This article discusses the working principle and applications of ultrasonic level sensors (a level transmitter with an ultrasonic sensor).
We have many methods we can use for non-contact level measurement, each with benefits and limits. Radar level measurement, for example, offers great accuracy, for a wallet-pinching price. Ultrasonic level sensors cost less and are easy to install and use, making them the most popular non-contact method for level measurement.
The ultrasonic level sensor’s working principle
Ultrasonic level sensors use the Time-of-Flight measuring principle to measure level. The device sends sound waves at a frequency higher than humans can hear, from 20 kilohertz to one gigahertz.
These waves bounce from the surface of the product, creating an echo that goes back to the sensor. Then, the sensor calculates the time the echo took to return to find out the level. It works in both: fluids and solids.
Common errors in ultrasonic level measurement
This principle seems simple. Yet, it´s important to keep in mind some technical aspects for getting accurate measurements.
- Air temperature can affect sound velocity and interfere with ultrasonic measurements. The hotter the air, the faster the sound travels. So, an integrated temperature sensor can help you compensate for this effect. The space between the ultrasonic level sensor and liquid must be at a uniform temperature to give you accurate data.
- The material you want to measure with the ultrasonic level transmitter must have a certain density to reflect ultrasonic waves. Sound travels faster through the air than through solids and liquids, so a significant difference in density between the air and your product results in a good signal.
- The ultrasonic level sensor has a blocking distance where it can’t read properly, so you must include that in your calculations. For more information on blocking distance, you can also read our article on this.
- Different materials affect sound waves differently. For example, helium atoms are less massive than air molecules and so at a given temperature, sound travels faster in helium than air. This is the reason when you inhale helium from a balloon; the pitch of your voice rises so dramatically.
- The profile of the liquid surface is an important point to consider. If the profile is turbulent, it results in foam. The readings are deflected due to foaming.
- Obstructions in tanks can cause multiple and false reflections, but nowadays, signal processing helps to ignore these problems. This issue can be eliminated up to a certain limit. However, Radar level transmitter can also be a solution to this issue.
- Ultrasonic level measurements get affected by the presence of vapor or steam above the measuring surface. This is because vapor interrupts the transmission and reflection of an ultrasonic signal.
- Vacuum applications are also not possible with an Ultrasonic level transmitter. Ultrasonic waves cannot travel through empty space, they need medium like gas, liquid or solid to travel and take measurements!
As long as you take these factors into account, you can use ultrasonic level sensors in many industries and applications. Let’s go over a few.
Ultrasonic level sensor applications
Ultrasonic water and wastewater level sensor
The water and wastewater industry strongly favors ultrasonic level sensors because they help with pump control, cycling and monitoring, overfill protection and more. In fact, ultrasonic level sensors have become the standard for most liquid level requirements.
Water and Wastewater applications use open channel flow monitoring technique for measurement of flow in various water systems. In this technique, the flow rate of water is determined by measuring the height of water with the help of an ultrasonic level sensor.
Ultrasonic liquid level sensor for chemicals
In the chemical industry, ultrasonic level sensor applications include level measurements for corrosive liquids, fuel glues, resins, paints, rubbers, and plastics. The chemical industry often measures potent products, so you’ll need a non-contact level measurement.
Ultrasonics level sensors work excellently on storage tanks for corrosive materials such as hydrochloric acid (HCl), sulphuric acid (H2SO4), and caustic soda (NaOH).
Still, you should make sure your sensor material is chemically compatible. Many ultrasonics come with wetted materials made of PVDF.
Ultrasonic food and beverage level sensor
Ultrasonic level sensors appear in this industry to measure grains, juices, powders, and more bulk solids in silos. But here, the sensors must meet hygienic requirements:
- The wetted parts must use certain materials that remain smooth and easy to clean. Buildup may ruin the product as well as the readings
- The sensor must meet the clean-in-place (CIP) temperature requirement. A hygienic cleaning cycle reaches up to 120 ˚C, so the sensor must withstand that heat for the length of the cycle.
- Sometimes, products can generate dust or noise that interferes with the signal. Choosing a highly sensitive sensor can eliminate this issue.
As a non-contact level sensor, an ultrasonic level sensor makes a good choice for wastewater, corrosive liquids and more. Ultrasonic level sensors are simple, low-cost devices that measure accurate and reliable data without affecting your product.
Also, there are some limitations to ultrasonic level measurement, which can be overcome by opting for radar level measurement.
To know more about ultrasonic level sensors, you can Ask Alex!