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The CM-3 verifies the electrical continuity of a rebar cage directly by measuring resistance with a relatively large current (0.5 Amp) through a rebar connection for 0.5 seconds.
In addition to verifying that the resistance is below 1 Ohm (ref. ISO 126969) the CM-3 also verifies the continuity check, confirming the residual voltage between the test points falls to 0 within 100 ms after the resistance measurement is complete.
A common Digital Multi Meter [DMM] is not a reliable instrument to verify reinforcement continuity. Concrete can be seen as a solid electrolyte that will generate its own small potentials. A DMM uses very small currents to measure resistance and can be influenced by the concrete potentials. The alternative and indirect method of measuring potentials between the rebars with a DMM is better and almost certain to give valid results.
CM-3 can remove the uncertainty by using a current that may be as much as 1000 times higher than a DMM. The test current applied by the CM-3 is also more in line with the level of currents that must be expected though the rebars from an ICCP installation.
A probe for easy rebar contact is supplied with the CM-2. The Probe is a spring loaded punch style contact that can penetrate surface rust.
The instrument and the probe accepts common 4 mm banana connectors, cable is not included. Resistance in measurement cables may easily be eliminated through the CM-2's calibration feature.
