mixture in the pressure range from 14 lb / ⁱⁿ² (9.84 g / ^mm2) to 1464 lb / ⁱⁿ² ( 1029.3 g / mm ² ). As can be seen from figure 3, the difference between pressure and compressibility for theoretically linear compressibility and real compressibility for a given gas mixture is negligible. 4 is a table showing the maximum difference between the theoretical linear compressibility and the actual compressibility of a number of other gases in the pressure range from 14 lb / ⁱⁿ² (9.84 g / ^mm2) to 1464 lb / ⁱⁿ² (1029.3 g / mm ² ). Figure 4 shows that there is approximately a linear relationship between compressibility and pressure for a wide range of gas mixtures in a pressure range from 14 lb / ⁱⁿ² (9.84 g / ^mm2) to 1464 lb / ⁱⁿ² (1029.3 g / mm ² ). Equation (2) shows that there is a linear relationship between pressure and density. In view of these linear and approximately linear relationships, a correlation method can be used to formulate an equation relating the flow density to pressure.

5 is a block diagram of a Coriolis flowmeter. A Coriolis flowmeter comprises a channel (502) with one or more tubes configured to hold fluid material. There is one or more pathogens (504) made to bring the channel into vibration with the natural frequency of the channel's bending vibrations. Sensors (506) are configured to measure the movement of the vibrating channel (502). A controller (508) is connected to pathogens 504 and sensors 506 and configured to control the operations of a Coriolis flowmeter. The controller (508) may be contained in one block or may be divided between multiple blocks. For example, electronic means may be associated with a Coriolis flowmeter, and these electronic means may be connected to an external computer running software that provides control of the flowmeter. During operation, the fluid material creates Coriolis forces in the vibrating channel, causing a phase shift in the vibrations between the two ends of the channel. Sensors measure the phase shift between two positions in the channel, and the controller determines the flow rate of the material based on the measured phase difference. A Coriolis flowmeter may have an integrated temperature probe (not shown) or may receive temperature data from an external sensor. Coriolis flowmeters can also determine the density of the material flow using the measured movement of the channel.

In one exemplary embodiment of the present invention, the density of the flowing material is used to output pressure in the flow of material. Figure 6 shows a block diagram of an iterative determination of flow pressure from flow density. At 602, the density of the material flowing through the Coriolis flowmeter is determined using the measured motion of the vibrating channel. Determining the density of a flowable material in a Coriolis flowmeter is known in the art. At step 604, the gas compressibility z is set to 1 in the following formula:

where P is the flow pressure, T is the temperature, M is the molar weight of the material flowing in the Coriolis flowmeter, and the first pressure is calculated. At step 606, the best z value is determined using the calculated pressure P. The gas compressibility z at a given pressure P can be determined using information from AGA Report No. 8, conversion tables for compressibility, state equations for compressibility, and the like. At 608, the pressure is recalculated using the new compressibility z. If the pressure value determined in step 608 does not converge to a predetermined threshold, the processing returns to step 606 where the best estimate of gas compressibility is determined using the last calculated value for pressure P. If the pressure value determined in step 608 converges to a predetermined threshold, pressure is successfully derived from the density of the flow. The deduced pressure can be used in a number of ways.

In one exemplary embodiment of the invention, pressure may be displayed or transmitted to a device external to the Coriolis flowmeter. For example, a pressure value may be transmitted to a monitoring device that monitors the pressure inside the pipe to detect unreliable pressure conditions. In another exemplary embodiment of the present invention, the pressure value can be used to correct the effect of pressure in the mass flow measurement by a Coriolis flowmeter. The pressure effect is typically set as a percentage of the flow rate per unit pressure change. A possible way to correct the pressure effect is to use equation (4):

where M _corrected is the adjusted specific mass flow rate, M _raw is the measured untreated specific mass flow rate, P _e is the pressure effect, P _static is the current pressure, P _cal is the pressure at which the flow rate is calibrated at the moment. P _e is typically a function of the geometry of a Coriolis flowmeter, for example, channel diameter, channel wall thickness, channel stiffness, etc. Equation (4) shows that if the pressure in the flowmeter is equal to the pressure at which the flowmeter is calibrated, then the adjusted flow is equivalent to the original (untreated) flow. If the current pressure is higher than the calibrated pressure, then the corrected flow will be less than the measured flow.

