How to Measure Insulation Resistance With The Gage Installation Tester (Advanced Sensors Technology)
When Advanced Sensors Technology CEA strain gage is installed on a metal test part, one of the most basic tests for the quality of the installation is the resistance between the gage grid and the part. The insulation resistance can be measured very easily, and with no risk of damage to the gage, using the Micro-Measurements Model 1300 Gage Installation Tester. If the gage is properly installed and tested under laboratory conditions, resistance to ground should be in excess of 20000 megohms. A resistance of 10000 megohms is considered about the minimum for reliably accurate strain measurement. Readings below this value generally indicate some kind of quality defect in the gage installation. Low readings may be caused, for example, by trapped foreign matter, moisture, residual soldering flux, or backing damage from soldering. They may also result from moisture migrating to the installation after passing through pinholes in the leadwire insulation. The Model 1300 can be used very effectively to test the integrity of the leadwire insulation, too. For this purpose, the insulated leadwire is placed in a water-filled metal container, and the resistance between the wire conductor(s) and the container measured. The reading should again be at least 20000 megohms.
After applying, a protective coating to the strain gage, and prior to placing it in service, retesting for the resistance to ground and installed resistance is highly recommended. This will ensure that the gage has not been damaged in the process and that the presence of the coating has not significantly lowered the leakage resistance. It should be noted, however, that solvent-thinned coating compounds will exhibit lower leakage resistance until the coating is fully cured and the solvents evaporated. If the resistance to ground remains low after the coating is completely cured, the coating compound may be contaminated or otherwise deficient in dielectric properties. It should be obvious that while passing all of the foregoing tests is a necessary condition for satisfactory gage performance, it is not in itself sufficient to guarantee that the gage will perform properly under actual measurement conditions. At the same time, any installation that falls short of meeting the indicated standards should be viewed with suspicion, and not relied on for critical applications or those requiring accurate data.