# How do I use full-bridge strain gauge circuit to measure F?

• APUGYael
In summary, the conversation discusses using a Wheatstone bridge with strain gauges to measure force instead of voltage. The two methods suggested are either measuring the voltage for a known load and using that as a reference point, or calculating the necessary force based on the material's tensile strength. The latter method is more theoretical and the former is a common practice known as calibration.
APUGYael
Hey all,

I am using a Wheatstone bridge with 4 strain gauges as resistors. I have a formula for the output voltage (Vout). My questions is how do I make it so instead of voltage I measure force?

Do I simply apply a set max. force (let's say 140N), see what voltage I get (Vout,max) and then use that information?

Example (bogus numbers):
140 N --> 0,5 V, so 70N --> 0,25V, etc.

Or is there a less practical and slightly more theoretical way?

I suppose that if you know the tensile strength of he material in which your Wheatstone is embedded, you could calculate the force necessary to deform that material enough to give you a certain Vout.

The hard way is to do the relevant calculations by hand, with this being a good place to start: https://www.omega.com/literature/transactions/volume3/strain.html.

The easy way is to do what you suggested in your OP - measure the bridge voltage for a known load. This is called calibration, and should be done even if you have done all the calculations. 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.

Asymptotic and Tom.G

## 1. How does a full-bridge strain gauge circuit work?

A full-bridge strain gauge circuit works by measuring the change in electrical resistance of a strain gauge, which is a small device made of a thin wire or foil that deforms under strain. The circuit consists of four strain gauges arranged in a bridge configuration, with two gauges on one side of the bridge experiencing tension and two on the other side experiencing compression. As the strain gauge deforms, the resistance changes, causing an imbalance in the bridge that is measured as an output voltage.

## 2. What materials are needed to build a full-bridge strain gauge circuit?

To build a full-bridge strain gauge circuit, you will need four strain gauges, a Wheatstone bridge, a power supply, amplifiers, and a data acquisition system. You will also need wires, connectors, and a circuit board to assemble the components.

## 3. How do I calibrate a full-bridge strain gauge circuit?

To calibrate a full-bridge strain gauge circuit, you will need to apply a known amount of strain to the strain gauges and measure the corresponding output voltage. This can be done using a known weight or force applied to the object being measured. The output voltage can then be compared to the expected output based on the properties of the strain gauges, and adjustments can be made to the circuit if necessary.

## 4. What are the advantages of using a full-bridge strain gauge circuit?

A full-bridge strain gauge circuit offers several advantages, including high accuracy and sensitivity, as well as the ability to measure both tension and compression. It is also relatively simple and inexpensive to construct, making it a popular choice for measuring strain in various applications.

## 5. How can I troubleshoot common issues with a full-bridge strain gauge circuit?

If you are experiencing issues with your full-bridge strain gauge circuit, there are a few common problems to check for. These include loose connections, incorrect wiring, or damaged strain gauges. You can also check the output voltage using a multimeter to ensure it is within the expected range. If you are still having trouble, consulting a professional or referring to the circuit's documentation may be helpful.

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