# Looking for a loadcell in the shape of a truss rod

Today I found myself looking for force measurement device (load cell) that can be easily attached to a educational truss structure (i.e. replace a rod in a truss). I'm sure that there are bound to be solutions for that, I just haven't come across them.

Anyway a bit more details. A friend of mine wants to give a truss building exercise for students. They idea is to have them design and then build it and then test it. The obvious solution for me was to use a scale and just measure the load that it collapsed, but he didn't want it to fail. He wanted for the students to see that when they apply a load on one node, then the structure on the rods changes (relatively) proportionally and that it can be close to what they predicted analytically.

So he insists on having a load cell that can be used to replace one of the rods and then apply a load.

Most load cells I've worked with are either very low profile and flat(pancake shaped) , or s-shaped, or others which don't really fit the bill.

I found online some information on LVDT force Sensors but there was not enough information and I'm not certain that this sensor will not extend during use (I am expecting the load cell to be a rigid structure, while the LVDT displacement sensors I know need to move).

So my question is. Can someone point to the direction of loadcells (or search terms) with the following specs:

• in the shape of rod between 100 and 250 mm long,
• with a maximum load in the order of 1 kN (tensile and compressive)
• a resolution of about 1 to 10N

or alternatively suggest a cost effective way to measure the force (tensile and compressive) on a truss?

PS: While I was looking I came across a term TE Connectivity Load Cell which I haven't managed to understand what does TE mean. I wonder if someone could enlighten me on that also.

• In engineering school, they had us glue calibrated strain gauges, each a (piezo??)-resistive bridge, to the members being tested. The exact shape and material could be altered slightly to facilitate attachment of the strain gauge, and it ended up being an exercise in calibration as much as anything. Nov 25, 2021 at 16:17
• Also, "TE Connectivity" is a company name, selling electronic components Nov 25, 2021 at 16:19
• Thanks @PeteW. I forgot to mention that the strain gauges were dismissed as an idea due to the "added" work of the calibration (which would make it impractical) but also because the strain gauge would report strain rather than force, and its mechanics 101 (so they haven't discussed yet strain and stresses).
– NMech
Nov 25, 2021 at 16:35
• Ok. Those LVDT based load cells look like a possibility, then. The LVDT is fundamentally a displacement measurement, but it looks like they calibrated them for you, with what looks like a shell that's an (aluminum?) machined spring. The electronics to read them might be a little more unique, don't know if that is a significant part of the cost these days. LVDT's also have nice dynamic response. The fact that it's an aerospace part might make it a bit expensive though. Nov 25, 2021 at 17:17
• @PeteW thanks. btw I'd accept that for an answer if you convert it. I expected them to be high - but its not coming out of my budget. I am surprised though that there is are no alternatives.
– NMech
Nov 25, 2021 at 17:34