Datasheet

Gage Installation Tester
www.vishaymg.com [e-mail] Document Number: 11301
52 Revision: 28-Aug-06
Model 1300
Vishay Micro-Measurements
FEATURES
• A compact, battery-powered instrument used to verify the
electrical quality of a strain gage installation BEFORE it is
placed in service
• Reads with the push of a button—no warm-up
• Reads insulation resistance (leakage) to 20 000 megohms
with 15Vdc
• Measures deviation of installed gage resistance from
precise standards to a resolution of 0.02 percent
• Ohmmeter scale for troubleshooting questionable instal-
lations
• Verifies the complete gage circuit, including leadwires
DESCRIPTION
Two of the most important measurements used to verify the
quality of a strain gage installation are insulation resistance
(leakage to ground) and shift in gage resistance due to
installation procedures. While these two measurements are
not a complete guarantee of eventual proper strain gage
performance, any installation that produces questionable
values should not be relied upon where accuracy of results
is necessary.
For example, a voltage difference between the specimen
and strain gage frequently exists. A low insulation resis-
tance will permit this voltage differential to introduce
extraneous signals during strain measurement.
Several sources of variations in insulation resistance and
shifts in gage resistance are:
• Insulation resistance in excess of 20 000 megohms should
be expected for foil strain gages when installed under
laboratory conditions. A value of 10 000 megohms should
be considered minimum. A reading below this value
generally indicates trapped foreign matter, moisture,
residual flux or backing damage due to soldering, as well
as incomplete solvent evaporation from an overcoating.
• Deterioration of the insulation resistance with time may be
an indication of an improperly coated installation.
• At higher test temperatures, particularly above +300°F
[+150°C], it is normal to expect lesser values. Ten meg-
ohms is considered to be the lower allowable value.
• Shifts in gage resistance during installation should not
normally exceed 0.5% when using room-temperature-
curing adhesives. Resistance shifts greater than 0.5%
generally indicate damage to the gage due to improper
handling or clamping. However, strain gages installed
using elevated-temperature-curing adhesives may exhibit
greater shifts in resistance due to adhesive lock-up at
elevated temperatures (difference in linear coefficient of
thermal expansion between the strain gage and
specimen). These shifts will vary depending upon the
specific cure temperature and materials used. The shifts
should never exceed 2% and should be uniform within
0.5%.