18003

Check PLC Program Logic

Access SINUMERIK Operate → Diagnostics → PLC → Program Status. Monitor coolant pump control bits (typically DB31.DBX for M08 command) and verify logic execution when M08/M09 commands are issued.

Use PLC program status to trace the signal path from NC command through to physical outputs

Verify Output Module Status

In SINUMERIK Operate → Diagnostics → Hardware → I/O Modules, check the digital output module controlling coolant pump relay. Look for red status indicators or fault bits on the output channel.

Ensure EMERGENCY STOP is active before checking physical connections

Test Pump Control Relay

Use PLC → Variable Status to force the coolant pump output bit ON/OFF and measure 24VDC at the pump control relay coil terminals. Verify relay contacts close/open with multimeter.

Check relay coil resistance (typically 500-2000 ohms) to verify coil integrity

Validate Feedback Circuit

Monitor the pump run confirmation input bit in PLC Variable Status while manually energizing the pump. Verify feedback signal reaches the SINUMERIK input module within the timeout period.

Typical feedback timeout is 2-5 seconds, check machine parameter MD for exact timing

Check Motor Overload Relay Status

Inspect the motor starter overload relay for tripped condition. Reset if tripped and note the overload setting versus motor nameplate current rating.

Do not reset overload relay more than twice without investigating root cause of overcurrent condition

Measure Motor Current Draw

Using clamp-on ammeter, measure all three phases of motor current during startup attempt. Compare readings to motor nameplate FLA rating and check for phase imbalance >10%.

Locked rotor current is typically 6-8 times normal running current

Test Pump Mechanical Freedom

With power disconnected and LOTO applied, manually rotate pump coupling or impeller to check for mechanical binding, debris, or bearing seizure.

Apply proper lockout/tagout procedures before accessing pump mechanical components

Verify Motor Electrical Integrity

Using megohmmeter, test motor winding insulation resistance to ground (should be >1 megohm). Check winding continuity and resistance balance between phases.

Winding resistance imbalance >5% indicates potential motor fault

Verify Feedback Signal Wiring

Check wiring from pump starter auxiliary contacts to SINUMERIK digital input module. Verify proper terminal connections and wire continuity using multimeter.

Auxiliary contacts are typically rated 5A at 250VAC but may fail at lower DC control voltages

Test Auxiliary Contact Operation

With pump starter energized, measure voltage across auxiliary contact terminals. Should show 0VDC closed, 24VDC open. Test contact resistance (<1 ohm when closed).

Verify circuit is de-energized before resistance measurements

Check Input Module Function

In SINUMERIK Diagnostics → Hardware → I/O Status, monitor the feedback input bit while applying external 24VDC test signal to input terminals. Verify input LED and software bit respond correctly.

Input threshold is typically 15VDC minimum for reliable switching

Validate Signal Timing

Use oscilloscope or PLC trace function to verify feedback signal timing relative to output command. Signal should activate within machine data timeout parameter (typically MD11602).

Add time delay relay if pump startup time exceeds SINUMERIK monitoring window

Check Coolant Monitoring Parameters

Access SINUMERIK Commissioning → Machine Data → Channel → Auxiliary Functions. Verify MD11600 (coolant monitoring enable) and MD11602 (coolant pump timeout) settings match machine requirements.

Typical timeout values range from 2-10 seconds depending on pump startup characteristics

Verify I/O Signal Assignment

In Machine Data → PLC → Signals, check DB31.DBX assignments for M08 output and DB21.DBX assignments for pump feedback input. Ensure correct bit positions match PLC program and hardware wiring.

Incorrect I/O assignments can cause unexpected machine behavior

Review Auxiliary Function Configuration

Check MD11610 (auxiliary function monitoring mask) to verify coolant pump monitoring is properly enabled. Validate MD22200-22299 series for M-code specific parameters.

Use machine data backup/compare function to identify recent parameter changes

Test Parameter Changes

After parameter corrections, perform controlled test of M08/M09 commands in MDI mode. Monitor alarm status and timing using SINUMERIK trace function to verify proper operation.

Always backup machine data before making parameter changes

Measure Control Power Supply Voltage

Using digital multimeter, measure 24VDC supply voltage at pump control relay and feedback circuit terminals. Voltage should be 24VDC ±10% under load conditions.

Low voltage can cause relay chatter and intermittent operation

Check Power Supply Loading

Measure total current draw on 24VDC supply with all coolant system components active. Compare to power supply rating and verify adequate capacity margin (>20%).

Inrush current during pump startup may be 3-5 times steady state current

Test Voltage Stability Under Load

Monitor 24VDC supply voltage with oscilloscope during pump start/stop cycles. Look for voltage drops >2VDC or excessive ripple that could affect relay operation.

Add capacitive filtering or larger power supply if voltage instability is observed