How to measure strain using a strain gauge?

Hey there! I'm [Your Name], and I work for a strain gauge supplier. Today, I'm gonna walk you through how to measure strain using a strain gauge. Strain gauges are super useful little devices that can tell you a whole lot about the stress and strain in different materials. Whether you're working on a big engineering project or just doing some DIY experiments, understanding how to use a strain gauge is a valuable skill.

What is a Strain Gauge?

Before we dive into the measurement process, let's quickly go over what a strain gauge is. A strain gauge is a sensor that measures the strain of an object. When an object is subjected to stress, it deforms, and this deformation is what we call strain. The strain gauge works by changing its electrical resistance in response to the strain. It's usually made of a thin wire or foil that's attached to the surface of the object you want to measure.

How Does a Strain Gauge Work?

The basic principle behind a strain gauge is the piezoresistive effect. When the wire or foil in the strain gauge is stretched or compressed, its resistance changes. This change in resistance is proportional to the strain applied to the object. By measuring the change in resistance, we can calculate the strain.

There are different types of strain gauges, but the most common ones are the bonded strain gauges. These are glued to the surface of the object using a special adhesive. The adhesive ensures that the strain gauge moves with the object, so it can accurately measure the strain.

Choosing the Right Strain Gauge

Now that you know what a strain gauge is and how it works, the next step is to choose the right one for your application. There are a few things you need to consider when making your choice:

• Gauge Factor: This is a measure of how much the resistance of the strain gauge changes for a given strain. A higher gauge factor means a more sensitive strain gauge.
• Resistance: The resistance of the strain gauge is important because it affects the electrical circuit you'll be using to measure the change in resistance. Most strain gauges have a resistance of either 120 ohms or 350 ohms.
• Size and Shape: The size and shape of the strain gauge depend on the surface area of the object you want to measure and the type of strain you're expecting. For example, if you're measuring the strain in a small, curved surface, you'll need a small, flexible strain gauge.

Preparing the Surface

Once you've chosen the right strain gauge, the next step is to prepare the surface of the object. This is a crucial step because a poorly prepared surface can lead to inaccurate measurements. Here's what you need to do:

• Clean the Surface: Use a solvent to clean the surface of the object and remove any dirt, oil, or grease. This will ensure that the adhesive bonds properly to the surface.
• Rough the Surface: Use sandpaper or a file to rough the surface slightly. This will increase the surface area for the adhesive to bond to.
• Apply the Adhesive: Apply a thin layer of adhesive to the surface of the object and the back of the strain gauge. Make sure the adhesive is evenly distributed.
• Attach the Strain Gauge: Carefully place the strain gauge on the surface of the object and press it down firmly. Make sure there are no air bubbles between the strain gauge and the surface.

Connecting the Strain Gauge

After you've attached the strain gauge to the surface of the object, the next step is to connect it to a measurement circuit. There are different types of measurement circuits, but the most common one is the Wheatstone bridge circuit.

The Wheatstone bridge circuit is a balanced electrical circuit that can measure small changes in resistance. It consists of four resistors, one of which is the strain gauge. When the strain gauge is subjected to strain, its resistance changes, and this causes an imbalance in the circuit. By measuring the voltage across the bridge, we can calculate the change in resistance and, therefore, the strain.

There are different configurations of the Wheatstone bridge circuit, including the quarter bridge, half bridge, and Full Bridge Strain Gauge. The full bridge configuration is the most sensitive and accurate, but it also requires more strain gauges.

Measuring the Strain

Once you've connected the strain gauge to the measurement circuit, you're ready to start measuring the strain. Here's what you need to do:

• Calibrate the Measurement System: Before you start taking measurements, you need to calibrate the measurement system. This involves applying a known strain to the object and adjusting the measurement circuit until the output voltage corresponds to the known strain.
• Take Measurements: Once the measurement system is calibrated, you can start taking measurements. Apply the stress or load to the object and record the output voltage from the measurement circuit. You can then use the calibration curve to convert the output voltage to strain.
• Analyze the Data: After you've taken the measurements, you need to analyze the data. This involves plotting the strain versus the stress or load and calculating the modulus of elasticity and other mechanical properties of the object.

Troubleshooting

Sometimes, things don't go as planned, and you may encounter some problems when measuring strain using a strain gauge. Here are some common problems and how to solve them:

• Poor Adhesion: If the strain gauge is not properly bonded to the surface of the object, it may not move with the object, and this can lead to inaccurate measurements. To solve this problem, make sure you clean and rough the surface properly before applying the adhesive.
• Electrical Noise: Electrical noise can interfere with the measurement signal and make it difficult to get accurate measurements. To reduce electrical noise, use shielded cables and grounding techniques.
• Temperature Effects: Temperature changes can affect the resistance of the strain gauge and lead to inaccurate measurements. To compensate for temperature effects, you can use a temperature compensation technique, such as a dummy strain gauge.

Conclusion

Measuring strain using a strain gauge is a relatively simple process, but it requires some knowledge and skills. By following the steps outlined in this blog post, you should be able to choose the right strain gauge, prepare the surface, connect the strain gauge to a measurement circuit, and take accurate measurements.

If you're interested in purchasing strain gauges or need more information about strain gauge measurement, feel free to reach out to us. We're a leading strain gauge supplier, and we have a wide range of strain gauges and measurement equipment to meet your needs. Contact us today to start a conversation about your project and see how we can help you.

References

• "Measurement of Strain with Strain Gages" by Vishay Precision Group
• "Strain Gage Handbook" by Omega Engineering