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Strain Gauge Bridge Completion Modules

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350 Ohm Quarter Bridge Strain Completion

Quarter Strain Bridge with Completion Circuit

The most common strain gauges used to quantify the state of stress on a test specimen’s surface, are uniaxial and rosette gauges.  For accurate measurements of stress and strain, these uniaxial and rosette gauges are independently connected as a Wheatstone bridge in a 3-wire quarter-bridge or half-bridge arrangement.

Strain Gauge Installations for Field Testing | Strain Gauge Services | tshirt-Strain Gauge Services Rectangular Rosette | Engineering Data Acquisition Tools: NI-9237 Bridge Input Module

Custom PTO Shaft Strain Gauge Transducer by ITM | Custom Strain Transducer Service | Custom Strain Gauge Measures KitchenAid Shaft Load

Today, most high-end data acquisition equipment manufacturers provide signal conditioning options for collecting data from single strain gauges.  Signal conditioning for strain gauges usually includes circuitry for bridge excitation voltage, quarter and half bridge completion arrangements, and shunt calibration.

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Are you looking for expert assistance with accurately measuring stress and strain? or, Do you need to rent or buy data acquisition equipment to collect stress and strain data? 

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Sometimes you may need to view or collect data from a single strain gauge using a device that only has analog voltage inputs and no strain signal conditioning.  This was precisely the case when I was working with the HX711 load cell/strain amplifier.  The HX711 requires a full bridge input so I instrumented my test specimens as such.  If I needed to use a single strain gauge with the HX711, I would have had to use an external bridge completion circuit.

What are your options for measuring single strain gauges with a device that only has voltage inputs or full bridge inputs?

Option 1: Buy a commercial off the shelf bridge completion modules.

The list below gives the specifications for some available bridge completion modules.  I plan on adding more completion modules to this list for future reference, so send me any additional completion options.

Strain Gauge Completion Modules
 
Manufacturer NI VPG Campbell Scientific
Model # NI 9926, NI 9945, NI 9944 MR1-10C-129, MR1-350-130, MR1-120-133 4WFBS1K, 4WFBS350, 4WFBS120
Description 3-Wire Quarter Bridge Completion 3-Wire Quarter Bridge Completion 3-Wire Quarter Bridge Completion
Resistance 1000 Ω, 350 Ω, 120 Ω 1000 Ω, 350 Ω, 120 Ω 1000 Ω, 350 Ω, 120 Ω
Strain Gauge Connector Terminal Block Solder Tab Terminal Block
Device Connector RJ50 Solder Tab Pins and Lead Wire

Option 2: Build your own circuit.

If you are building a product or are in the strain business long term, building your own circuit may be a cost effective alternative to the potentially more expensive off the shelf bridge completion option.  I have built a few bridge completion circuits in the past.  Here is a list of things to keep in mind when designing a circuit.

  1. Use high precision, low resistance temperature coefficient resistors
  2. The voltage source used for bridge excitation should be from a stable source like a reference since the output of a Wheatstone bridge is inversely proportional to the excitation voltage Vout/Vex.
  3. Use remote sensing to compensate for errors in excitation voltage from long lead wires
  4. Amplification will increase measurement resolution and improve signal-to-noise ratio
  5. Filter data to remove external, high-frequency noise

For more information about bridge completion or our strain gauging services, contact Ryan Welker @ (844) 837-8797 x701.

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Strain Gauge Installations for Field Testing

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iTestSystem Tip: Strain Gauge Rosette Analysis

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When troubleshooting structural failures or validating FEA models through testing, strain gauge rosettes are used to find the full state of strain at areas of concern around the structure.  iTestSystem’s Rosette Analysis tool is used to calculate the principal strain, principal strain angle, shear strain, principal stress, and other values from strain gauge rosette data. This video shows how to use the Rosette analysis tool.

For questions about using the Rosette Analysis tool or other iTestSystem analysis tools contact Chase Petzinger.

Download your free version of iTestSystem today.

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Strain Gauge Installations for Field Testing

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shaft torque sensor

Image1: Shaft torque strain gauge installation example for field testing

Our engineers and technicians have epoxied, soldered and spot welded strain gauges for applications ranging from high temperature exhaust systems to miniature load cell measurements. Every application requires a unique understanding of the strain measurement requirements including installation environment.

If the strain gauge installation is to survive in the field you must plan for the conditions it will undergo. Three important variables that you should account for are temperature range, liquid exposure, and potential impact forces. These variables determine the type of strain gauge, epoxy, solder, wiring, coating, and impact/wear protection to use in the application. The table below shows which variables affect your installation choices.

  Gauge Epoxy Solder Wiring Coating Covering
Temperature  
Liquid Exposure      
Impact Forces      

Table1: Strain gauge installation variables

For more information about ITM’s strain gauging services contact Ryan Welker at email: ryan.welker@itestsystem.com or phone: 1.844.837.8797 x702

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ITM @ VIATC 2019: Vibration Institute Annual Training Conference

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Come see us at the VIATC 2019 Exhibit Hall in Booth 33!

