micro-measurements@vishay.com
Weldable Patterns
Vishay Micro-Measurements
Document Number: 11519
Revision 03-Sep-03
www.vishaymg.com
94
Special Purpose Sensors - Weldable Patterns
Vishay Micro-Measurements Weldable Strain Gages and
Temperature Sensors are specially designed for spot weld-
ing to structures and components. They are ideal for appli-
cations where test or environmental conditions preclude
clamping and curing an adhesively bonded gage installation.
These gages are equally advantageous when strain mea-
surements 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.
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.
Refer to Instruction Bulletin B-131 and Catalog A-110 for
further information on installation and protective coatings,
and to Bulletin 302 for specifications on the Model 700
Welding/Soldering Unit.
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.
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.
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.
Strain range is ±5000µin/in (±5000µm/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).
Strain range is ±5000µin/in (±5000µm/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 Vishay
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.
®
Teflon is a Registered Trademark of DuPont.
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 Vishay 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.
MEASUREMENT CONSIDERATIONS
micro-measurements@vishay.com
Weldable Patterns
Vishay Micro-Measurements
Document Number: 11519
Revision 03-Sep-03
www.vishaymg.com
95
Special Purpose Sensors - Weldable Patterns
GAGE PATTERN RES. DIMENSIONS
AND DESIGNATION IN
Actual Size Shown. OHMS
Insert Desired S-T-C No. in Spaces Marked XX. Length Width Thick Length Width Length Width
CEA-XX-W250A-120 120 ±0.4% 0.63 0.34 0.005 0.230 0.125 0.44 0.17
CEA-XX-W250A-350 350 ±0.4% 16.0 8.6 0.13 5.84 3.18 11.2 4.3
CEA-XX-W250C-120 120 ±0.4% 0.90 0.90 0.005 0.230 0.125 0.44 0.17
CEA-XX-W250C-350 350 ±0.4% 22.9 22.9 0.13 5.84 3.18 11.2 4.3
LWK-XX-W250B-350 350 ±0.4% 0.88 0.32 0.005 0.250 0.125 0.62 0.17
22.4 8.1 0.13 6.35 3.18 15.7 4.3
LWK-XX-W250D-350 350 ±0.4% 1.15 1.15 0.005 0.250 0.125 0.62 0.17
29.2 29.2 0.13 6.35 3.18 15.7 4.3
WWT-TG-W200B-050 50 ±0.4% 0.71 0.43 0.005 0.200 0.200 0.52 0.26
@ +75°F 18.0 10.9 0.13 5.08 5.08 13.1 6.6
(+24°C)
Most flexible and conformable pattern. Type 326-DFV and 330-DFV flat
three-conductor cable typically used to solder directly to copper-coated
tabs.
Tee rosette, used in biaxial stress states where directions of principal
stresses are known. See W250A pattern for typical leadwire
recommendations.
Wide-temperature-range linear pattern with 10-in (250-mm)
preattached leads. Teflon insulation is pretreated for best bond to
protective coatings.
Tee rosette, used in biaxial stress states where directions of principal
stresses are known and a wide operating temperature range is
required.
Easy-to-use temperature sensor that can be welded or adhesively
bonded to the test structure. For standard bondable temperature
sensors, see pages 100-102.
ACTIVE GRID
MATRIX
CARRIER
