From Stress to Signal: Understanding the Functions of Strain Gauge Converters

What is the Strain?

Strain is the relative change in the length of a component or structure under stress. This can consist of an extension (elongation) or contraction (compression). Strain can result from forces or moments (mechanical strain) applied to a structure, as well as thermal expansion in the case of temperature changes. The indirect force measurement via strain sensors determines the mechanical strain.

Fig 1. The strain

What is a Strain Gauge?

A strain gauge is a type of sensor that measures the strain or deformation of a material under stress. When a strain gauge is attached to a structure and the structure is subjected to stress, the strain gauge produces a small electrical signal that varies in response to changes in strain.

A strain gauge typically consists of a thin metal wire or foil that is bonded to the surface of the material being measured. As the material is subjected to stress, the wire or foil is stretched or compressed, causing its resistance to change. This change in resistance produces a small electrical signal that can be measured and used to determine the strain on the material.

Strain gauges are used in a wide range of applications, such as load cells, pressure sensors, and torque sensors, to measure and control physical variables in industrial, automotive, and aerospace applications. The output signal from a strain gauge is typically very small, on the order of microvolts or millivolts, and must be amplified and conditioned by a strain gauge converter before it can be used for measurement or control purposes.

What is a Strain Gauge Converter?

A strain gauge converter is a device used to convert the small electrical signals produced by a strain gauge into a form that can be used for measurement or control purposes. A strain gauge converter amplifies and conditions the signal from the strain gauge, making it easier to measure accurately.

Strain gauge converters can be analog or digital, and may incorporate features such as filtering, scaling, and temperature compensation. They are commonly used in a variety of applications, such as load cells, pressure sensors, and torque sensors, to measure and control physical variables in industrial, automotive, and aerospace applications.

Fig 2. The strain gauge Converter

History of Strain Gauge Converter

The history of the strain gauge converter dates back to the mid-19th century when French physicist Charles-Augustin de Coulomb discovered the phenomenon of piezoelectricity. Piezoelectric materials generate an electrical charge when subjected to mechanical stress, and this principle was later used to develop the first strain gauges.

In the early 20th century, the first practical strain gauges were developed by Edward E. Simmons and Arthur C. Ruge at the Massachusetts Institute of Technology (MIT). These early strain gauges were bonded to a structure and relied on the change in resistance of a metal wire or foil under strain.

In the 1940s, the Wheatstone bridge circuit was introduced, which greatly improved the sensitivity and accuracy of strain gauge measurements. The Wheatstone bridge circuit used multiple strain gauges in a bridge configuration, with an amplifier to boost the output signal.

The first electronic strain gauge amplifier was developed in the 1950s by Harold E. Edgerton and Kenneth J. Germeshausen at MIT. This amplifier used vacuum tube technology and provided a significant improvement in the accuracy and reliability of strain gauge measurements.

Since then, strain gauge converters have continued to evolve, with the introduction of solid-state electronics and digital signal processing techniques. Today, modern strain gauge converters are highly accurate, reliable, and versatile devices used in a wide range of applications in industry, research, and engineering.

What is the Construction of a Strain Gauge Converter?

Strain gauge converters can have different constructions depending on the type and the manufacturer, but most of them consist of the following basic components:

1. Signal conditioning circuit

This is the main part of the converter and it amplifies and filters the output signal from the Wheatstone bridge circuit. The signal conditioning circuit may also include a low-pass filter to remove noise from the signal.

1. Power supply

Strain gauge converters require a power supply to operate. This can be a battery or an external power source such as an AC adapter.

1. Output circuit

The output circuit of a strain gauge converter converts the amplified signal into a usable output format. This can be a voltage or current signal, a digital signal, or a frequency-modulated signal.

1. Housing

The housing of a strain gauge converter protects the internal components from damage and provides a means of mounting the converter.

1. Connectors

Strain gauge converters typically have input and output connectors for connecting the Wheatstone bridge and the output signal to other devices or systems.

1. Calibration adjustments

Some strain gauge converters may have calibration adjustments that allow for fine-tuning of the output signal.

Fig 3. The strain gage converter

How does a strain gauge converter work?

