Types of Level Sensors and Level Transmitters
Time:2023-01-09 Read:306
Reading guide: What are the difference and relationship between level sensors and level transmitters? How does they work? Supmea makes these questions no longer a secret.

What is a Level Sensor?

A level sensor detects the level of liquids, other fluids or fluidized solids. When the sensor detects the liquid level, it converts the sensed data into an electrical signal output. Level sensors are used in a wide range of applications. For example, when the water level in a coffee machine is lower than the set sensor position, the sensor sends a signal to remind you to add water. Similarly, the liquid level sensor can also realize the anti-overflow function. It can also be used in washing machines, water dispensers, tea machines, medical equipment, industrial equipment, and other electrical appliances and equipment that need to detect liquid level.

Level Sensor

What is a Level Transmitter?

The level transmitter is a common liquid level measuring instrument. It is made on the basis of the principle that the measured liquid static pressure is proportional to the height of the liquid. According to the pressure of liquids with different specific gravity at different heights, the pressure is linear. The principle is to realize the accurate measurement and transmission of the volume, liquid height, and weight of water, oil, and paste and is widely used in many fields. 

Liquid level transmitters are widely used in the measurement and control of liquid levels in rivers, underground water levels, reservoirs, water towers, and containers. It is a sensor that converts the pressure of liquid into liquid level by measuring the pressure of the liquid. Pressure is directly proportional to the height of the liquid. Level transmitters can be divided into whether they need to have a display or whether they need a remote transmission. The sensor core is usually made of diffused silicon piezoresistor, ceramic capacitor, or sapphire, which has the characteristics of high measurement accuracy, compact structure, and good stability.

Level Transmitter

Level Sensors VS. Level Transmitters

As a liquid level measurement and display instrument, a liquid level transmitter has been widely used in engineering applications due to its convenient installation, high measurement accuracy, and long service life. 

It is divided into two categories. One is the contact type, including single flange static pressure/double flange differ-pressure liquid level transmitters, float type liquid level transmitter, magnetic liquid level transmitter, submersible liquid level transmitters, electric internal float level transmitters, electric float level transmitters, RF capacitive liquid level transmitters, magnetostrictive level transmitters, servo level transmitters, etc. The other is the non-contact type, which is divided into ultrasonic level transmitters, radar level transmitters, and so on. The liquid level transmitters that are used more in daily life include input liquid level transmitters, single flange liquid level transmitters, double flange liquid level transmitters, radio frequency capacitive liquid level transmitters, ultrasonic level transmitters, radar level transmitters, etc.

Types of Level Transmitters

1. Single flange liquid level transmitter

Single-flange liquid level transmitters include flat flanges and flange liquid level transmitters with insert barrels, both of which use the self-gravity of the measured medium to measure the height of the liquid level. Single-flange liquid-level transmitters are suitable for mediums with high viscosity and easy crystallization and are generally used for the installation of open containers or equipment.

Single flange liquid level transmitter

2. Double flange liquid level transmitter

The double-flange liquid level transmitter is a differ-pressure transmitter, which provides a reliable measurement method to avoid the measured medium from directly contacting the transmitter's isolation diaphragm. The main features are as follows. First, it is necessary to isolate the high-temperature medium from the transmitter. Second, the measuring medium has a corrosive effect on the sensitive components of the transmitter, suspending liquid or high-viscosity medium. Third, the measured medium is solidified or crystallized due to changes in the environment or process temperature. What is more, replacing the measured medium requires strict purification of the measuring head. Double flange liquid level transmitter is mainly used in the measurement of liquid level in sealed pressure vessels.

Double flange liquid level transmitter

3. Submersible liquid-level transmitter

The submersible liquid level transmitter includes a rod type and a arm type. Its principle is based on the principle that the measured liquid static pressure is proportional to the height of the liquid. It uses the piezoresistive effect of diffused silicon or ceramic-sensitive elements to convert the static pressure into electricity signal. It is converted into 4-20mADC standard current signal output with temperature compensation and linear correction. This transmitter has the characteristics of convenient installation, strong adaptability, etc. Therefore, it can perform high-precision measurement from water, oil to paste with high viscosity. Plus, it is not affected by the foaming and deposition of the measured medium. It is generally used for the installation of open containers or equipment.

Submersible liquid-level transmitter

4. RF capacitive liquid level transmitter

The principle of the radio frequency (RF) capacitive liquid level transmitter is as below. When the level probe and the conductive liquid form a capacitor, the metal inner core of the probe line is one pole of the capacitor. Then the conductive liquid is the other pole of the capacitor, and the middle is a high-stability teflon (PTFE). That is, the insulating outer layer of the probe line is used as the medium between the two poles. With the change in the liquid level, the area of the liquid surrounding the probe line changes accordingly, so that the relative area of the two poles of the capacitor changes. When the liquid level rises, the capacitance increases and the radio frequency circuit converts this change into an analog signal output. The RF capacitive level transmitter is as simple as measuring high temperature and pressure vessels as measuring normal temperature and pressure. And the measured value is not affected by the temperature, specific gravity of the liquid to be measured, or the shape and pressure of the container. The RF capacitive liquid level transmitter is mainly used for acid and alkali, chloride, organic solvent, liquid CO2, ammonia, PVC powder, ash, oil-water interface, medicine, and other liquid level measurements.

5.Ultrasonic Level Transmitter

The ultrasonic level transmitter uses the piezoelectric crystal in the transducer to emit ultrasonic waves and receive the echoes reflected from the surface of the level. By measuring the time interval between ultrasonic emission and reception, the ultrasonic transmission distance is calculated to complete the level of accurate measurement.

Ultrasonic level transmitter is a non-contact measuring instrument with strong anti-interference ability. It is very convenient to install, maintain and use, and is more suitable for industrial sites with complex environments. It adopts a low-power, small-blind zone transceiver-type special ultrasonic sensor, which has high measurement accuracy, stable operation, and temperature compensation function.

6.Radar Level Transmitter

The radar level transmitter is a microwave level gauge, which is an application of microwave (radar) positioning technology. It transmits energy waves through a device that can emit energy waves (usually pulse signals). And the energy waves are reflected by obstacles. And then the reflected signal is received by the receiving device. The change in material level is determined according to the time difference of the energy wave movement process. The microwave signal is processed by the electronic device and finally converted into an electrical signal related to the material level.

Radar Level Transmitter

Due to the low level of energy radiation, the energy wave used by this device is a pulsed energy wave (the frequency is generally lower than that of the smart radar level gauge). Generally, the maximum pulse energy of the pulse energy wave is about 1mW (the average power is about 1μW), which will not cause radiation damage to other equipment and personnel.

Level Transmitter Types

Types of Liquid Level Sensors

The more common liquid level sensors are photoelectric liquid level sensors, capacitive liquid level sensors, and ultrasonic liquid level sensors. The photoelectric liquid level sensor uses the principle of refraction of light on the interface of two different media. What's more, the capacitive liquid level sensor has a built-in MCU chip, which is controlled by an algorithm, and judges whether the water tank is empty by sensing the difference in capacitance value when there is water and no water. The ultrasonic liquid level sensor sends ultrasonic waves, which will be reflected to form echoes when encountering obstacles.