Level switches and level transmitters are two different types of liquid level measurement instruments. Level transmitters have a more complex structure. They enable continuous liquid level measurement and output continuous electronic signals. Level switches, however, only perform point-level measurement, outputting simple switch and alarm signals. This article will detail their differences.
What is a Level Switch?
A level switch monitors the height of a liquid level. It detects the fluid level through an internal sensor and converts the detection results into an electrical signal. It triggers related operations or alarm signals in response to changes in the media level. The signal is output to control the operation of other equipment or issue warning signals. Level switches play an important role in various industries.
What is a Level Transmitter?
A level transmitter detects and displays real-time liquid level height. It converts the liquid level height into a continuous signal. Common signal outputs include 4-20mA or HART and Modbus digital communication protocols. We can integrate liquid level information into monitoring systems.
The Main Differences Between Level Switches and Level Transmitters
In terms of measurement accuracy, level switches have a simpler structure and lower accuracy than level transmitters. For example, a float-type level switch can achieve an accuracy of ±10 mm.
In terms of output signals, level transmitters convert the liquid level into corresponding electronic signals, such as 4-20 mA, 0-10 V, or RS-485. These signals are integrated with the control system to implement complex control logic. These electrical signals can be connected to PLCs, data loggers, and other devices for data processing. Level switches are controllers that generate alarms or switch signals based on signals from level sensors to maintain a constant liquid level. Level transmitters have higher accuracy than level switches because their design is more sophisticated than that of level switches. For example, a float-type level transmitter can achieve an accuracy of ±5 mm.
In terms of purchase cost, level transmitters are more complex and have more additional features than level switches, resulting in higher production costs. However, level transmitters also have higher ongoing maintenance costs.
In terms of measurement type, level switches are primarily used for monitoring liquid level points, while level transmitters are primarily used for continuous level measurement. Level switches simply control the liquid level, while level transmitters can connect to corresponding secondary instruments to analyze and record the liquid level.
Working Principle of a Level Switch and a Level Transmitter
Working Principle of Level Switches
Tuning Fork Level Switch
A pair of piezoelectric crystals mounted on a base causes the tuning fork to vibrate at a specific resonant frequency. When the tuning fork comes into contact with the measured medium, its frequency and amplitude change. These changes are detected and processed by an intelligent circuit. The switch converts them into a switch signal for level alarm or control purposes. To extend the fork into the tank, the switch is typically mounted to the tank side or top using a flange or threaded process connection.
Read More about: Tuning Fork Level Switches
Float Level Switch
The float level switch is primarily designed and manufactured based on the principles of buoyancy and static magnetic fields. The position of the magnetized float within the measured medium is influenced by buoyancy. Changes in the liquid level cause the magnetic float to shift position. The magnet within the float interacts with the sensor, generating a switch signal.
Capacitive Level Switch
It detects whether the liquid level has reached or departed from a specific position (point) by monitoring capacitance changes. At its core is a capacitor system where one electrode (typically a probe or sensing rod) serves as one plate of the capacitor, the container wall (or another reference electrode) acts as the other plate, and the measured liquid and air function as the dielectric between the two plates.
Rotary Paddle Level Switch
The rotational resistance exerted by the material against the rotating paddle activates the switch’s overload detector. The relay outputs a switch-type signal (on/off), triggering an alarm signal from the external control circuit while simultaneously controlling the feeder.
For example, when the switch functions as high-level control, when material contacts the blade, the switch issues an alarm signal and stops the feeder. When functioning as low-level control: When material leaves the blade, the switch issues an alarm signal and starts the feeder.
Read More about: Liquid Level Controllers and Level Switches
Working Principle of Level Transmitters:
Capacitive Level Transmitter
Capacitive level transmitters operate based on the principle of capacitive sensing. When the height of the measuring electrode dipped by the measured medium changes, its capacitance changes. They can convert changes in the level of various materials and liquids into a standard current signal, which is transmitted remotely to a control room for secondary instruments or computers for centralized display, alarms, or automatic control.
Read More about: Capacitive Level Sensor for Industrial Level Measurement
Float level transmitters
Float level transmitters operate based on the principles of buoyancy and magnetic coupling. A float moves up and down along a measuring tube with the liquid level. The tube contains a measuring element. Under the influence of an external magnetic field, the measured liquid level signal is converted into a resistance signal proportional to the liquid level change. This signal is then converted into a 4-20 mA or other standard output signal.
Ultrasonic Level Transmitter
Ultrasonic level transmitters operate based on the propagation and echo reflection of ultrasonic waves. Ultrasonic level transmitters do not require contact with the measured medium. During measurement, the ultrasonic sensor emits an ultrasonic pulse. The pulse wave reaches the measured liquid surface and is reflected. The receiver then receives the returning ultrasonic signal and converts it into an electrical signal.
By precisely measuring the time it takes for the ultrasonic wave to be transmitted, reflected, and then received, combined with the known speed of sound, the distance between the object being measured and the sensor can be calculated. This, in turn, allows the liquid level to be determined.
Radar Level Transmitter
Radar level Transmitters utilize the principle of microwave echo ranging to achieve non-contact liquid level measurement. They transmit a high-frequency radar signal. When the signal hits the surface of the medium, a portion is absorbed, a portion is scattered, and a portion is reflected to the radar level meter. By measuring the time difference between transmission and reception, the liquid level can be calculated.
Read More about: Radar Level Transmitter and Guided Wave Radar Level Transmitter: The Real Difference
Level Transmitters and Level Switches Application Scenarios
Different media require different level measurement instruments. Based on our experience, level transmitters are suitable for continuous level measurement and applications requiring level analysis. Level switches are suitable for simple level control applications. The following is a detailed introduction to their application scenarios.
