Fault Isolation / Half-Split
A systematic technique for finding the faulty section by dividing the circuit in two at every step, halving the search area. It is far faster than replacing components at random: on a line with ten connections the fault point is typically reached in three or four measurements.
The method starts by putting the measurement point in the middle of the line. If the signal or voltage is present there, the fault is in the forward half; if not, it is in the back half. The half determined to be sound is not measured again and the search area is halved at every step.
- Order: the supply is checked first, then the return path, then the signal chain. Looking for a signal in a circuit whose supply has not been verified is a waste of time.
- Keep a record: note every measurement and its result; otherwise you measure the same point again.
- One variable: change one thing at a time. Changing two components together leaves it unclear which one fixed it.
- Comparison: if there is a second channel or a similar device in the same system, comparing measurements quickly gives you the expected value.
This discipline prevents progress by part-swapping in the "the device does not work" situation after installation. In most cases the fault is not in the device but in the line, and a half-split search finds it in a few minutes.
The context in which this term is used: Installation, redundancy and field continuity