The process by which a strain gauge converter works can be broken down into several steps:

1. The strain gauge is bonded to the surface of the object or structure being measured. When the object is subjected to stress or strain, the resistance of the strain gauge changes, producing a small electrical signal.
2. The electrical signal from the strain gauge is typically very small, in the range of microvolts to millivolts. The first step in the strain gauge converter is to amplify the signal to a level that can be easily measured or processed by other instruments or control systems.
3. The amplified signal may still contain noise and other unwanted artifacts. To remove these unwanted signals, the strain gauge converter may include filtering and other signal conditioning techniques.
4. The output signal from the strain gauge converter is typically in a standardized form, such as a voltage or current signal, that can be easily interfaced with other instruments or control systems.
5. Depending on the application, the strain gauge converter may also include features such as temperature compensation, calibration, and linearization to improve the accuracy and reliability of the measurement.

Fig 4. Interface Strain Gauge Converter

How Many Types Does a Strain Gauge Converter Have?

There are several types of strain gauge converters, each with its characteristics and applications. Here are some of the most common types:

Voltage Output Amplifier

Working principle: This type of converter works by amplifying the bridge output voltage, which is proportional to the strain applied to the gauge, and producing a proportional DC voltage output.

Usage: Voltage output amplifiers are simple and widely used for strain measurement applications, such as force, weight, and pressure measurement.

Pros: Simple, widely used, and inexpensive.

Cons: Sensitive to noise and temperature variations.

Current Output Amplifier

Working principle: This type of converter works by amplifying the bridge output voltage and producing a proportional DC output.

Usage: Current output amplifiers are less sensitive to noise and temperature variations than voltage output amplifiers, and are commonly used in applications such as load cell and torque measurement.

Pros: Less sensitive to noise and temperature variations than voltage output amplifiers.

Cons: More complex than voltage output amplifiers.

Digital Output Converter

Working principle: This converter digitizes the bridge output voltage and produces a digital output signal.

Usage: Digital output converters are immune to noise and temperature variations, and can be easily interfaced with digital processing systems. They are commonly used in industrial automation and process control applications.

Pros: Immune to noise and temperature variations, easy to interface with digital processing systems.

Cons: More expensive than analog converters.

Frequency Output Converter

Working principle: This converter converts the bridge output voltage into a frequency-modulated signal.

Usage: Frequency output converters are useful for wireless and remote sensing applications, as well as for applications that require high immunity to electromagnetic interference.

Pros: Useful for wireless and remote sensing applications, high immunity to electromagnetic interference.

Cons: Limited resolution compared to analog converters.

Signal Conditioner

Working principle: This converter conditions the bridge output voltage to remove noise, amplify the signal, and filter the output.

Usage: Signal conditioners are commonly used in industrial applications where noise and environmental factors can affect the signal. They are used in combination with other types of converters to produce an output signal.

Pros: Removes noise, amplifies the signal, and filters the output.

Cons: More expensive than simple voltage or current output amplifiers.

Wheatstone Bridge

Working principle: The Wheatstone bridge circuit is used to measure small changes in resistance due to strain.

Usage: The Wheatstone bridge is commonly used with strain gauges to measure small changes in resistance, and can be used in combination with other types of converters to produce an output signal.

Pros: Simple and inexpensive.

Cons: Requires a stable power source and is sensitive to temperature variations.

Table 1. Comparing different types of strain gauge converters

Note: This table is not exhaustive and there may be other factors to consider when selecting a strain gauge converter for a specific application.

What are Strain Gauge Converter Applications?

Strain gauge converters are widely used in a variety of industrial and scientific applications where measuring strain or force accurately is necessary. Some common applications include:

1. Load cells: Strain gauge converters are used in load cells to measure weight or force applied to the load cell.
2. Pressure sensors: Strain gauge converters are used in pressure sensors to measure changes in pressure, such as in industrial and medical equipment.
3. Torque sensors: Strain gauge converters are used in torque sensors to measure the amount of torque being applied to a rotating object.
4. Industrial automation: Strain gauge converters are used in industrial automation to monitor and control the performance of machines and equipment.
5. Structural engineering: Strain gauge converters are used in structural engineering to monitor the stress and strain of buildings, bridges, and other structures.
6. Aerospace and aviation: Strain gauge converters are used in aerospace and aviation applications to measure the stress and strain on aircraft components.
7. Medical devices: Strain gauge converters are used in medical devices to measure the force applied during medical procedures, such as in catheters and orthopedic devices.
8. Robotics: Strain gauge converters are used in robotics to measure the force applied by robots during manufacturing and other industrial processes.

These are just a few examples of the many applications where strain gauge converters are used. They are useful in any situation where accurate measurement of force, weight, or pressure is required.

Installation and Maintenance

How is the Strain Gauge Converter Used?

