Ultrasonic level switches can measure liquid levels in tanks and bins. Due to the non-contact measurement, level switches can be used to measure clean liquids as well as corrosive liquids. In general, ultrasonic level switches can be divided into two categories. One is the ultrasonic level sensor based on the addition of a relay to send a switching signal. The other type is a non-contact ultrasonic level switch, also called an external ultrasonic level switch. It is directly affixed to the surface of the tank, through the detection of sound waves, to determine the height of the medium.
This article will introduce the knowledge of ultrasonic level switches.
What is an Ultrasonic Level Switch?
The ultrasonic level switch is a kind of switching device that utilizes ultrasonic technology for liquid level detection. It can quickly and accurately detect the liquid level height and has been widely used in all kinds of industrial occasions. It usually consists of a transmitter, a receiver, an amplifier, a circuit board and a housing. The ultrasonic level switch can be used only by placing it above the inspected liquid or attaching it to the outer wall of the tank. There is no need to touch the liquid level. The ultrasonic level switch will sound an alarm when the medium exceeds or falls below the set point.
Advantage:
- Support customization.
- Simple operation.
- Easy to install.
- Low maintenance cost.
- Wide measuring range.
- High measurement accuracy.
Disadvantage:
- High cost compared to float level switches and tuning fork level switches.
- Restricted installation location: cannot be installed in the inlet and outlet ports.
- Top-mounted ultrasonic level switches cannot be used in vacuum and high-pressure environments.
- Cannot be installed in high-temperature environments.
Ultrasonic Level Switch Working Principle
The General Top-Mounted Ultrasonic Level Switch transmits a set of ultrasonic waves of fixed frequency to the surface of the medium to be measured by a transmitter and receives the returned ultrasonic signals by a receiver. Changes in the liquid level position will cause a time delay of the reflected signal. Through the measurement of ultrasonic transmission and reception time, which can calculate the liquid level height. At the same time, the relay converts the level into a control signal output. This realizes the monitoring and control of the detected medium level.
An external ultrasonic level controller, also known as an external level switch. It is a new type of liquid level monitoring and alarm device. The high-frequency ultrasonic pulse generated by the sensor of the liquid level controller can pass through the vessel wall. And this pulse will propagate in the vessel wall and liquid, and will be reflected. Through the detection and calculation of this reflection characteristic, it can be judged whether there is liquid in the container at the monitoring point. And at the same time, the level controller can output signals to the backstage electrical appliances or other equipment. This realizes the monitoring or control of the liquid level.
Ultrasonic Level Switch Application
The common top-mounted ultrasonic level switch has a wide range of applications in industry. It can be used for level detection, control and alarm of fluid media in various industrial fields. such as pumps, tanks, pools, boilers and other occasions. Because it is not affected by the nature of the medium, it can be applied to a variety of different liquid media. such as water, oil, acid, alkali and other media level detection and control. The use of ultrasonic level switches can also avoid the safety hazards caused by touching corrosive liquids. So it is widely used in chemical, pharmaceutical, food, metallurgy, electronics, environmental protection and many other industries.
The external ultrasonic level switch is mainly used for monitoring the liquid level of storage tanks. It realizes the upper and lower limit alarms or monitors whether there is medium in the pipeline (dry state protection). It can be applied to liquid level process control in pharmaceutical, petroleum, chemical, electric power, food and other industries. For the monitoring of toxic and highly corrosive hazardous liquids, this product is the ideal choice.
The following are the application conditions of the external ultrasonic level switch:
- Material of the measured vessel (tank): the vessel wall where the ultrasonic probe is installed is required to be made of hard material that can transmit the signal well. For example: carbon steel, stainless steel, various hard metals, fiberglass, epoxy resin, hard plastics, ceramics, glass, hard rubber and other materials or other composite materials.
- Wall thickness of tested tanks (vessels): 2～70mm;
- Type of tested tanks: horizontal tanks, spherical tanks, tanks, vertical tanks and so on.
- Medium to be measured: not affected by medium density, dielectric constant, temperature, pressure, purity, viscosity and other factors.
Ultrasonic Level Switch Selection
Selection of a suitable ultrasonic level switch requires comprehensive consideration of the measurement object, environmental conditions, product characteristics and other aspects.