If the Coriolis flowmeter displays the flow pressure using the measured density, then the molar weight and temperature of the material flowing through the flowmeter are required. Temperature may be measured using a sensor in the flow meter or may be provided from an external temperature sensor. The molar weight of the gas can be entered by the user or provided from an external source. If the user enters a molar weight for the material, he can enter it directly by typing on the keyboard or he can enter it indirectly by identifying the flowing material by its name or gas composition. If the user enters a fluid name or gas composition, the Coriolis flowmeter can use the conversion table to determine the corresponding molar weight for that material.

In another exemplary embodiment of the present invention, the measured fluid density is used to determine the current pressure using a calibrated pressure / density ratio at the high pressure point and at the low pressure point. Since the pressure / density ratio is approximately linear, after the meter has been calibrated at two different pressure points, the pressure can be inferred from the current density without iteration. During calibration, the pressure in the flow meter must be accurately measured. 7 is a flowchart showing a method for calibrating a flow meter at two pressure points. At 702, a first level pressure acts on the material in the flowmeter. At 704, material density is measured using a flow meter at a first pressure. At step 706, second level pressure acts on the material in the flowmeter. At step 708, the density of the material is measured at a second pressure. When calibrating the flowmeter, material may flow through the flowmeter or may be static inside the flowmeter. The flowmeter can be calibrated for each type of material flowing through the Coriolis flowmeter. In one exemplary embodiment of the invention, the high and low calibration points can be stored in a table for various types of material for which measurements can be made in the flow meter. If the type of material flowing through the meter is introduced into the flowmeter, it will refer to the conversion table to find calibration points for this type of material.

After the flowmeter is calibrated for a given material, the material pressure can be determined from the density using equation (5):

- текущая измеренная плотность материала, протекающего через расходомер. На фиг.8 представлен график, показывающий отношение плотности к давлению для Ekofish в диапазоне давлений от 314 фунт/дюйм² (220,8 г/мм²) до 1014 фунт/дюйм² (712,9 г/мм²). Как можно видеть из фиг.8, совпадение между линейной линией и действительной кривой довольно близкое.where P _determined is the specific pressure, P _low is the pressure at the low pressure calibration point, P _high is the pressure at the high pressure calibration point, ρ _low is the density measured at the calibration point at low pressure, ρ _high is the density measured at the calibration point at high pressure, ρ _current

- the current measured density of the material flowing through the flow meter. 8 is a graph showing the density ratio for Ekofish pressure in the pressure range from 314 lb / ⁱⁿ² (220.8 g / mm ²⁾ to 1014 lb / ⁱⁿ² (712.9 g / mm ^2). As can be seen from Fig. 8, the coincidence between the linear line and the actual curve is quite close.

In another exemplary embodiment of the invention, the calibration information of the high and low pressure can be adjusted taking into account changes in the temperature of the fluid material. FIG. 9 is a flowchart for determining a current temperature-adjusted flow pressure using high and low pressure calibration points. At 902, compressibility is determined for each of the high and low pressure calibration points. Compressibility can be determined using three methods (rough AGA method 1, method 2 or detailed method) disclosed in AGA Report No. 8, conversion tables for compressibility, state equations for compressibility, etc. At 904, the average molar weight for the high and low pressure calibration points is determined. The representation of equation (1) in the form for a solution with respect to molar weight has the form:

where M is the molar weight of the material, P is the measured pressure at the low and high pressure calibration points, Z is the compressibility determined in step 902, T is the temperature measure at the high and low calibration points, ρ is the density measured at the high and low calibration points pressure, R - constant. The molar weight for the high pressure calibration point is averaged with the molar weight of the low pressure calibration point to obtain the average molar weight. At 906, the current pressure P is determined using equation (5) and stored as the “last pressure estimate”. At 908, a new value for compressibility z is determined using the “latest pressure estimate”, current temperature, average molar weight of the material, and current density. In step 910, a “new pressure estimate” is calculated according to equation (3) using the compressibility determined in step 908, the average molar weight determined in step 904, current density and current temperature. At 912, a “new pressure estimate” is estimated using the following equation:

