Reading SINAMICS G120C Current via Telegram 352 on PROFINET

1. Overview

The SINAMICS G120C is a compact, wall-mount / cabinet-mount frequency inverter that communicates natively with SIMATIC S7-1200 / S7-1500 controllers over PROFINET IO. When the cyclic telegram is set to Siemens Telegram 352 (PZD-6/6), the drive transmits six process data words to the PLC at every bus cycle, including a normalized actual current value (IAIST) in PZD3.

This reference covers the full signal chain:

1. Hardware and firmware prerequisites for Telegram 352 on the G120C.
2. Project engineering in TIA Portal (device configuration, slot assignment, IO addresses).
3. Reading the six PZD words with DPRD_DAT or direct symbolic access.
4. Converting the normalized IAIST to engineering units (Amps) using parameter r2002 / p2002.
5. Commissioning verification and a troubleshooting matrix for the most common faults.

The same scaling law applies to SINAMICS G120 (with CU240E-2 / CU250S-2 Control Units), G120D, G120P and SINAMICS V20 / V90 / S210 when Telegram 352 is selected, because the normalization is a SINAMICS-platform convention rather than a G120C-specific feature.

2. Prerequisites

3. Telegram 352 PZD Layout

Telegram 352 is a Siemens-specific, free-configurable telegram with 6 process data words in each direction. On the G120C the default interconnect is:

The interconnect shown is the Startdrive default after inserting the drive. If the receiving PLC only sees "zero" in PZD3 while PZD1 / PZD2 update correctly, the BICO source for IAIST on the drive has been overwritten; restore it to r0068[0] in the expert list (parameter p2051[2] = 6 for IAIST, p2061[2] = 0).

3.1 Status word ZSW1 bit map (PZD1 drive → PLC)

4. Configuring Telegram 352 in TIA Portal

1. Open the device view of the G120C and select the PROFINET interface submodule.
2. In the Properties pane under PROFINET interface → Telegram configuration, click Add telegram and pick SIEMENS telegram 352, PZD-6/6.
3. Confirm the IO addresses the compiler assigns. For a typical project you will see:
   • Inputs: IW256 … IW266 (six 16-bit words → 12 bytes starting at 256).
   • Outputs: QW256 … QW266.
4. Download the HW config to the PLC and the drive.
5. Open the drive's online dialog and verify in Communication → Telegram monitoring that the cyclic frame is present and r2050[0..5] mirror the received setpoints.

5. Reading the PZD with DPRD_DAT

The standard, vendor-neutral approach is to call DPRD_DAT (Read consistent data of a DP standard slave / PROFINET IO device) once per telegram slot. Telegram 352's six PZD words are consistent only if read in a single call when the input area starts on a word boundary.

5.1 Ladder (FBD) variant

// One call reads all 12 input bytes (6 PZD words) into DB "DriveTlg".TlgIn
CALL DPRD_DAT(
    LADDR := 256,                    // PROFINET input start address
    RET_VAL := "DriveTlg".retVal,    // Return code (W#16#0000 = OK)
    RECORD := "DriveTlg".TlgIn       // ANY pointer to 12 bytes
);

Define DriveTlg.TlgIn as a 12-byte ARRAY[0..11] of BYTE or a structure with six INT members:

TYPE Telegram352_In :
    STRUCT
        ZSW1    : INT;   // Status word 1
        NIST_A  : INT;   // Actual speed
        IAIST   : INT;   // Actual current (normalized to p2002)
        MIST    : INT;   // Actual torque (normalized to p2003)
        PIST    : INT;   // Actual power (normalized to p2004)
        ZSW3    : INT;   // Status word 3 / free
    END_STRUCT;
END_TYPE

5.2 Symbolic IO access (preferred on S7-1500)

Starting with TIA Portal V14 and S7-1500 FW 1.8, PROFINET subslots can be addressed symbolically. After activating IO device substitution → symbolic name, the PLC tags are generated automatically:

#Status_Word  := "G120C".PROFINET_Interface.Telegram_352.ZSW1;
#Speed_Hz     := "G120C".PROFINET_Interface.Telegram_352.NIST_A;
#Current_raw  := "G120C".PROFINET_Interface.Telegram_352.IAIST;
#Torque_raw   := "G120C".PROFINET_Interface.Telegram_352.MIST;
#Power_raw    := "G120C".PROFINET_Interface.Telegram_352.PIST;

6. Scaling the IAIST to engineering units

The IAIST value arriving in PZD3 is a signed 16-bit integer normalized to p2002 (reference current, in Amps). The official Siemens normalization is 100 % = 16384 (4000_H). One LSB therefore represents:

I_LSB = p2002 / 16384 [A]

Actual current in Amps:

I_actual = IAIST_raw × p2002 / 16384 [A]

