Level transmitters play a key role in industry, ensuring accurate level measurement during production. However, regular calibration is essential to maintain their reliability and accuracy.

Understanding the basic principles of level transmitters

A level transmitter is an instrument used to measure the height or level of a liquid by converting a physical change in level into a measurable electrical signal. The basic principle can be understood through the following key aspects:

  • Measuring principle:

The basic task of a level transmitter is to measure the height or level of a liquid. It can be applied in liquid containers, tanks, tanks or pipelines and determines the level by measuring the distance between the surface of the liquid and some reference point.

  • Sensing principle:

Different types of liquid level transmitters use different sensing principles. Some of the common ones include float, pressure, ultrasonic, radar, capacitive and guided wave radar. Each principle has its own applicable scenarios and advantages.

  • Float type level transmitter:

This type of transmitter contains a float that floats up and down as the liquid level changes. By means of a sensor connected to the float, the change in the float’s position can be measured and converted into an electrical signal. This is a mechanical sensing principle.

Float Level Transmitter
Float Level Transmitter
  • Pressure type liquid level transmitter:

Utilizes the relationship between liquid pressure and liquid height. A change in liquid level will cause a change in pressure, and the sensor measures this pressure change and converts it to a level signal. This principle is commonly used in closed containers.

These transmitters utilize the timing of ultrasonic or radar pulses to measure the distance between the liquid surface and the sensor. By measuring the echo time of the signal, the height of the liquid level can be determined.

Utilizes changes in capacitance to measure liquid level. When the liquid level changes, the capacitance changes, and the sensor measures this capacitance change and converts it into a corresponding electrical signal.

Utilizes a microwave signal that propagates through a guided wave tube and reflects back when the signal encounters the surface of the liquid. By measuring the time of reflection, the height of the liquid level can be determined.

  • Output signal:

The output signals of the level transmitter are usually current signals (e.g. 4-20mA) or voltage signals, which can be used in automation systems, monitoring instruments or data acquisition systems to realize real-time monitoring and control of liquid level.

How is a level transmitter calibrated and why is it important?

Calibration of level transmitters

Calibration of a level transmitter is a critical step in ensuring the accuracy of its measurements. The calibration process can vary depending on the type and manufacturer of the level transmitter, but in general, the following are general calibration steps:

  • Isolating the transmitter:

Isolating the level transmitter from the process by closing the valve or ensuring the vessel is empty, depending on the type of level transmitter.

  • Zero calibration:

Zero calibration adjusts the output of the transmitter when there is no level change. Disconnect the transmitter from the process or place it in an empty vessel. Adjust the zero setting until the transmitter output matches the desired zero output.

  • Span calibration:

Span calibration adjusts the transmitter output as the level changes from minimum to maximum range.

Fill the vessel to the maximum level and adjust the span setting until the transmitter output matches the desired maximum output.

  • Midpoint calibration (if applicable):

For some applications, especially where there is a non-linear tank shape, calibration is performed at the midpoint to ensure accuracy over the entire measurement range.

  • Verify calibration:

The level transmitter is placed under actual operating conditions to verify that its output signal matches the actual level.

  • Record calibration parameters:

Record the date of calibration, zero setting, span setting, and any adjustments or comments for future reference.

Why is calibration of level transmitters important?

  • Guaranteed accuracy:

Calibration ensures that the output of the level transmitter matches the actual level. Accurate level measurement is essential for monitoring and controlling production processes.

  • Improve safety:

In some industrial processes, accurate monitoring of liquid levels is critical to prevent spillage or over-venting. Accurate calibration improves system safety.

  • Ensure production quality:

In some industrial applications, variations in liquid level can have a direct impact on production quality. With accurate calibration, it is possible to ensure that the level in the production process is controlled within specified limits.

  • Comply with regulations and standards:

In some industries, regulations and standards require that level transmitters be calibrated periodically to ensure that they meet specific accuracy and performance standards.

  • Extend equipment life:

Periodic calibration helps to detect and correct possible problems with level transmitters in a timely manner, thereby extending the life of the equipment.

  • Data accuracy:

In automation systems and data acquisition systems, accurate calibration of level transmitters ensures the accuracy of the data obtained from the sensor, making it a reliable process monitoring tool.

Calibration of level transmitters is a critical step in maintaining the stability of production processes and ensuring equipment performance. It helps to guarantee the reliability, safety and efficiency of industrial systems.

Isolation valves for liquid transmitters

The use of best-in-class isolation valves is critical to the performance and reliability of liquid transmitters. A best-in-class isolation valve should have the following features and functions to meet the high standards of liquid transmitter isolation:

  • Valve type:

Selection of the proper type of isolation valve, such as a ball, butterfly, or globe valve, depends on the specific application requirements and fluid medium.

  • Material selection:

Use high quality materials that are corrosion and abrasion resistant to ensure that the isolation valve has good durability and stability in a variety of fluid media.

  • Sealing performance:

Excellent sealing performance is an important feature of isolation valves, ensuring complete isolation of the system in the closed state and preventing liquid leakage and contamination.

  • Operation mode:

Convenient manual or automated operation methods are provided to meet the operation and control needs of the system. The automated system allows for remote operation and intelligent control.

  • Size and flow characteristics:

The size and flow characteristics of the isolation valve should match the liquid transmitter and the entire process system to ensure precise fluid control during operation.

  • High-pressure and high-temperature resistance:

For applications that require handling of high pressure or high temperature fluids, isolation valves should be resistant enough to ensure safe operation.

  • Prevent cross-contamination:

Best-in-class isolation valves should be designed to prevent cross-contamination between different fluids, especially in applications that require handling different product batches.

  • Easy maintenance:

Provide a design that is easy to maintain and overhaul to reduce maintenance costs and minimize downtime.

  • Standards and certification compliance:

Conforms to relevant industry standards and certification requirements, such as API, ISO, etc., ensuring that isolation valves are designed and manufactured to meet industry standards.

  • Long life:

High-quality materials and sophisticated manufacturing processes are utilized to ensure long life and reliability of isolation valves.

Top-quality isolation valves help ensure that liquid transmitters can be easily and safely isolated from fluid flow during maintenance, replacement or commissioning phases, increasing system reliability and stability.


To summarize level transmitter calibration, follow the manufacturer’s guidelines to ensure accurate and reliable measurements. Regular calibration is a critical step to ensure system performance and safety, and helps improve the accuracy of level measurements. Document parameters after calibration and follow safety standards to ensure personnel and equipment safety. By carefully executing calibration steps, you can guarantee the reliable operation of your level transmitter in industrial processes.

Apure not only provides instruments for level measurement, but also a variety of instruments for measuring different parameters of water quality analysis, pressure measurement instruments, temperature measurement instruments, etc. If you have any questions, please contact us.