Let’s first introduce the application of liquid level switches. Liquid level switches mainly control the liquid level.
Applications of level switches
Level switches primarily control liquid height to prevent overflow or dry-running. They are used in applications such as:
Chemical and Petrochemical (Oil)
Agricultural fuel tanks. Pressure washers (fuel level). Generators (fuel level). Lawnmowers (fuel level). Wind turbines (gear oil level). Agriculture
Chemical application injectors (golf courses/agriculture) and agrochemical storage tanks.
Food and Beverage
Industrial dishwashers. Food warmers. Water heaters. Steam kettles and storage tanks.
Flood/Inlet/Event Detection
Provides alerts when water is detected in basements and similar locations.
HVAC
Air conditioner condensate water levels. Cooling tower water levels. Chillers, glycerin levels, and boiler water levels.
Production Process Monitoring
Maintains operational efficiency by prompting timely replenishment through low-level warnings. Enables effective pump operation and refill control.
Water and Wastewater
Water storage tanks. Sewage treatment systems. Filtration systems. Industrial carpet cleaners (water tanks). Industrial floor scrubbers (water tanks) and pump skids (pump protection).
Level Transmitter Applications:
A level transmitter is a sensor that converts liquid height into an electrical signal. Level transmitters are primarily used in the following industries.
- Level transmitters monitor liquid levels in containers such as storage tanks and reactors. Real-time level monitoring prevents hazardous situations like overflows or dry-running.
- Level transmitters monitor the storage of raw materials, finished products, and semi-finished goods. For example, in beer production, level transmitters ensure fermentation process stability through liquid level monitoring.
- Level transmitters monitor the storage of raw materials and finished products. Additionally, they monitor solvent and reaction liquid levels during pharmaceutical processes.
- Level transmitters monitor liquid levels in oil storage tanks, natural gas storage tanks, and transmission pipelines. They also monitor drilling fluid levels to ensure smooth drilling operations.
- Level transmitters monitor liquid levels in reservoirs, water towers, and wastewater treatment tanks. They also monitor chemical and sludge levels during water treatment processes to control treatment operations.
- Level transmitters play a vital role in water resource management by monitoring water levels in rivers, lakes, and reservoirs. This is critical for flood forecasting, drought monitoring, and water resource planning.
- At wastewater treatment plants, level transmitters monitor liquid levels in treatment tanks and sludge tanks.
Factors to Consider When Selecting a Level Switch and Level Transmitter - 3 points
Level switches and level sensors are common level measurement instruments. Faced with a wide variety of level switches and level transmitters, we’ve summarized the following selection tips.
1. Determine the Type of Measured Medium
Different media have different physical and chemical properties, so different media require different measurement instruments.
Key factors to consider include medium temperature, corrosiveness, adhesion, and the presence of impurities. If the medium has high viscosity, a non-contact measurement instrument is recommended.
2. Confirm the planned installation location of the instrument.
If drilling a hole in the measurement vessel is not possible, an ultrasonic or radar-based instrument can be used. If drilling is required, a float level switch or tuning fork level switch can be considered.If you are unsure of the installation location, you should discuss with the supplier to recommend a suitable level measurement instrument based on the operating conditions.
3. Confirm the signal output requirements
Based on the output method, level measurement instruments can be divided into continuous measurement and switch measurement types. Continuous measurement instruments can detect liquid level changes in real time, enabling uninterrupted monitoring. However, liquid level switches only provide a switching signal and are only suitable for monitoring and controlling specific points.
Therefore, when real-time monitoring of liquid level changes is required, continuous measurement instruments such as float level gauges or magnetic flap level gauges should be purchased. For point-based level monitoring, switch-type instruments such as tuning fork level switches or ball float level switches should be selected.
Clearly, the best tool is the one that will do the job well. When selecting an instrument, we should choose the appropriate measuring tool based on the specific working conditions. It is recommended to consult with professionals to avoid losses.
Sino-Inst Featured Level Switch and Level Transmitter
What is the difference between a level indicator, a level transmitter, and a level switch?
Generally, level indicators only display liquid height.
Level switches cannot continuously measure the liquid level. They trigger a switch signal to control circuits when the level exceeds or falls below a set point.
Level transmitters, however, enable continuous liquid level measurement. They output real-time electronic signals for analysis, recording, and storage.
What is the purpose of a level switch?
The primary function of a level switch is to monitor liquid height and trigger corresponding control or alarm actions based on preset level thresholds.
What are the advantages of level transmitters?
- High measurement accuracy: Level transmitters utilize advanced sensing technology and signal processing algorithms to achieve high-precision liquid level measurement.
- Wide applicability: Suitable for various liquid media and measurement environments, including high-temperature, high-pressure, and highly corrosive conditions.
- High reliability: Featuring a solid-state structure with no moving parts, ensuring high reliability and extended service life.
- Simple installation and maintenance: Easy to install and maintain.
- Signal output with automation integration capabilities
All in all, the distinctions between level switches and level transmitters are complex. Understanding these differences is critical for selecting the right level measurement instrument. We trust this article has provided you with a clear understanding of their differences and hope it proves helpful.
Sino-Inst possesses over two decades of liquid level measurement expertise. If you remain uncertain whether to purchase a liquid level switch or transmitter, please contact us anytime. You will acquire the most cost-effective solution by consulting our professional engineers. We will deliver your most satisfying purchasing experience.
