231-4310

Verify E-stop Button Status

Physically inspect all emergency stop buttons on the machine to ensure they are pulled out (released position) and not mechanically stuck or damaged.

Before resetting E-stop, ensure no personnel are in hazardous areas and machine conditions are safe for operation.

Check Safety Relay Module

Locate the safety relay module (typically Pilz PNOZ or similar) and verify the status LEDs indicate proper reset state. Look for reset button on the safety relay that may need to be pressed after E-stop release.

Many Heidenhain retrofits use safety relays with automatic or manual reset modes - check configuration if reset doesn't occur automatically.

Monitor PLC Enable Signals

Access MOD function > PLC > Status and check marker M_ENABLE or machine-specific enable markers (often M100-M199 range). Verify these change state when E-stop is reset.

Note the exact marker names in your machine PLC program - common designations include M_GENERAL_ENABLE, M_DRIVES_ENABLE, or M_SAFETY_OK.

Verify Enable Signal at Drive

Measure 24VDC at the drive amplifier enable input terminal (typically X31/5 or X41 depending on inverter model). Signal should be present when E-stop circuit is properly reset.

Use appropriate voltage measurement tools - do not short terminals or measure with control power off.

Check PLC Diagnostic Display

Navigate to MOD > PLC > Status (or press PLC key then Status soft key). Review all input markers (I markers) for door switches, guard positions, and safety inputs to identify which interlock is open.

Create a list of critical safety inputs during commissioning - typical inputs are I0-I31 for guards, doors, and enable switches.

Review PLC Program Logic

Access the PLC program (MOD > PLC > Program) and search for conditions controlling M_ENABLE or drive enable outputs. Look for safety logic blocks that may be preventing enable signal activation.

Search for 'ENABLE' or 'M_ENABLE' text strings in the PLC program to quickly locate relevant logic sections.

Inspect Physical Interlock Switches

Physically verify that all machine guards are properly closed, door switches are engaged, and limit switches are in normal operating position. Check for damaged or misaligned switches.

Never bypass safety interlocks - repair or adjust switches to proper function rather than defeating safety circuits.

Test Interlock Sequence

Systematically close each guard/door and monitor PLC inputs to verify proper input signal changes. Confirm enable outputs activate when all interlock conditions are satisfied.

Some machines require specific interlock sequencing (e.g., main door before chip conveyor guard) - check machine documentation for proper enable sequence.

Verify PLC Output Activation

In MOD > PLC > Status, locate the output marker controlling axis enable (commonly O markers or Q markers depending on PLC type). Verify the output shows active when enable is commanded.

Output markers for individual axes often follow patterns like O_ENABLE_X, O_ENABLE_Y, or may be in sequential ranges like O10-O17 for multi-axis machines.

Measure Voltage at PLC Output Terminal

With enable commanded, measure 24VDC at the PLC output module terminal block for the axis enable signal. This confirms the PLC hardware is switching properly.

Identify correct common (0V) reference for the output module - some use separate commons for different output groups.

Check Drive Amplifier Enable Input

Measure voltage at the drive inverter enable input terminal (X31/5-6, X41, or X43 depending on drive model). Compare to PLC output measurement to identify wiring break location.

Heidenhain typically interfaces with drives using 24V enable signals on X31 for older UM/UVR drives or X43/X44 for newer UEC/MVC inverters.