Implementing Ramp-Down for Fuji ACE Drives with S7-1200 in TIA

Overview

The ramp function (also called a ramp generator, ramp limiter, or setpoint ramp) is a fundamental building block of any variable-frequency drive control scheme. In its mathematical form, the continuous ramp is the integral of a rectangular pulse: r(t) = a·t·u(t) where u(t) is the unit step and a is the slope. In a discrete PLC implementation, the discrete-time equivalent becomes a fixed increment per scan:

y_k = y_k-1 + Δsetpoint · (T_cycle / T_ramp)

where Δsetpoint is the difference between the target and the previous output, T_cycle is the OB1 scan time (or the interrupt OB time when the ramp runs in a cyclic interrupt), and T_ramp is the user-entered ramp time in seconds. The same equation applies for ramp-down when the target is below the current output; the increment becomes negative.

This article implements ramp-up and ramp-down generation on a SIMATIC S7-1200 (any CPU 1211C/1212C/1214C/1215C/1217C) that commands a Fuji FRENIC-ACE series AC drive (FRN-Ace / FRN__AR1S-4□) via either a 0–10 V analog output or PROFINET. The program runs in STEP 7 Professional V13 and is forward-compatible with V13 SP1, V14, V15, V15.1, V16, V17, and V18 because it uses only standard IEC 61131-3 constructs.

Prerequisites

System Architecture

The S7-1200 reads commands from the HMI or upstream process, runs the ramp FB in OB1 (or in a cyclic interrupt OB30 at 100 ms), and writes the limited setpoint to the analog output that drives the Fuji ACE frequency reference terminal [12] (0–10 V) or [C1] (4–20 mA current loop). The drive itself also has internal acceleration/deceleration ramps (parameters F07/F08). For coordinated control, the PLC ramp is the master and the drive ramp is set short (0.1 s) so the drive follows the PLC profile without lag. The drive's internal ramp then acts as a fail-safe backup if the fieldbus drops.

Fuji ACE Drive Parameter Table for Ramp Control

Configure the FRENIC-ACE parameters below before commissioning. Settings are loaded via the drive keypad (FRENIC Loader) or PROFINET acyclic services. Default values shown are factory defaults; change them to match the application.

Wiring the S7-1200 Analog Output to Fuji Terminal [12]

For 4–20 mA control, use the SB 1232 AQ 0–20 mA (6ES7 232-4HB30-0XB0) and wire to terminal [C1] (current input) and [11] (common). On the drive, set parameter C40 to 1 to enable current input, and use C41 for the gain.

Implementing the Ramp Function Block in SCL

Create a new SCL source or FB in the project tree. The block is split into a generic FB_Ramp (positive or negative slope) and a project-specific FB_RampDown wrapper that handles the enable, the emergency stop, and the unit conversion from the S7 REAL (Hz) to the AQ integer (0–27648 for ±10 V, 0–27648 for 0–10 V, 0–27648 for 0–20 mA).

FB_Ramp (SCL)

FUNCTION_BLOCK "FB_Ramp"
{ S7_Optimized_Access := 'TRUE' }
VERSION : 0.1
   VAR_INPUT
      bEnable     : BOOL;     // TRUE: ramp follows setpoint
      rSetpoint   : REAL;     // Target value (engineering units)
      rRampUp     : REAL;     // Ramp-up time in seconds
      rRampDown   : REAL;     // Ramp-down time in seconds
      rCycleTime  : REAL;     // Call period in seconds (e.g., 0.1)
      rRampStop   : REAL;     // Emergency stop time in seconds
   END_VAR

   VAR_OUTPUT
      rOutput     : REAL;     // Current ramp value
      bComplete   : BOOL;     // TRUE when rOutput == rSetpoint
   END_VAR

   VAR
      rLastOutput : REAL;     // Previous output value
   END_VAR

BEGIN
   // Default state
   bComplete := FALSE;

