Product introduction

Gas roots flowmeter is a kind of gas monitoring and measuring instrument with high precision, high reliability and wide range.

Intelligent gas roots flowmeter is a new type of flowmeter which integrates flow, temperature, pressure sensors and intelligent instrument on the basis of roots flowmeter.

Intelligent gas roots flowmeter is an ideal instrument for measuring non-corrosive gases such as natural gas, city gas, propane, nitrogen, industrial inert gas, etc.

Main features of the product:

★Wide range:

According to different specifications, the highest range can reach 1: 216

★Low initial flow:

According to different specifications, the minimum starting flow can reach 0.04m3/h.

★High precision and repeatability:

The long-term accuracy is not affected by the medium, and the long-term operation is stable.

★Low pressure loss:

According to different specifications, the pressure loss is 0.08kPa-0.58kPa.

★High integration and low power consumption

Adopting advanced microcomputer technology and high-performance integrated chip.The whole machine has powerful functions and superior performance.

★Compact structure:

Pressure sensor, temperature sensor and flow sensor are all built in, making the structure more compact.

★Digital pressure temperature sensor

Digital temperature sensor and digital pressure sensor are configured, calibrated and verified separately, and are convenient to replace, maintain and use.

★Segment correction

According to the flow frequency signal, the instrument coefficient can be automatically linearly corrected in six segments to improve the wide range accuracy of the instrument.

★Complete data storage function

E2PROM data storage chip is used to store user parameters, manufacturer parameters and timely data storage function to prevent data loss in case of sudden power failure. In case of power failure, internal parameters can be stored permanently.

★The basic output is complete.

The intelligent flowmeter has a base meter pulse output, a working condition or standard temperature and pressure pulse signal output, and a calibration pulse output. RS485 interface can also output 4 ~ 20mA standard analog signals according to user's requirements.

★Data traceability management

Real-time database can be queried and analyzed through RS-485 communication interface.

★GPRS real-time management system

In this series, Type B meter has GPRS transmission function. It can realize transmission function online, with long timing and fixed point. It is extremely easy to set up GPRS wireless network system.

The structure and working principle

Intelligent roots flowmeter is composed of 5 parts (see figure 1)

product-520-490

Figure 1 Composition Diagram Of Intelligent Roots Flowmeter

1)gas roots flowmeter 2) flow sensor 3) pressure sensor 4) temperature sensor 5)intelligent flow totalizer

Working Principle of Intelligent Gas Roots Flowmeter (see figure 2)

Intelligent gas roots flowmeter is mainly composed of shell, conjugate rotor and intelligent flow totalizer. A pair of conjugate rotors installed in the metering chamber maintain the correct relative positions of the rotors through precision-machined adjusting gears under the action of the inlet and outlet pressure difference (p in > p out) of the circulating gas. The best working clearance is maintained between the rotors, between the rotors and the shell, and between the rotors and the wallboard, thus realizing continuous non-contact sealing. Each revolution of the rotor outputs four times the effective volume of the metering chamber. The metering process and working principle are shown in fig. 1 (only a quarter cycle is shown in the figure).

Position 1

Gas enters the upstream chamber of the instruinstrument

Position 2

Gas pushes the roots to rotate.

Position 3

Gas exits the metering chamber through the metering chamber

Position 4

Each pair of rotors rotates once to discharge equal volume of gas 4 times.

Intelligent flow totalizer working principle

The intelligent flow totalizer consists of temperature and pressure detection, flow sensor and microprocessor unit. The microprocessor in the intelligent flow totalizer performs temperature and pressure compensation and compression factor correction according to the gaseous equation, which is as follows:

product-274-50

Type:

Qn: Volume flow rate in standard state (m3/h);

Qg: Volume flow rate under working condition (m3/h);

Pg: Gauge pressure (kPa) at pressure detection point of flowmeter;

Pa: Local atmospheric pressure (kpa);

Tg: Absolute temperature of medium (273.15+t) (k);

T: Temperature of medium to be measured (℃);

Zn: Compression coefficient in standard state;

Zg: Compression coefficient under working condition;

Tn: Absolute temperature in standard state (273.15+20) (k);

Pn: Standard atmospheric pressure (101.325 kPa).

Note: Natural gas Zn/ZG = Fz2, FZ is called super compression factor.

