An experiment to get the accuracy of strain gages

Technical Learning Home W hen external forces are applied to a stationary object, stress and strain are the result. Stress is defined as the object's internal resisting forces, and strain is defined as the displacement and deformation that occur. For a uniform distribution of internal resisting forces, stress can be calculated Figure by dividing the force F applied by the unit area A:

An experiment to get the accuracy of strain gages

Connecting a Quarter-Bridge strain gage to channel 0. The example shown in figure 5 is simple. However, it does not permit the continuous monitoring of the excitation voltage. An alternate method is to have two Analog Input Read functions, as shown in figure 6.

They must be placed in a Stacked Sequence loop to prevent a conflict of available resources error. This type of loop required that all tasks within Stack Zero be performed then those tasks in Stack One, etc. In this mode, there is not a conflict for cpu resources.

The voltage across nodes C-A should be zero initially, i. But the 4 resistors will not be perfectly balanced. Your virtual instrument needs a mechanism to zero out or balance the bridge.

National Instruments discusses strain gage configurations and balancing. Similarly, your textbook discusses it too.

Figure 7 shows one possible mode to balance the bridge. True loop of initial bridge balance. False loop of initial bridge balance. Essentially, the user starts the VI and pushes a toggle to start an initial bridge balance.

The VI takes multiple readings 10 in this figure of the unstrained system and maintains a running average. After an average offset is established, turn off the initialization process.

Now all subsequent readings would subtract the averaged initial offset from the reading providing a neutral, balanced output.

There are advantages quick, inexpensive, etc. Several items to study in figure 7. On the left and right sides of the while loop there are down and up arrowheads.

These are shift registrers. Create them by right clicking on the while loop perimeter and "add a shift register". They get added as pairs. Shift Registers allow variables to be used in the next while loop iteration. Right click on the left arrowhead with the wire tool and create a constant.

This value will be used as the initial value prior to the start of the while loop. Follow the logic and see how the running average is determined.

How to know a strain gauge's accuracy? | Physics Forums

Use the LabView help to get more information on shift registers. At this stage, our bridge is balanced and from lecture we know that and we know that.

An experiment to get the accuracy of strain gages

We measure the change of voltage with respect to the excitation voltage. So we can rearrange and solve for the change of R and then the strain.

Diagram view of strain. With the VI running and balanced it is time to calibrate the bridge. One can add shunt resistors to simulate known strains and compare the measured-strain x-axis to the known-strain via shunt resistor y-axis. Insert at least two different shunt resistors and perform a linearization on these results to create a slope and intercept for the calibrated-strain final output.

An experiment to get the accuracy of strain gages

After adjusting the slope and intercept on the VI, and recording to disk, flip the lid of the soda can and watch the change in strain readings. Stop the VI, check that all your data appears intact and reasonable.

Repeat the procedure for the other soda can.

What Is A Strain Gauge?

A possible sequence might be: E Run VI and record to disk for a few seconds F continue recording and push the initial bridge balance.Feb 09,  · Hello all. I am looking over various strain gauges as I need to purchase one for my project. However, I have never worked with them before, and I cannot seem to figure out how to know its accuracy (able to detect a certain change in pressure, for example changes of the scale of 1mmHg), seeing as none of the datasheets seem to have that kind of data.

The purpose of this experiment is to improve the results obtained in experiment 1 by the previous measurement method by using a Wheatstone bridge (Figure 2) that comprises of four nominally identical strain gauges. Nov 16,  · The calculations allow you to design a gage installation to get a predetermined sensitivity and accuracy, but do not take into account certain practical realities, such as the exact effect of nearby stress concentrations.

The object of this experiment is to determine the performance of the strain gauge potential divider. Use the patching leads supplied to connect the equipment as shown in Figure Confirm that this is the same circuit as that shown in Figure STRAIN GAGES practical Strain GaGe meaSurementS introduction W ith today’s emphasis on product liability and energy stress-strain diagrams.

To do accurate stress analysis studies for these materials, it is necessary to determine the stress-strain properties, including Poisson’s. It describes the absolute physical limits for the resolution of strain gage transducer signals and how carrier frequency technique can get very close to the boundary of .

How to know a strain gauge's accuracy? | Physics Forums