How to Choose an Ultrasonic Liquid Level Sensor

Release date:2023年07月17日 Article author:SKE Reading quantity:1147

Liquid level measurement is a common measuring task in industrial production, which involves the monitoring and control of the surface height of various liquid or solid materials. According to different working principles and application scenarios, liquid level transmitters can be divided into two categories: contact type and non-contact type. The contact liquid level sensor means that the sensor is in direct contact with the measured medium, such as capacitive type, conductivity type, float type, etc.; the non-contact liquid level sensor means that the sensor does not directly contact the measured medium, but through emission and receive some kind of signal to measure liquid level, such as ultrasonic, radar, photoelectric, etc.

 

This article mainly introduces a non-contact liquid level measuring instrument, ultrasonic liquid level sensor, which uses ultrasonic waves to measure the liquid level in the air. The ultrasonic liquid level sensor is easy and convenient to install, not affected by the liquid viscosity and density, suitable for various media, and is widely used industrial production. But it is undeniable that in the actual application, ultrasonic liquid level sensors also have limitations such as blind zones in measurement, pressure vessels and volatile media that cannot be measured. Therefore, purchase a suitable ultrasonic liquid level sensor, and correct installation and usage is related to whether the ultrasonic liquid level sensor can be better used in production.

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1. Choose the Appropriate Ultrasonic Liquid Level Sensor

 

Selecting the right ultrasonic liquid level sensor should consider the following factors:

  • Range: The range refers to the maximum distance that the ultrasonic liquid level sensor can measure, generally in meters. When selecting the range, it should be determined according to the height of the measured container and the highest and lowest liquid levels. In general, when measuring liquids, select the model according to the nominal range. However, if the measuring liquid has bubbles with a large coverage, it is necessary to increase the range. If the thickness of the bubbles exceeds 5cm, it is not recommended to use. If there is a lot of dust or steam in the air, please consult the manufacturer's technical engineer before purchasing whether to choose a large-range ultrasonic liquid level sensor.

 

  • Probe material: The choice of probe material is mainly determined by the corrosiveness of the application environment. In the general weak acid and weak alkali environment, you can use ordinary probes (such as ABS). In strong corrosive occasions, you should use anti-corrosion probes (such as PVDF). In strong acid and alkali environment, it is necessary to use a large-range ultrasonic liquid level sensor if there is fog, but not recommended if there was large fog.

 

  • Output signal: output signal refers to the electrical signal that the ultrasonic liquid level sensor converts the measurement result into, generally there are two kinds of signal, analog signal and    digital signal. Analog signal refers to the conversion of measurement results into voltage or current changes according to a certain ratio, such as 0-5V, 4-20mA, etc. It is suitable for occasions connected with display instruments or controllers. Digital signal refers to the conversion of measurement results into digital codes according to a certain protocol, such as RS485, Modbus, etc.,   and is suitable for occasions connected to computers or networks.

 

  • Other parameters: In addition to the above three main parameters, there are some other parameters that need to be selected according to specific applications, such as resolution, accuracy,  temperature compensation, alarm function, etc. Resolution refers to the smallest distance change that an ultrasonic liquid level sensor can distinguish, generally in millimeters. Accuracy refers to  the error between the measurement result of the ultrasonic liquid level sensor and the actual value, generally in percentage or millimeter. Temperature compensation means that the ultrasonic      liquid level sensor can automatically adjust the measurement results according to the change of the ambient temperature to reduce the influence of temperature on the sound speed. The alarm    function means that the ultrasonic liquid level sensor can send out sound and light or electrical signal prompts when the liquid level reaches the preset value.

 

2. Installation of Ultrasonic Liquid Level Sensor

 

To install the ultrasonic liquid level sensor mainly needs following steps:

  •  Choose a proper installation location. The ultrasonic liquid level sensor should be placed horizontally on the top of the container and vertically aligned with the liquid surface or the surface of   the measured medium. The installation location should avoid factors affecting measurement accuracy such as vibration, fluctuation, foam, dust or strong electromagnetic interference as much as possible. The installation location should also be convenient for construction, observation and maintenance.