Technical Parameters And Main Functions

Accuracy grade:

Class 1.0：Qmax-0.2Qmax ±1.0% 0.2 Qmax-Qmin ±2.0%

Class 1.5：Qmax-0.2Qmax ±1.5% 0.2 Qmax-Qmin ±3.0%

Products that are not specially marked shall be delivered in accordance with Class 1.5 precision. For other precision, special instructions shall be required for customization when ordering.

Flow meter specifications, parameters and performance indicators (see table 1)

Conditions of Use

Standard condition: P=101.325 kPa T= 293.15K

Conditions of use:

ambient temperature:-25 ℃ ~+80 ℃.

medium temperature:-20 ℃ ~+60 ℃

relative humidity: 5% ~ 95%

atmospheric pressure: 86 kpa ~ 106 kpa

Electrical Performance Indicators:

Working power supply:

Internal power supply: 1 section of 3.6VDC lithium battery, which can work normally when the battery voltage is between 3.1V and 3.6V. When the voltage is lower than 3.1V, replace the battery.

External power supply: 24 VDC 15%, ripple ≤ 5%, suitable for 4 ~ 20ma output, pulse output, RS-485, etc.

Overall power consumption:

External power supply, ﹤1W

Internal power supply, average power consumption ≤1m W, can work continuously for more than 5 years.

Working Condition Pulse Output Mode

Working condition pulse signal, which directly outputs the working condition pulse signal detected by the flow sensor through optocoupler isolation amplification, with high level ≥20V and low level ≦ 1V This pulse is mainly used to calibrate the instrument.

The frequency signal proportional to the standard volume flow rate is output through optocoupler isolation amplification, with high level ≥20V and low level ≤ 1V.

Scaling the pulse signal, with output amplitude of 0 ~ 3v and output pulse width of 500ms. This pulse is mainly used for IC card control devices or other equipment for city gas metering. This signal 1m3 outputs one pulse.

Current Output:

4 ~ 20mA Standard Analog Current Output Function

It is directly proportional to the standard volume flow rate, 4mA corresponds to 0 Nm3/h, 20mA corresponds to the maximum standard volume flow rate (this value can be set).

The output form is two-wire system or three-wire system.

RS485 Communication

Through the built-in RS485 standard interface, it can be connected with host computers such as personal computers and PLC for serial communication. It can display medium pressure, temperature, instantaneous flow rate, accumulated standard flow rate, battery voltage, etc.

GPRS communication

Serial communication is carried out through the built-in GPRS system. The remote meter reading system can be realized

Display medium pressure, temperature, instantaneous flow rate, accumulated standard flow rate, battery voltage, etc.

Valve Control Output:

It can choose valve control type, direct control valve, realize independent control and remote control.

Selection

Flowmeter Selection

The user shall estimate the maximum and minimum volume flow rate of the pipeline according to the gas transmission rate of the pipeline and the temperature and pressure range that the medium may reach, and correctly select the flowmeter specification. When both calibers of flowmeter can cover the lowest and highest volume flow, small calibers shall be selected under the permission of pressure loss.

Type selection calculation is based on formula (1)

Qg=Zg/Zn*Pn/(Pg+Pa)*Tg/Tn*Qn=101.325/(Pg+Pa)*(1/ Zn/Zg)*( Tg/293.15)Qn

Type:

Tg, Pg and Pa have the same meanings as above,

Qg is the volume flow rate,

Qn is the standard volume flow rate,

Zn/Zg values are listed in Table 2.

Due to the large calculation step size, the data in the table are for reference only. The data in the table are calculated according to the natural gas real density Gr=0.600 and the mole fractions of nitrogen and carbon dioxide are both 0.00. When the medium pressure is lower than 0.1 Mpa, it can be estimated by Zn/Zg=1.00.

Selection Examples:

It is known that the actual working pressure of a certain gas supply pipeline is 0.5 MPa to 0.6 MPa (gauge pressure), the medium temperature range is -10℃～+40℃, and the peak gas supply amount is 400 ~ 500 Nm3/h. The local atmospheric pressure is 101.3kPa, and it is required to determine the diameter of the flowmeter.

Analysis: Since the flow range given in Table 1 above is the flow range under actual working condition, it is necessary to convert the standard temperature and pressure flow into the working condition flow before selecting the appropriate diameter.

Calculation: When the medium pressure is the lowest and the temperature is the highest (the influence of natural gas compression factor may not be considered in the estimation and selection), the medium has the maximum volume flow when it is in the peak period of gas supply, so there are:

product-644-191