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# Pre-Wired Strain Gages From OMEGA [VIDEO]

A strain gage is an electro-mechanical sensor whose resistance varies with applied force. It converts force, pressure, tension, weight, etc., into a change in electrical resistance which can then be measured.

This is possible since the electrical conductance, the inverse of resistance, is for many materials dependent on the instantaneous geometry of the material.

For a simple element like a piece of wire, the resistance is proportional to its Length (L) divided by its Cross Sectional Area (A). In this case, when the wire is compressed, its relative resistance will decrease; and when it is stretched, it’s relative resistance will increase. Knowing the resistance of the wire in its resting state, it is possible to calculate the amount of applied strain based on how the resistance changes.

The measurement application is explained by strain gage manufacturer, OMEGA Engineering:

In order to measure strain with a bonded resistance strain gage, it must be connected to an electric circuit that is capable of measuring the minute changes in resistance corresponding to strain. Strain gage transducers usually employ four strain gage elements that are electrically connected to form a Wheatstone bridge circuit. A Wheatstone bridge is a divided bridge circuit used for the measurement of static or dynamic electrical resistance. The output voltage of the Wheatstone bridge is expressed in milli-volts output per volt input. The Wheatstone circuit is also well suited for temperature compensation.

The number of active strain gages that should be connected to the bridge depends on the application. For example, it may be useful to connect gages that are on opposite sides of a beam, one in compression and the other in tension. In this arrangement, one can effectively double the bridge output for the same strain. In installations where all of the arms are connected to strain gages, temperature compensation is automatic as resistance change (due to temperature variations) will be the same for all arms of the bridge.

OMEGA recently introduced their KFH series of strain gages, which supersedes the existing KFG portfolio. Available in single piece quantity for \$165.00 (KFH-3-350-C1-11L3M3R ) these pre-wired strain gages feature:

• No Soldering at the Measuring Point
• Linear Gages, 0.3 mm to 20 mm Grids
• XY Gages (Tee Rosettes) 0.6 to 6 mm Grids
• 0°/45°/90° Planar Rosettes 0.6 to 6 mm Grids
• Configured with 2 x 1-m leads or 3 x 3-m leads
• Either 120 or 350 resistance
• Each Gage has 50 mm of PTFE Cable before Transitioning to AWG 28 Leads to Prevent Leads from Adhering During Installation
• Rugged Polyimide Carrier
• Fully Encapsulated Gages for Protection from the Environment

This video shows a demonstration of attaching and using an OMEGA strain gage:

Visit the OMEGA Engineering Strain Gages Homepage for complete information, data sheets, application notes and to speak directly with one of their representatives.

(Video Credit – Eugene Potapov )

(Image Credit – Omega )

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