LLGQ Gas Roots (Roots) Flowmeter

General

The gas roots flowmeter has been used as a volumetric meter for more than 100 years.  With the features such as high precision, wide range, small volume, light weight, convenient installation and maintenance, reliable and durable service life, it is widely used in natural gas, coal gas, air and other gas flowmeters.It is an ideal flowmeter device for urban gas, oilfield chemical, scientific research and other departments at home and abroad.

Features

• It integrates high-precision temperature, pressure, flow sensor and intelligent volume corrector to detect the temperature, pressure and flow of the measured gas and perform automatic flow track and compensation and compression factor correction.

• Use advanced microcomputer technology and high-performance integrated chip, it has powerful functions and superior performance.

• The circuit uses the surface mount technology, with compact structure, strong anti-interference ability and high reliability.

• Use advanced micro-power high-tech, the whole machine has low power consumption, that is, it can run with built-in battery for long time, and can be operated by external power supply.

• According to the flow frequency signal, the meter factor can be automatically corrected linearly in five segments, to improve the accuracy of the meter.

• With fault self-diagnosis and alarm function, high reliability, LCD display, clear and intuitive, easy to read.

• The flowmeter has a pulse signal output, and can also output 4~20mA standard analog signal according to user needs.

• The meter has its own real-time database, and it forms a meter reading network through R5-485 communication interface to facilitate centralized data collection and real-time management.

• Use advanced micro-power technology, low power consumption. It can run for more than five years using built-in battery. It displays the flow value locally with various signal output functions to meet the needs of different fields and systems. It uses EEPROM data storage to save user parameters, manufacturer parameters and a certain history.

• Use high-contrast three-line LCD display for displaying date, standard cumulative flow, standard instantaneous flow, medium temperature, pressure, and battery voltage.

• With real-time data storage function, it can avoid data loss when battery is replaced or suddenly power down. In the power-off state, internal parameters can be permanently saved.

Structure and Working Principle

(1). The flowmeter consists of 5 parts (see Figure 1)

Figure 1  Schematic diagram of the flowmeter structure

1. Intelligent flow totalizer     2.Flow sensors     3.Pressure sensor     

4. Temperature sensor        5.Gas roots flowmeter (mechanical)

(2)Intelligent gas roots flowmeter working principle (see Figure 2)

The intelligent gas roots flowmeter consists of a housing, a conjugate rotor and an intelligent flow totalizer. Under the action of the pressure difference between the inlet and outlet of the circulating gas (P inlet>P>outlet),the pair of conjugate maintain the correct relative position of the rotor through the precision-machined adjusting gear.The optimum working gap between the rotor, the rotor and the housing, and the rotor and the wall plate achieves a continuous non-contact seal. For each revolution of the rotor,it outputs four times the effective volume of the metering chamber, and the number of revolutions of the rotor is transmitted to the intelligent flow totalizer through the magnetic sealing coupling device and the speed reducing mechanism, to display the cumulative volume of the output gas.

(The figure shows only a quarter cycle).

3.Intelligent flow totalizer working principle

The intelligent flow totalizer consists of temperature and pressure detection analog channel, flow sensor channel and microprocessor unit, and is equipped with an external signal interface to output various signals. The microprocessor in the intelligent flow totalizer performs  temperature and pressure compensation and compression factor correction according to the gas equation. The gas equation is as follows:

Where:

Qn: volume flow rate under standard condition (m3/h);

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

Pg: meter pressure at the flowmeter pressure detection point (KPa)

Pa: local atmospheric pressure (KPa);

Tg: absolute temperature(273.15 + t) (K) of the medium;

t: measured medium temperature (°C);

Zn: compression factor under standard condition;

Zg: compression factor under working condition;

Tn: absolute temperature (273.15+20) (K) under standard state;

Pn: standard atmospheric pressure (101.325KPa);

P: P = Pa + Pg.

Note: for natural gas Zn/Zg=Fz2 and Fz is called the ultra-compressed factor, this product is calculated according to the formula in SY/T6143-1996 standard of China national petroleum corporation.

 Main Technical Parameters and Functions

1.LLGQ series gas roots flowmeter has typical error curve and pressure loss curve of volumetric gas flowmeter. See Figure 2 for details. The main technical parameters of various specifications are listed in Table 1.

1. Flowmeter specifications                                          Table 1

2.Modeling description                                                 Table 2