Diagnostic Coverage
This is the ratio showing how large a portion of the dangerous faults that can occur in a circuit can be detected automatically. It is expressed as a percentage and is one of the inputs to the performance level calculation; if there is no monitoring at all, the ratio is taken as zero.
Diagnostics does not prevent the fault; it prevents the fault from staying hidden. A hidden fault is dangerous because the protection is already gone while the system looks healthy, and when a second fault arrives the result turns directly into a hazard.
- Classification: below 60 per cent is none, between 60 and 90 per cent is low, between 90 and 99 per cent is medium, and 99 per cent and above is considered high.
- Typical methods: welding monitoring by wiring the normally closed auxiliary contacts of the contactors in series, cross-monitoring that compares the state of two channels, cyclic test pulses.
- Its limit: diagnostics can only report what it detects; if the detected fault is not rectified, it contributes nothing.
In a crane panel the cheapest and most effective diagnostics is monitoring the contactor auxiliary contacts. The relay output of the radio remote control receiver feeds the input of this monitoring chain; when a contactor welds, the chain does not close and restarting is prevented. This addition costs a few wires and one auxiliary contact block.
The context in which this term is used: Wireless Crane Remote Control Selection Guide