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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.
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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. |
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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.
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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. |
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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. |
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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. |
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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. |
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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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