Strain gauge converters are typically used in combination with strain gauges, which are attached to a material or structure to measure the amount of strain or deformation that occurs when a load is applied. Here is a general overview of how strain gauge converters are used:

1. Install the strain gauge: The first step is to attach the strain gauge to the material or structure being measured. The strain gauge is typically glued or bonded to the surface using a special adhesive.
2. Connect the strain gauge to the bridge circuit: Once the strain gauge is attached, it is connected to a Wheatstone bridge circuit, which is a circuit that measures changes in resistance. The Wheatstone bridge circuit consists of four resistors, one of which is the strain gauge.
3. Apply a load: A load is applied to the material or structure being measured. As the load is applied, the strain gauge experiences a change in resistance, which is measured by the Wheatstone bridge circuit.
4. Amplify and convert the signal: The Wheatstone bridge circuit output is a small voltage that needs to be amplified and converted to a more useful form. This is where the strain gauge converter comes in. The converter takes the Wheatstone bridge output and amplifies and converts it to a more useful form, such as a voltage or current output, a digital signal, or a frequency-modulated signal.
5. Display or process the output: The output from the strain gauge converter can be displayed on a meter, recorded by a data logger, or processed by a computer or other digital processing system.

How to Calibrate the Strain Gauge Converter?

Calibrating a strain gauge converter is an important step in ensuring accurate and reliable measurements. The calibration process involves adjusting the output signal of the converter to match the actual strain or force being measured. Here are the general steps for calibrating a strain gauge converter:

1. Set up the strain gauge converter and the equipment being measured in a controlled environment. The environment should be free from vibration, electromagnetic interference, and other sources of noise.
2. Apply a known load or strain to the equipment being measured. This can be done using weights, a hydraulic or pneumatic device, or another method.
3. Measure the output signal of the strain gauge converter using a meter, oscilloscope, or other measuring device. Record the output signal and the applied load or strain.
4. Repeat step 3 at multiple load or strain levels, covering the expected range of measurement.
5. Use the recorded data to calculate the calibration coefficients for the strain gauge converter. These coefficients may include gain, offset, linearity, and temperature coefficients.
6. Enter the calibration coefficients into the strain gauge converter or the data processing system to adjust the output signal to match the actual load or strain being measured.
7. Verify the calibration by applying known loads or strains to the equipment being measured and comparing the output signal to the expected values.

It is important to perform regular calibrations of strain gauge converters to ensure accurate and reliable measurements over time. The calibration process should be documented and performed by trained personnel using appropriate equipment and procedures.

What are the Strain Gauge Converter Advantages and Disadvantages?

Advantages of Strain Gauge Converters

1. High accuracy: Strain gauge converters can provide highly accurate measurements of strain or force, with resolutions as fine as fractions of a percent.
2. Versatility: Strain gauge converters can be used to measure a wide range of materials and structures, from small laboratory specimens to large industrial equipment.
3. Non-intrusive: Strain gauge sensors are non-intrusive, meaning they do not significantly alter the behavior or properties of the material or structure being measured.
4. Cost-effective: Strain gauge converters are often cost-effective compared to other types of sensors, making them a popular choice for many applications.
5. Easy to use: Strain gauge converters are relatively easy to install and use, with simple wiring and output options.

Disadvantages of Strain Gauge Converters

1. Temperature sensitivity: Strain gauge sensors and converters are sensitive to temperature changes, which can affect the accuracy of measurements. Compensation techniques may be required to minimize temperature effects.
2. Calibration: Regular calibration is required to maintain accuracy over time and account for sensor and component aging.
3. Limited dynamic range: Strain gauge sensors and converters have a limited dynamic range, meaning they can only measure a certain range of strain or force before saturating.
4. Susceptibility to noise: Strain gauge signals can be susceptible to electrical noise and interference, requiring careful installation and shielding to minimize these effects.
5. Installation difficulty: Strain gauge sensors require careful installation and attachment to the material or structure being measured, which can be challenging in some applications.

Overall, the advantages of strain gauge converters make them a popular choice for many applications, while the disadvantages highlight the need for careful attention to installation, calibration, and environmental factors to ensure accurate and reliable measurements.

How to Choose the Right Strain Gauge Converter Types?

