英文文献-流量计在农田灌溉中的应用分析

The Analysis of Flowmeter Applied in Farm IrrigationAbstractThe f lowmeter is a k ind o fmeters that is used to mesure liqu id flow in the pipe line. A ltrason ic conta in the info rmation of velocity o f f low of liquid when it transm its in flow ing liquid, the technology o f altrason ic computes ve loc ity of flow depend ing on mesuring transm itt ing t ime of a ltrason ic across the channe;l The electromagnetic flowmeter is a k ind of meters that depend on Faraday law of e lectromagnetic induction and is used to mesure vo lume flow o f e lectric liqu id, electromagnet ic technique used in mesuring velocity o f flow makes use o fmagnetic field bu ilt art ific ially in flow andm esures comp lex po tent ia l d ifference across the flow. Both o f them w ill be w idely used in farm irrigat ion.Key words: flowm eter；ultrason ic；e lectromagnet ic；irrigat ion1 introduction forewordA wide range of flow measurement and instrumentation, classification method are many, with the rotor flow meter, flowmeter throttle flowmeter, fine joints and volumetric flowmeter, electromagnetic flowmeter, ultrasonic flowmeter and weir, etc. All kinds of flow meters, each product has its specific applicability, also has its limitation. According to the measured object has closed pipes and open channel divided into two categories; According to the purpose and can be divided into the total measurement and flow measurement, the instrument called total table and flow meter, respectively.Total table measuring traffic flows through the pipe, over a period of time is the amount of flow in a short period divided by the time of business. In fact, the flow meter is usually equipped with cumulative flow device, and for the use of total table, table and total also have flow transmission device. Therefore, strictly to flowmeter and total table has no practical significance. According to the principles of measuring points and strong principle, the principle of thermal and acoustic, optical and electrical theory principle and the principle of atomic physics, etc. 2 Ultrasonic flowmeter Ultrasonic wave travels in the flow of fluid in fluid velocity on load information, through the received ultrasound can detect the flow velocity of the fluid, thereby converted to traffic. According to the test, can be divided into transmission speed difference method, doppler method, beam deflection method, noise method and correlation method and so on a different type of ultrasonic flowmeter. Ultrasonic flowmeter is along with the rapid development of integrated circuit technology in nearly a dozen years to a fluid metering applications. Ultrasonic flowmeter is a kind of non-contact measuring instrument, suitable for the measurement is not easy to contact, not easy observation of fluid and reduce runoff. Its linkage with the water level meter can be open water flow measurement. Using ultrasound wave flow meter without installing measuring element in the fluid, so it will not change the fluid flow state, and does not produce additional resistance. Instrument installation and maintenance are not affect the production line operation, so it is an ideal energy-saving Flow meter. All kinds of ultrasonic flow meter can be installed outside the tube, is the contact measurement, the instrument cost has nothing to do with pipe diameter size to be measured; And other types of flow meter as the diameter increases, the cost increase, so the greater the diameter ultrasonic flowmeter than other types of the same function of the function of the flow meter price is more superior, is thought to be better reduce runoff measuring instrument. The doppler method ultrasonic flowmeter can measure two-phase mediumTraffic, so it can be used for sewage and domestic sewage and other dirt flow measurement. In power plant, the portable ultrasonic flowmeter was used to measure turbine into water, quantity of steam turbine cycle, reduce runoff, than in the past, the skin of the pipe current meter far more convenient. Ultrasonic flow juice can also be used for gas measurement. 2 cm 5 m, the applicable scope of the pipe diameter from several meters wide open channel or trough to 500 m wide rivers can be used. In addition, the flow measurement accuracy of ultrasonic measuring instrument is almost not affected by measurement of body temperature, pressure, the effects of parameters such as viscosity and density, and can be made into non-contact and portable measuring instrument, it can solve the other type is difficult to measure by instrument of strong corrosion resistance, electrical conductivity, radioactive and flammable and explosive medium flow measurement problem. In view of the non-contact measurement characteristics, again with reasonable electronic circuit, an instrument can be adapted to a variety of pipe diameter and flow range measurement. Ultrasonic flowmeters ability to adapt is also the other instrument incomparable. Ultrasonic flowmeter has some of these advantages, so it is more and more attention, and to the development of product seriation and generalization, is now made into different channels of standard type, high temperature, explosion-proof type and wet type instrument, to adapt to the different media, different occasions and different pipe flow measurement.3 The magnetic flowmeter Electromagnetic flowmeter is the fifties and sixties of the 20th century has been developed rapidly with the development of electronic technology and a new type of flow measurement instrumentation. Electromagnetic flowmeter is made according to Faradays law of electromagnetic induction and used to measure the conductive liquid volume flow meter. Because of its unique advantages, has been widely applied in industry and agriculture of various conductive liquid flow measurement, such as all kinds of acid, alkali, salt and other corrosive media and all kinds of slurry flow measurement, formed the unique applications. On the structure, electromagnetic flowmeter consists of two parts, electromagnetic flow sensor and converter. Sensor installed on the pipeline, its role is to flow into the pipe of liquid volume flow value linear transform into induced electric potential signal, and through the transmission line will be sending the signal converter. Converter is installed in place not too far from the sensor, it will flow from sensor signal amplifier, translates into standard electrical signal output is proportional to the traffic signal, for display, accumulated and adjusting control. 