Ryan Welker and Mark Yeager (CAT III Vibration Analysts) will be there to answer questions about our iTestSystem engineering measurement platform, our on-site testing services, LabVIEW consulting, and strain gauging services.

When: July 24 & 25th

Where: The VIATC 2019 conference and exhibit hall will take place at the Lexington Center, connected by a joint lobby to the Hyatt Regency Lexington.

Lexington Center
430 West Vine Street
Lexington, KY 40507

Strain Gauge Shunt Equivalent Calculations in iTestSystem

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When making strain measurements it is important to perform a shunt calibration both before and after the actual measurements are acquired.  Shunt calibrations ensure accurate strain measurements by adjusting the sensitivity or gain of the data acquisition equipment to compensate for leadwire resistance and other scaling errors.

iTestSystem takes advantage of the shunt calibration circuits included in the National Instruments (NI) cDAQ strain modules.  The NI-9235, NI-9236, and NI-9237 strain modules contain an internal shunt resistor that when switched on “shunts” across one leg of the strain circuit’s wheatstone bridge.  When active, the shunt resistor offsets the strain measurement by a constant strain which is calculated using the equivalent shunt calculation.  The equivalent strain/shunt value is dependent on the strain gauge configuration, gauge resistance, shunt resistance, gauge factor, and material properties.

In the latest version of iTestSystem, we added a built-in strain gauge shunt equivalent calculator that can be accessed from the strain configuration page.  This calculator has allowed us to speed up the calibration process and eliminate hand calculation errors.

For a free trial of iTestSystem and the equivalent shunt calculation tool, contact chase.petzinger@itestsystem.com.

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ITM Live Demo Series: iTestSystem with NI FieldDAQ

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As a part the ITM Live Demo series, we’re excited to release this video featuring iTestSystem and National Instruments FieldDAQℱ hardware to assist with your data collection projects.

At ITM, we’re always on the lookout for tools that will help us take tough measurements.  When we heard that NI was introducing a new device that features IP65/67-rated ingress protection, we were very excited.  In many industrial or off-way environments, there is potential for fluids to splash or leak onto exposed hardware.  Could the NI FieldDAQℱ be a solution for these types of environments?

Watch now as I demonstrate how to use an NI FieldDAQℱ Strain Device with iTestSystem for data logging and answer the question; Will it work while submerged in water?

If you’re interested in learning more about iTestSystem or FieldDAQℱ, feel free to contact one of our test specialists by e-mail at info@itestsystem.com or phone at (844) 837-8797.

ITM Strain Gauging Services

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Garrison Dam

Quantifying stress, strain and force within a structure using real world strain gauge measurements is commonly used to verify FEA models and estimate a component’s fatigue life.  Our engineers and technicians have planned and implemented challenging strain gauge installations for our customers around the globe.  Information from these strain gauge installations has allowed our customers to validate their designs and improve their product’s reliability.

For more information about these applications and our strain gauging services, contact Ryan Welker via email ryan.welker@itestsystem.com or phone: (844) 837-8797 x702

Smart structures: If walls could talk

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Marquette University Engineering

Sensors in Marquette University’s Engineer Hall provide students with an interactive learning center.

By Robert Farrell

https://csengineermag.com/article/smart-structures-if-walls-could-talk/

I would like to give a special thanks to all those who contributed to the success of  this project.

Related link: Custom Software Integration Allows for Novel Monitoring System for Instrumented Educational Building — A CASE STUDY of Marquette University’s Engineering Hall

NIWeek 2016 – Marquette University’s “Smart Building”

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NIWeek 2016 ITM Smart Building Booth

Special thanks to the Penny Write, Tommy Glicker, Chris Davis, Rob Reichmeider, and the rest of the NI Team for allowing us to take part in your DAQ pavilion at NIWeek 2016.  See you next spring!

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Marquette University’s “Smart Building” Provides Real-World Data

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Marquette University Engineering

MILFORD, OH– Integrated Test & Measurement (ITM) announces a “Smart Building” program in partnership with Marquette University. This unique initiative allows next generation structural engineers to perform large-scale experiments and obtain real-time results using data collected on the very building in which they are learning. ITM was selected to provide the technology and services for the program.

MU DAQ App

Powerful Software – Powerful Results

The system is powered by ITM’s configurable iTestSystem software platform. The software allows users to organize, acquire and view important engineering data using National Instruments (NI) hardware. Using iTestSystem, a building monitoring system was created to collect data from a weather station together with more than 120 strain gauge sensors installed along beams, braces and columns inside the Engineering Hall at Marquette University.

The system not only measures wind speed on the five story structure; it can actually “feel” the wind load during gusts and record its impact on the facility. Data is broadcast in real time to anyone plugged into the servers through their mobile device. Observing the data allows students to understand how a building’s systems “share lateral load” during wind events. In addition, instruments along support beams in the Engineering Materials and Structural Testing lab allow students to analyze moving loads as the crane moves around the bay. At the same time floor sensors measure the impact of people moving through the building. This information will impact future building design and potential building code modifications.

For more information, visit https://3.133.116.34