Liquid level switch, also known as water level switch, liquid level sensor, as the name implies, is a switch that controls the on-off of the line through the liquid level. Liquid level switch, also known as water level switch, liquid level sensor, as the name suggests, is a switch used to control the liquid level. From the form, it is mainly divided into contact type and non-contact type. Commonly used non-contact switches include capacitive liquid level switches, and contact-type float level switches are the most widely used. Electrode liquid level switch, electronic liquid level switch, capacitive liquid level switch can also be realized by contact method.
LIQUID LEVEL SWITCH TYPES
① Capacitive Level Switch
The capacitive liquid level switch adopts the difference change of tiny capacitance (usually PF) caused by the detection of liquid level changes, and is processed by a dedicated ADA capacitance detection chip (which can output a variety of signal communication protocols, such as: IO, BCD, PWM, UART, IIC…) to detect the water level and output the signal to the output terminal.
The biggest advantage of capacitive liquid level detection is that it can detect the change of water level or liquid in the container through any medium, which greatly expands the practical application, and effectively avoids the disadvantages of the traditional liquid level detection method of poor stability and reliability.
② Float level switch
The float level switch uses a micro switch as a contact output. When the angle of the upward line on the horizontal plane exceeds 28°, the steel ball inside the float level switch will roll to the micro switch or leave the micro switch, so that the contact signal of the liquid level switch ON or OFF is output.
There is also another type of float level switch, which uses a mercury switch as a contact output. When the liquid level rises and contacts the float, the float changes with the angle of the water level rising with the weight as the center. When the angle of the rising line above the water surface exceeds 10°, the liquid level switch will have an ON or OFF contact signal output.
③ Electronic liquid level switch
The electronic liquid level switch detects the water level through the built-in electronic probe, and then the chip processes the detected signal. When it is judged that there is water, the chip outputs a high level of 24V or 5V, etc. (PNP type or NPN type can be used) , when it is judged that there is no water, the chip outputs 0V. The high and low level signals are read by PLC or other control circuits, and drive electrical appliances such as water pumps to work. Electronic level switches can be installed horizontally or vertically.
④ Tuning fork level switch
The tuning fork type liquid level switch is designed and manufactured using the principle of tuning fork vibration. It is on the base of the induction rod of the tuning fork liquid level switch, the tuning fork rod is driven through the piezoelectric chip, and the vibration signal is received by another piezoelectric chip, so that the vibration signal can be circulated, and the induction rod can be resonated. When the material is in contact with the induction rod, the vibration signal gradually becomes smaller, until the resonance stops, the control circuit will output the electrical contact signal. Due to the natural principle that the sensitivity of the induction rod decreases sequentially from the front to the back seat, when the material in the tank and the surrounding of the barrel are piled up and touch the base of the induction rod (the rear) or discharge, no error signal will be generated.
Simply put, the tuning fork generates mechanical vibration under the excitation of piezoelectric crystal, and this vibration has a certain frequency and amplitude. When the tuning fork is submerged in liquid or solid, the vibration frequency and amplitude of the tuning fork will change. This frequency change is detected by the electronic circuit and outputs a switch value.
⑤ Cable float level switch
The cable float level switch is designed based on the principles of gravity and buoyancy. The structure is simple and reasonable. It mainly includes a floating body, a large-capacity micro-switch set in the floating body, a driving mechanism that can turn the switch on and off, and a connection with the switch. connected three-conductor cable.
The remarkable feature of this liquid level switch is that its performance is stable and reliable (no malfunction caused by the fluctuation of the liquid level).
⑥ Ultrasonic Level Switch
The externally attached ultrasonic liquid level switch adopts ultrasonic detection technology, which solves the shortcomings of the traditional liquid level switch and is not affected by the foam and water vapor on the liquid surface. The side-mounted ultrasonic liquid level switch uses the aftershock signal of ultrasonic waves in the pipe wall medium, which greatly improves the stability and penetration, and can be applied to containers of various materials, including: alloy steel, stainless steel, plastic, glass and various synthetic material.
The externally attached non-contact ultrasonic liquid level switch provides a solution for the level measurement of containers, especially high-pressure, corrosion, and closed containers. The probe is closely attached to the outer wall of the container, and single-point level measurement can be completed without drilling holes. This technology is not affected by factors such as medium pressure, temperature, foam, gas, reflection coefficient, etc., so it is suitable for engineering control of various liquid levels in the pharmaceutical, petroleum, chemical, electric power, food and other industries. This product is an ideal choice for the detection of dangerous liquids, which can meet various application requirements and adapt to various harsh environments. At the same time, it has extremely high reliability and high stability.
How does the float level switch apply to water treatment control?
In water treatment, liquid level control is often related to the safety, economy and feasibility of the entire process.
In a water treatment process, there are generally raw water, intermediate water tanks, production water tanks, backwash water tanks, and even waste liquid tanks. There are large and small volumes. Generally, the production water tank and the raw water tank will be relatively large, especially in large production lines. At this time, multiple liquid level switches are often used in the water tank to control multiple liquid levels. Each liquid level corresponds to different actions, such as the start and stop of the pump and the start and stop of the produced water. Some tanks, although large, do not necessarily require multiple level switches.
For example, in an RO pure water production line, RO concentrated water is used as backwash water and stored in the backwash water tank. In the backwash water tank, there is only one liquid level switch, that is, the low liquid level control switch, which is used to detect the amount of water in the water tank during backwashing without detecting whether the water tank is full. Because RO produces pure water continuously, concentrated water cannot be discharged. For the product water tank, you need to set the low level and high level control switches. The high liquid level switch is used to detect whether the water tank is full, and if it is, the water production is stopped; the low liquid level switch is used to monitor whether the water produced in the product water tank is sufficient when the water is used.
Rotary level switch VS Tuning fork level switch
Rotary level switch
The rotary material level switch series is a material level switch used for solid materials (including powder, granular, block, gel, etc.). It has the characteristics of good sealing, strong overload capacity (with overload protection), light and easy installation, and large output contact capacity. Materials with different specific gravity can be realized by adjusting the tension of the spring, and the parts in contact with the materials are all made of stainless steel. The rotary switch has been widely used in chemical, plastic, cement, medicine, feed, food and other industries.
Tuning fork level switch
Tuning fork level gauge series is a general level switch. The tuning fork is excited by the internal crystal to generate resonance. When the tuning fork is covered by solid material, the vibration frequency changes and is detected by the electronic circuit, thereby outputting a switch value to achieve the purpose of alarm or control. It is widely used in petrochemical, metallurgy, light industry, building materials, environmental protection and other industries to realize the upper and lower limit alarm and control of material level.
