Standard Weldable Patterns
Special Use Sensors—Weldable Strain Gages
Micro-Measurements Standard Weldable Strain Gages
and Temperature Sensors are specially designed for spot
welding to structures and components. They are ideal
for applications where test or environmental conditions
preclude clamping and curing an adhesively bonded
gage installation. These gages are equally advantageous
when strain measurements must be made at an elevated
temperature, but the nature of the test object does
not permit the use of an elevated-temperature-curing
adhesive.
Strain range is 5000 ꢀin/in ( 5000 ꢀm/m), and normal
operating temperature range is –100° to +200°F (–75°
to +95°C). Short-term maximum temperature is +300°F
(+150°C).
LWK-Series Weldable Strain Gage—Nickel-chromium
alloy grid, encapsulated in fiberglass-reinforced epoxy
phenolic. The LWK gage is provided with a three-wire lead
system with 10 in (250 mm) of Teflon®-insulated leadwire.
This construction simplifies leadwire temperature
compensation and provides for easy connection of the
lead system to the instrumentation cable. Minimum
installation radius is generally limited to 2 in (50 mm).
Surface preparation requirements are minimal; only an
appropriate solvent cleaning and abrasion of the test part
surface with silicon-carbide paper or a small, hand-held
grinder is needed. Spot welding is accomplished with
a portable stored-energy hand-probe spot welder, such
as the Model 700. Environmental protection is as easily
applied to a welded gage installation as to an adhesively
bonded gage.
Strain range is 5000 ꢀin/in ( 5000 ꢀm/m), and normal
operating temperature range is –320° to +500°F (–195°
to +260°C). Short-term maximum temperature is +550°F
(+290°C).
WWT-Series Temperature Sensor—High-purity nickel
foil grid encapsulated in fiberglass-reinforced epoxy-
phenolic, and equipped with integral three-tab terminal
to facilitate leadwire attachment. The temperature sensor
is normally installed on a flat surface of the workpiece,
but, in any case, should always be oriented with the
gridlines in the direction of minimum strain to avoid strain-
induced errors (see Micro-Measurements Tech Note
TN-506, “Bondable Resistance Temperature Sensors and
Associated Circuitry”). With an appropriate LST Matching
Network, the temperature response characteristic of the
nickel can be linearized and scaled for direct readout (in
degrees) with any strain indicator.
Refer to Instruction Bulletin B-131 and MM Strain
Gage Accessories Data Book for further information on
installation and protective coatings. For specifications
about the Model 700 Welding/Soldering Unit, please refer
to the product datasheet.
DESCRIPTION AND PERFORMANCE
General—All sensors are laboratory-prebonded, with a
high-performance adhesive, to thin [0.005 in (0.13 mm)]
metal carriers. Sensor grids are fully encapsulated for
protection against handling and installation damage.
Standard weldable strain gages are offered in two
series to meet differing performance requirements. Both
series are available in either 06 or 09 self-temperature
compensation. Strain gages with 06 S-T-C have Inconel
carriers, while S-T-C 09 gages and temperature sensors
are mounted on 300-series stainless steel.
SEALED WELDABLE STRAIN GAGES
Micro-Measurements also offers a line of sealed weldable
strain gages that have a polymer coating in place that
offers instant protection from moisture. Please see the
datasheet available at: www.vishaypg.com/doc?11519
CEA-Series Weldable Strain Gage—Polyimide-
encapsulated constantan foil grid, with large, rugged,
copper-coated tabs. In most cases, the carrier can be
contoured to a radius as small as 1/2 in (13 mm). The CEA
Series is ideal for direct leadwire attachment, before or
after installation.
Teflon is a Registered Trademark of DuPont.
MEASUREMENT CONSIDERATIONS
It is important to note that operating characteristics
of weldable strain gages (gage factor, transverse
sensitivity, and thermal output) are specified for the
basic strain gage itself—without the metal carrier. Thus,
the properties are measured by bonding a conventional
strain gage directly to an appropriate calibration
specimen, following standard methods specified for
all Micro-Measurements strain gages. This procedure
assures the most accurate results, independent of
the variables introduced by welding. In particular, the
user should be aware that the gage factor specified
on the engineering data sheet accompanying the gage
applies only to the basic strain gage, without the shim.
The effective gage factor of the weldable assembly
(after welding to the test member) is commonly 5 to
10% lower than this, due primarily to the stiffness of
the shim. The reduction in gage factor is not subject to
quantitative generalization, because it depends on the
cross-sectional properties of the test specimen, and
on the mode of loading (e.g., bending versus direct
stress). It has been demonstrated, however, that for a
group of like specimens, loaded in the same manner,
the weldable gages exhibit very good repeatability
and uniformity of response. Therefore, when test
requirements dictate greatest accuracy, the weldable
gages should be calibrated on a specimen of the same
material and cross section as the test part, and under
the same mode of loading.
Document No.: 11519
Revision: 08-Feb-2018
For technical questions, contact
mm@vpgsensors.com
www.micro-measurements.com
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