Installing Load Cell at the top of a Moving Platform 2

[Gustavo Silvano]

Hello there!

I'm an Electrical Engineer here in Brazil, and I'm currently working at a steelmill plant. I'm working on a project where I want to measure the weight of a load. Currently we have a kind of car that is moved by a pneumatic cylinder. This car go forward and backward constantly. What I want to do is to install 4 load cells on the top of each car, and a steel sheet on top of the load cell, so that the weight will be equally distributed along all load cells.
My question is, this car moves, as I said before, and the cylinder of the car goes up and down. But when I'll measure the weight, the car will be stationary.
I want to know is, will this arreagment be effective? Do you guys see any problem with this project?
Remember that the two cars will be installed with load cells, so that the load will be placed only at the top of the load cells.
The picture attached will show you something similar of what I want.

Best regards.

Gustavo

 

[btrueblood]

You will need some exceptionally rugged load cells, but I see no reason why your plan won't work, as long as the system is regularly calibrated. Friction, warps/dents and resulting side-loading of the load cells will need to be allowed for, but well designed load cells can be had that are insensitive to such. I do wonder why a single load cell wouldn't work, or at most 3.

That said, it would be far cheaper and likely almost as accurate, to measure the cylinder pressure on what appear to be lifting cylinders on each car. I.e. fill the cylinder until the bars are lifted, close the fill valve and let the pressure settle, convert cylinder pressure to weight. Or is that the current system, and the noise in your weighing data due to friction is thought to be too high?

Regardless of the method, regular re-calibration with known loads (check weights) would be a good idea and hopefully give early indications when the sensors go south.

 

[Gustavo Silvano]

btrueblood, thanks for the advice. Indeed I think that I can use only two load cells.
I didn't understood what you've meaned by measuring the cylinder pressure. What I'm going to measure is the weight above the platforms (as ilustraded on the picture attached), and not the pressure of the cylinder.
Is that what you thought that I was going to do?

 

[controlsdude]

i have never seen a check weigh-er on a transfer car. You will get inaccurate data from the weights. The structure that the load cells ride on a structure that needs to be rigid enough to the floor that is not moving. Is there a conveyor that is rigid that the transfer car moves all the loads thru? Put the scale underneath this conveyor that would be rigid. In my experience this is the best way or typical way that works. This setup will let you use this in trade.

 

[SwinnyGG]

Gustavo:

What btrueblood is saying is that when the cylinders activate to lift the load, the pressure in the cylinders is directly related to how heavy the load is.

If you measure the pressure in the cylinders accurately enough, you can measure the weight without any additional equipment.