A level measurement transmitter is an instrument that provides continuous level measurement. It can be used to determine the level of a liquid or bulk solid at a specific time. It can measure the level of media such as water, viscous fluids, and fuels, or the level of dry media like bulk solids and powders.
Level measurement transmitters are suitable for various applications, such as vessels, storage tanks, and even rivers, ponds, and water wells. These transmitters are commonly used in industries like material handling, food and beverage, power generation, chemicals, and water treatment. Now, let's explore several common types of level meters.
Submersible Level Sensor
Submersible level sensors operate on the principle that hydrostatic pressure is proportional to liquid height. They utilize the piezoresistive effect of diffusion silicon or ceramic sensors to convert hydrostatic pressure into an electrical signal. After temperature compensation and linearity correction, this signal is converted into a standard electrical signal output. Based on this output signal, users can determine the depth of the liquid level.
Since the measurement principle of submersible level gauges is based on liquid hydrostatic pressure, they are unaffected by bubbling, sedimentation, or electrical characteristics of the measured medium, offering high accuracy and stability. The sensor part of the submersible hydrostatic pressure transmitter can be directly immersed into the liquid, while the transmitter part can be fixed with a flange or bracket, making installation and use very convenient.
These sensors use advanced isolated diffusion silicon sensing elements. They can be directly placed into a container or water body to accurately measure the height from the sensor tip to the water surface, outputting the water level via a 4–20mA current or RS485 signal.
Ultrasonic Level Meter
An ultrasonic level meter is a digital level instrument controlled by a microprocessor. During measurement, the sensor emits pulsed ultrasonic waves. These sound waves are reflected by the target surface and received by the same sensor, then converted into an electrical signal. The distance between the sensor and the target object is calculated by measuring the time between the emission and reception of the sound waves.
Its advantages include having no moving mechanical parts, high reliability, simple installation, and non-contact measurement, making it unaffected by liquid viscosity or density.
Its disadvantages are relatively lower accuracy, the potential for measurement blind zones, and unsuitability for pressurized vessels or volatile media.
Radar Level Meter
Radar level meters operate on the principle of transmit-reflect-receive. The antenna of the radar level meter emits electromagnetic waves, which are reflected by the surface of the measured object and received back by the antenna. The time taken for the electromagnetic wave to travel from emission to reception is proportional to the distance to the liquid level. The radar level meter records the pulse wave's time-of-flight. Since the propagation speed of electromagnetic waves is constant, the distance from the liquid level to the radar antenna can be calculated, thus determining the height of the liquid level.
In practical applications, radar level meters primarily operate in two modes: Frequency Modulated Continuous Wave (FMCW) and Pulsed Wave. Level gauges using FMCW technology consume more power, typically use a 4-wire system, and have more complex electronic circuits. In contrast, radar level meters using Pulsed Wave technology have lower power consumption, can often operate on a 24VDC 2-wire power supply, are easier to make intrinsically safe, offer high accuracy, and have a broader range of applications.
Guided Wave Radar Level Meter
The guided wave radar level transmitter operates on the same basic principle as the radar level meter, but it sends microwave pulses along a sensor cable or rod. The signal travels to the liquid surface, reflects back to the sensor, and proceeds to the transmitter housing. Integrated electronics within the transmitter housing determine the liquid level based on the time it takes for the signal to travel along the sensor and return. This type of level transmitter is widely used in industrial applications across all fields of process technology.