Analysis of the principle and installation key points of DHE-RD guided-wave radar level gauge

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Measurement principle: The guided wave radar level gauge is a type of radar level gauge that operates on the principle of time-domain reflection (TDR). The electromagnetic pulses emitted by this gauge travel at the speed of light along the steel cable or probe. When they encounter the surface of the medium being measured, some of these pulses are reflected, forming echoes that return to the pulse emitting device along the same path. The distance between the emitting device and the surface of the medium being measured is proportional to the time it takes for the pulses to travel between them; by calculating this value, the liquid level can be determined. Installation Guide: The installation guide below applies to cable-type and rod-type probes used for measuring solid particulate materials and liquid substances. Coaxial tube probes are only suitable for liquid objects. The installation location should be as far away as possible from the discharge port and the feed port. For metal and plastic containers, they do not touch the walls across the entire range. If it is a metal tank, the level gauge should not be installed at the center of the tank. It is recommended to install it at 1/4 of the silo diameter. The minimum distance between the cable-type or rod-type probe and the tank wall shall be 30 centimeters. The bottom of the probe is approximately 30 mm from the bottom of the tank. The minimum distance between the probe and obstacles inside the tank shall be no less than 200 mm. If the bottom of the container is conical, the sensor can be installed at the center of the tank top, allowing measurement all the way to the bottom of the tank. The input reflected pulse signal is transmitted along the cable to the instrument’s electronic circuitry, where the microprocessor processes this signal to identify the echoes generated by the microwave pulses on the surface of the material. The correct identification of echo signals is carried out by intelligent software. The distance D from the surface of the material is proportional to the time duration T of the pulse: D = C × T/2, where C is the speed of light. Since the distance E of the empty tank is known, the level L can be calculated as: L = E – D. The output is determined by entering the height of the empty tank E (which corresponds to the zero point), the height of the full tank F (which corresponds to the full scale), as well as some application parameters; these parameters enable the instrument to adapt itself to the measurement environment. Corresponds to a 4-20mA output. Installation guidelines for guided wave radar level gauges when measuring liquids: The following installation instructions apply to guided wave radar level gauges with rod-type and cable-type probes; the measurement and installation methods for tube-type probes are not affected by these guidelines. The recommended distance between the installation position l and the tank wall is 1/6 to 1/4 of the tank’s diameter (at least 300 mm; at least 400 mm for concrete tanks). l It should not be installed in the middle of a metal tank, nor at the discharge port. When selecting the probe length, ensure that the bottom of the probe is at least 30 mm above the bottom of the tank. Pay attention to the temperature of the medium as well as any obstacles inside the tank. l During installation, make sure that the probe is at least 200 mm away from any obstacles. Elimination of interference: The software can be used to suppress interference echoes, thereby achieving optimal measurement results. l Bypass pipes and waveguides (only applicable to liquids): For fluids with a viscosity of less than 500 cSt, bypass pipes, waveguides, or tubular systems can be used to avoid interference. For liquid measurements, when the viscosity is ≤500 cst and adhesion is not a concern, the tubular probe is the best option. Its advantages include: excellent reliability; it can be used with any medium having a dielectric constant of 1.4 or higher, and the measurement is independent of the medium’s conductivity; obstacles inside the tank or the length of the tube do not affect the measurement; it can withstand higher lateral pressures compared to rod probes. For media with high viscosity, it is recommended to use rod probes.

Regarding the installation of the instrument on horizontal or vertical tanks: both tubular and rod probes can have a maximum length of 6 meters. For tanks where the measurement distance exceeds 6 meters, an 8mm cable probe can be used. The installation and fixing methods are the same as those for measuring in solid powder silos. There is no limit on the distance from the tank wall, as long as the probe does not come into contact with it. If there are many obstacles inside the tank or they are too close to the probe, a tubular probe should be used.

For measuring corrosive media: if measuring such media, a guided-wave radar level gauge with a plastic sleeve can be used.

Measurement range: H – Maximum measurement range; L – Distance when the tank is empty; B – Top blind zone; E – Minimum distance from the probe to the tank wall. The top blind zone refers to the minimum distance between the highest level of the material and the measurement reference point. The bottom blind zone refers to the distance near the very bottom of the cable where accurate measurement is not possible. The effective measurement distance is between the top blind zone and the bottom blind zone. Note: Using a guided-wave radar level gauge can ensure reliable measurement of the liquid level in the tank only when the material is located between the top blind zone and the bottom blind zone. The product’s performance is not affected by factors such as liquid density, the electrical properties of the material, turbulence on the liquid surface, or foam. It features a four-line text display; a simple menu-based interface facilitates on-site operation, while remote operation and monitoring are also possible. Diagnosis can be carried out through on-site indicator lines. Electronic components can be replaced without having to open the tank. When a safety level of SIL 2 is required, a safety interlock system (overflow protection) is provided in accordance with IEC 61508/IEC 61511-1. Product features: 1. The “ELL signal analysis technology” meets the highest requirements for level measurement. 2. High versatility: It can measure liquid levels as well as material levels, and meets the measurement requirements for different temperatures, pressures, and media. The maximum measurement temperature can reach 400°C (customization available), and the maximum pressure can reach 4 MPa (customization available). It can also be used in harsh environments such as those with corrosive conditions or high impact forces. 3. Anti-clogging: The unique circuit design and sensor structure ensure that measurements are not affected by debris accumulating on the sensor, eliminating the need for regular cleaning and preventing inaccurate readings. 4. Maintenance-free: There are no moving parts during the measurement process, so there is no risk of mechanical component damage, and no maintenance is required. 5. Anti-interference: Being a contact-based measurement method, it has strong anti-interference capabilities and can overcome the effects of steam, foam, and stirring on the measurement. 6. Accurate and reliable: Various measurement methods ensure higher accuracy; the measurements are not affected by environmental changes, offering high stability and a long service life.