The "C" version for the 2400 series offers a Contact Check function. The Contact Check function detects measurement error due to excessive resistance in the force or sense leads WHILE performing 4 wire measurements.
It is important to note the contact check function does not apply current to the Device Under Test (DUT). A pulse is sent to the Hi source and Hi sense and to the Lo source and Lo Sense terminals. The resistance is then compared to a trip point resistance value. The Trip point is configurable for either 50 ohm, 22 ohm or 2.1 ohm. If the resistance of the DUT connections is higher than the Trip point resistance, it is considered an "open lead" and the microprocessor is notified. This notification can be communicated to your test system on the front panel, over the GPIB bus, or with the instrument's digital I/O.
The primary benefit of the Contact Check feature is the ability to verify good connections with the DUT before the measurement is made. This allows avoidance of false product failures by detection of contact fatigue, loose or broken connections, or relay failures.