VRPD Rotary Positive Displacement Gas Flowmeter
Brief Description：
Rotary positive displacement gas flow meter is a high precision, high reliability, wide range of gas monitoring and measuring instruments.
The intelligent Rotary positive displacement gas flow meter is a new type of flow meter that integrates flow, temperature, pressure sensors and intelligent instruments on the basis of a positive displacement flow meter.
It is an ideal instrument for measuring non-corrosive gases such as natural gas, city gas, propane, nitrogen, industrial inert gas.
Main Features:
● Wide measuring range: According to different specifications, the maximum turn down ratio can be up to 1:216.
● Low starting flowrate: According to different specifications, the minimum starting flowrate can be down to 0.04m3/h.
● High precision, high repeatability: Accuracy is not affected by the medium. It can run long-term with stable accuracy.
● Small pressure loss: According to different specifications, the pressure loss is 0.08kPa - 0.58kPa.
● High integration and low power consumption: Using 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, which makes the structure more compact.
●Digital pressure, temperature sensor: The instrument is equipped with a digital pressure sensor and a digital temperature sensor both of which could be calibrated and inspected individually. It makes replacement, maintenance and use of the flowmeter easy.
● Segmentation correction: According to the flow frequency signal, the meter coefficient can be automatically corrected linearly in six segments to improve the wide range accuracy of the meter.
● Complete data storage function: The flow meter E2PROM data storage chip, save user parameters, manufacturer parameters, timely data storage function, can prevent data loss when power failure suddenly, in the power failure state, internal parameters can be permanently saved。
● Multiple options of output
The intelligent flow meter has a base meter pulse output, a working condition or a standard condition pulse signal output, and a calibration pulse output. RS485 interface output, can also output 4 ~ 20mA standard analog signal according to user needs.
● Data traceability management
Real-time database, through RS-485 communication interface, can be queried and analyzed
● GPRS real-time management system
In this series, type B flow meter has GPRS transmission function, which can realize transmission function on line, timing and fixed point, and it is extremely easy to set up GPRS wireless network system.
Main structure of the intelligent roots flow meter
Intelligent roots flow meter is composed of 5 parts:
1. Intelligent flow accumulator
2. Flow sensor
3. Pressure sensor
4. Temperature sensor
5. Roots flow meter body
Please refer to the picture right.
Working principle
The intelligent gas roots flowmeter is mainly composed of a casing, a conjugate rotor and an intelligent flow totalizer. The pair of conjugate rotors installed in the metering chamber maintain the correct relative position of the rotor by the precision-machined adjustment gear under the action of the pressure difference between the inlet and outlet of the flow of gas (Pin>Pout). The optimal working clearance is maintained between the two rotors, the rotor and the housing, and between the rotor and the wall plate, achieving a continuous contactless seal. Each revolution of the rotor outputs four times the effective volume of the metering chamber. The measurement process and working principle are shown in Figure 1 (only one quarter cycle is shown in the figure).
Main Specification and functions
Standards:
This flowmeter is in conformity with the measurement technical specifications and standards of JB/T 7385-1994 "Gas Roots Flowmeter" and JJG633-2005 "Gas Volumetric Flowmeter Verification Regulations", in line with the national standards GB3836.1-2010 "Explosive Environment No. 1 Part: General Requirements for Equipment and GB3836.4-2010 "Explosive Environments Part 4: Intrinsically Safe "i" Equipment".
