Full Wheatstone Bridge Strain Gage Sensor

The default construction of a strain gauge transducer uses a full Wheatstone bridge often with multiple backings distributed around the transducer hardware. This offers the best accuracy and insensitivity to off-axis loading, but for lower-cost sensors a single full-bridge pattern can be used. This represents several advantages over two or more backings, the most obvious is the reduced labour to install the strain gauge. The single backing and foil offers better temperature response not just due to the locality of the sensing elements but also because thermal output scatter is virtually eliminated.


Accuracy and Insensitivity to Off-Axis Loading.


Full bridge gages also offer easier installation for on-site applications such as power output calculations (torsion measurements) in ship drive shafts. The physical size and location make multi-backing installations problematic at best, so a single backing with only 4 or 5 solder connections enables easy and accurate installation with minimal time and effort.


The strain gage has been in use for many years and is the fundamental sensing element found in many types of precision force measuring transducers, including pressure, torque, load, and position. The Wheatstone bridge electrical circuit is most commonly used to sense strain gage resistance changes. This circuit requires four electrical resistance elements connected into a series/parallel configuration. One, two, or four strain gages can serve as the four resistance elements, with precision resistors making up the partial configurations.






The full-bridge circuit (with four active strain gages) provides for the highest measurement sensitivity and the best extraneous temperature cancellation. Built using Micro-Measurements' Advanced Sensors strain gage technology, the full Wheatstone bridge strain gages offer improved grid-resistance tolerance and grid-to-grid temperature matching compared to traditional gages. Micro-Measurements offers a wide range of pattern configurations and resistance ranging from 350 Ω to 20 kΩ. The addition of gold-plated solder pads improves lead wire attachment and solder-joint reliability, reducing the chances of solder pad oxidation prior to attaching the lead wires.


Compared to bonding multiple individual strain gages, the full-bridge devices provide simplified, more precise alignment and reduced bonding operations. All four active arms of the Wheatstone bridge circuit are formed on a single carrier, allowing the entire bridge to be bonded at one time. All intra-bridge connections are integrated into the pattern, thus eliminating intra-bridge soldering. Eliminating intra-bridge wiring and soldering helps to reduce zero TC problems. With no internal bridge wiring required, soldering is reduced to just four instrument wire connections, which greatly improves reliability.



In addition, with all four arms of the Wheatstone bridge being manufactured simultaneously from a single piece of foil, grid-to-grid thermal characteristics are more closely matched, and thermal output is cancelled in the bridge circuit. Micro-Measurements sensors are available in a variety of sizes, configurations, and mounting technologies.


Applications: Pressure transducers, Torque transducers, Automotive drive shafts and axles, Medical devices / force feedback, Infusion pump pressure measurement




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Yuval Hernik

StrainBlog Editor in Chief