Wednesday, December 15, 2010
Weak current College】 【several common flowmeter basics and compare】.
<br> <br> Flow measurement is one of the four important process parameters (the other is the temperature, pressure and level). Closed tube flowmeter with its use of technology category, as follows: <br> Differential pressure flow meters (DP .) <br> This is the most common flow technology, including the orifice, venturi and Sonic nozzle. DP flow meter can be used to measure the most liquid, gas and steam flow velocities. DP flow meter has no moving parts, widely used, .easy to use. But the plug, it produces an effect of pressure loss of accuracy. Flow measurement accuracy depends on the pressure gauge accuracy. <br> Volumetric flow meter (PD) <br> PD meter used to measure liquids or gas volume flow .rate, it will introduce measurement space fluid, and calculate the number of rotation. Impeller, gear, such as piston or orifice to shunt fluid. PD flowmeter accuracy is high, is measuring viscous liquid one of several ways. But it also produces an unrecoverable .error, the pressure and is equipped with moving parts. <br> Turbine flow meter <br> When fluid passes through the turbine flow meter, fluid so that the rotor spinning. Rotor rotation speed and the speed of the fluid. By rotor feel fluid .average velocity, the total flow or inferred. Turbine flow meter can accurately measure the clean liquid and gas. Like PD flowmeter, turbine flowmeter will also have an unrecoverable error, the pressure will also require moving parts. <br> Electromagnetic Flowmeter <br> .With conductive fluids in flow through electromagnetic fields, by measuring the voltage can be fluid. Electromagnetic Flowmeter has no moving parts, is not affected by the fluid. In full pipe conductivity liquids when measuring accuracy is high. Electromagnetic flow meter can be used to measure .the velocity of slurry flow. <br> Ultrasonic Flowmeter <br> Propagation time method and the Doppler effect method is often used in Ultrasonic Flowmeter to measure fluid way of average speed. Like other speed meter as the measurement of volume flow meter. It is .unimpeded flow meter, if ultrasound transducer installation in pipeline logging, you need to insert. It is suitable for almost all of the liquid, paste, high accuracy. But pipeline pollution affect accuracy. <br> Vortex flowmeter <br> Vortex flowmeter is in .a fluid placed a bluff tour took place in the Vortex, tour-speed and fluid proportional to the speed to calculate the volume of traffic. Vortex flowmeter for measuring liquid, gas or steam. It has no moving parts, no dirt. Vortex flowmeter produces .noise, but also require fluid has a high flow rate, to produce the vortex. <br> Thermal mass flowmeter <br> By measuring fluid temperature or heat sensor to measure fluid speed reduction. Thermal mass flowmeter has no moving parts or hole that can .accurately measure the gas flow. Thermal mass flow meter is a small number of measurement of the mass flow of technology one of the few used for measurement of large-diameter gas flow technology. <br> Coriolis flowmeter <br> This meter using vibration fluid .pipe production and mass flow rate corresponding to the measurement of deflection. Coriolis flowmeter for liquids, pastes, gas or steam mass flow measurement. High accuracy. But on the pipe wall for regular maintenance, to prevent corrosion. <br> Electromagnetic Flowmeter <br .> Measuring principle: Faraday proved a conductor in a magnetic field campaign will generate an electromotive force, induction. Using electromagnetic measuring principle, the fluid is the movement of the conductor. EMF is relative to the stream express and two electrodes are detected, then the .transmitter will be magnified, according to pipe cross sectional area flow calculation. <br> Constant magnetic field changes from polar alternating switch DC current. <br> Measuring system consists of a transmitter and a sensor. <br> It also comes in two models .: integrated, transmitter and sensors consist of a whole machinery unit; separable, transmitter and sensors are mounted separately. <br> Transmitter: Promag50 (use button operation, two-line display) sensor: PromagW (DN25 ... 2000) <br .> Technical parameters <br> Measurement variables: velocity. <br> Enter the variable measuring range: typical v = 0. 1 ... 10m / s with specified precision operational flow range: more than 1000: 1 input signal status input (aux .): U = 3 ... 30vDC, Ri = 5 k Ω, electrical isolation. Configurable: cumulative amount (S) reset, measuring value, error reduction. Current input (only if Promag53): active / passive optional, electrical isolation resolution .: 2 μ A active: 4. 