liquid level transmitter (hydrostatic liquid level meter / liquid level transmitter / liquid level sensor / water level sensor) is a kind of pressure sensor for measuring liquid level. Based on the principle that the static pressure of the measured liquid is proportional to the height of the liquid, the hydrostatic level transmitter (liquid level meter) adopts isolated diffuse silicon sensitive element or ceramic capacitive pressure sensitive sensor to convert the static pressure into an electric signal, which is then converted into a standard electric signal (generally 4-20mA/1-5VDC) after temperature compensation and linear correction.
Liquid level transmitter (can be used in a variety of working conditions, such as vessels, storage tanks, and even rivers, pools and wells. These transmitters are commonly used in the material handling, food and beverage, power, chemical and water treatment industries. Now, let’s learn about a few commonly used liquid level transmitters.
How many types of liquid level transmitter are there?
One type is contact type, including single-flange hydrostatic / double-flange differential pressure level transmitter, float level transmitter, magnetic level transmitter, input level transmitter, electric internal float level transmitter, electric float level transmitter, capacitance level transmitter, magnetostrictive level transmitter, service level transmitter, etc. The second type is non-contact type, divided into ultrasonic level transmitter, radar level transmitter, etc…
The second category is non-contact, which is divided into ultrasonic level transmitter, radar level transmitter and so on. Static pressure input level transmitter (level meter) is suitable for level measurement of various media in petrochemical, metallurgy, electric power, pharmaceutical, water supply and drainage, environmental protection and other systems and industries. Compact structure, simple adjustment and flexible installation for users to easily use the convenience of 4 ~ 20mA, 0 ~ 5v, 0 ~ 10mA and other standard signal output by the user according to the need to choose. Measuring liquid level using hydrostatic principle is an important application of pressure sensors. The use of special intermediate cable with ventilation conduit and specialized sealing technology not only ensures the sensor’s watertightness, but also makes the reference pressure chamber and the ambient pressure, thus ensuring the high accuracy and stability of the measurement.
Submersible level sensor
Based on the principle that the hydrostatic pressure is proportional to the height of the liquid, submersible level sensor uses the piezoresistive effect of diffused silicon or ceramic sensor to convert the hydrostatic pressure into electrical signal. After temperature compensation and linear correction, it is converted into 4-20mADC standard current signal output. The sensor part of submersible hydrostatic pressure transmitter can be directly put into the liquid, and the transmitter part can be fixed with flange or bracket, so that it is very convenient to install and use.
Submersible level sensor is made of advanced isolation type diffused silicon sensitive element, which can be directly put into the container or water to accurately measure the height from the end of the sensor to the water surface, and output the water level through 4 – 20mA current or RS485 signal.
Ultrasonic level meter
Ultrasonic level meter is a digital level instrument controlled by microprocessor. In the measurement, the pulse ultrasonic wave is sent out by the sensor, and the sound wave is received by the same sensor after being reflected by the object surface, and converted into an electrical signal. The distance between the sensor and the object under test is calculated by the time between the sound wave transmitting and receiving.
The advantages are no mechanical movable part, high reliability, simple and convenient installation, non-contact measurement, and not affected by the viscosity and density of liquid.
The disadvantage is that the accuracy is relatively low, and the test is easy to have blind area. It is not allowed to measure pressure vessel and volatile medium.
Radar level meter
The working mode of radar liquid level meter is transmitting reflecting receiving. The antenna of radar liquid level meter emits electromagnetic waves, which are reflected by the surface of the measured object and then received by the antenna. The time of electromagnetic waves from transmitting to receiving is proportional to the distance to the liquid level. The radar liquid level meter records the time of pulse waves, and the transmission speed of electromagnetic waves is constant, then the distance from the liquid level to the radar antenna can be calculated, so as to know the liquid level of the liquid level.
In practical application, there are two modes of radar liquid level meter, namely frequency modulation continuous wave and pulse wave. The liquid level meter with frequency modulated continuous wave technology has high power consumption, four wire system and complex electronic circuit. The liquid level meter with radar pulse wave technology has low power consumption, can be powered by two-wire system of 24 VDC, easy to achieve intrinsic safety, high accuracy and wider application range.
Guided wave radar level meter
The working principle of the guided wave radar level transmitter is the same as that of the radar level gauge, but it sends microwave pulses through the sensor cable or rod. The signal hits the liquid surface, then returns to the sensor, and then reaches the transmitter housing. The electronics integrated in the transmitter housing determines the liquid level based on the time it takes for the signal to travel along the sensor and return again. These types of level transmitters are used in industrial applications in all areas of process technology.