Guided wave radar is a kind of instrument that uses electromagnetic wave to measure liquid level and material level, which is often used to measure the position of liquid, slurry or solid particles in industrial environment. It has the characteristics of high precision, durability and adaptability to a variety of working conditions. The following is a detailed explanation from the basic principle, working process, applicable conditions, advantages and disadvantages.
1. How it works
Guided wave radar is based on Time Domain Reflectometry (TDR), which transmits and reflects electromagnetic waves to measure the position of the medium.
• Core components:
• Sounding rod or cable: the carrier that guides the propagation of electromagnetic waves.
• Transmitter: emits low-energy, high-frequency electromagnetic waves (usually microwaves).
• Receiving device: receiving the electromagnetic wave signal reflected back.
• Electronic unit: processing and analyzing signals and output measurement results.
• Measurement process:
1. The instrument emits electromagnetic waves through the probe rod or cable.
2. Electromagnetic waves propagate along the probe rod or cable, and when encountering the measured medium (such as liquid or solid particles), some electromagnetic waves will be reflected back because the dielectric constant of the medium is different from that of air.
3. The instrument records the time it takes for electromagnetic waves to be emitted and reflected back (time of flight).
4. According to the propagation speed of the electromagnetic wave in the probe rod (known), calculate the distance of the wave from the probe to the surface of the medium.
5. Combined with the length of the probe rod and the size of the container, calculate the liquid level or material level.
2. Operating conditions
Guided wave radar is widely used in industrial fields, suitable for a variety of complex conditions, as follows:
2.1 Liquid Measurement
• Clean liquids such as water, solvents, oils.
• Viscous liquid: such as petroleum, resin, slurry, etc.
2.2 Measurement of solid particles
• Low density solids: such as plastic particles, powders.
• High density solids: such as sand, cement, grain, etc.
2.3 Complex Operating Conditions
• High temperature and high pressure: Guided wave radar can withstand extreme temperatures (such as up to 400 ° C) and high pressure environments.
• Volatile or foam surfaces: Foam or volatile liquid surfaces can interfere with other measurement methods, but guided wave radars can usually cope.
• Corrosive media: Through the selection of corrosion-resistant materials (such as teflon coated probe rod), it can be used in corrosive environments such as acid and alkali.
3. Advantages and disadvantages
3.1 Advantages
1. High precision: The measurement accuracy is usually up to ±2 mm, which is very suitable for process control requiring high accuracy.
2. Not affected by working conditions:
• Not affected by changes in temperature, pressure, density, viscosity and other medium properties.
• Penetrable to dust, steam or foam.
3. Wide range of application: almost all liquids and most solids can be measured.
4. Maintenance-free: no moving parts, small wear, long service life.
5. Flexible installation: It can be installed on the top of the container and measured by the probe rod or probe cable.
3.2 Disadvantages
1. High installation requirements:
• The probe rod or cable should be kept at a certain distance from the vessel wall to avoid interference.
• There are requirements for the length of the probe rod, and the applicable measurement range is limited (usually within tens of meters).
2. Depends on the installation environment:
• If there are stirrers or obstructions in the container, it may interfere with the signal.
• For some very low dielectric constant media (such as some oil products), the reflected signal is weak, affecting the measurement.
3. High cost: Compared with other traditional level gauges (such as float type, pressure type), the initial cost is higher.
4. High signal processing requirements: under complex conditions, advanced signal processing technology may be required to distinguish multiple reflections.
4. Summarize the example
Suppose you have a bucket filled with water, you take a probe pole (guided wave radar), let a beam of electromagnetic waves propagate along the probe pole towards the surface of the water, when the electromagnetic wave reaches the surface, due to the different dielectric constants of water and air, part of the wave is reflected back. The radar equipment measures the back and forth time of the beam and can calculate the distance from the surface of the water to the starting point of the probe rod, thus knowing the height of the water.
Compared to the traditional "measuring the depth of the bucket with a ruler" method, the guided wave radar is not only fast and accurate, but also can work in harsh environments, such as the water in the bucket is high temperature or stirred.
Through this method, guided wave radar can accurately measure liquid level or material level under complex conditions, which is suitable for various industrial applications. However, it is necessary to pay attention to the installation environment and measurement conditions in use to exert its best performance.
Thank you
