1、 Contact type liquid level sensor
The detection part of this type of sensor needs to be in direct contact with the measured medium.
1. Floating ball liquid level sensor
Working principle: Based on Archimedes' principle of buoyancy. There is a floating ball inside the sensor that moves up and down with the change of liquid level. This mechanical motion can be converted into electrical signals (such as switch signals or continuous signals) through magnetic, mechanical, or resistive means.
2. Static pressure (input type) liquid level sensor
Working principle: Based on the principle of hydrostatics, the static pressure at a certain point in a liquid is proportional to the height of the liquid column above that point. The sensor is placed at the bottom of the liquid to measure the static pressure generated by the liquid, and then converted into liquid level height based on the liquid density.
3. Capacitive liquid level sensor
Working principle: Consider the sensor probe and container wall as two plates of a capacitor, with air and liquid as the intermediate medium. Changes in liquid level can cause changes in dielectric constant, resulting in changes in capacitance value. The liquid level height can be determined by measuring the capacitance value.
4. Ultrasonic liquid level sensor (contact type)
Note: Ultrasonic waves are usually non-contact, but there are also types of guided wave radar (GWR) or contact ultrasonic sensors whose probes extend into the medium. It emits high-frequency pulses along a rod or cable, which reflect off the liquid surface and measure distance by calculating the time difference.
2、 Non contact liquid level sensor
This type of sensor does not come into contact with the measured medium and is usually installed at the top of the container.
1. Ultrasonic liquid level sensor (non-contact)
Working principle: The sensor emits ultrasonic pulses to the liquid surface and receives the echo reflected back from the liquid surface. By calculating the time difference between ultrasonic emission and reception, combined with sound velocity, the distance from the sensor to the liquid level is calculated to obtain the liquid level height.
2. Radar level sensor (microwave)
Working principle: Similar to ultrasound, but emits high-frequency electromagnetic waves (microwaves). Electromagnetic waves propagate at the speed of light, reflect off liquid surfaces, and measure distance by measuring the operating time of microwaves.
3. Laser liquid level sensor
Working principle: Similar to radar and ultrasonic principles, but emitting a laser beam. Distance is measured by measuring the time difference between the emission and reflection of a laser beam.
4. RF admittance level switch
Working principle: This is a switch for point measurement, non continuous measurement. It determines whether the probe is covered by the medium by detecting changes in radio frequency admittance between the probe and the container wall, and outputs a switch signal (high/low alarm).
Summary and Selection Guide
