What is a Strain Gauge?
Let's review the operating mechanism, types, and recommendations for selection.
A strain gage is a sensor component that measures "strain" (rate of change) when an object is in tension or compression. They are widely used in the aircraft, railroad, steel, civil engineering, and construction industries, as well as for clinical medicine and rehabilitation. As strain gauges are so small and rarely visible, few people may notice many applications for which they are actually used.
The following is an explanation of the mechanism and use cases of strain gauges and how to employ them for measurements, as well as key points for selecting products.
A Strain Gauge is a Sensor Component That Measures the Strain of an Object
The amount of change refers to the extent by which an object is stretched when pulled, or contracted when compressed. Strain refers the ratio of the amount of change in an object to its original length.
By measuring strain, we can determine the strength limitations of a metal component or physical quantities such as load, pressure and torque (torsional force applied to a shaft), to name a few examples. Strain gauges are widely used in various applications such as product quality control and research and development.
As strain gauges are so small, the mass of the strain gauge itself can be ignored when measuring strain. Strain gauges can be attached directly to the object to be measured, such as metal or plastic, or through the use of an adhesive.
Strain Gauge Structure
Strain gauges are constructed by attaching a metallic foil resistive element onto an electrical insulator base (e.g., polyimide) and coating it with silicon or other material. Load is sensed by the metallic foil resistive element to measure the strain. Sizes vary from product to product, but the length of the gauge section can be as small as a few millimeters.
Strain Gauge Mechanism
When force is applied to an object, expansion and contraction occurs even though it may not be visible to the naked eye. To measure that strain, a strain gauge is attached to the object.
When the metallic foil resistive element of a strain gauge expands or contracts in proportion to the object, the electrical resistance changes. This mechanism is used to calculate the magnitude of strain applied to the object.
Strain Gauge Application Examples
Compact and lightweight yet highly accurate and relatively inexpensive, strain gages are used for testing the strength of products, measuring load at production plants, and found in many other day-to-day products. Let’s take a closer look at some specific examples of use.
Scales & Weighing Instruments
Strain gauges can be used in digital scales and weighing instruments. The resistance of the strain gauge when a person or object is placed on it is converted to a numerical value to indicate the weight or mass.
Computer Pointing Sticks
Computer pointing sticks are designed to move the cursor up, down, left, or right in the desired direction by using a strain gauge to detect the amount of strain from applying force with a finger.
Smartphone Drop Test
Strain gauges are also used in strength tests related to the subjected impact to smartphones when they are dropped. A strain gauge is attached to the smartphone being tested, and measures the acceleration and strain when dropped.
How to Use a Strain Gauge
Strain gauges are generally attached to the object for which strain is being measured. Note that measurement errors may occur depending on the method of adhesion. First, the surface of the application area must be cleaned. A degreasing solvent is used to remove oil. Lift the strain gage with tweezers and attach it with adhesive or other means so that there are no bubbles remaining. After the adhesive has set, ensure appropriate moisture-proofing treatment.
Required Equipment for Strain Measurement
As the resistance that can be measured with strain gages is so small, resistance is converted to voltage to calculate the strain. To convert strain into voltage and display it as a numerical value, a strain measuring instrument must be connected. The strain measuring instrument receives the signal from the strain gauge, amplifies it, and displays the numerical value digitally.
DAS-406C Amplifier
DC dynamic strain amplifier with high sensitivity and wide frequency response to 200 kHz. In addition to strain, the DAS-406C is able to measure stress, pressure, torque, vibration, and acceleration, and is used for a wide range of applications.
Bridge Box
The bridge box efficiently converts minute changes in resistance caused by strain on the gauge into voltage using a Wheatstone bridge circuit. Connect the strain gauge leads to the terminals and the plug portion to various measuring instruments.
Strain Gauge Selection
Strain gauges come in a wide variety of sizes, with gauge lengths ranging from about 0.2 mm to 8 mm. As different products have different resistance values, select a type that is appropriate for the required measurement target.
The materials and adhesives also differ in the temperature range in which they can be used. Different types should be used depending on whether there are temperature variations in the environment being measured, such as when the object being measured is subject to high temperatures or located in a harsh environment.
MinebeaMitsumi’s polyimide foil strain gauges, for instance, are able to handle temperatures from -50°C to 200°C when heat-curing adhesives are used with heat-resistant wires and terminals. In contrast, if epoxy foil strain gauges or polyimide foil strain gages are used, the temperature range is from -30°C to 70°C unless the adhesive and other materials are within the compatible temperature range.
If You Need a Strain Gauge, Contact Us About Our Extensive Lineup
Strain gauges are used in research and development, such as testing the strength of products, and are one of the components of day-to-day products like scales. Their high level of measurement accuracy and ease of handling make them suitable to a wide range of applications in many fields.
MinebeaMitsumi’s strain gauges have excellent sensitivity, stability, and fatigue life, and their wide usable temperature range enables strain measurements in a variety of situations. Furthermore, FEM analysis enables the design and proposal of the most suitable resistor patterns for targets being measured, such as two-element (half-bridge) or four-element (full-bridge) configurations. If you are seeking to deploy strain gages, don’t hesitate to send us an inquiry.