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2. GAGE INSTALLATION
The 4200ER strain gages are supplied fully sealed and pre-tensioned with the plucking coil
mounted. A preliminary check is advisable and this is made by connecting to the readout
box and observing the displayed readout (see readout instructions, Section 3). The
observed reading should be around the mid-range position (see Table 1). Pressure on the
gage ends should make this reading decrease.
Check the resistance between the two lead wires (usually red and black). For the model
4200ER it should be around 180 ohms. Remember to add the cable resistance at
approximately 14.7
/1000' or 48.5
/km (at 20°C, multiply by 2 for both directions). If the
gage contains a thermistor, check its resistance (usually the white and green lead wires)
with an ohmmeter. Check the reading against that which should be obtained at the existing
ambient temperature. See Appendix B for the resistance to temperature conversion and
resistance v. temperature table.
Return any faulty gages to the factory. Gages should not be opened in the field.
2.1. Adjusting the Desired Range
Gages are supplied with the wire tension set in approximate rmid-range If the range needs to
be at some other position this is accomplished by the following procedure: Attach the red and
black leeds to a readout box with the channel position set in the D and the mode for
microstrain. Grip the small collar under the shrink tube and rotate the end flange adjacent to
it as shown in Figure 2
Figure 2 Adjusting the range
Rotate clockwise to decrease the initial reading and counter-clockwise to increase the
reading. Please remember that although the readings are taken on Channel D, in the digits
output mode, the digits shown are not directly in microstrain but must be converted to
microstrain by multiplying the observed digits change by the gage factor given on the
calibration sheet.
