NMB Sensors Strain Gages Transducers
 
 

Static Strain
Dynamic Strain
Current Carrying Capacity
Operating Temperature Range
Strain Range
Strain Sensing Materials
Temperature Compensation
Lead Wire Material and Insulation

Measuring strain requires careful selection of strain gage, bonding adhesive, protective coating or coatings and lead-wires to construct a sensor system. This section will help you select a strain gage for Stress Analysis and for Load-cell and Transducer manufacturing.

Static Strain
For static strain measurement, particularly for long-term load conditions, selection of parts for sensor system have the most significant bearing on successful measurement. Select a strain gage and other components of installation that will provide the maximum electrical and dimensional stability, repeatability and with minimum difficulty of installation.

Use NMB's E and F series strain gages for most general-purpose applications and use B series strain gages where long term accuracy and stability is of concern.


Dynamic Strain
Measuring dynamic strain without regard to static strain level places lesser demands on the strain gage sensor system stability and temperature sensitivity. Select a strain gage constructed for longer fatigue life. Pay attention to maximum strain level (combined static and dynamic strain) at the peak of dynamic cycle.

Use NMB's E and F series strain gages for most general-purpose applications and use B series strain gages where long term accuracy and stability is of concern.

NMB's J and Y series strain gages provide all the benefits of a flexible backing with extended fatigue life over the B, E and F series strain gages.


Current Carrying Capacity
Strain gage size, grid design, thermal conductivity of bonding material and adhesive as well as the "heat-sink" capability of element to which these are attached place a practical limit on current carrying capacity of the strain gage. This can range from as low as 6 mA when bonded to plastics to a high of 50 mA when bonded to a good thermal conductor. To the practitioner, this limitation imposes limits on bridge excitation voltage that affects overall sensitivity of strain measurement.

NMB's B, E and F series strain gages are designed to maximize this capability.


Operating Temperature Range
Operating temperature limits of a strain gage sensor will be determined by the limits of each of the components used in the system. When measuring static strain, pay careful attention to temperature compensation and electrical stability of the strain gage and sensor system. Using a strain gage with temperature compensation tailored for test article to which strain gage is applied can significantly reduce temperature sensitivity. Use of a "dummy" gage when a strain gage with preferred temperature compensation is not available or when there is room for only one sensing gage is dictated by available space, can improve the temperature sensitivity of the overall sensor.

NMB's E and F series strain gages are an excellent choice for most general-purpose applications. Use NMB's B series strain gages when accuracy, repeatability and long term stability over an extended temperature range is required.


Strain Range
The strain range or maximum allowable percentage elongation of strain gage is determined by degree of anneal of the foil, geometry of the strain sensing grid and the elastic properties of the strain gage backing and the adhesive used.

NMB's E, F, J, K and Y series strain gages with grids lengths of 3 mm (1/8") or greater will measure strains upto 5% or 50,000 microstrain. Strain gages of these series with shorter grid lengths will typically measure strains of 2% to 3%. The B series strain gages are limited to 2% or 20,000 microstrain.

Microstrain is defined as micrometer per meter or micro-inch per inch.


Strain Sensing Materials
Copper-Nickel Alloy or Constantan is the most frequently used material for strain gages. It is ideal for static strain measurement because of its low and controllable temperature coefficient. Recommended temperature range for Constantan is from -70 °C to +200 °C (-100 °F to +400 °F). Nickel-Chrome Alloy or Evanohm® is used for high temperature static and dynamic strain measurements. This alloy also provides wide temperature compensation range and an excellent zero stability to +300 °C (+600 °F).

NMB's B, E, F, J and K series strain gages are constructed with Copper-Nickel or Constantan foils. NMB's Y series strain gages are constructed using Evanohm® foils.


Temperature Compensation
The Copper-Nickel Alloy and the Evanohm® Alloy foils can be processed to meet a range of temperature coefficients. Using this ability of these foils and by a careful selection of custom made alloys, NMB manufactures a complete line of self-temperature compensated strain gages.
Use NMB E and F series strain gages for general purpose and B series strain gages for long-term, high-accuracy stress analysis applications.

Use NMB J series strain gages for general-purpose transducer and load-cell production.

Use NMB K series strain gages for high accuracy load-cell and transducer production.

Use NMB Y series strain gages load-cell and transducer production where
High resistance for low power consumption, long fatigue life under high-strain level or high operating temperatures are required by design.


Lead Wire Material and Insulation
Select leads with materials that have low and stable resistivity, minimum temperature coefficient of resistance, and are coated with insulating material / s that are equivalent as a minimum, to the electrical insulating quality of the selected strain gage backing and adhesive used. The operating temperature characteristics of the insulating material should be well above the operating temperature conditions the sensor will encounter.

 

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