Types of non-contact level measurement
When it comes to level measurement, sensors act as either contact or non-contact instruments. For contact sensors, you can have float level switches, conductive level switches, vibrating forks – the list goes on. These usually cost less than non-contact level transmitters but have fewer features.
However, some applications need to avoid contact between the measuring instrument and the product, so non-contact devices make more sense. For these, we have three main types:
- Non-contact radar
- Ultrasonic level transmitter
- Laser level transmitter
So without further ado, let’s see how each works so you can choose the one that fits your application best.
We also call these free space radars, because vendors like to make up different names for the same device. Regardless, this device uses the time-of-flight (ToF) principle to measure level continuously.
If you don’t know much about this principle, then read our article on it. And if you don’t have the time for that right now, then I’ll give you 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, revealing the level of the tank.
Just like any other instrument, non-contact radars 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
- Needs a minimum distance from the tank wall
- Liquid needs a minimum dielectric constant
- Turbulence inside the tank can affect readings
Non-contact radars 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.
This wireless device counts as one of the plug-and-play options. It uses GSM technology to send data to a cloud system that you can access through a portal. If you’ve never seen an IoT application, then there you have it.
Unfortunately, all your data goes exclusively through GSM, so you better have good reception wherever you install the device. Also, it can only measure up to five meters. If you have a bigger tank than that, then you’ll need to consider other options.
Fortunately, the simplicity of the device makes it easy to install. You can mount it with a pair of screws, slide and lock it to a bracket, or even stick it to a surface using 3M tape.
If you want an easy-to-install, plug-and-play device, then have a look at the details of the WLR05-2G/001 in our shop.
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 device 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.
Ultrasonic level transmitters
Our second type of non-contact device uses the same working principle as radars but a different type of wave. Ultrasonic level transmitters use mechanical waves, where radars use electromechanical waves.
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.
Now let’s see some options in the market.
EcoMeter series from E-Sensorix
Here we have another plug-and-play solution. If you need a cheap and easy-to-use ultrasonic, then this one might help you.
The EcoMeter from E-Sensorix consists of a wireless sensor with an integrated antenna and a local graphic display. If you need the antenna farther 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.
Also, this device will only work in tanks less than three meters high with a 19.999-liter capacity. So if you want to measure a small tank, then the EcoMeter line could work for you. But if you have something larger, then you should keep looking.
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 device has the option of 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.
You can learn more about the Prosonic T FMU30 in our shop.
Laser level transmitters
Last but not least, we have the laser level transmitters. These devices also use the time-of-flight working principle to measure level. So no need to repeat the explanation, right?
Again, it only differs in type of wave. It uses lasers, which travel at the speed of light. Lasers won’t have problems with dielectric constants like radars or vapor like ultrasonics. 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.
So let’s have a look at some options.
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 these devices may suit you. But first you’ll need to determine the needs of your process. If you have your process conditions and characteristics already figured out, then your shopping will go much more smoothly.
And if you need help selecting the right device for your application, then drop us a message in our chat or send us an email at firstname.lastname@example.org.