The characteristics of the measured medium should be clarified. Whether it is water, oil, chemicals or slurry, etc. Because there are differences in the ability of different media to reflect and absorb sound waves.
Process and environmental conditions need to be analyzed in depth. On the one hand, the temperature range should be considered. It includes medium temperature and ambient temperature. The temperature will determine the required operating temperature range of the instrument and whether the instrument needs to have the ability to compensate for temperature. On the other hand, the pressure inside the vessel must be determined. Ultrasonic switches are usually more suitable for atmospheric or micro-pressure environments.
Determine the specific installation requirements. First, determine the mounting method, whether threaded or flanged. And make sure that the mounting interface can be matched to the opening on the vessel. If the tank cannot have an opening at the top, then the only option is an externally attached ultrasonic level switch. At the same time, when planning the installation location, avoid obstacles, such as agitators, heating coils, feed ports, etc., that may interfere with the sound waves.
A suitable output signal and electrical interface need to be selected. In terms of output signals, the most commonly used is the relay output. The relay can be used directly to control the pump or trigger an alarm. Some models also provide analog or digital interfaces. They are suitable for more complex control or monitoring scenarios. The electrical connection should also be chosen according to the requirements, whether to use a cable outlet or a junction box. It is necessary to confirm whether the corresponding waterproof and dustproof level is required.
Sino-Inst Featured Level Switch
Maintenance, Repair and Precautions for the External Ultrasonic Level Switch
1. Use, maintenance and repair:
1) Pay attention to keep the external ultrasonic level switch clean. Try to make it waterproof, moisture-proof, corrosion-proof and avoid violent collision with other objects.
2) If the ambient temperature of the level controller installed outdoors exceeds the rated temperature. Corresponding protective measures should be taken to ensure its normal operation.
When the ambient temperature is too high, avoid direct sunlight. keep away from heat sources. And pay attention to ventilation and heat dissipation. When the ambient temperature is too low, use the instrument protection box or other anti-freezing measures. And pay attention to keep the level controller dry.
2. Precautions
(1) The maximum permissible ambient temperature range of the ultrasonic level switch is -50～+60℃. When the temperature of the measured medium causes the ambient temperature to exceed the tolerance range of the ultrasonic level switch. Corresponding protective measures must be taken.
(2) The installation of the level controller should avoid the influence of an external heat source.
(3) Users are not allowed to replace the parts of the level controller at will (except for wearing parts);
(4) The wearing parts (rubber seals, etc.) should be replaced periodically;
(5) Please note that when operating and using the liquid level controller. It is strictly prohibited to open the cover with electricity in dangerous places (explosive gas environment)!
Sino-Inst's customized case:
Sino-Inst supplies both top-mounted ultrasonic level switches and external level switches. The following is the solution of the top-mounted ultrasonic level switches we supplied to our customer:
Ultrasonic level switch for water
- Measuring medium: water
- Power supply: 24vdc
- Analog output: 4-20mA
- Relay output: 1 or 2
- Measuring distance: 10m
Ultrasonic level meter for diesel
- Structure Split sensor
- Measuring range: 7m (adjustable within 10m)
- Measuring medium: diesel measurement
- Power supply: 24 VDC
- 4-wire: 4-20 mA + 2 relay outputs
- 5-digit LED display
- Suitable temperature: ambient
- Sensor corrosion-resistant
- 15m cable
Are ultrasonic height measurements accurate?
Ultrasonic level accuracy is typically ±0.5% to ±0.1%. Sino-Inst’s ultrasonic level measurements are accurate to ±2mm.
Improving measurement accuracy can be achieved through regular calibration and maintenance.
Which is better, a radar level sensor or an ultrasonic level sensor?
Both radar level sensors and ultrasonic level sensors measure liquid level by non-contact means. Radar level sensors are the better choice if high accuracy, a wide range and a harsh environment are required. If the application is simple and cost is a concern, ultrasonic level sensors may be more appropriate.
Read More About: Split-type Ultrasonic Level Transmitter For Level-Level Difference Measure
What distance can an ultrasonic sensor detect?
Sino-Inst’s ultrasonic level sensors have a detection distance of 0-20m.
In conclusion, ultrasonics play an important role in liquid level control. If you need to buy an ultrasonic level switch, please send us an email or call us. We will be online 24 hours a day to recommend the right level control solution for you.
