Siemens Alarms 2110/2120/2130 NCK Hardware Fault Resolution

Introduction to NCK Hardware Alarms

An abrupt dropout of the NC ready relay contact during a heavy milling operation immediately causes all feed axes to enter follow-up mode, forcing a sudden and uncontrolled stop across the active channel. This emergency-level interruption occurs when the SINUMERIK Numerical Control Kernel (NCK) detects hardware anomalies, such as an overheated enclosure or a failing cabinet fan. The physical consequence is severe: a clamping axis (clamp) can instantly lose its holding position, or a high-speed spindle can experience uncontrolled deceleration. In the worst-case scenario, the system interprets this electrical instability as a mechanical runaway, leading to a damaged workpiece or a shattered tool in the chuck as axes drift outside safe operating tolerances.

Technical Summary

Specification	Details
Command Codes / Alarms	2110, 2120, 2130
Modal Group / Category	NCK / Hardware Diagnostics
Brands Covered	Siemens (SINUMERIK 840D sl, 808D ADVANCED)
Critical Parameters	MD10100 $MN_PLC_CYCLIC_TIMEOUT, MD10120 $MN_PLC_RUNNINGUP_TIMEOUT
Main Constraint	Temperature limits (60°C +/- 2.5°C), fan speed threshold (7500 rpm), axis re-referencing on power loss

Quick Read

• Temperature Threshold: Ambient control enclosure temperature must never exceed the 60°C threshold to avoid thermal damage.
• Sensor Reset: The internal temperature must decrease by at least 7°C before the 2110 temperature alarm can be reset.
• Fan speed monitoring: The 24 VDC cooling fan triggers alarm 2120 if its rotation speed drops below 7500 rpm.
• Encoder Voltage Failure: Alarm 2130 indicates a severe encoder power loss (5V/24V) or D/A converter (+/- 15V) supply failure.
• Complete Re-referencing: You must perform a complete axis re-referencing after recovering from an encoder voltage fault to maintain spatial accuracy.
• PLC Cyclic Limit: A loop hanging in the PLC user program that fails to increment the life counter every 10 ms triggers a sign-of-life timeout.

Basic Concepts of Hardware Monitoring

Siemens CNC controllers utilize hardware monitoring systems to protect delicate processor boards and feedback electronics from catastrophic failure. When NCK hardware faults like the 2110 temperature alarm or the 2120 fan alarm occur, the control executes an immediate safety shutdown to halt motion. The NC ready relay drops out instantly, and axes are forced into follow-up mode. This prevents thermal degradation from permanently damaging the Numerical Control Unit (NCU), but it introduces severe production risks on the shop floor.

In extreme machining environments, managing cabinet temperature is a key operational task. If the enclosure reaches 60°C ± 2.5°C, the NCK triggers a safety warning. However, if the active cooling fan degrades below 7500 rpm (from its standard rated speed of approximately 8700 rpm), heat builds rapidly. If short circuits occur in the power feeder cables, they trigger the 2130 encoder undervoltage alarm, which immediately halts axis control. Without continuous feedback power, a clamping axis can lose its holding position, causing workpieces to dislodge under heavy cuts, or a spindle could spin out of control, similar to the ds1512-excess-velocity-alarm encountered on other motion controllers.

Programmers and operators must remember that these system alarms are not simple software conditions that can be cleared by pressing RESET on the operator panel. Resolving a 2110 temperature alarm requires lowering the physical temperature of the sensor by at least 7°C. Similarly, recovering from a 2130 encoder undervoltage fault requires a physical check of the encoder cables for short circuits, followed by a mandatory manual re-referencing of all axes in that channel to guarantee dimensional precision.

Command Structure and Diagnostic Syntax

The NCK monitors hardware modules and power supplies at a low level, independent of the active G-code program. When an anomaly is detected, the control generates a system message to pinpoint the module and error source. These system alarms are distinct from standard geometry warnings because they originate directly from the system kernel and require immediate operational attention.

The diagnostic output uses a parameterized template to convey crucial details. Rather than outputting simple static strings, the control populates runtime variables detailing which CNC channel is affected, the specific system error number, and diagnostic arguments representing internal physical readings.

Syntax Structure

[Channel %1:] System error %2 %3 %4

Where %1 is the channel number, %2 is the system error number, and %3 and %4 represent internal safety diagnostic parameters.

