Vortex flowmeter communication type

Vortex FlowmeterIt is a fluid oscillation type flow meter developed based on the principle of Karman vortex street, with high signal-to-noise ratio, high sensitivity, and strong seismic resistance. The signal circuit adopts single-chip technology for data processing, encapsulating the CPU unit, storage unit, display unit, communication unit, and other functional modules in the amplification circuit, with very stable zero point and accuracy. Widely applicable to the measurement and control of superheated steam, saturated steam, compressed air, general gases (oxygen, nitrogen, hydrogen, natural gas, coal gas, etc.), water, and liquids (such as water, gasoline, alcohol, benzene, etc.) in industries such as petroleum, chemical, metallurgical, thermal, textile, paper, etc.

Vortex flowmeter communication type, with RS485/232 and Modbus protocol, HART protocol type.

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485 communication characteristics：

Due to its excellent resistance to noise interference, long transmission distance, and multi station capability, RS-485 interface has become the preferred serial interface. Because the RS485 interface is composed ofA half duplex network typically only requires two wires, so RS485 interfaces are transmitted using shielded twisted pair cables. The RS485 interface connector adopts a 9-pin plug socket of DB-9, and the RS485 interface with the smart terminal adopts DB-9 (hole). The keyboard interface RS485 connected to the keyboard adopts DB-9 (pin).

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485 communication protocol:（Communication Protocol for Vortex Flow Meter）（MODBUS-RTU）

1. RTU Data Format Description

1.1 Communication mode

This instrument adopts MODBUS RTU format. The protocol is used for data communication in master-slave query mode.

1.2 Data Format

The format of each byte (11 bits) in RTU mode is:

The encoding system is 8-bit binary

Each byte has 1 start bit, 8 data bits (sending the least significant bit first), 1 parity bit, and 1 stop bit

Note: When using unverified data, 2 stop bits are required

Five baud rates are available: 1200, 2400, 4800, 9600, 19200

Note:

(1) In RTU mode, an idle interval of at least 3.5 characters is used to distinguish message frames.

(2) The entire message frame must be sent in a continuous stream of characters.

(3) The idle interval between two characters should not exceed 1.5 character times.

1.3 Address

The protocol stipulates that the address of the instrument is "0-255", and the "0" address is used for broadcasting. This protocol does not support broadcasting, and other addresses are reserved.

2. Command Description

2.1 This instrument uses one instruction from the MODBUS protocol:

Command 03 Read single or multiple hold registers

2.2 Data Format

The data format in the protocol is: floating point number. Modbus first sends the most significant word. The encoding order of the data in this agreement is 3412, and the decoding order is 1234.

The 32 single precision floating-point number SINGLE format is IEEE754, which is equivalent to 4 bytes and arranged in the order of 3-4-1-2.

After decoding into 1-2-3-4 order, the bits from highest to lowest are the 31st, 30th, 29th, „„, and 0th bits, respectively.

Note:

31 bits is the sign bit (S), where 1 indicates that the number is negative and 0 is positive; 30-23 bits, a total of 8 bits are order codes; 22-0 digits, a total of 23 digits are the tail.

The format of command 03 is as follows (read register command):

Meaning of Exception Code:

'01' - Function code error, the function code of this agreement is 0x03

'02' - Register physical address error, 0 ≤ starting physical address+register quantity ≤ 12

'03' - Register quantity error, 0 ≤ Register quantity ≤ 12

Note:

Accumulated traffic=Accumulated volume over 100 x 100+Accumulated volume below 100

Default setting of instrument: machine number -1; Baud rate -9600; Parity Check - No Check

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Vortex FlowmeterCommunication typeCommon model: DVS-DS50F11T

Model annotation: Vortex flowmeter, medium is steam, DN50， The material of the watch body is 304 stainless steel, with a medium temperature of room temperature and a rated pressure of 1.6MPa; The 485 communication interface supports MODBUS protocol, 24V power supply, and is equipped with carbon steel installation flanges, bolts, nuts, and other fasteners.

(485 communication output below 250 ° C)

(High temperature type 485 communication output above 250 ° C and below 330 ° C)

Vortex flowmeter communication type, often used with secondary instrumentsIntelligent traffic integratorUsed in conjunction or directly integrated into the PLC system.