   IF bEnable THEN
      // Select ramp-up or ramp-down based on direction
      IF rSetpoint > rLastOutput + 0.001 THEN
         // Ramp UP
         rOutput := rLastOutput
                  + (rSetpoint - rLastOutput) * rCycleTime / rRampUp;
         IF rOutput >= rSetpoint THEN
            rOutput := rSetpoint;
            bComplete := TRUE;
         END_IF;

      ELSIF rSetpoint < rLastOutput - 0.001 THEN
         // Ramp DOWN
         rOutput := rLastOutput
                  - (rLastOutput - rSetpoint) * rCycleTime / rRampDown;
         IF rOutput <= rSetpoint THEN
            rOutput := rSetpoint;
            bComplete := TRUE;
         END_IF;

      ELSE
         // Setpoint already reached, hold
         rOutput := rSetpoint;
         bComplete := TRUE;
      END_IF;

   ELSE
      // Emergency stop: ramp to 0 (or minimum) using rRampStop time
      IF rLastOutput > 0.0 THEN
         rOutput := rLastOutput
                  - (rLastOutput * rCycleTime / rRampStop);
         IF rOutput < 0.0 THEN rOutput := 0.0; END_IF;
      ELSIF rLastOutput < 0.0 THEN
         rOutput := rLastOutput
                  + (-rLastOutput * rCycleTime / rRampStop);
         IF rOutput > 0.0 THEN rOutput := 0.0; END_IF;
      END_IF;
   END_IF;

   rLastOutput := rOutput;
END_FUNCTION_BLOCK

FB_RampDrive (Project Wrapper)

FUNCTION_BLOCK "FB_RampDrive"
{ S7_Optimized_Access := 'TRUE' }
VERSION : 0.1
   VAR_INPUT
      bEnable      : BOOL;
      bRunFwd      : BOOL;     // From HMI or sequence
      bRunRev      : BOOL;
      rHzSetpoint  : REAL;     // 0.0 .. 50.0 Hz (or 60.0)
      rRampUpSec   : REAL;     // Typical: 10.0
      rRampDownSec : REAL;     // Typical: 15.0
      rCycleTime   : REAL;     // 0.1
   END_VAR

   VAR_OUTPUT
      rHzOutput    : REAL;     // Hz after ramp
      iAQRaw       : INT;      // 0..27648 for AQ
      bRunFwdOut   : BOOL;     // To drive terminal FWD
      bRunRevOut   : BOOL;     // To drive terminal REV
   END_VAR

   VAR
      fbRamp       : FB_Ramp;
      rMaxFreq     : REAL := 50.0;
   END_VAR

BEGIN
   // Clamp setpoint to ±max frequency
   IF rHzSetpoint > rMaxFreq  THEN rHzSetpoint := rMaxFreq;  END_IF;
   IF rHzSetpoint < -rMaxFreq THEN rHzSetpoint := -rMaxFreq; END_IF;

   // Drive ramp block
   fbRamp(bEnable     := bEnable,
          rSetpoint   := rHzSetpoint,
          rRampUp     := rRampUpSec,
          rRampDown   := rRampDownSec,
          rCycleTime  := rCycleTime,
          rRampStop   := 3.0,            // 3 s emergency stop
          rOutput     => rHzOutput,
          bComplete   =>);

   // Convert Hz to analog output raw value (unipolar 0..10 V)
   IF rHzOutput >= 0.0 THEN
      iAQRaw := REAL_TO_INT(rHzOutput / rMaxFreq * 27648.0);
   ELSE
      iAQRaw := 0; // Reverse handled via REV terminal, AQ stays 0..10 V magnitude
   END_IF;

   // Run commands (interlock FWD and REV)
   bRunFwdOut := bRunFwd AND NOT bRunRev AND bEnable;
   bRunRevOut := bRunRev AND NOT bRunFwd AND bEnable;
END_FUNCTION_BLOCK

