4
Connect the gage to the Readout to take a reading (see section 3). The reading should be stable and
in the range of 4000 to 5000.
Checks of electrical continuity can also be made using an ohmmeter. Resistance between the gage
leads should be approximately 180 ohms, ±10 ohms. Remember to add cable resistance when
checking (22 AWG stranded copper leads are approximately 14.7
/1000' or 48.5
/km, multiply by
2 for both directions). Between the green and white should be approximately 3000 ohms at 25° (see
Table B-1), and between any conductor and the shield should exceed 2 megohms.
2.2. Crackmeter Installation
CGEO-CR Model Surface Crackmeter can adopt welding fixture and anchoring manners. You can
first weld anchor rod directly on steel member, and then install transducer on anchor rod through
the bolts of elbow joint. Another is grouting anchor rod, it adopts a length of twisted-steel
connected with the elbow joint. Besides, the factory can also make special forms of installation
parts upon requirement.
75 mm
10mm
Thread
Figure 3 – Standard Grouting Anchor Rod
When setting the gage position using a portable readout (see section 3) use the ranges in Table 2 to
determine the proper position.
Mid-Range
Measure Extension
Measure Retraction
4500-5000
2500-3000
6500-7000
Table 2 - Crackmeter Reading Ranges
Note also that the calibration sheet supplied with the Crackmeter shows actual readings at zero,
25%, 50%, 75% and 100% of the range of extension. These readings can be used as a guide to set
the Crackmeter in any part of it's range, either in anticipation of closure or opening of the crack.
The Crackmeter can be extended until the desired reading (see Section 3 for readout instructions) is
obtained and then held in this position while the distance between the anchor points (threaded studs
on ball elbow joints, see Figure 1) is measured. This measurement can then serve as a guide for
drilling or welding the anchor points.
Caution: Do not rotate the shaft of the Crackmeter. This may cause irreparable damage to the
instrument. The alignment pin on the transducer shaft and slot on the body serve as a guide for
alignment.
2.2.1. Installation using Weldable Fixtures
