Level sensors can use either contact or non-contact measuring principles. Contact sensors include float switches, conductive level switches, vibrating forks, and other measuring devices that are in contact with the measured product. They are usually cost-effective and straightforward to use, but have fewer features than non-contact level sensors and require certain conditions to work well. A float switch, for example, as the name suggests, floats, which is only possible in certain types of liquids.
Non-contact level sensors are the premium end of the spectrum of level measurement devices. They use more complicated measuring principles that don’t require contact with the measured product. This makes them more expensive but also more versatile.
Non-contact level sensor types
This article discusses the working principles and applications of the three main non-contact level sensor types and recommends some popular devices from each category.
Some applications need to avoid contact between the measuring instrument and the product because the product is corrosive or has some other properties that would disrupt measurement. This is where non-contact level sensors shine.
What is a non-contact radar level sensor?
We call them non-contact radar level sensors because some radar level sensors (guided wave radars) are actually in contact with the measured product. Some vendors call them free space radars because you can never have enough names for a device. If you’d like to know more about the types of radar level measurement, check out this article.
A non-contact radar level sensor uses the Time-of-Flight (ToF) principle to measure level continuously. This measuring principle is almost coextensive with non-contact radar level measurement, but not quite. If you would like to know more about it, read our guide. In any case, here’s a quick recap:
Time-of-flight devices measure the time it takes for waves to travel from point A to point B and back. They send out mechanical or electromagnetic waves that bounce back when they hit a surface – in this case, the product. By measuring a wave’s travel time, the transmitter can calculate the distance between the radar and the fluid and consequently the level of product in the tank.
Just like any other instrument, non-contact radar level sensors have their pros and cons. These lists don’t cover everything, but they should give you an idea of what you’ll get.
- Easy installation
- Low maintenance
- No moving parts
- Requires a minimum distance from the tank wall
- Liquid needs a minimum dielectric constant
- Turbulence inside the tank can affect readings
Non-contact radar level sensor recommendations
Non-contact radar level sensors in the market range from simple plug-and-play units to complex devices with self-diagnosis and digital protocols. Let’s have a look at some of the options.
EcoMeter series from E-Sensorix
The EcoMeter series is a plug-and-play solution. If you need a cheap and easy-to-use ultrasonic level sensor, this might be what you are looking for.
The EcoMeter from E-Sensorix consists of a wireless sensor with an integrated antenna and a local display. If you need the antenna further away for a better signal, then get the 9-meter extension cable. But keep in mind that you can’t disconnect and reconnect this cable to the sensor. You can also read our Product Review here.
The EcoMeter will only work in tanks less than three meters high with a 19.999-liter capacity. If you want to measure level in a small tank, then the EcoMeter line could be for you. But if you have something larger, then you should keep looking.
For an analog system, you may want to choose the Microplot FMR10. This device resembles the Senz2 WLR05-2G/001 in a few ways, the first being that neither has a built-in display.
However, you can set up both devices wirelessly. The FMR10 has Bluetooth via the mobile app. It also has a larger measuring range than the WLR05-2G/001, up to eight meters. And because of its size and thread connections, you can fit it even in small spaces, making very flexible.
If you want a radar level sensor with more capabilities, then check out the Magnetrol R86. This device can measure up to 40 meters and offers analog, HART, or Foundation Fieldbus for communication.
If you need to use it in intrinsically safe areas or areas with explosion risk, the R86 also has ATEX Ex d, Ex ia, and CSA IS approvals, among others. It also comes with an LCD display that you can use to set it up and configure it.
What is an ultrasonic level sensor?
The second main type of non-contact level sensor is also a Time-of-Flight device, but with a different type of wave. Ultrasonic level sensors use mechanical waves, where radars use electromechanical waves. If you would like to know more about the differences, check out our article on ultrasonic vs radar level measurement.
You’ll find similar pros and cons here, but the difference comes in the limitations. Radars don’t work well for low dielectric liquids or processes which have dielectric or viscosity changes.
You won’t have those problems with ultrasonics, but turbulence, foam, steam, and vapor can affect readings. And if you have a vacuum in your tank, this device won’t work, as the waves won’t travel in a vacuum.
Recommended ultrasonic level sensor
Prosonic T FMU30
If you have an analog control system and want a bit more than the EcoMeter but don’t have a lot of cash, then consider the Prosonic T FMU30.
This ultrasonic level sensor offers a local display to make local configuration possible. It also has a better measuring range compared to the EcoMeter, eight meters for continuous liquid level measurement and three and a half for solids. And if you need explosion proofing or intrinsically safe approvals, the FMU30 also offers those.
What is a laser level sensor?
Last but not least, we have laser level sensors. These devices also use the time-of-flight working principle to measure level but with a third kind of wave: lasers. However, we must note that there are laser level sensors that don’t count as Time-of-Flight devices because the light travels in only one direction.
Lasers, as any other forms of light, are waves (thought also particles), traveling at the speed of light. Unlike ultrasonics, laser level transmitters don’t have problems with dielectric constants like radars or vapor. They will, however, have problems with suspended particles in your tank.
Suspended particles can scatter the light from the laser and result in inaccurate readings. Fortunately, you can set the device closer to the tank wall than radars and ultrasonics can get.
Recommended laser level sensors
OptioLaser S300 Liquid
You won’t find as many laser level transmitters on the market as you will ultrasonics and radars. Hawk Instruments, however, has options for you. The OptioLaser S300 Liquid measures the level of liquids, naturally. It has a range of up to 200 meters or 50 if you have clear liquids, but it can’t measure anything lower than 46 centimeters.
As for accuracy, the S300 has an accuracy of four centimeters. And for communication, it offers analog, RS232, and HART.
If you want a laser device with more features, then the ABB LLT100 might fit your needs. ABB designed this device specifically for industrial use and harsh environments.
The LLT100 doesn’t have the range of the S300, only 30 meters for liquids and 100 for solids. In both applications, it has a minimum range of half a meter. It has better accuracy, however, at 11 millimeters.
For communication, you get analog and HART. You also get the option of a display and approvals such as CE, ATEX, IECEx, FM, 3A. And one more thing – you can use it in hygienic processes.
If you want non-contact level measurement, then one of the above devices will certainly suit you. Ultrasonic, radar, and laser devices have different strengths, applications, and costs, so you should start with determining which one your process calls for. If you have your process conditions and characteristics already figured out, then your shopping will go much more smoothly.
If you are unsure and need help selecting the right device for your application, please ask our engineers!