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Working principle

If a non streamlined vortex generator (flow resistant fluid) is set up in the fluid, two columns of regular vortices are alternately generated from both sides of the vortex generator. This type of vortex is called a Karman vortex street, as shown in Figure (1).

Figure (1)

The vortices are arranged asymmetrically downstream of the vortex generator. Assuming the frequency of vortex occurrence is f, the average velocity of the incoming flow of the measured medium is V, the width of the upstream face of the vortex generator is d, and the diameter of the body is D, according to the principle of Karman vortex street, the following relationship is obtained:

Formula (1) for f=StV/d

In the formula:

F - frequency of Karman vortex generated on one side of the body

St Strouhal number (dimensionless number)

V - Average flow velocity of fluid

D - width of vortex generator

From this, it can be seen that the instantaneous flow rate can be calculated by measuring the separation frequency of the Karman vortex street. Among them, Strouhal number (St) is an dimensionless unknown variable,

Figure (2) shows the relationship between Strouhal number (St) and Reynolds number (Re).

In the straight part of the curve table with St=0.17, the frequency of vortex release is proportional to the flow velocity, which is the measurement range of the vortex flow sensor. As long as the frequency f is detected, the flow velocity of the fluid inside the pipe can be obtained, and the volumetric flow rate can be calculated from the flow velocity V. The ratio of the measured number of pulses to the volume is called the instrument constant (K), as shown in equation (2)

　

K=N/Q (1/m ³) formula (2)

In the formula: K=instrument constant (1/m ³).

N=number of pulses

Q=Volume flow rate (m ³)

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Specification

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Determination and installation design of instrument caliber

Instrument selection is a highly valued task in instrument applications, and the correctness of instrument selection will directly affect whether the instrument can operate normally Therefore, when users and design units choose our company's products, please carefully read the information in this section, carefully check the process parameters of the fluid, and feel free to contact our sales or technical support department at any time to ensure the correct selection.

1、 Determination of applicable flow range and instrument diameter

The selection of instrument caliber is determined based on the flow range. The measurement range of vortex flowmeter with different calibers is different. Even if the same caliber flowmeter is used for different media, its measurement range is also different. The actual measurable flow range needs to be determined through calculation.

（1） The flow range of air and water under reference conditions is shown in Table (2), and the reference conditions are as follows:

1. Gas: Normal temperature and pressure air, t=20 ℃, P=0.1MPa (absolute pressure), ρ=1.205 kg/m3, υ=15 × 10-6 m2/s.

2. Liquid: Room temperature water, t=20 ℃, ρ=998.2kg/m3, υ=1.006 × 10-6m2/s.

（2） The basic steps for determining the flow range and instrument diameter are:

1. Clearly define the following working parameters.

(1) Name and composition of the tested medium

(2) Minimum and commonly used working conditions、maximum flow

(3) Minimum, common, and maximum pressure and temperature of the medium

(4) Viscosity of the medium in working condition

2. The vortex flowmeter measures the working state volume flow rate of the medium, so the working state volume flow rate of the medium should be calculated based on the process parameters first. The relevant formula is as follows:

(1) Given the standard state volumetric flow rate of a gas, the operating condition volumetric flow rate can be calculated using the following formula

Formula (3)

(2) Given the standard state density of the gas, ρ, the operating density can be calculated using the following formula

(3) Convert the known mass flow rate Qm to volume flow rate Qv

In the formula:

Qv: Volume flow rate of the medium under operating conditions (m3/h)

(Qv=3600f/K K: Instrument coefficient)

Qo: Volume flow rate of the medium under standard conditions (Nm3/h)

Qm: Mass flow rate (t/h)

ρ: Density of the medium under working conditions (kg/m3)

ρ o: Density of the medium in standard state (kg/m3), standard state density of commonly used gas media, as shown in Table (3)

P: Operating condition gauge pressure (MPa)

t: Operating condition temperature (℃)

3. Determination of the lower limit flow rate of the instrument. The upper limit of the applicable flow rate of vortex flowmeter is generally not calculated, and the selection of the diameter of vortex flowmeter is mainly for the calculation of the lower limit of flow rate. The calculation of the lower limit flow rate should meet two conditions: the minimum Reynolds number should not be lower than the limit Reynolds number (Re=2 × 104); The vortex intensity generated by the stress type vortex flowmeter at the lower limit flow rate should be greater than the allowable value of the sensor vortex intensity (the vortex intensity is proportional to the lift ρ v2). These conditions can be expressed as follows:

The measurable lower limit flow rate for operating conditions determined by density:

Linear lower limit flow determined by kinematic viscosity:

Formula (7)

In the formula:

Q ρ: Minimum volumetric flow rate (m3/h) that meets the requirements of vortex strength

ρ 0: Density of the medium under reference conditions

Q υ: Minimum linear volumetric flow rate (m3/h) that meets the minimum Reynolds number requirement

ρ: Density of the tested medium under working conditions (kg/m3)

Q0: Minimum volumetric flow rate of the instrument under reference conditions

(m3/h)

υ: Kinematic viscosity of the medium under working conditions (m2/s)

υ o: Kinematic viscosity of the medium under reference conditions (m2/s)

Calculate Q ρ and Q ν using formulas (6) and (7). Compare Q ρ and Q ν to determine the measurable lower limit flow rate and linear lower limit flow rate of the flow meter:

Q_υ≥QρThe measurable flow range is Qρ～Qmax , The linear flow range isQυ～Qmax

Q_υ<Qρ: Measurable flow range andThe linear flow range is

Q_ρ～Qmax

Qmax: Upper limit volume flow rate of vortex flowmeter(m³/h)

4. The upper limit flow rate of the instrument shall be based on the upper limit flow rate in Table (2) The upper limit flow rate of gas should be less than 70m/s, and the upper limit flow rate of liquid should be less than 7m/s

When the medium measured by the user is steam, the commonly used unit of measurement is mass flow rate, which is t/h or Kg/h. Due to the varying densities of steam (superheated steam and saturated steam) at different temperatures and pressures, the determination of the steam flow range can be calculated using formula (8)

Formula (8)

In the formula:

ρ: Density of steam (kg/m3)

ρ0：1.205kg/m3

Q Steam: Steam mass flow rate (t/h)

6. Calculate the pressure loss and detect whether the pressure loss has an impact on the process pipeline. Formula (unit: Pa):

Δ p=Cd ρ V2/2 formula (9)

In the formula:

ρ: Density of working medium (kg/m3)

V: Average flow velocity (m/s)

When the measured medium is a liquid, in order to prevent gasification and cavitation, the pipeline pressure should meet the following requirements:

Formula (10) for p ≥ 2.7 Δ p+1.3p0

In the formula:

Δ p: pressure loss (Pa)

P0: Saturated vapor pressure of liquid at operating temperature (Pa absolute pressure)

Po: Vapor pressure of fluid (Pa absolute pressure)

8. Vortex flowmeters are not suitable for measuring high viscosity liquids. When the calculated lower limit of measurable flow does not meet the design process requirements, other types of flow meters should be considered for selection.

9. If both calibers can meet the requirements through calculation, in order to improve measurement efficiency and reduce costs, the smaller caliber meter should be selected. It should be noted that the commonly used amount should be kept at 1/2 to 2/3 of the upper limit of the flow range as much as possible

Δ p: pressure loss (Pa) Cd: pressure loss coefficient

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Example of selection:

Example 1：When the gas pressure, temperature, and flow rate under standard conditions are known

A certain compressed air has a standard flow rate range of QN=1200-12000Nm3/h, pressure P=0.7Mpa (gauge pressure), and temperature t=30 ℃. Try to determine the diameter of the flowmeter.

Step 1: Calculate the working condition volume flow rate of compressed air

According to formula (3):

The lower limit volume flow rate for operating conditions is:

Qvmin=QN×0.101325×(273.15+t)/293.15/（P +0.1）

=1200×0.101325×(273.15+30)/293.15/（0.7 +0.1）

=157(m3/h)

The upper limit of flow rate for operating conditions is Qvmax=1570 (m3/h)

Step 2: Based on the operating flow range of 157-1570m3/h, refer to Table (2). The flow meters that meet the lower limit flow conditions are DN80, DN100, and DN125. Considering the upper limit flow rate of 1270m3/h, usage effect, and economic cost, DN100 is initially selected. The operating flow range of DN100 flow meter is 100-1700m3/h, which is close to the operating flow range. DN100 flow meter is initially selected, but the measurable lower limit flow of DN100 flow meter under this operating condition should be specifically calculated. Calculate the measurable lower limit flow rate of DN100 flowmeter under this operating condition:

According to formulas (4) and (6):

That is, the measurable lower limit flow rate of the flowmeter under this operating condition is 37.46m3/h, which is much lower than the required lower limit flow rate of 157m3/h. Therefore, it is determined to use a DN100 flowmeter.