4 Application of flowmeters in farmland irrigation In the national economy, water conservancy construction is the important measure of agricultural development in our country. Without irrigation water conservancy construction, especially right is very important to master the methods of flow measurement in irrigation systems. At present there are two main methods, namely the speed - area method and hydraulic method, each method has its unique flow sensor (detection). Speed - method of measuring flow rate is multiplied by the average velocity by water channel cross-sectional area, and the flow velocity at some particular point is through the flowmeter measurement. Use this method test flow generally have 3 different parties.Type: one is the velocity distribution law; 2 it is 0. 6 h (h is the distance of the water surface to the bottom of the canal); Three is 0. 2 h 0. 8 h method. Velocity distribution law is measuring several points between water surface and the drainage at the bottom of flow velocity, and determined by the measuring point on a vertical surface speed curve, press speed curve defined area divided by the depth, can calculate the average speed; 0. 6 h to measure is below the surface of 0. 6 h of single point flow velocity, and assumes that the value is the median of the full speed; 0. 2 h 0. 8 h to measure the water surface under 0. 2 h and 0. 8 h, depth of the flow rate of the two, this is the average of the two readings can estimate for average velocity value.The three methods are at any given measurement area average speed is calculated. The number of channels along the entire width of the depth and a single vertical plane measuring points are different. Many European countries in a single surface depth measurement requirement when 5 points, and the United States believes that measure 2 points enough. The number of depth depends on the width of the channel. Sounding for 5 15 times in Europe, in the United States for 8 to 18. Error of measurement by the lead times and at every point of the measuring time, the speed - area methods average error is less than 6%. Use speed - area method of flow measurement has two technologies should pay special attention to two points: one is to use ultrasonic flowmeter, another is the use of electromagnetic flowmeter. 60 Makes the geometrical relation between towards upstream and downstream direction of the sound pulse time lag. The shape of the channel decided to adopt a single path system or multipath system, which USES one or several receive pairs. Flow of the electromagnetic technology was established using conductive water flow in the artificial magnetic field, then measured across the water potential difference on both sides of the synthesis. Electromagnetic flowmeter is mainly composed of drains, excitation spool and a pair of electrodes. 5 The choice of flowmeter Flowmeter selection is to point to in accordance with production requirements, from the meter according to the actual situation of products supply to comprehensively consider the safety, accuracy and efficiency of measurement, and according to the current body of properties and flow condition determine the flow quantity of sampling device and measuring instrument and measuring instrument of form and specifications. Flow measurement of reliable safety first is the measurement way, that will not happen in the operation of the sampling device in the electric circuits of the mechanical strength or failure caused by the accident; Followed by measuring both under normal production or fault condition does not affect the safety of production system. On the basis of guarantee the safe operation of the instrument, and strive to improve the accuracy of the instrument and energy saving. Could satisfy the requirement of accuracy for this, not only have to choose display instrument, and according to the characteristics of the measured medium choose reasonable measurement way. For main generator, the steam flow measurement is vital because of its security and economical efficiency of the coal-fired power plant, generally USES the mature standard throttling the load with differential pressure flowmeter. Chemical water treatment of the sewage and dirt flow and fuel, respectively, belong to low viscous flow Reynolds number, dont apply the standard throttling. Is generally selected to dirt flow round orifice and other non-standard throttling with differential pressure gauge or ultrasonic doppler flowmeter, and viscous flow can target type or cuneate, displacement and flow meter, etc. Turbine inlet water, condenser circulating water and heat recovery steam of heat recovery unit are big diameter (400 mm) above the flow measurement parameters, due to processing and create difficulties loss of pressure big, generally do not choose standard throttling devices. Depending on the requirement of the measurement accuracy and the characteristics of measured medium, inserting type flowmeter, velocity components are respectively