Geokon 4911, Руководство по установке, Страница: 8 / 27

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2. INSTALLATION
2.1 Preliminary Test
A preliminary check should be performed before installing gauges in the field. To perform the
preliminary check, complete the following steps:
Warning! Do not lift the strain meter by the cable.
1) Connect the gauge to a readout box. (See readout instructions in Section 3.) Observe the
displayed readout.
2) Compare the zero reading given on the calibration report to the current zero reading. Under
normal circumstances the two readings should not differ by more than 25 digits (10
microstrains), however, shocks incurred during shipping may cause larger shifts. If the
reading is within 100 digits (40 microstrains) of the factory zero, and is stable, it is safe to
proceed with the installation.
3) Pull on the strain meter ends; confirm that digits on the readout rise as the tension increases.
Checks of electrical continuity can be made using an ohmmeter. The resistance between the two
lead wires (usually red and black) should be around 50 ohms. Remember to add the cable
resistance, approximately 14.7 Ω for every 1000 ft. (48.5 Ω per km) at 20 °C. Multiply these
factors by two to account for both directions.
Resistance between the two thermistor wires (usually white and green) varies with temperature.
Use Table 5 in Appendix B to convert the resistance to temperature and compare the result to the
ambient temperature.
Resistance between any conductor and the shield should exceed two megohms.
If the strain meter fails any of the preliminary tests, see Section 5 for troubleshooting.
2.2 Installing Model 4911, “Sister Bar”
Sister Bars are usually installed using standard iron tie wire. Ties near the ends and at the one-
third points are sufficient if the gauge is being wired to a larger section of rebar or to horizontal
bars. Wiring at the one third points alone is sufficient if the gauge is being wired in parallel to the
structural rebar. Route the instrument cable along the rebar system and tie it off every three to
four feet (one-meter) using nylon cable ties. Avoid using the tie wire on the instrument cable as it
could cut the cable. See Figure 3 and Figure 4 on the following page.
Be sure to note the location and serial numbers of all instruments during the installation process.
This information is necessary in order to apply the proper calibration factors and determine strain
characteristics when reducing data.