If the equation is true, then a “new pressure estimate” is set as the current pressure. If the equation is false, then the “new pressure estimate” is saved as the “last pressure estimate”, and the processing returns to step 906. Using this iterative method, the effects of temperature changes in the fluid material can be taken into account when determining the pressure using the calibration points high and low pressure.

Claims (8)

1. A method for determining pressure, comprising:
measuring the density of the material flowing through the Coriolis flowmeter (602);
determination of the pressure of a fluid material from the measured density, characterized by the following steps:
(a) setting the compressibility value z to 1 in the equation

and calculating the value for pressure P (604), where T is the measured temperature, M is the molar weight of the material flowing in the Coriolis flowmeter, ρ is the density and R is a constant ;,
(b) using the calculated pressure value P to determine a more accurate value for compressibility z (606);
(c) using a new, more accurate value for compressibility z to recalculate the value for pressure P (608);
(d) repeating steps (b) and (c) until, as a result of convergence, the pressure value is within predetermined limits. 2. The method according to claim 1, in which the user is prompted to enter the molar weight (M) of the material passing through the flow meter. 3. The method according to claim 1, in which the user is prompted to enter the type of gas, while the Coriolis flowmeter determines the molar weight (M) of the material passing through the flowmeter based on the type of gas. 4. The method according to claim 1, further comprising transmitting a certain flow pressure to an external device. 5. Coriolis flowmeter configured to perform the method according to claim 1, containing:
a channel made to accommodate a fluid material (502);
at least one pathogen configured for channel vibration (504);
first and second sensors (506) configured to measure the movement of the vibrating channel;
a sensor configured to measure the temperature of the fluid material;
a processor configured to determine the density of the fluid material based on the movement of the vibrating channel (508),
wherein the processor is configured to determine the pressure of the flowing material based on the determination of density by performing steps (a) to (d). 6. A method for determining pressure, comprising:
(a) calibrating the ratio of density to pressure of a Coriolis flowmeter for a material for a low pressure point;
(b) calibrating the ratio of density to pressure of a Coriolis flowmeter for a material for a high pressure point;
(c) maintaining two calibrated relationships for the material;
(d) determining the current pressure for the material based on the measured current density and two stored calibration relationships, characterized by the following steps:
(e) determining compressibility z for high and low pressure points (902);
(f) determining the average molar weight M for the high and low pressure points;
(g) the definition of "the latest assessment of P pressure" using the equation

where T is the temperature, M is the average molar weight of the material flowing in the Coriolis flowmeter, ρ is the density and R is the constant,
(h) determining the new compressibility z using the “latest pressure rating P”;
(i) calculating a “new pressure estimate” (910);
(j) repeating steps (g) to (i) until, as a result of convergence, the value of the “new pressure estimate” is within predetermined limits. 7. Coriolis flowmeter configured to perform the method according to claim 6, containing:
a channel made to accommodate a fluid material (502);
at least one pathogen configured for channel vibration (504);
first and second sensors (506) configured to measure the movement of the vibrating channel;
a sensor configured to measure the temperature of the fluid material;
a processor configured to determine the density of the fluid material based on the movement of the vibrating channel (508);
moreover, the processor is configured to determine the pressure of the flowing material based on the determination of density by performing steps (a) to (j). 8. The Coriolis flowmeter according to claim 7, containing a memory region containing data on the ratio of pressure to density for the flowing material at two different pressure points, the pressure of the flowing material is determined using the density of the flowing material and the ratio of pressure to density at two pressure points.

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