 

  • Make sure the installation height is reasonable. The ultrasonic liquid level transmitter must be installed a certain distance above the highest liquid (material) level to avoid the blind zone of the instrument measurement. Ultrasonic liquid level sensors with different ranges have different corresponding blind zone sizes. For specific values, please refer to the product manual or the data provided by the manufacturer.

 

  • Avoid interference from obstacles. Within the ultrasonic emission angle of the sensor (generally 10°), there should be no obstacles, such as pipes, container supports, pump valve equipment, etc., to avoid false echoes. At the same time, the ultrasonic waves emitted by the sensor must not intersect the feed flow.

 

  • Connect the power and signal wires. In the case of power failure, connect the sensor to the display instrument or controller according to product manual or the wiring diagram provided by the manufacturer. If the ultrasonic liquid level sensor is used outdoors or in a humid environment, it is necessary to pay attention to the way of cable entry and routing to prevent water or moisture from entering the instrument.

 

  • Debug parameters and functions. After power on, set the parameters and functions of the instrument according to the product manual or the operation method provided by the manufacturer, such as range, resolution, filter, commissioning parameters and functions (continued). alarm, etc. If there are false echoes or noise signals, they can be filtered out or reduced through program adjustment.

 

  • Observe measurement results and status. After debugging the parameters and functions, observe whether the display results and status of the instrument are normal, consistent with the actual liquid level, whether there is any abnormality or alarm prompt. If there is a problem, you can check and deal with it according to the product manual or the troubleshooting method provided by the manufacturer.

 

3. Precautions and Troubleshooting of Ultrasonic Liquid Level Sensor

 

When using ultrasonic liquid level sensors, you also need to pay attention to the following aspects:

  • Clean and calibrate regularly. During use, the ultrasonic liquid level sensor may be polluted by dust, water vapor, oil, etc., which may influence the effect of transmitting and receiving ultrasonic waves. Therefore, the emitting surface of the sensor needs to be cleaned regularly, and calibrated according to the product manual or the method provided by the manufacturer to ensure the accuracy of the measurement.

 

  • Avoid overpressure or negative pressure. Ultrasonic liquid level sensors are generally suitable for normal pressure environments. Overpressure or negative pressure will affect the speed of sound wave propagation and affect measurement accuracy. Severe overpressure or negative pressure may even cause the ultrasonic liquid level sensor to fail to work properly. Therefore, when     using an ultrasonic liquid level sensor, the pressure balance inside and outside the tank should be maintained, or an ultrasonic liquid level sensor suitable for high-pressure or low-pressure environments should be selected.

 

  • Observe explosion protection regulations. If the ultrasonic liquid level sensor is used in an explosion-proof area, such as the measurement of flammable and explosive media, an ultrasonic liquid level sensor with explosion-proof performance should be selected, and the installation regulations in the national explosion-proof hazardous area should be followed to ensure safety.

 

If you encounter a fault or abnormal situation when using the ultrasonic liquid level sensor, you can troubleshoot it according to the following steps:

  •  Check whether the power and signal lines are connected correctly, and whether there is any open circuit or short circuit.

  •  Check whether the sensor is installed correctly and whether there is any tilt or displacement.

  •  Check whether the emitting surface of the sensor is clean and whether there is any phenomenon such as blocking or adhesion of pollutants.

  •  Check whether there are obstacles or strong reflectors within the emission angle of the sensor.

  •  Check whether the pressure inside and outside the container is balanced, whether there is overpressure or negative pressure, etc.

  •  Check whether there are large-area bubbles, mist, foam, etc. in the measured medium.

  •  Check whether the instrument parameters and functions are set correctly, and whether there is any misoperation or misadjustment.

 

In short, the ultrasonic liquid level sensor is a non-contact liquid level measuring instrument, which has the characteristics of simple and convenient installation, is not affected by liquid viscosity and density, and is suitable for various media. However, when using ultrasonic liquid level sensors, attention should also be paid to selecting the appropriate model and material, installing and debugging correctly, cleaning and calibrating regularly, and avoiding various interferences and failures to ensure the accuracy and stability of the measurement. If you have any questions or needs about ultrasonic liquid level sensors, please feel free to contact us, we will wholeheartedly provide you with professional services and solutions.