Level measurement for silos and its challenges!
With so many ways to measure level, it can get confusing for consumers shopping for a new device. Fortunately, we’ve covered most of the principles here at Visaya.
Each has specific requirements for installation and performance, and you can fit different principles in the same application. It just depends on what your process needs and what you want.
More than anything else, you need to understand those points. Otherwise, you’ll create problems for yourself and others. If you want to review some of our earlier content, you can go to our level measurement page here and see all the posts we have up so far.
Today, we’ll discuss level measurement for solid materials in silos. You have many options on the market, but a new solution with strong appeal appeared shortly after Emerson Automation Solutions bought APM Automation Solutions. We’ll discuss that, along with other relevant points in silo measurement.
This article will cover these topics:
- Measuring level in silos
- Types of level measurement for solids
- 3D level scanner
- Field communication – what’s the best option?
Measuring level in silos
This type of level measurement has some odd challenges, like incrustation and dust. But you’ll find silos everywhere, which creates many scenarios to explore.
Currently, we have two standard solutions (radar and laser), one old-school method (manual – yes, indeed), and a brand-new technology (3D scanning). Let’s go over three different industries and possible applications in each.
Food and beverage
Everyone thinks of grain silos here, right? Heck, most people think of them when the word “silo” pops up. But a lot of food and beverage ingredients wind up in silos. Let’s talk about two of them.
- Sugar: One of the foundations of the industry, sugar lives in silos before going to the production process. Build-up issues can occur in sugar silos, so your solution has to work around this condition and measure the volume accurately.
- Malt: If you like beer, then you know about malting, right? Like sugar, you’ll encounter build-up problems. And unlike sugar, you’ll also bump into dust issues. That means you need a solution to handle both and still deliver accurate numbers.
Yes, you’ll see silos in the cement industry. Didn’t I say we have silos everywhere? So what goes in these?
- Coal: Part of the cement process constantly sends coal from the silo to the production line. If you have an event, then the operator needs a way to shut down the process. So the level solution here should constantly provide reliable data.
- Cement: After production but before the water and mixing and footprints, the not-yet-cement goes into silos. Usually, unmixed cement creates a lot of dust – like malt, but with less tasty results. Anyway, you get build-up and accuracy factors here too.
I’m sure you’re getting the idea, but we’ll hit one more example before we move on.
Granular Potash: The final product usually winds up in a big dome-shaped silo. Ever seen one of those? Regardless, the challenge to measure volume in this area can affect inventory.
Types of level measurement for solids
It’s fascinating how many ways we’ve come up with to measure level in solids, from simple to fancy. Some of these methods have a requirement list as long as your arm! Check out a few of the options:
- Weight and cable system (yo-yo)
- Ultrasonic level transmitter
- Guided radar
- radar and laser
- Laser level transmitter
- Load cells
As I’ve said before, any option has pros and cons. So let’s get into the details of four ways to measure silo levels.
Yup, no joke and no Industry 4.0 at all! It seems hard to believe, but some companies out there still measure level manually. One of the biggest drawbacks to this method is making sure the worker measured the level correctly.
For one, the measuring device must always be stored and handled properly. For two, the measuring must happen the same way every time. Even if you have the same person doing it every time, you always have to leave room for human error.
Machines can’t do everything – yet – but they definitely stand as the better way to do this one thing. So let’s discuss a few of those.
Radar is a great option for level measurement for silos. Some companies using guided radars, and others deploy free-space radars. So what’s the best option? All our regular readers know the answer to this question – it depends on your application.
The free space radar can measure a long range and doesn’t make contact with the product. In most of the models on the market, you’ll get an accuracy of +-2 millimeters (mm). And guided radars can measure short and medium distances, but the sensor comes in contact with the product. It has about the same accuracy.
In the minus column, any radar device will only measure one spot, and you have to have the sensor angled properly to measure the right point.
In the plus column, if you use linearization you can measure the mass and volume of your product. This sort of measurement doesn’t show the profile of the product inside the tank, but maybe you don’t need that.
Once upon a time not terribly long ago, people considered lasers the bleeding edge of technology. Now we use them as toys.
Still, they have their place in work as well, and they’ve become more popular in level measurement for silos. Back when I used to visit customers, I remember seeing laser devices side by side with radar to check performance in applications.
We have a similar problem here, though – you only measure one spot in the pile of product. Through linearization, you can get a similar result as the radars.
3D level scanner
Now we come to the latest solution. To improve measurements in silos, vendors developed level meters that work in three dimensions.
The 3D level scanner sends low-frequency acoustic waves to multiple points on the product in the silo. The product reflects the waves back to the scanner’s three antennas.
The low frequencies perform better in dust than the high frequencies used in other level meters. And the three antennas can triangulate the signals that return to them, so the device can create an X, Y, and Z graph with the data.
Now you can calculate the volume present in the silo. Also, you can view the product format using specific tools. In large silos, you may need more than one 3D meter to scan the whole silo.
So why hasn’t everyone switched to these gadgets? Because they cost more, of course. The wallet makes the final decision in most cases. And as I mentioned before, you may want all the tiny details, but you may not need it for your application.
Field communication – what’s the best option?
No matter which device you pick, you’ll need a way to get its data from it to you. Due to the height and difficulty of access inherent in silos, I recommend wireless all the way. A wireless connection brings easy integration and remote access.
You’ll have an uphill climb – in the snow, barefoot, carrying your little sister on your back – to convince me otherwise, but you can always give it a go in the comments.
So if you have a silo full of product that you need to keep an eye on, then you have several factors to mull, among them:
- How much money and time do you have to invest?
- What type of measurement do you need?
- How much risk is involved?
- Can you get local support from the vendor?
- Does your team need training to use the device?
You get the picture. As much as we may wish for a one-size-fits-all solution, life just doesn’t work that way.