If you want a percentage of motor rated current (for bar graphs, HMI faceplates), use:

I_percent = 100 × I_actual / p0305 [%]

Because p2002 is normally pre-loaded to 150 % of p0305, an IAIST reading of 10923 (≈ 2/3 of 16384) corresponds to:

I_actual = 10923 × (1.5 × 1.5 A) / 16384 = 1.50 A (100 % of motor rated)

6.1 Closed-loop SCL implementation

// Inputs
#IAIST_raw    : INT;     // From PZD3
#p2002        : REAL;    // Reference current, normally 1.5 × p0305
#p0305        : REAL;    // Motor rated current
#I_act_A      : REAL;
#I_act_pct    : REAL;

#I_act_A   := INT_TO_REAL(#IAIST_raw) * #p2002 / 16384.0;
#I_act_pct := 100.0 * #I_act_A / #p0305;

6.2 Ladder alternative

      ITD                       // Convert IAIST INT → DINT
      DTR                       // DINT → REAL (in accumulator 1)
      L 1.5e+0                 // Load default p2002 multiplier placeholder
      *R                       // Multiply
      L 1.6384e+4             // Load 16384.0
      /R                       // Divide
      T "Drive".I_act_A        // Store REAL
      L "Drive".p0305          // Load rated current
      /R                       // → fraction
      L 1.0e+2                // 100 %
      *R                       // → %
      T "Drive".I_act_pct

6.3 PEEK_WORD direct access (S7-1500 only)

On S7-1500 the input area can be polled without DPRD_DAT by peeking the process-image partition directly. This is useful when integrating the read inside an existing function block that already runs in OB1 with the process image in PIP 0.

#Current_raw := PEEK_WORD(
    area       := 16#81,                              // Process image inputs (PIP 0)
    byteOffset := UINT_TO_DINT(#I_DRIVE_BASE_ADDR) + 4, // +4 bytes = 2 words past ZSW1
    dbNumber   := 0
);

#Current_A := INT_TO_REAL(#Current_raw) * #p2002 / 16384.0;
#Current_pct := 100.0 * #Current_A / #RatedCurrent;

7. Putting it together — a reusable Telegram 352 FB

The Siemens application example "SINAMICS G120 / S120 Telegram 352 with SIMATIC S7" (entry ID 70155469) provides FB11 SINA_TLG352 as a reference implementation. The signature is:

The FB internally calls DPRD_DAT and DPWR_DAT once and unpacks the six words. The scaling math (IAIST → Amps) is intentionally not inside the FB; do it downstream so the block stays reusable for VFDs with different p2002.

// Excerpt: drive-side control word set
"DriveDB".STW1.0 := TRUE;   // ON / OFF1
"DriveDB".STW1.1 := FALSE;  // OFF2 (1 = no OFF2)
"DriveDB".STW1.2 := FALSE;  // OFF3
"DriveDB".STW1.3 := TRUE;   // Enable operation
"DriveDB".STW1.7 := FALSE;  // Fault acknowledge pulse (set TRUE for one cycle)
"DriveDB".NSOLL_A := REAL_TO_INT(#n_set_Hz * 16384.0 / #p2000);

8. Verification & commissioning checks

1. Stop the drive (no enable, OFF1 = 0) and read IAIST — the value must be exactly 0 with low jitter. Any offset indicates the BICO source on p2051[2] has been re-wired.
2. Enable the drive with a small positive setpoint and load the motor to ~50 % rated current with a brake / dynamometer. Confirm:
   • ZSW1 bit 2 = 1 (operation enabled)
   • NIST_A follows NSOLL_A
   • IAIST ≈ 0.5 × 16384 = 8192 ± 50
3. Reverse the rotation. The IAIST remains positive (regen is signed on 4-Q hardware, but G120C unipolar).
4. In Startdrive trace, compare IAIST × p2002 / 16384 against r0027 (smoothed absolute current). The two traces must overlay within ± 1 %.
5. Verify on the HMI that the bar graph reads 100 % at motor rated current.

9. Troubleshooting matrix

10. Parameter quick-reference

11. Notes on related telegrams and platforms

Telegram 352 is the most convenient choice for G120C because all four key actuals (speed, current, torque, power) are pre-wired. The other options behave as follows:

On SIMATIC S7-300 / S7-400 with classic STEP 7 the same scaling formula applies, but you must generate the GSD file manually from the G120C GSDML and use SFC14 / SFC15 instead of DPRD_DAT / DPWR_DAT.

On third-party PROFINET masters (e.g. Allen-Bradley, Beckhoff, B&R) keep the 16384 normalization constant; do not substitute the S7 analog-input 27648 scaling unless you also re-scale the drive-side reference parameter, which is not possible.