Example 2: When the steam pressure, temperature, and operating flow rate are known

The measuring medium is superheated steam, with a steam temperature of 320 ℃, a pressure of 1.5MPa (absolute pressure), and a flow range of 3t/h to 25t/h. Determine the diameter of the flow meter.

Step 1: Calculate the volumetric flow range of steam under the equivalent air reference condition. According to Appendix (2), the density of steam in this state is 5.665 Kg/m3, as calculated by formula (8):

Step 2: According to the equivalent reference flow range of 765-6379m3/h, refer to Table (2) and find that the DN200 caliber is more suitable for this flow range.

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Installation design of instruments

The correct installation of instruments is an important part of ensuring their normal operation. If not installed properly, it can affect the accuracy of instrument use, and in severe cases, it can affect the service life of instruments and even damage them.

（1） Installation environment requirements:

1. Try to avoid strong electrical equipment, high-frequency equipment, and strong switching power supply equipment as much as possible. The power supply of the instrument should be separated from these devices as much as possible.

2. Avoid direct effects from high-temperature heat sources and radiation sources. If installation is necessary, insulation and ventilation measures must be taken.

3. Avoid high humidity and strong corrosive gas environments. If installation is necessary, ventilation measures must be taken.

4. Vortex flow meters should be avoided from being installed on pipelines with strong vibration as much as possible. If installation is necessary, pipeline fastening devices must be added at the 2D upstream and downstream locations, and anti vibration pads must be added to enhance resistance

Vibration effect.

5. It is recommended to install the instrument indoors and pay attention to waterproofing when installing outdoors. Special attention should be paid to bending the cable into a U-shape at the electrical interface to prevent water from entering the amplifier housing along the cable

Inside.

6. There should be ample space around the instrument installation point for wiring installation and regular maintenance.

（2） Installation requirements for instrument pipelines:

1. Vortex flowmeter has certain requirements for the upstream and downstream straight pipe sections of the installation point, otherwise it will affect the flow field of the medium in the pipeline and affect the measurement accuracy of the instrument. The length requirements for the upstream and downstream straight pipe sections of the instrument are shown in Figure (III)

Note: The regulating valve should not be installed upstream of the vortex flowmeter as much as possible, but should be installed at 10D downstream of the vortex flowmeter.

1. The inner diameter of the upstream and downstream piping should be the same. If there is a difference, the inner diameter Dp of the piping and the inner diameter Db of the vortex instrument body should satisfy the relationship:0.98Db ≤ Dp ≤ 1.05Db and upstream and downstreamjoin in marriage

The tube should be concentric with the inner diameter of the flow meter body, and the different axial degrees between them should be less than 0.05Db

As shown in Figure (4b)

When measuring high and low temperature media, attention should be paid to insulation measures. The high temperature inside the converter (inside the header housing) should generally not exceed 70 ℃; Low temperature can easily cause condensation inside the converter, reducing the insulation impedance of the printed circuit board and affecting the normal operation of the instrument.

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Vortex FlowmeterReal photos of products in the same series:

(Flange type)

(Sanitary type)

(Threaded connection)

(High temperature type)

(Online voltage stabilization compensation type)

(Different calibers)

(Anti corrosion type)

(Insertion type)

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After sales and warranty

Shanghai Shihong Instrument Co., LtdAll products supplied:

Provide free telephone consultation, guidance on installation and debugging services;

Negotiate on-site guidance for installation, debugging, and other matters, and only charge reasonable travel expenses;

Large quantities can provide free on-site guidance for installation and debugging.

Service Objective:No matter how long the product is used, as long as you find us, we will solve all your problems until you are satisfied. We believe that our years of practical experience in the flowmeter industry can bring you satisfactory services.

24-Hour Hour Hotline:(Same WeChat account)