雷达料位测量原理和主要技术因素
Principle and main technical factors of radar level measurement
雷达料位计采用非接触式测量方法，是一种理想的经济型产品，适用于储料罐、静井或外接腔体等.
The radar level gauge adopts non-contact measurement method, which is an ideal economical product, which is suitable for storage tank, static well or external cavity
雷达料位计是利用回波测距原理。发射天线向被测目标发射微波（即发射波），被测目标的微波被接收天线接收（即回波），信号处理器将发射信号与接收信号比较，计算出被测距离，并可算出相应的料位值
Radar level meter is based on echo ranging principle. The transmitting antenna transmits microwave (i.e. transmitting wave) to the measured target, and the microwave of the measured target is received by the receiving antenna (i.e. echo). The signal processor compares the transmitted signal with the received signal, calculates the measured distance and calculates the corresponding material level value
微波脉冲来回传播时间t由下式决定：
The back and forth propagation time t of microwave pulse is determined by the following formula:
t=2a/c (1)
t=2a/c (1)
式中a—天线到被测目标的距离
Where a is the distance between the antenna and the measured target
c—微波传播的速度（光速）
C-The speed of microwave propagation (light speed)
由于微波在传播途径上有衰减和干扰反射，故测量的关键是要能接收到反射回波，并识别出有效回波。接收的回波能量Pk可用简化的雷达方程表示如下：
Since microwave has attenuation and interference reflection in the propagation path, the key of measurement is to receive the reflected echo and identify the effective echo. The received echo energy PK can be expressed by the simplified radar equation as follows:
Pk=Pτx C x GiGtGr/r4 (2)
Pk=Pτx C x GiGtGr/r4 (2)
式中： Pτ—天线辐射功率
Where: P τ - radiation power of antenna
C --- 经验系数，由经验决定
C -- empirical coefficient, determined by experience
Gi--- 由目标表面介电特性及面积决定的反射增益
GI is the reflection gain determined by the dielectric properties and area of the target surface
Gt，Gr—天线发射和接收效率
GT, GR - antenna transmitting and receiving efficiency
r—天线与目标间的距离
R - distance between antenna and target
接收的回波能量大小与天线的发射和接收效率以及天线辐射功率有关，故雷达料位计的天线设计和形状很关键，现有的天线除号角天线（喇叭口）和棒状天线外，还有平面天线和抛物面天线，为用于介电常数较小的物料，将天线、喇叭口或安装导波管一直延伸到储料罐或仓内，来传递发送和接收的电磁波，增强回波的信号。
The received echo energy is related to the transmitting and receiving efficiency of the antenna and the radiation power of the antenna. Therefore, the design and shape of the antenna of the radar level gauge is very important. Besides the horn antenna (horn mouth) and rod antenna, there are also planar antenna and paraboloid antenna. For materials with small dielectric constant, the antenna, bell mouth or waveguide tube are extended to the storage It is used to transmit and receive electromagnetic wave and enhance echo signal.
接收的回波能量大小与物料表面的介电特性有关，介电常数ε高，反射率高，得到的回波强度也高；介电常数ε低，物料会吸收部分微波的能量，回波强度也较低。通常要求被测物料的介电常数ε：液体为ε>1.8,固体ε>2.5， 水泥厂固体ε>2.5，水泥的介电常数ε为3。
The received echo energy is related to the dielectric properties of the material surface. With high dielectric constant ε and high reflectivity, the echo intensity is also high; when the dielectric constant is low, the material will absorb part of the microwave energy, and the echo intensity is also low. It is usually required that the dielectric constant of the material to be measured is ε > 1.8 for liquid, ε > 2.5 for solid, ε > 2.5 for solid in cement plant and 3 for cement.