Working principle and selection of radar level gauge

Working principle and selection of radar level gauge

1. The working principle of the radar level gauge

The radar level gauge uses ultra-high frequency electromagnetic waves to transmit to the liquid surface of the detected container through the antenna. When the electromagnetic waves hit the liquid surface and reflect back, the instrument detects the time difference between the transmitted wave and the echo, thereby calculating the height of the liquid surface.The better the conductivity of the measured medium or the greater the dielectric constant, the better the reflection effect of the echo signal.

The radar level gauge is mainly composed of a transmitting and receiving device, a signal processor, an antenna, an operation panel, and a display.Transmit-reflect-receive is the basic working principle of radar level gauge.It is divided into time difference and frequency difference.

The time-of-flight type is that the emission frequency is fixed, and the height of the measured liquid level is measured by measuring the running time of the emission wave and the reflection wave, and through an intelligent signal processor.The relationship between the running time of this type of radar level gauge and the distance of the liquid level is: t=2d/c.In the formula, C is the electromagnetic wave propagation speed, C=300000km/s; d is the distance between the liquid level of the measured medium and the probe, m; t is the time from the emission of the electromagnetic wave to the reception of the reflected electromagnetic wave by the probe, s.

The frequency difference method measures the frequency difference between the transmitted wave and the reflected wave, and converts the frequency difference into an electrical signal proportional to the measured liquid level.The transmitting frequency of this liquid level gauge is not a fixed frequency, but an adjustable frequency with constant amplitude.

2. The characteristics and main performance parameters of the radar level gauge

The radar level gauge shows its excellent performance under harsh measurement conditions such as flammable, explosive, highly corrosive, high temperature, and viscous, and is especially suitable for the measurement of large vertical tanks and spherical tanks.The performance of liquid level gauges from different manufacturers is different, please refer to the relevant information of the manufacturer for details.The understanding of its performance is conducive to the correct use of radar level gauge.

3. Selection of radar level gauge

The antenna is a key component of the radar level gauge, and the shape of the antenna determines the focus and sensitivity of the radar wave.

The horn antenna is suitable for most occasions, and the focusing characteristics are particularly good.This type of antenna is selected for many storage tanks on site, but it is not suitable for the measurement of corrosive media.

The mounting flange of the rod antenna is small in size, has good chemical stability, is easy to clean, and is not sensitive to the adhesion of condensed water. It is especially suitable for measuring corrosive media (such as sulfur) and high-precision measurement in narrow installation short pipes .

The under-flange antenna is suitable for high temperature media, corrosive media or environments where top mounting is not possible.

The parabolic antenna has good focusing and is not affected by heating steam. It is especially suitable for in-tank measurement of large containers with heating steam, such as the measurement of residual oil and asphalt. The measurement range can reach 40m