20mA, Ri ≤ 150 Ω, Uout = 24VDC, shorting against current <br> Passive: 0 / 4. 20mA, Ri ≤ 150Ω, Umax = 30VDC. .<br> Output variables <br> Output signal current output: active / passive optional, electrical isolation, time constant optional (0.05 ... 100s), the full value of optional, temperature coefficient: typical 0.005% or / ℃; resolution: .0.5 μ A <br> Active: 0 / 4 ... 20mA, RL <700 Ω (HART: RL ≥ 250 Ω) <br> Passive: 4 ... 20mA, max.30VDC, Ri ≤ 150 Ω <br .> Pulse / frequency output: <br> Passive, collector 30VDC, 250mA, electrical isolation. frequency output: the full frequency 2 ... 1000Hz (fmax = 1250Hz), open / close ratio 1: 1 <br> Pulse width: Max .10s. pulse output: pulse value and pulse polarity optional, maximum pulse width can be set (0.05 ... 2s), maximum pulse frequency optional material transmitter casing, integrated shell: powder-coated cast aluminium; wall mounted shell: cast aluminum sensor .casing, DN25 ... 300: powder-coated cast aluminium; DN350 ... 2000: coated steel model specifications: 50W9H-UD0A1AK2C4AW (DN900), 50W is 50 series; 9H said caliber as 900mm (DN900); U said substrate material .is based on an ester; D represents the process connection / material for ST37-2 PN10DIN250l, flange (applies to DN200-DN2000); 0 indicates that the electrode material (all electrode) 1.4435/316 l stainless steel; A representation calibration 0.5% ..5 point calibration; 1 description certified as no special certification; the second A indicates no riot; K that shell protection to IP68, separable, wall-mounted; 2 indicates separation with 10m cable; <br> Environmental conditions: ambient temperature-20 .... + 60 ° c (sensors, transmitters), installed in the shade, avoid direct sunlight, especially in warm climatic zones. <br> Measurement accuracy reference conditions: meet DIN19200 and VDI/VDE264l, medium temperature: + 28 ° c .± k, environment temperature: + 22 ° c ± k, warm-up time: 30 minutes <br> Installation should pay attention to when, and only when you full pipe in order to obtain accurate measurements, avoid the following installation location: < .br> Pipeline highest point installation (easy aggregation bubble) <br> Direct installation in a pipeline down the open prior to export. <br> Note do not pump inlet side of the installation flow tube to avoid pumping pressure caused by the flow tube lining .damage. When you use the reciprocating, diaphragm, or when you need to install plunger pump pulse throttle valve. <br> When the down pipe length less than 5 m, after installation of the sensor a siphon or an operable. To avoid possible low .voltage and for measuring pipe lining damage. Guarantee full pipe to reduce gas. <br> Installation position: the most suitable position can help prevent gas accumulation and measuring tube of residue stockpiling. <br> Vertical installation; this orientation on easy automatic air duct .system is ideal and not empty tube detection electrode. <br> Standard installation: measuring electrode plane must be horizontal, which can prevent the entrainment air bubbles produced by electrodes in a short time. Note: empty tube detection feature only when the measurement device for .horizontal installation and transmitter casing up time to work properly. If very intense vibration, sensor and transmitter mounted separately. <br> Base, support: If the nominal diameter of DN ¡ .ý 350, can bear sufficient load base install transmitter. Note do not allow the use of the bounding box of the weight bearing live sensor. This makes the frame deformation and damage internal excitation coil. If possible, it is best to avoid installing sensors such .as valves, elbow, three links. <br> Ensure that the following required import and export straight to ensure measurement accuracy: entry length> export DN 10 × 5 × length> DN sensor and transmitter ground sensor is <br> Pipeline Center .location <br> Grounded: the sensor and the media must have the same potential to ensure measurement accuracy and avoid electrodes and corrosion damage. Equi by sensor built-in reference electrode. If the media without lining and grounding, fluidity in the metal pipe, .it can be connected to the transmitter casing and meet the requirements for the grounding. For separable ground ibid .. <br> Note: If you are unsure whether or not the media to proper grounding should install grounding ring. <br> Troubleshooting: < .br> Electromagnetic Flowmeter <br> If, on the start or the operation fails, usually according to the following checklist troubleshooting, directly find the cause of the problem and the appropriate solutions. <br> <br> <br>.