21740

Navigate to Siemens SINUMERIK 840D HMI menu: Offset > Machine Data > search for MD 10330 FASTIO_ANA_OUTPUT_WEIGHT[n] where n is the affected output channel number from the alarm message.

Review the current scaling value and compare against the maximum expected output command from the spindle control or analog output module (typically 0-10V corresponds to 0-32767 internal units or equivalent).

Increase MD 10330 value to accommodate the full range of spindle/axis commands. Typical range is 10000-32000 depending on your application. Document the change in the machine parameter audit log.

Power cycle the control or use Siemens parameter reload function to activate the change, then verify alarm no longer occurs during spindle ramp-up or servo command sequences.

Check the spindle parameter block: Navigate to Offset > Machine Data > search MD 37110 (SPINDLE_MAX_SPEED) and verify the maximum spindle speed setting aligns with your D/A converter and analog output scaling.

Examine the active part program or manual spindle command: verify S-word values do not exceed the machine's rated spindle speed. Consult the NC program and PLC interface for any override or scaling logic that might amplify the speed command.

Recalculate the MD 10330 FASTIO_ANA_OUTPUT_WEIGHT[n] scaling factor using the formula: Weight = (32767 / Max_Spindle_Speed_in_RPM) or equivalent for your output range, ensuring the full spindle envelope is covered.

Update MD 10330 with the recalculated weight value, perform a control restart, and re-run the spindle acceleration test at maximum speed to confirm alarm 21740 no longer appears.

Verify the hardware specification of the analog output module (typically listed as part of the I/O expansion module in the SIEMENS configuration). Cross-reference the module part number (e.g., KL2XXX for TwinCAT or ACP10 terminals) with the datasheet to confirm output voltage range and D/A resolution.

Check the NCK configuration via HMI: Offset > System Data > Analog Outputs or equivalent menu path to review the declared output voltage range (0-10V vs. 0-8V, 0-5V, etc.) and verify it matches the installed hardware.

If a hardware mismatch is confirmed, either upgrade the analog output module to support the required range, or reduce MD 10330 FASTIO_ANA_OUTPUT_WEIGHT[n] to stay within the hardware's actual capability and recalibrate spindle speed commands accordingly.

Reduce scaling only if spindle performance requirements allow; otherwise hardware upgrade is required.

After hardware correction or MD adjustment, clear the alarm via HMI acknowledge function and perform a full analog output test using the SINUMERIK diagnostics menu to confirm signal integrity across the full operating range.