Correct orientation of shear beam load cell

[kjoiner]

Hello,

This should be a simple question, but I'm getting different answers. I have a Transcell, SBS-250 shear beam load cell. My understanding is that this model load cell is meant to operate in one direction only. The application is similar to a floor scale where the body of the load cell is mounted to a plate and a leveling foot is screwed into the other end and foot contacts the floor. There is an arrow on the end of the load cell. The simple question is which way should the arrow point - toward the floor and the foot or toward the sky? I don't want to apply a force to the load cell in the wrong direction and damage it. Thanks.

Kyle

 

[IceStationZebra]

Floor or sky - it doesn't matter. The force is still going through the load cell the same way. The scale applies 1G down and the floor is applying 1G up. The only issue might be water protection - point the cable down to help keep water out.

The big problem with non-static installations is how tolerant the load cell is of side (horizontal) loads. Think of a semi driver hitting the brakes while driving over the scales! If this is you look at some type of isolation or travel limiting device.

ISZ

 

[kjoiner]

ISZ,

Thanks for the reply. I contacted the manufacturer and they recommended pointing the arrow toward the sky. The most apparent difference with the orientaion is the voltage output when the cell is loaded. If the arrow is down, the voltage is negative, if pointed up, the voltage is positive. We've been able to handle that so far with the eletronics but I'm also following up to make sure we don't damage the cells by loading them in the wrong direction. This particular application is static in that we are just loading items on to a shelf suspended on the load cells so dynamic loads are not much of a problem. We do have another application where we will be rolling a load onto a scale and you make an excellent point. We have taken great pains to avoid side loading the cells and have oriented them where possible so that any dynamic loads are directed along the load cell and not to the side.

Kyle

 

[IceStationZebra]

Good point, I hadn't considered the output polarity. In my day job as a test engineer it doesn't matter because we can just add a negative to our scale factor in the data acquisition system. Good luck. ISZ

 

[rob768]

In our load cell it does make a differnce, since output is usually 4-20 mA. If you have the load cell upside down, you won't get any output. If it is a straingauge based loadcell, as most are, you cannot damage it by using it upside down.

cheers
rob

 

[kjoiner]

Hello,

ICZ,

Our electrical engineer that designs the software was able to handle the polarity issue as you mentioned in the software.

I'm waiting on a response from the load cell manufacturer to confirm that we are OK loading the cells either way becuase we've got a couple of systems out in the field with the arrows pointing down per the initial recommendation from our local rep.

Kyle

 

[IceStationZebra]

I assume that the load cells are installed but not powered up yet?

By the way, it is a little more complicated than multiplying by -1. The input amplifier also has to handle the maximum negative value without clipping or getting confused. Most data acquisition systems used by test engineers are set up for taking strain gage data during structural tests (amongst other things), which can go positive and negative in moments, so this issue is easily handled for me.

Since your electrical engineer gave you a thumbs up it sounds like you don't have this problem with this project, but it is a consideration in the future as I would guess that many of the off-the-shelf scale conditioners aren't. It is probably a little cheaper/easier to design the amp to only accept a positive input.

Cheers, ISZ

 

[kjoiner]

ISZ,

I turned the load cells over the other day so that the arrow is pointing up and we are now getting positive voltages. We plan to do some follow up work on the systems in the field and will probably re-orient them as well so that all of our sytems put out a postive voltage for consistency. Thanks again for your help and I'll let you know things turn out.

Kyle