Accuracy:
Grade 1.0：Qmax-0.2Qmax ±1.0% 0.2 Qmax-Qmin ±2.0%
Grade 1.5：Qmax-0.2Qmax ±1.5% 0.2 Qmax-Qmin ±3.0%
The default accuracy the flowmeters is grade 1.5 without special note. Other accuracy is available on request
Flowmeter specifications, basic parameters and performance table:
| Model | Nominal Diameter | Down Ratio | Measuring Range M3/h | Start-up Flowrate M3/h | Pressure Loss at Qmax KPa | Factor | Pmax MPa | Nominal Pressure MPa | Material |
| VRPDG-10 | 25 | 12:1 | 0.5-10 | 0.04 | 0.10 | <0.6 | 1.6 | Aluminium Alloy | |
| VRPDG-16 | 25 | 20:1 | 0.8-16 | 0.04 | 0.10 | 7633.37 | |||
| VRPDG-25 | 40 | 25:1 | 1-25 | 0.07 | 0.10 | 4694.65 | <2.0 | 2.5 | |
| VRPDG-40 | 40 | 40:1 | 1-40 | 0.07 | 0.14 | 3892.31 | |||
| VRPDG-60 | 50 | 65:1 | 1-65 | 0.1 | 0.10 | 1584.24 | |||
| VRPDG-85 | 50 | 70:1 | 1.1-85 | 0.1 | 0.14 | 1584.24 | |||
| VRPDG-100 | 80 | 70:1 | 1.5-100 | 0.1 | 0.11 | 987.581 | |||
| VRPDG-150 | 80 | 120:1 | 1.2-150 | 0.12 | 0.15 | 730.785 | |||
| VRPDG-200 | 80 | 70:1 | 3-200 | 0.15 | 0.18 | 479.837 | |||
| VRPDG-250 | 100 | 80:1 | 3-250 | 0.11 | 0.18 | 306.804 | <1.2 | 1.6 | |
| VRPDG-300 | 100 | 120:1 | 2.5-300 | 0.11 | 0.13 | 306.804 | |||
| VRPDG-450 | 100 | 110:1 | 4-450 | 0.1 | 0.20 | 231.350x2 | |||
| VRPDG-500 | 100 | 125:1 | 4-500 | 0.1 | 0.20 | ||||
| VRPDG-650 | 150 | 80:1 | 8-650 | 0.65 | 0.35 | 86.7083 | Aluminium Cast ion | ||
| VRPDG-1000 | 150 | 90:1 | 11-1000 | 0.76 | 0.45 | 61.8990 | |||
| VRPDG-1600 | 200 | 64:1 | 25-1600 | 1.2 | 0.50 | 50.2425 | |||
| VRPDG-3000 | 250 | 40:1 | 75-3000 | 8.0 | 0.45 |
Working Conditions:
Standard state condition: P=101.325 kPa, T= 293.15k
Working condition: Ambient temperature: -25℃ - +80℃; Medium temperature: -20℃ - +60℃
Relative humidity: 5% - 95%; Atmospheric pressure: 86KPa - 106KPa
Electrical Performance:
Power supply: Internal power supply: One piece of a 3.6V DC lithium battery, the instrument can work normally when the battery voltage is 3.1V to 3.6V.
External power supply: ±24VDC±15%, ripple ≤±5%, suitable for 4~20mA output, pulse output, RS-485, etc.
Power Consumption: For external power supply: less than 1w
For internal power supply: Average power consumption ≤1m W. The instrument can work continuously with one piece of the battery for more than five years.
Working condition pulse output:
The working condition pulse signal detected by the flow sensor is directly isolated, amplified and output by the optocoupler, and the high level is ≥20V, and the low level is ≦1V. This pulse is mainly used to calibrate the meter;
The frequency signal proportional to the standard volume flow is isolated, amplified and output by the optocoupler, high level ≥ 20V, low level ≤ 1V.
The calibration pulse signal has an output amplitude of 0 to 3V and an output pulse width of 500ms. This pulse is mainly used for IC card control devices or other equipment for city gas metering. The flow meter outputs 1 pulse for 1m3 .
Current output: 4～20mA standard analog current output function
In proportion to the standard volume flow, 4 mA corresponds to 0 Nm3/h, and 20 mA corresponds to the maximum standard volume flow (this value can be set).
The output form is: two-wire or three-wire
RS485 communication:
It can be connected to a host such as a personal computer or a PLC through the built-in RS485 standard interface for serial communication. Can display media pressure, temperature, instantaneous flow, cumulative standard flow, battery voltage, etc.
GPRS communication:
Serial communication is carried out via the built-in GPRS system. It can works for a remote meter reading system
Display media pressure, temperature, instantaneous flow, cumulative standard flow, battery voltage, etc.
Valve control output:
Optional valve control, direct control of valves for independent control and remote control
