granular bulk, silos


Thread Starter

Vincent Merlin

In order to know the level of grains in my polyester silos, is it possible:

- to inject a fixed amount of gas that can be identified into a silo
- to measure the concentration of the gas
- to calculate space capacity in the silo?


Everybody talks about capacitance, conductance, radar, laser, but this other solution looks nice too.

My silos are full of grains for animals, I have to be sure that the gaz is safe.

I tried to find informations but I missed. Someone could help me?

Best regards,

Vincent Merlin
Interesting approach. It should be possible. Your grain particle size distribution would need to remain fairly consistent for meaningful measurements over time. You would have to fully ventillate the silo prior to each measurement. If you use an atmospheric gas such as CO2 or Argon, you'll need to take a reference reading first before injecting the gas. Helium is inert, cheap, disperses readily throught out a filled vessel and relatively safe. The equipment to accurately measure the gas concentration could be expen$ive. Add in the ventillation equipment and you can get more expensive than other methods.

How big are these silos? You said they are polyester silos, are they polyester tanks supported on a framework or are they permanent structures attached to a footing? If it is the first then by far the cheapest and easiest is to place load cells under the framework legs and weigh the silos. The load cells can be wired together so that the outputs "summ" so that the output=the combined load on all load cells, or if your weight is evenly distributed, put a load cell under only one frame leg and shim the others.
Hi Vincent,
I'm sure that sounds like a good idea, but wouldn't it be easier to measure the relative mass of grains in the silo. It just seems like a less cumbersome and more efficient way of doing it. Plus, it's completely non invasive. Just What I think any how.
Good luck

Merlin Vincent

I 've read many different opinions about load cells. My polyester silos are not huge, the height is: only 10 meters for the biggest and 5.5 meters for the smallest. They are fixed on the ground by bolts, and I don't really understand how can I place load cells under the legs if I want my silo to be still in productive use. Have you heard about L-CELL from Kistler-Morse ??? It looks nice but a bad surprise is always a possibility. The most important thing : I want to be informed when my silos are almost vacuum, so precision is not important.

..paddle, vibration, tuning fork, load cell, ultrasonic, radar, guided wave, laser, plumb bob, thermal dispersion, resistive tape......haaaaaa!!!

I need some help!!!!
Please....a device cheap, easy with security...
Best regards
Ive used load cells for many years without any trouble. There are two types of failures, a yeild failure where the load cell "beam" is stressed to yielding, and an electrical faliure. Unless your framework gets hit by a truck a properly sized load cell should not yield. If the electronics fail then you'll get an empty silo indication when it is acutally full. But you won't run out. I recommend a puck type load cell. One side of the load cell will bolt to the ground pad, the silo leg will bolt on the other side. An example of this type of load cell can be seen at "":

As for the possibility of failure, any sensor can fail. From time to time as you pass by the silo a visual check that the reading is about the same as the observed level should suffice in your application.
This thread sounds like a farm project trying for the most economical solution. How about a simple, cheap mechanical device. Here is what I am thinking. I am assuming that the silo is manually filled. You need a sheet metal ball about 300mm to 500mm in diamter and about 3Kg in mass, maybe less depending on what your grain is. Attach a vinyl coated steel cable to this ball and attach the other end to a switch at the top of the tank. Use a heavy duty limit switch or cable pull type switch that can support the weight of the ball and cable. You could also use a pulley arrangement to mount the switch elsewhere if you wanted. When you fill the silo pull the ball up to the top of the grain and leave the cable slack. As soon as the ball is free hanging you'll get your alarm.

Ken Stokesberry

Are there any other particulars you can provide. IE: Is it vented to atmosphere?

I am not familiar with "polyester" silos but my first thought would be a contact level reading would be the simplest, most cost effective and a
commonly used with granular solids.

this would limit your electronics to just what is necessary if needed at all.

Another good alternative would be the weight measured by load cells. this would be more expensive but would be more conducive to continuous monitoring.

Kenneth D. Stokesberry
Instrumentation Tech

Vladimir E. Zyubin

Hello Merlin,

You ought to say the reasons of unfitness for every method. E.g., why do you reject capacitance? (Two metal plates and the simple
circuit) It is cheap and reliable.

The reason will help to find the method.
Best regards,
Vladimir mailto:[email protected]


You mention that you want to know when the silo's are 'almost vacuum'. Are the silo's air tight? If so, you could use a pressure transducer. Also,
rather than inject a gas and measure density, how about pumping in atmospheric air, measuring flow going in, and then watch for a pressure change inside the vessel? The amount of air required to raise the pressure xx psi should tell you the volume of the air space inside the vessel.

Just a thought....

--Joe Jansen
What glue is required for polyester? Can you drill a couple of holes and glue small sight glasses in the side?

Vince Dooley

George \(Jim\) Hebbard

I write:

An (unfilled) patent I started to develop years ago makes use of the echo effect and digital signal processing to measure certain conditions of the silo internal volume. This is essential a public disclosure of that principle.

A transmitter fires a shaped sonic burst into the silo and a embedded computer monitors the initial pulse and the return (reflection) sound waves. Pattern matching is used generate output data which includes among other characteristics, a pitch, volume and time response that varies greatly from full to empty.

The audio electronics are cheaper and more bullet-proof than rf or other technics. Maintenance cost is less than mechanical solids-seekers. You are welcome to develop this idea further.



You could do this, or even put small "bubbles" on the inside wall, hang a light source from the top of the silo (or use a skylight, tho cloudy days
would be a problem), and use cheap photo-detectors to detect the light. By setting a few of them at differeing levels, you could detect when you are getting low. Grain would cover the sensors that are below the level, blocking the light from the detector.

--Joe Jansen

vincent Merlin

Your idea sounds like a good one. It's an interesting approach. I can drill a couple of holes and fix "bubbles" in a polyester silo. But dust is a problem and I know nothing about photo-detectors. I tried to find informations and pattents about this device but it's quite difficult. I hope you could give me Web Sites or more explanations.

Best regards.
Merlin Vincent


Dear Vincent,
You mentioned a number of possible technologies in your message. However you did not mention ultrasonic level measurement as one of the possibilities. Did you try ultrasonic level measurement for solids? Solid Applied Technologies ( "": ) offers products dealing with exactly this type of application. The products are capable of
measuring up to a range of 40 meters. The transmitted ultrasonic waves cover an area which is determined by the sensor's transmitting\receiving angle.
When the surface is not flat the sensor detects many echoes from the grains area with somehow different distances . In another words, the sensor detects many "targets" with different
distances. Algorithms embedded in the instrument, are processing and averaging all the measured distances - resulted in one averaged level
result. Installations carried out on grain silos were successful with both main SolidAT ultrasonic models. You are welcome to contact me directly for
farther details.

Best regards,
E. Duzy
[email protected]