Control Parameters

Parameter Name	Identifier	Function	Standard Value / Range
PLC Cyclic Timeout	MD10100 $MN_PLC_CYCLIC_TIMEOUT	Defines the cyclic sign-of-life monitoring time frame for the PLC to increment its counter.	100 ms
PLC Running-up Timeout	MD10120 $MN_PLC_RUNNINGUP_TIMEOUT	Defines the maximum allowable time for the PLC to start up and send its first sign-of-life.	1.0 second
Spindle Velocity Limit	MD35100 $MA_SPIND_VELO_LIMIT	Sets the maximum allowed spindle rotation speed to prevent chuck damage or spindle runaway.	Machine dependent

Brand Applications

Siemens

Siemens handles hardware diagnostic routines through a deeply integrated NCK and PLC handshake. If the NCK cabinet fan fails, or if the environment exceeds the temperature limit of 60°C, the controller activates internal machine data timers. Depending on the exact control series, the system will respond with aggressive safety measures to protect its expensive physical components. In Siemens systems, hardware faults cannot be overridden or bypassed, ensuring that operators physically resolve cabinet ventilation problems before continuing production.

Brand Comparison

Feature / Alarm Behavior	SINUMERIK 840D sl	SINUMERIK 808D ADVANCED
Fan Fault Action	Automatically and forcefully shuts off the module after a certain time to protect NCU from thermal destruction.	Switches NC to follow-up mode, disables NC Start in the channel, and sets interface signals.
Hardware Protection	Aggressive self-preservation (forceful processor board shutdown).	Standard follow-up mode protection.
NC Start Availability	NC Start is completely unavailable as the unit performs a hard power-off.	NC Start is disabled in the active channel via interface signals.

Technical Analysis of Hardware Safety

Siemens controls distinguish themselves from other CNC brands through highly granular, strictly segmented alarm code ranges and robust PLC integration. First, Siemens explicitly divides alarms by their underlying hardware or software source. For example, channel-specific alarms fall between the 010000 and 019999 ranges, whereas drive-specific hardware faults and thermal alerts are routed to the 200000 to 299999 SINAMICS alarm blocks. This clear separation helps maintenance teams rapidly identify whether a fault originates in the logic execution layer or the high-power inverter modules.

Second, Siemens features a deeply intertwined NC/PLC architecture that actively monitors system integrity. The NCK monitors the PLC's sign-of-life counter every 10 milliseconds. If the PLC user program hangs—for instance, failing to increment the internal NC/PLC interface counter within the time frame defined by MD10100 $MN_PLC_CYCLIC_TIMEOUT—the NCK misinterprets this pause as a hardware freeze and triggers a PLC sign-of-life timeout to safely paralyze the machine before physical damage occurs. Unlike Fanuc systems which track PMC and machine-side failures via pmc-alarms-pc030-pc090-pc097, Siemens manages PLC-NCK integration through strict sign-of-life timeouts. In contrast to NCK hardware safety shutdowns, standard programming geometry errors such as a ps0062-illegal-depth-rough-cut only block the execution of specific canned cycles without dropping the NC ready relay.

Finally, the hardware architecture exhibits aggressive self-preservation behaviors. On the SINUMERIK 840D sl, the detection of a missing or failing fan triggers an automatic safety routine that forcefully shuts down the processor board entirely, sacrificing the active machining cycle to protect the expensive NCU. By contrast, the SINUMERIK 808D ADVANCED relies on follow-up mode, disabling NC Start in the channel and utilizing interface signals to protect the machine while keeping the control powered.

Program Examples

Siemens G-Code Example

; Siemens NCK Hardware Safety Verification
MSG ("Check ambient temperature before spindle start")
$A_OUT[7] = 1
M0
; Spindle start is only executed after manual check
M3 S1200
M5
M30

dry run

During a dry run, the operator activates the program without a workpiece. The CNC displays the text Check ambient temperature before spindle start on the screen and sets the system analog/digital output $A_OUT[7] to high (1), which can trigger an external cabinet cooling fan or ventilation system. The program then encounters the program stop M0 command, which immediately halts program execution. The operator must physically verify the cabinet temperature. Once confirmed, pressing the Cycle Start button resumes the program, starting the spindle at 1200 rpm (M3 S1200), followed by a spindle stop (M5) and program end (M30).

