Question 1

Differential pressure level transmitters

Accepted Answer

The measurement principle of Differential pressure level transmitters is to measure the liquid level by converting the change of liquid level height into the change of differential pressure. This conversion is achieved by balancing the vessel to form a reference water column. The key to its accurate liquid level measurement is the accurate conversion between liquid level and differential pressure.

Using a differential pressure transmitter to measure boiler drum level must take into account certain physical properties of the fluid. The steam drum contains a two-phase mixture of water and steam under saturated conditions. The density of water and steam varies with saturation temperature or pressure. The density of saturated steam on the water surface, as well as the density of saturated water in the drum, must be considered.

Maybe you can refer to: Rosemount-Boiler Drum Level Transmitter Calibration

More about: Use Differential Pressure Transmitter to Measure Liquid Level

Question 2

Displacer Level Transmitters

Accepted Answer

The Displacer Level Transmitter works based on the principle of buoyancy.

When the liquid level is at 0, the torsional moment generated by the torsion tube by the gravity of the float is the largest. The rotation angle of the torsion tube is at 0°.

When the liquid level gradually rises to the highest level, the torsion tube is subjected to buoyancy to generate a torque torque and rotates through an angle. The transmitter converts the angle into a 4~20mA DC signal. The signal is proportional to the measured liquid level.

The density change of the medium in this measurement method will affect the measurement accuracy. Mechanical vibration will also cause inaccurate readings.

Question 3

Electrical contact level sensors

Accepted Answer

The electrical contact level sensors belong to the connected tube type level sensors. The principle is to measure the liquid level by using the characteristics that the electrode in the boiler water has a small impedance to the cylinder and the electrode in the steam has a large impedance to the cylinder.

The conductivity of boiler water in high-pressure boilers is generally tens of thousands to hundreds of thousands of times greater than that of saturated steam. Therefore, the indication value of the electric contact level gauge is less affected by changes in the pressure of the steam drum. It can easily transmit liquid level signals remotely. .

However, the reliability of the sampling sensor is poor, the mechanical seal of the motor is easy to leak, the service life of the electrode is short, the indication is discontinuous, and there is a certain amount of maintenance.

Extended Reading: FMCW Radar for High Temperature Level Sensor

Question 4

Measurement principle

Accepted Answer

Guided Wave Radar Level Transmitter is a liquid level transmitter based on the principle of time domain reflectometry (TDR).

The electromagnetic pulse propagates along the steel cable or probe at the speed of light. When encountering the surface of the measured medium. Part of the pulse of the Guided Wave Radar Level Transmitter is reflected to form an echo and return to the pulse transmitter along the same path. The transmitter and the measured medium The distance from the surface is proportional to the travel time of the pulse in between. The liquid level height is calculated.

Question 5

Features

Accepted Answer

The advantages of the Guided wave radar level transmitter are contact measurement. Signal stability. Measurement unaffected by liquid density and electrical properties. Maintenance free, etc.

However, when the guided wave radar level gauge measures high temperature and high pressure liquids, the measured value will have a large deviation due to the polarization of the air. And the greater the distance between the measurement reference point (flange) and the surface of the measurement medium. The resulting The larger the systematic error.

1) The measurement is accurate.

Density and dielectric constant changes of the medium, as well as fog and foam, have no effect on the measurement. At the same time, the deposition and fouling of the medium on the wave guide have little effect on the liquid level measurement. This is because the signal transmission in the waveguide is not affected by liquid level fluctuations and obstacles in the tank, etc. The feedback signal received by the instrument is correspondingly stronger.

Furthermore, the detected interfering spurious signals in the return signal are extremely small. It is only necessary to detect the transit time of the electromagnetic wave. No signal processing and discrimination is required. Therefore, the measurement of the drum level is accurate.

2) It is convenient to measure and adjust.

Because electromagnetic waves are constant. When programming configuration, only need to input relevant parameters such as measuring range on site. No migration is required to change meter ranges and field calibrations. Greatly improve the efficiency of adjusting the instrument.

More about Advantages of Coaxial Probes

3) Low installation cost and easy maintenance.

Guided wave radar level transmitter consumes less energy. The two-wire transmission method greatly saves the installation cost.

At the same time, the quick universal joint between the probe and the transmitter makes the installation easier. It is more conducive to future maintenance.

Extended reading: Float Level Sensors – Single and Multipoint

Year: 2022

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