Siemens S120 frequency converter maintenance and configuration

The cable length of 24V electronic power supply should not exceed 10 meters, and the signal cable (such as encoder, digital input) should not exceed 30 meters. Long cables can cause voltage drops and introduce interference.

4. Typical wiring errors of control unit CA310

X124 (24V power supply): Two "+" terminals are internally short circuited, and two "M" terminals are internally short circuited, used for loop power supply. But if the digital output load is large, it must be powered separately.

X120 EP Terminal (Enable Pulses): If Safety Integrated Basic Functions are enabled, terminals 7 (EP+24V) and 8 (EP M1) need to be connected to 24V, otherwise the pulse will be blocked. If the safety function is not used for simple applications, it is necessary to ensure that these two terminals have 24V (usually through short circuiting or external power supply).

Stop input: TB3-7 (Stop) and TB3-8 (Stop) must be closed (short circuited or connected in series with a normally closed button), otherwise the driver will report "Stop input missing" and cannot run.

LED diagnosis and startup troubleshooting of control unit CU310

The front panel of CU310-2 (PN or DP) has four LEDs: RDY (Ready), COM (Communication), OUT>5V (Encoder Power Supply) MOD。 Understanding their colors and flicker patterns at different stages is the core of quickly locating problems.

LED behavior during startup phase (approximately 1 second after power on):

All orange LEDs stay on for about 1 second → power on normally.

If RDY red slow flashes (2Hz), COM red slow flashes → file error (memory card not inserted or damaged, or firmware missing).

If RDY red is constantly on, COM orange is constantly on → firmware is loading.

LED fault indication during operation phase:

Measures for handling the meaning of LED status

RDY red flashing 2Hz general fault check parameter settings, read fault codes.

RDY red/green alternating 0.5Hz is missing software license installation license.

RDY orange flashing 0.5Hz DRIVE CLiQ component firmware upgrade is waiting to be completed.

COM red flashing 2Hz bus communication interrupt (PROFINET/PROFIBUS) to check cable, master station status, and address settings.

COM green flashing 0.5Hz, no cyclic communication established (main station did not send set values), check PLC program or controller configuration.

OUT>5V, orange constant light encoder power supply is 24V (note: if the encoder is 5V, it may be damaged). Confirm the encoder model and modify the power supply voltage in the parameters.

Common troubleshooting process for startup failures:

RDY does not light up after power on → Check X124 24V power supply (20.4-28.8V).

RDY green is always on but the motor does not rotate → Check if the X120 EP terminal is 24V; check if the status word bit2 (Operation enabled) is 1; Force the control word 0x0F through the STARTER software.

PROFIBUS communication failure (COM red flashing 2Hz) → Check if the address switch (next to X21 of CU310-2 DP) is set to a valid address (1-126) and does not conflict with other stations; Check if the terminal resistor is activated at both ends of the bus.

DRIVE CLiQ communication error (RDY flashing orange) → Check if the DRIVE CLiQ cable (such as 6FX2002-1DC00) is connected correctly and if the plug is securely locked; Ensure that the PM-IF plug between the power module and the control unit has no bent pins.

Selection of incoming side components and EMC category

SINAMICS S120 is configured with different input filters based on EMC categories (C1, C2, C3, C4). For most industrial environments (secondary environments), it is required to meet the C3 category; If it needs to be used in a home/commercial environment (primary environment), it must meet the C2 or C1 category.

Requirements for meeting various types of standards:

C4: No filter, limited to the second environment only.

C3: Use external or internal input filters recommended by Siemens, with motor cable length ≤ 50m (PM240-2) or ≤ 25m (PM340).

C2: Add an incoming reactor (Uk ≥ 4%) on the basis of C3, and further shorten the length of the motor cable (PM240-2 needs to be ≤ 50m and pulse frequency ≤ 4kHz).

C1: The PM240-2, in conjunction with an external filter, meets the first environmental limit.

Misconceptions in the selection of incoming reactors:

Mistakenly believing that reactors are optional. In fact, incoming reactors must be used in the following situations:

The power supply voltage distortion is significant (such as multiple frequency converters sharing the same transformer).

Need to reduce incoming current harmonics to comply with IEEE 519.

The power capacity is more than 10 times the rated capacity of the frequency converter.

When using an IT system without a filter, the incoming reactor can help limit the fault current.

The wiring terminals of the reactor cannot be interchanged (input 1L1/1L2/1L3, output 2L1/2L2/2L3), otherwise incorrect coil polarity will cause heating and performance degradation.

Selection and Overheating Protection of Braking Resistors:

The Blocksize power module integrates a brake chopper internally, requiring only an external brake resistor (such as 6SL3201-0BE12-0AA0). The resistance value must meet the requirements of "Resistance value of the external braking resistor" in the manual (such as PM340 FSA 400V resistance ≥ 390 Ω).