国民经济中，我国农业发展的重要举措 是 农田水利的大力兴建。 In the national economy, an important measure for China's agricultural development is the vigorous construction of farmland water conservancy. 水利工程建设离不开灌溉，特别是正确掌握灌溉系统中测流量的方法至关重要。 The construction of water conservancy projects is inseparable from irrigation. Especially, it is very important to correctly grasp the method of measuring flow in the irrigation system. 都 有 它的 独特流量传感部分。 At present, there are mainly two methods, namely the speed - area method and the hydraulic method, and each measurement method has its unique flow sensing part.
二 是使用电磁流量计 。 There are two techniques that should be paid special attention to using the speed - area method to measure flow: one is to use an ultrasonic flowmeter , and the other is to use an electromagnetic flowmeter .
放在 渠道的两边，使 超声 波的路径和水流方向之间的角度在45° ～ 60° 范围内。 Ultrasonic technology calculates the flow velocity by measuring the propagation time of the ultrasonic wave across the channel. The transmitter and receiver are placed on both sides of the channel so that the angle between the path of the ultrasonic wave and the direction of the water flow is in the range of 45 ° to 60 ° . This relationship causes a time difference between sound pulses in the upstream and downstream directions. 还是采用 多路径系统， 也就是 采用一个或 者 若干个发射接收配对。 The shape of the channel determines whether a single-path system or a multi -path system will be used , that is, one or several transmit and receive pairs.
再 测量横跨水流两边的合成电位差。 The electromagnetic technology of current measurement is to use the artificial magnetic field established in the conductive water flow, and then measure the composite potential difference across the water flow. 一般 主要 是 由水渠、励磁线卷和一对电极组成。 The electromagnetic flowmeter is generally mainly composed of a water channel, an excitation coil and a pair of electrodes.
In order to ensure the service life and accuracy of the flowmeter , pay attention to the anti-vibration requirements of the meter when selecting the model. In hot and humid areas, choose a hot and humid meter. 正确 的 选择仪表的规格也是保证仪表使用寿命和准确度的重要一环，应 该 特别注意静压 以 及耐温的选择。 The correct selection of instrument specifications is also an important part to ensure the life and accuracy of the instrument. Special attention should be paid to the selection of static pressure and temperature resistance. 也就是 耐压程度应 该 稍大于被测介质的工作压力，一般取1.25 倍 左右为佳 ，以保证不发生泄漏或 者 意外。 The static pressure of the instrument, that is, the pressure resistance level should be slightly greater than the working pressure of the measured medium, and it is generally better to take about 1.25 times to ensure that no leakage or accident occurs . The choice of the measuring range is mainly the choice of the upper limit of the scale. 容 易过载，损坏仪表； 而 选大了，有碍于测量的准确性。 If you choose a small size, it is easy to overload and damage the meter; if you choose a large size, it will hinder the accuracy of the measurement. 为好 。 Generally, it is better to select 1.2 to 1.3 times of the maximum flow value in actual operation . 该 考虑流量测量元件所造成的能量损失。 For long-term contact meters installed on production pipelines, the energy loss caused by flow measurement elements should also be considered. 该 选用多个压损较大的测量元件，如节流元件等。 In general, multiple measuring elements with large pressure loss, such as throttling elements, should not be selected in the same production pipeline .
者 流量计 对各种流体 以 及流动情况都能适应的。 In short, no measurement method or flow meter can adapt to various fluids and flow conditions. Different measurement methods and structures require different measurement operations, methods of use, and conditions. Each type has its own advantages and disadvantages. 该 在对各种测量方式和仪表特性做全面比较的 了解 ，选择适于生产要求的 ，不但 安生可靠 而且 又经济耐用的最佳型式。 Therefore, we should make a comprehensive comparison of various measurement methods and instrument characteristics , and select the best type that is not only safe and reliable but also economical and durable that is suitable for production requirements . With the development of China's agricultural modernization and the realization of precision agriculture, flow meters will play an increasing role in farmland irrigation.