What causes Siemens SINUMERIK alarm 25000?

Encoder cable damage or loose connections causing signal interruption. Physical damage to cables from machine movement or contamination can break signal continuity.. Contamination on encoder scale or reading head disrupting optical signals. Metal chips, coolant, or dirt on the glass scale interfere with the light path between LED and photodiode.. Power supply voltage issues to the encoder causing weak or unstable signals. Insufficient 5V or 15V supply voltage prevents proper signal generation.. Encoder mounting problems creating excessive runout or vibration. Loose mounting brackets or worn couplings cause mechanical instability affecting signal quality.. Grounding problems or electromagnetic interference corrupting encoder signals. Poor shield grounding or nearby electrical noise sources can induce false signals.. Internal encoder electronics failure in signal processing circuits. Age-related component failure in the encoder's internal amplification or signal conditioning circuits.. Incorrect encoder parameters in the CNC control system. Wrong resolution settings or signal type configuration prevents proper signal interpretation..

How do I fix Siemens SINUMERIK alarm 25000?

1. Step 1: Check encoder cable connections at both encoder and control ends for looseness, corrosion, or damage. Look for bent pins, moisture intrusion, or cable strain at connectors. 2. Step 2: Inspect encoder scale and reading head for contamination, scratches, or physical damage. Clean with isopropyl alcohol and lint-free cloth if contaminated. 3. Step 3: Measure encoder power supply voltages at the encoder connector using multimeter. Verify 5VDC and 15VDC are within 5% tolerance under load. 4. Step 4: Check encoder cable continuity and insulation resistance using megohmmeter. Test each signal wire individually and verify shield continuity to ground. 5. Step 5: Observe encoder signals on oscilloscope to check for proper amplitude, phase relationship, and signal integrity. Look for 1Vpp sine waves 90 degrees apart. 6. Step 6: Verify encoder mechanical mounting for runout and vibration using dial indicator. Check coupling alignment and bearing condition if rotary encoder. 7. Step 7: Test encoder grounding by measuring resistance from encoder housing to machine ground. Should be less than 1 ohm with no voltage potential difference. 8. Step 8: Swap encoder feedback cable with known good axis to isolate cable versus encoder failure. If alarm follows cable, replace cable assembly.

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Siemens SINUMERIK Controller

Servo/Axis · Advanced · 30-120 minutes

Alarm 25000

Siemens Alarm 25000 - Hardware Fault of Active Encoder

SIEMENS alarm 25000 fires when the SINUMERIK control detects corrupted, missing, or invalid encoder feedback signals that prevent reliable position determination. The control continuously monitors encoder signal integrity through the DRIVE-CLiQ interface and triggers this fault when quadrature signals are lost, contaminated, or fall outside acceptable voltage thresholds.

Siemens SINUMERIKServo/AxisAdvanced30-120 minutes

25000

Siemens Alarm 25000 - Hardware Fault of Active Encoder

Encoder Hardware Fault

Root Cause Summary

SIEMENS alarm 25000 fires when the SINUMERIK control detects corrupted, missing, or invalid encoder feedback signals that prevent reliable position determination. The control continuously monitors encoder signal integrity through the DRIVE-CLiQ interface and triggers this fault when quadrature signals are lost, contaminated, or fall outside acceptable voltage thresholds.

Safety

Axis must be re-referenced after clearing
Position data is unreliable
Disconnect power to the CNC machine before working on any electrical components.
Be careful when working near moving parts. Ensure the axis is locked or disabled before performing any maintenance.
Use proper grounding techniques when working with electrical connections to prevent electrical shock.
Refer to the CNC machine's safety manual for specific safety precautions.
High voltages may be present in the CNC control cabinet. Only qualified personnel should work inside the cabinet.
Ensure the axis is properly supported before disconnecting the encoder to prevent uncontrolled movement due to gravity.
Be aware of potential pinch points when working around moving axes.
Always power down and follow lockout/tagout procedures before physical inspections

Causes and Fixes

1
Check DRIVE-CLiQ Connection Status
Navigate to Diagnostics > Hardware > DRIVE-CLiQ and verify all encoder connections show 'OK' status. Check for yellow/red indicators on affected axis.
Use the DRIVE-CLiQ topology view to identify exactly which connection segment is failing.
2
Inspect Encoder Cable Routing
Examine encoder cable for damage, especially at cable carriers and entry points. Check separation from power cables (minimum 10cm for unshielded).
Always power down before disconnecting encoder cables to prevent damage to DRIVE-CLiQ interface.
3
Verify Cable Continuity
With system powered down, use multimeter to check continuity on encoder cable pins. Verify shield connection and measure insulation resistance (>10MΩ).
SINUMERIK encoder cables typically use 15-pin D-sub or M23 connectors - check pinout in drive documentation.
4
Test with Spare Cable
If available, temporarily replace encoder cable with known good spare and clear alarm using NC Reset. Monitor for alarm recurrence during axis movement.

DIY Feasiblehigh confidence

Call a technician if:

·Encoder replacement required
·Drive module hardware failure confirmed
·Multiple axes affected simultaneously
·Safety-critical axis involved

Prevention

Regular encoder cable inspection during PM
Maintain proper cable routing away from power cables
Monitor encoder signal quality trends
Keep spare encoder cables in stock
Document working encoder parameters

Common Mistakes

Swapping encoder cables between axes without parameter changes
Ignoring intermittent alarms until complete failure
Not checking cable shield grounding
Assuming encoder fault when drive hardware is failing
Modifying encoder parameters without understanding signal requirements

Related Alarms

25001 25002 25010 31001 31002

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Always verify with your machine manual or a certified technician before performing service procedures.