Load cell problem

[djklocek]

Hello.

I have a load cell problem. I'd like to know if anybody knows some tips about the design. I have a load cell which has 2 holes inside, conected by a long hole and I have to make it better. That's why I'd like to ask, what will happen if I decrese size of holes, make the holes bigger, get rid of a long hole, etc etc. what are the general rules? Do you have any links with nice materials about it? Thank you in advance and best regards.

[fredrik]

I'm not sure I understand what you are saying, and what the problem is?

Are you talking about a mechanical load cell (force transducer)? A common load cell design is based on strain gages, which is usually somehow glued inside depending on the design. If you modify the mechanics the general thing (the flexing parts) that I can imagine happens is that you change the factory calibration characteristics of the transducer (Newton to microStrain rating). But it's hard to tell without knowing how it looks and where the active transducer element is mounted. OTOH there is nothing that stops you from making our own calibration.

 

/Fredrik

[djklocek]

Hello.

I attached a nice picture made in paint of my loadcell. I'm supposed to make this load cell better because now creep, histeresis and linearity are too bad. so what should I do first, where should I start? hmmm Best regards.

 

ps. blac dots are gages - 2 each side

[fredrik]

It looks a standard design type called "binocular" type. I'm not sure what tools you have but many things have impacy, clearly the choice of material in the beam of course, and a general balance act when making load cells is that on

 

1) one hand you want a high strain on the position on the transducer, to get a good signal to noise ratio. Things affecting this is material properties and dimensions.

 

There are "special" expensive strain gages with a high gage factor for applications where the material dimensions simply isn't a variable, but most standard type strain gages have a typical gage factor of around 2.

 

2) OTOH you do not want too much strain, because it will increase non-linearity, and lifetime of both the material and the strain gage itself. Lifetimes are typically measured in load cycles for a particular load level. What's the expected lifetime of the product?

 

In general I see two ways, either you just use your experience and make a prototype and make a measurement series so you can estimate the transducer quality, and adjust if needed.... or you try to make the theoretical strain/load calculations on the beam and apply material data and estimate the optimum dimensions.

 

If you are looking for sample designs, I'd suggest googling "binocular load cell design", perhaps you can even find some standard formulas for that type of design. But of course there are plenty of other design types for load cells.

 

/Fredrik

[djklocek]

Thank you very much for your answer. Yes, it would be very nice if I did some theoretical strain/load calculations but I was searching google last 2 days for some nice formulas, that I would be able to understand and still nothing. Does anybody know some nice calculation formulas or links? Thank you and best regards