Choosing the right strain gauge converter depends on several factors, including the application requirements, the type and size of the material or structure being measured, and the measurement range and accuracy required. Here are some key considerations when selecting a strain gauge converter:

1. Measurement range: Determine the maximum and minimum expected strain or force values for your application, and choose a strain gauge converter with a measurement range that covers these values.
2. Accuracy: Consider the required measurement accuracy for your application, and choose a strain gauge converter with an accuracy that meets or exceeds these requirements.
3. Sensor type: Choose a strain gauge converter that is compatible with the type of sensor you plan to use, such as a foil or semiconductor strain gauge sensor.
4. Signal conditioning: Consider the type and quality of signal conditioning and output options provided by the strain gauge converter, such as voltage or current output, filtering, and amplification.
5. Environmental factors: Consider the temperature range, vibration, and other environmental factors that may affect the performance of the strain gauge converter and choose a device that is designed to operate in these conditions.
6. Power supply: Choose a strain gauge converter that is compatible with your power supply requirements, such as AC or DC power, and the voltage and current ratings of your power source.
7. Budget: Consider the cost of the strain gauge converter and its associated components, and choose a device that fits within your budget while still meeting your performance requirements.

By considering these factors and consulting with a supplier or manufacturer of strain gauge converters, you can choose the right type of device for your specific application.

Conclusion

In conclusion, a strain gauge converter is a type of electronic device used to measure strain or force in various materials and structures. By converting the electrical resistance changes of a strain gauge sensor into a voltage or current output, strain gauge converters provide precise and accurate measurements of mechanical stress and deformation. There are several types of strain gauge converters available, each with its advantages and disadvantages. When choosing a strain gauge converter, it is important to consider factors such as the required measurement range, accuracy, environmental conditions, power supply, and budget. Overall, strain gauge converters are essential tools for a wide range of industries, from aerospace and automotive to medical and industrial automation.

To recap

1.What is a strain gauge converter?

A strain gauge converter is an electronic device that converts the changes in electrical resistance of a strain gauge sensor into a measurable output, typically voltage or current.

2.How does a strain gauge converter work?

A strain gauge converter works by measuring the changes in electrical resistance of a strain gauge sensor when subjected to mechanical stress or deformation. These changes are then converted into a measurable output signal that can be used for data analysis or control.

3.What are the different types of strain gauge converters?

The main types of strain gauge converters include bridge amplifiers, charge amplifiers, and digital signal conditioners.

4.What are the advantages of using a strain gauge converter?

The advantages of using a strain gauge converter include high accuracy, reliable performance, and the ability to measure small changes in strain or force.

5.What are the applications of strain gauge converters?

Strain gauge converters are used in a wide range of industries and applications, including aerospace, automotive, construction, medical, and industrial automation.

6.How can a strain gauge converter be calibrated?

A strain gauge converter can be calibrated by comparing its output signal to a known reference signal and adjusting the calibration parameters accordingly.

7.Can a strain gauge converter be used for both static and dynamic measurements?

Yes, strain gauge converters can be used for both static and dynamic measurements, depending on the specific model and application.

8.What is the maximum measurement range of a strain gauge converter?

The maximum measurement range of a strain gauge converter depends on the specific model and application and can range from microstrain to several thousand pounds.

9.What is the typical accuracy of a strain gauge converter?

The typical accuracy of a strain gauge converter can range from 0.1% to 0.05% of the full-scale measurement range.

10.How do environmental factors affect the performance of a strain gauge converter?

Environmental factors such as temperature, humidity, and vibration can affect the performance of a strain gauge converter and may require additional measures to ensure accurate measurements.

11.What are the disadvantages of using a strain gauge converter?

The disadvantages of using a strain gauge converter include the need for careful installation and calibration, susceptibility to electrical noise, and limited measurement range.

12.Can a strain gauge converter be used in hazardous environments?

Yes, some strain gauge converters are designed for use in hazardous environments and may include features such as explosion-proof enclosures and intrinsically safe circuits.

13.What are some of the top brands that manufacture strain gauge converters?

Some of the top brands that manufacture strain gauge converters include HBM, Vishay Precision Group, Omega Engineering, TE Connectivity, MTS Systems Corporation, and Zemic Europe.

14.How do I choose the right strain gauge converter for my application?

When choosing a strain gauge converter, it is important to consider factors such as the required measurement range, accuracy, environmental conditions, power supply, and budget.

15.How can I ensure the long-term reliability of my strain gauge converter?

To ensure the long-term reliability of a strain gauge converter, it is important to follow the manufacturer's installation and maintenance instructions, regularly calibrate the device, and protect it from environmental factors such as moisture and vibration.

References

https://www.industrysearch.com.au/interface-strain-gauge-converter-dig-usb/p/160037

https://www.bu.edu/moss/mechanics-of-materials-strain/

https://alvi.com.au/strain-gauge-signal-converter/

https://www.knick-international.com/en/products/interface-technology/proline/strain-gauge-transmitters/