What is a Proving Ring?

Jacob Queen

Scientists and engineers often use proving rings as a way to measure force. The devices are made using a ring of metal with a spring-like consistency. Inside the ring there is a screw attached to a dial with measurements on it and a plate that vibrates after being struck with something. The contraption in the center works to show the ring's diameter after it has been compressed or stretched, which produces a reliable force measurement that can be used for other purposes.

Architects designing buildings may need to know exactly how much weight a material can withstand before using it in a particular part of the design.
Architects designing buildings may need to know exactly how much weight a material can withstand before using it in a particular part of the design.

To use a proving ring, a person will exert force on the ring in some way—generally either pushing from both ends or pulling it apart—and then strike the plate to start vibrations. At this point, the screw is generally turned until it touches the plate and stops it from vibrating. When the vibration stops, the number on the dial will show exactly how much force was used on the ring. The metal used to make the rings is often quite thick, so any flexing will often be very slight, which facilitates the need for precise measurement tools.

Proving rings are often used to calibrate the amount of force used within various force-testing devices. Once the calibration is set, other materials are placed in the devices, and it is possible to see if they can withstand the same force that was being applied to the proving ring. In this way, scientists can determine the exact strengths of various materials.

The proving ring was invented primarily because scientists needed a precise way to test the durability of various materials. Two scientists named Herbert Lucius Whittmore and Serge Nicolas Petrenko worked together to invent the devices after World War 1, and they used them to study new materials that were being invented at that time. Engineers were often excited to try new space-age materials in their designs, but they were also skeptical.

When scientists create new materials for building or use in products, sometimes there is a concern about the tolerances of the materials. Engineers who are designing machines or architects designing buildings may need to know exactly how much weight a material can withstand before using it in a particular part of the design. If this data is not precise enough, there is the possibility of a costly or dangerous accident. The proving ring allows for a very precise and reliable definition of force tolerance for nearly any material, which can help avoid these kinds of accidents.

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Discussion Comments


@MrMoody, Nony: I can confirm that proving rings are still used in laboratory apparatus, although electronic force measurement instruments are used more often these days. The drawbacks of proving rings are as follows: Proving rings exhibit a reasonable amount of measurement hysterisis.

Proving rings can store a lot of potential energy, which means that they can fly off if something goes wrong. It also means that your system may be hard to control displacement with.

Finally, mechanical dial gauge based proving rings cannot record results automatically, which often means lots of time writing values down.


@nony - I think there are digital meters in laboratory equipment. Nothing in the article suggests that the proving ring, built the old fashioned way, is inferior however.

The proving rings give precise measurements and they have been in use for quite some time. There is no indication that they are flawed simply because they use mechanical dials or springs to deliver their readings.


I have seen some of these proving rings and other examples of tensile test equipment. The proving rings that I’ve seen all use manual dials for their readouts.

Does anyone know if there are digital proving rings? I ask because digital technology is usually considered to be more accurate in things like weighing scales.

It may not apply here, but I think it might be the case. I believe that the manual dials would wear out over a period of time, and eventually start becoming more inaccurate in their readouts.

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