231-E002

Check Emergency Stop Circuit Status

Navigate to MOD > Service > PLC Status and monitor emergency stop relay states. Check X121 input signals for proper emergency stop chain continuity.

Ensure machine is in safe state before checking emergency stop circuits

Measure Relay Coil Resistance

Power down and measure emergency stop safety relay K1 coil resistance. Should read per manufacturer specifications (typically 200-500 ohms).

Check relay part number against Heidenhain approved components list

Verify Contact Operation

Manually operate emergency stop and verify all NO/NC contacts change state properly using multimeter. Replace relay if contacts are welded or not switching.

Use LOTO procedures when testing emergency stop circuits

Check Cable Connections at X121

Inspect all connections at X121 connector on TNC control. Verify pins for -NE2 (CC424) or -ES.B (CC61xx) are tight and free of corrosion.

Use contact cleaner on connector pins if oxidation is present

Perform Continuity Test

With power off, test continuity from X121 emergency stop input pins through the complete safety circuit to the emergency stop relay contacts.

Disconnect safety circuit from 24V supply before continuity testing

Check for Ground Faults

Measure insulation resistance between emergency stop circuit conductors and machine ground. Should read >1 megohm at 500VDC test voltage.

Flex cables while testing to identify intermittent wire breaks

Check Safety Module Status

Access MOD > Service > Hardware Info and verify safety input module status. Look for any error flags or communication faults with safety circuits.

Note the safety module firmware version for compatibility verification

Perform Safety Circuit Self-Test

Execute safety system self-test via MOD > Service > Safety Test. Monitor test results for T2 output and corresponding input signal verification.

Self-test will cycle emergency stop circuits - ensure machine is safe

Verify Input Signal Levels

Using oscilloscope, measure actual voltage levels at safety input pins during T2 test pulse generation. Compare with expected 24VDC logic levels.

Check for proper signal timing - test pulse should be 100ms duration

Check Safety Monitoring Parameters

Navigate to MOD > Machine Parameters and verify MP7251.0 (Safety monitoring active) and MP7251.1 (Emergency stop monitoring) are correctly set per machine documentation.

Document current parameter values before making changes

Verify Test Pulse Timing

Check MP7251.5 (Test pulse duration) is set to manufacturer specification, typically 100ms. Incorrect timing can cause signal comparison failures.

Only modify parameters with proper authorization and backup

Reset Safety Configuration

If parameters are incorrect, restore from known good backup or reset to factory defaults via MOD > Service > Reset Safety Parameters.

Perform complete safety function test after parameter changes