Glossary · Functional safety
Diagnostics
Also known as: diagnostic functions, diagnostic tests
In functional safety, diagnostics are functions that detect faults, degraded conditions, or loss of safety capability. They allow the system to react, for example by reaching a safe state or preventing a restart.
- Functional safety
- Data and interfaces
In one sentence
Diagnostics detect faults and lost safety capability so a system can react before a hidden failure becomes dangerous.
Example
A safety PLC tests its outputs with short test pulses and compares the redundant position switches of a robot cell door; a discrepancy stops the cell and blocks the reset.
How it applies
- Functional safety: Diagnostics are only useful together with a defined fault reaction. Specify what is detected, how quickly and what the system does next.
- Integrated systems: Diagnostic results often travel over networks to HMIs and maintenance systems. Treat diagnostic messages as data with a defined meaning, timestamp and source.
- Technical documentation: Operators and service staff need the diagnostic messages explained: meaning, likely cause, safe corrective action. A message catalog maintained in one place avoids drift between the HMI and the manual.
- Evidence: Faults that diagnostics cannot detect remain hidden until a proof test reveals them.
Diagnostics vs. proof test
Diagnostics run automatically during operation. A proof test is a periodic, often manual test intended to find the dangerous failures that diagnostics do not reveal.