bolt-on strain gage

[azny]

one option we are looking at for measuring load in silos is the use of bolt-on strain gages. we know the preferred practice is to use load cells but this is not an option for us in our configuration. we are looking for comments, both pro and con, for using bolt-ons, what accuracy levels we should expect, who makes the best in class, and any other useful suggestions. Thanks in advance

 

[Ron]

If you are using these on a steel container device (silo), then they should work fine. If you are using on concrete, maybe not!

Critical is the bolt attachment and "slack" in the bolt-to-bolt hole clearance. Ideally you will have no slack (bolts are almost "press fit" to the holes). If you have slack, it might be difficult to get an accurate calibration as the "slack" movement might vary.

If you are using on steel, I would probably go with a welded strain gage. If on concrete, I would go with a protected, bonded strain gage with a gage length of at least 4 inches.

 

[Compositepro]

"Strain gage" may not be the correct term for what you are seeking. The term usually refers to the basic foil or wire type sensor. These are mounted to something else to create load cells or extensometers.

 

[IceStationZebra]

Compositepro - While I agree with you, there are several products sold as bolt-on strain gages. They are often used on cranes for monitoring loads in the structures. There are also products for concrete testing sold as weld-on strain gages, but are actually similar devices that are welded to rebar then embedded in concrete.

Azny - The installation is going to depend largely on the joint details. You need to some up with a consistent installation procedure so you can compare apples-to-apples.

As far as technology is concerned, some use foil gages and some use sputter technology. The foil gages are a slightly more linear/accurate. The sputter gages can be laser trimmed to provide slightly better temperature compensation.

And remember that you are averaging the stress seen between the fastening bolts. Localized stresses will be higher.

ISZ