Error Analysis

Alarm Code	Trigger Condition	Operator Symptom	Root Cause / Fix
Alarm 2110	Cabinet ambient temperature sensor reaches 60°C ± 2.5°C threshold.	Alarm display message; active machining cycle stops and axes drop into follow-up mode.	Enclosure overheating due to external heat or failed air conditioning. The sensor can only be reset after the physical temperature is reduced by at least 7°C.
Alarm 2120	NCK 24 VDC cooling fan speed drops below 7500 rpm (rated speed: 8700 rpm).	Alarm display warning; depending on series (e.g., 840D sl), the NCU may forcefully shut down.	Fan motor degradation or dust accumulation in the cooling path. Replace the entire fan unit and NCK battery assembly immediately.
Alarm 2130	Power supply failure in the encoder (5V/24V) or D/A converter (± 15V).	NC not ready relay drops out; axes are immediately immobilized.	Short-circuit in encoder cables or failing power supply module. Check cables for physical cuts and complete axis re-referencing after restoring power.

Application Note

Position loss on a clamping axis (clamp) represents a catastrophic failure when encoder power fails during a critical cut. If a short circuit in the power line triggers the 2130 encoder undervoltage alarm, the physical holding torque degrades, allowing the clamping force to release the workpiece while the spindle is still spinning. Operators attempting to quickly clear the error and hit Cycle Start will cause a collision because the axis positions are no longer aligned. To prevent structural damage to the turret or chuck, maintenance personnel must completely re-reference all axes in the channel before commanding any automatic movement. Merely resetting the alarm at the panel does not restore coordinate alignment. If an encoder undervoltage occurs, the coordinate system is considered lost, and physical re-homing is the only reliable path to restore dimensional accuracy.

Related Command Network

• WAITP(x): Halts block change for positioning axes until the specified axis reaches its exact target position, preventing movement during encoder feedback fluctuations.
• WAITS(x): Prevents block change for spindles until the positioning spindle reaches its exact target, eliminating runaway risks.
• MSG(string): Displays diagnostic messages on the operator panel to instruct users to perform physical cabinet checks before initiating automatic cycles.
• M00: Halts program execution forcefully, allowing operators to verify enclosure temperature and cooling fan operation before resuming motion.
• $A_OUT[x]: Sets digital system outputs to trigger external safety equipment, such as cabinet cooling fans, when ambient heat increases.

Conclusion

Preventive maintenance of cabinet ventilation and encoder cabling is the only reliable defense against NCK hardware faults. When operating in high-temperature or high-humidity facilities, regular checks of the 24 VDC fan's tachometer reading and physical cabinet filters prevent unexpected shutdowns and subsequent work-in-progress scrap. Ensuring the enclosure remains below 60°C avoids the lengthy cool-down delay required to reset the 2110 sensor, keeping the shop floor productive and axes safely aligned.

Frequently Asked Questions

How do you clear a Siemens Alarm 2110 temperature fault?

To clear Alarm 2110, you must physically cool down the enclosure until the internal temperature drops by at least 7°C below the 60°C warning threshold. Simply attempting to clear the alarm using the software RESET button will fail because the hardware sensor has a built-in hysteresis constraint; you must check and clean the cabinet air filters or open the enclosure doors to speed up the cooling process before attempting to resume machining.

What should you do when a Siemens Alarm 2120 fan speed error appears?

When Alarm 2120 appears, the 24 VDC cooling fan has dropped below the critical speed of 7500 rpm, indicating mechanical wear or dirt buildup. You must immediately shut down the CNC, order a replacement fan and NCK battery pack assembly, and swap the unit out; on 840D sl systems, delaying this replacement will cause the safety system to forcefully power down the NCU, which can lead to scrapped parts mid-cycle.

Why must all axes be re-referenced after resolving a Siemens Alarm 2130 fault?

Alarm 2130 signals a loss of power to the encoders or D/A converters, which corrupts the control's absolute position tracking. You must perform a complete manual axis homing and re-referencing sequence on the affected channel before running any automatic program; executing movement without re-referencing will result in out-of-tolerance dimensions or severe collisions because the physical axis position no longer aligns with the digital coordinates.