1 Structure and principle of the liquid volumetric flowmeter calibration device
The liquid accumulation calibration device consists of the quick connector, hydraulic hose, hydraulic filter, standard flowmeter, temperature transformer, pressure transformer, computer system, hydraulic source, etc. The hydraulic oil source also includes a hydraulic oil tank, variable frequency motor, hydraulic variable pump, hydraulic safety valve, and other components. The main features are compact installation, easy use, the same calibration medium, strong movement ability, and the ability to provide hydraulic oil. The working mode of the liquid flow controller is as follows: match through quick connection and replacement, and lead the hydraulic hose into the displaced liquid flow controller calibration device; The hydraulic power converter of the investment department generates clean and stable liquid flow through the hydraulic pump, hydraulic filter, etc. Capture the cumulative flow value determined by the computer system using the calibrated flowmeter and the standard flowmeter, and capture the temperature and pressure on the calibrated flowmeter and the standard flowmeter; The measured value error of calibrated flow is determined by the computer software system.
2 Main characteristics and application of common liquid flowmeter
2.1 Volumetric flowmeter
Volumetric flow meters (also called volume-specific flow values) are general-purpose instruments with the highest accuracy. The measured components can also be divided into the following main features: pitch circle (two rotors), plate flow measurement, oval gear flow measurement, rotary piston flow measurement, circulation flow measurement, etc. ① Advantages: high measurement accuracy; It can be used for measuring high viscosity fluid and simple phase fluid; The instrument does not need external energy to directly record the total flow. It is easy to install without special requirements for front and rear tangent lines. ② Disadvantages: not suitable for high temperature and low temperature; Type of measuring center with limited diameter; Pressure drop; Periodic calibration is required. ③ Application: Volume traffic signs, due to their high-precision measurement in energy, petroleum, medicine, food, chemistry, and other fields, especially raw materials and other fields, must be measured for storage, transfer, and distribution, and used as the basis for a financial settlement, or as a legal indicator of the contract between two tax dealers.
2.2 Differential
The differential is one of the most commonly used flowmeter types, which can be divided into diverter flowmeter, Wenzhou flowmeter, average line current, etc. according to the test piece (inlet instrument). The main characteristics are as follows: ① Advantages: There is a wide range of measurement methods for single-phase fluid, including mixed fluid; Simple structure, easy maintenance, the long service life of control components and detonators, display equipment produced by different manufacturers, improving economies of scale. ② Disadvantages: general customization accuracy; Large pressure loss (orifice plate, nozzle, etc.) The assembly constraint shall be high, and there shall be enough straight pipelines before and after assembly. ③ Nozzle: When measuring the flow in the closed pipe for the first time, the differential can be used for projects under different conditions where the flow is about 1/4-1/3 of the total flow.
2.3 Ultrasonic assistance
The ultrasonic flowmeter can be generally divided into plug-in type, pipe section type, external clamp type, and portable type. ① Advantages: non-contact measurement of large diameter, large flow calculation; Pressure loss, no fluid disturbance; Suitable for every liquid, easy to install and maintain. ② Disadvantages: When the measured liquid contains bubbles or noise, the measurement accuracy will be affected; The temperature range of the measured liquid is limited by the heat of the ultrasonic protection and the communication materials between the switch and the line, and the original data for measuring the high temperature of the liquid is incomplete. ③ Application. Ultrasonic velocimeter is often used in petroleum, chemistry, metal, electric power, and other fields, and is often used to measure the emission reduction of gas pipelines in factories, fluids, and work areas.
2.4 Turbine speed
Intel Remax accelerated technology plan has been expanded to multiple categories in mass production, and its main features are as follows: ① High precision, usually ± 0.25% r - ± 0.5% r, up to ± 0.25% r - ± 0.5% r; Repeat at most 0.05% r-0.2% r for a short time; Zero contact movement, sturdy and durable. ② Disadvantages: The physical characteristics of the liquid have a great influence on the flow characteristics; Calibration characteristics cannot be saved for a long time. ③ Application. The turbine flow counter is usually used to measure oil, organic liquid, inorganic liquid, and liquid frozen body. The first terminal of the main raw material pipeline is used for commercial calculation of automobile exhaust, gas stations, and light hydropower plants.
2.5 Vortex flowmeter
The vortex flowmeter is the latest flowmeter, but it has developed rapidly and has become a common category. Its main characteristics are as follows. ① Advantages: wide application range, liquid, gas, and steam flow measurement can be used; Small pressure loss; Easy installation, simple and durable structure. ② Disadvantages: poor anti-interference ability; Straight pipe section is required before and after installation; The application experience in pulsating flow and multiphase flow is still lacking. ③ Application. A vortex flowmeter is widely used in the factory water supply system, and its application will be limited in the case of high viscosity, low flow rate, and small diameter.
3 General criteria for flowmeter selection and calibration device
Determine the technical requirements for flow measurement and the correctness of the flowmeter, that is, the accuracy requirements for measuring liquid; The flow measurement is repeated, that is, the same measurement is performed multiple times under specific conditions to repeat the same measurement. The expression of flow measurement, that is, whether the flow is mass flow or flow, real-time flow, or cumulative flow. Command and remove the transmission function if necessary. Specifies whether the flow measurement is displayed as a mechanical or electronic title. If the flowmeter does not meet the technical requirements of the measured liquid, measurement errors may also occur.
For the description of the flow calibration liquid calibration device, according to the flow requirements in jgg667-2010: ① The expanded uncertainty of the standard setting should generally not exceed 1/3 of the maximum allowable flow, because the expansion rate of the calibration device is 0.22%. ② Output or. The input line in the equipment used for online identification shall not include redirection between the flowmeter and the equipment designed as a locked cabinet without an intermediate circuit. ③ "When the flowmeter is greater than 1.0, the flowmeter and liquid temperature must be measured according to the standard, and the temperature and pressure shall be measured near the standard flowmeter or calibrated flowmeter. Therefore, the liquid flow controller is applicable to the acceptance accuracy standard of Class 1.0 (allowable deviation ± 1.0%) and subsequent fluid calculation.
