Thank you for your question.

It really sounds like your trying to do it all in one giant step. Perhaps you should break the problem down into smaller chunks.

A strain gauge is like a resistor, a strain gauge bridge is made of 4 resistive elements.

All the resistors in the bridge should be of the same value, 120 Ohms is often used in industry. The resistors must be the same value to balance the bridge. There are other techniques to balance a bridge, but for clarity in this case we’ll assume the bridge must be balanced by the four resistors having the same resistance.

When you have setup your bridge you should attach the active strain gauge (assuming you have only one active element in your bridge) to the area where you are interested in knowing the strain. I am afraid we cannot offer advice about where to attach your gauge.

You should then be able to read back a value of zero volts from your bridge, then when your material under test has some forced applied, which produces a strain in the area your gauge is attached, you’ll see the voltage from the bridge change to something other than zero. This voltage change is proportional to the strain in that gauge.

You simply then use the bridge and gauge factor, supply voltage, output voltage and non-deformed and deformed gauge resistance values to calculate the strain.

Thank you for your comments.

Your points are well made and correct sir. The picture was intentionally a 2 wire system in order to illustrate that the strain gauge at a very basic level is a very long single piece of wire, or more simply a resistor. The first part of the article attempts to explain to the reader what a strain gauge is and how they work in a very basic sense before moving on to more complex actual real world issues.

As the article tries to show in figure 4 the classical quarter bridge configuration is in fact a 3 wire system. The wires connecting to the gauge in figure 4 should be the same length and as your rightly state they should follow the same route, for the reasons you state. By following these points the bridge will be balanced by virtue of the fact the resistance of the lead wires will be the same.

Your point about the lead wiring running together is a valid point, in most cases this sort of point is glossed over, but with experience and wisdom with strain gauges these things are learnt. Thank you for sharing your knowledge with our readers.