# Need a way to approx. weight of a tractor trailer being loaded

1. Feb 12, 2010

### scooter1900

Hi All,
I have a question, which is how do I figure out what the weight is of a 45' tractor trailer that is being filled with a semi-solid product and the tractor is not attached to the trailer.
I'm thinking of using the pressure of the air bags by inflating them to raise the trailer up and get a pressure which I could match to the scaled weight to come up with a chart which would tell me went I hit this pressure, approx weight would be this amount.

Another problem I have is the trailer. When I inflate the air bags, the trailer will rise up about 8" and the weight moves to the front with the potential of breaking the front jacks. If this happens, the trailer front hits the ground and I would have a real mess.
I am thinking 2 trailer stands under the front would stop this along with wheel chocks so the trailer would not move.
The problem arose because some trailers end up underloaded or overloaded. In both cases it cost money!

Regards,
Scooter

2. Feb 12, 2010

### stewartcs

So basically you want to know how much of the product is being loaded into the trailer right?

Just calculated the volume of the trailer (the portion that is full of the product) and multiply it by the specific weight of the product.

CS

3. Feb 13, 2010

### scooter1900

That's where the problem comes in, The product has a variation in the weight of it depending on how much water is removed from it.

Regards,
Scooter

4. Feb 13, 2010

### Doug Huffman

Instead of your airbags, making a resilient system, use the springs/tires. Each rig gets a table of sag height versus weight and a distance scale.

5. Feb 13, 2010

### MotoH

Calculate for intervals of how much it weighs with so much % of water content.

Calculate for 10% water content, 20%, 30% and so on. Once you know the approx. weight of each water content percentage, you can guesstimate how much the actual product will weigh once you know its actual water content.

6. Feb 13, 2010

### Doug Huffman

Now it sounds like you're trying to acquire two bits of information.

7. Feb 18, 2010

### stewartcs

I suppose using scales are out of the question then?

CS

8. Feb 18, 2010

### Topher925

How do you account for changes in temperature?

The most practical solution is just to use a scale. You don't necessarily need to weigh the hole trailer, but just the objects that are being placed into the trailer. Are things being loaded with a fork truck or trolly?

9. Feb 28, 2010

### taupune

Use a truck scale, like one of those in freeways. Just a suggestion. If its not easy than try to make the trailer float, by making it waterproof, and creating a small pool of water.

10. Mar 1, 2010

### brewnog

Tyre pressures and contact areas?

11. Mar 2, 2010

### Harry Hazard

I suggest using a strain gage mounted on a nearby bridge, or constructing a simply supported platform and bonding the strain gage to that.

A strain gage gives a resistance value in ohms based on the amount of strain(stretch) in the member its boned too. Once you have that, you can apply known weights to the bridge or simply supported member to get strain values. Then take the strain values collected and develop an equation using a regression method in excel, usually linear. Now armed with your equation, you can reasonably approximate the weight of the truck given a resistance value.

Information about strain can be found http://www.efunda.com/formulae/solid_mechanics/mat_mechanics/strain_gage_rosette.cfm" [Broken]

Last edited by a moderator: May 4, 2017
12. Mar 3, 2010

### scooter1900

The trailer cannot be weighted by scale because it is loaded and picked up when the mill calls and says it is full. There is no tractor attached to the trailer.

We are going to try blocking the front of the trailer with jacks up by the pin. Then measure from the bottom of the trailer to the floor when empty, then Full. The tractor driver will then weight the trailer on a scale and we will record that info to construct a chart based on data gathered.
Don't know if temp will effect it much, Trailer is inside building when loading and warm. Goes directly to scale house to be weighted.
Material is dropped by auger into the truck.
The goal is to make it so the people at the mill can look at a measurement and know the truck is not overloaded or underloaded.
What could prevent this from not working? (I know acts of God, etc.) :-)
Sorry for taking so long to reply.

Scooter

13. Mar 3, 2010

### mgb_phys

If the trailer is unhitched what about putting a load cell under the front legs.
Assuming the trailer is loaded fairly evenly with bulk material it's easy to get a weight from this. If you were loading a single heavy piece you would also need the distance from the wheels.

You can get portable scale pads for on site checking of trucks before they hit the highway.

14. Mar 3, 2010

### scooter1900

Hi There,

I will check out load cells. Are Load cells another name for portable scales? Any sites with good info on load scales for a novice? I checked out putting portable scales under the trailer but they cannot be left under a trailer for long periods of time. It tends to ruin them. The State Police use them to check trucks but they drive you on and drive you off very quickly. ( I know because, been there, done that)
What are your thoughts on our idea of measuring from the trailer to a fixed object( floor )??
I am also learning about strain gauges, not sure how to hook up but still reading.
Regards,
Scooter

15. Mar 3, 2010

### Harry Hazard

16. Mar 3, 2010

### mgb_phys

Load cells are basically weight measuring cylinders, they are generally a load cell inside - but that doesn't matter.
They look like a small hydraulic bottle jack with a cable coming out to a digital readout.

You can also get them to attach to a crane hook, which is another approach, like a giant fishing scale!

17. Oct 11, 2011

### Ms.CindyB.

Scooter, I would like to ask you a question. Could you please post here if you are still watching this thread, or send me a private message if see this message?

Cindy