Calling the Block from OB1 (LAD/FBD view)

// In OB1 - call once per scan (or use OB30 for 100 ms cyclic interrupt)
"FB_RampDrive_DB"(
   bEnable     := NOT "Emergency_Stop",    // Global safety input
   bRunFwd     := "HMI".RunFwd,
   bRunRev     := "HMI".RunRev,
   rHzSetpoint := "HMI".Speed_SP,
   rRampUpSec  := 10.0,                    // 10 s ramp-up
   rRampDownSec:= 15.0,                    // 15 s ramp-down (longer for inertial loads)
   rCycleTime  := 0.1,                     // 100 ms
   rHzOutput   => "HMI".Speed_PV,
   iAQRaw      => "AQ_SpeedRef",          // wired to AQ 0
   bRunFwdOut  => "DO_FWD",               // wired to Q0.0
   bRunRevOut  => "DO_REV"                // wired to Q0.1
);

Cyclic Interrupt Variant (OB30)

Calling the FB in OB1 is acceptable for slow ramps (≥ 5 s), but the cycle time will drift with program length. For deterministic timing, use a cyclic interrupt OB:

1. Project tree → CPU → Program blocks → Add new block → Organization block → OB30 (Cyclic interrupt).
2. Set phase offset to 0 ms, cycle time to 100 ms.
3. Call FB_RampDrive_DB from OB30 instead of OB1. Pass rCycleTime := 0.1.
4. Move the output iAQRaw write to OB1 (writes to peripherals are allowed in any OB; OB30 execution is non-preemptive to OB1 only on S7-1200).

Alternative: Ladder Logic (LAD) Ramp

If the project forbids SCL, the same logic is achievable in LAD using a math block chain. Below is a one-line slope generator using the standard IEC blocks. Replace the discrete components with the equivalent network:

// Network 1: Slope selector
   |---[ rSetpoint > rLastOutput ]---( MOV rRampUp -> rRampActive )---|
   |---[ rSetpoint < rLastOutput ]---( MOV rRampDown -> rRampActive )--|

// Network 2: Increment per cycle
   |---[ 100 ]--[ DIV rRampActive ]--[ MUL rCycleTime ]--|
   |                                                       v
   |---[ rSetpoint - rLastOutput ]--[ MUL ]--[ ADD rLastOutput ]--[ LIMIT ]--> rOutput

// Network 3: Hold and store
   |---[ bComplete ]---( MOV rOutput -> rLastOutput )---|

Configuration of the Analog Output in TIA Portal V13

1. Open the device view of the CPU.
2. Drag the signal board AQ 1x12 bit (6ES7 232-4HA30-0XB0) into the slot. If using a SM 1232 instead, insert it on the right side of the CPU rack.
3. Select the analog output channel (e.g., A0) and set:
   • Output type: Voltage
   • Range: 0..10 V
   • Diagnostics: enable short-circuit and wire-break.
4. In the program, write the integer value directly: %QW64 := iAQRaw; (address depends on slot). For symbolic access, the symbol "AQ_SpeedRef" is mapped automatically by TIA Portal once the variable is assigned in the PLC tag table.

PROFINET Alternative to Analog Wiring

For installations where the drive is more than 30 m from the PLC, PROFINET is preferred because it eliminates analog drift. The FRENIC-ACE supports PROFINET via the optional OPC-ACE-PN card or the integrated FRN-Ace PROFINET variant. Cyclic process data are:

To integrate, install the GSDML file GSDML-Vx.x-Fuji-ACE-PN-xxxxxxxxx.xml from the Fuji Electric download portal under Options > Manage general station description files (GSD) in TIA Portal. The device appears under Other field devices > PROFINET IO > Drives > Fuji Electric > FRENIC-ACE. Map the four I/O slots above and connect them in the device configuration. The ramp FB then writes to NSOLL_A instead of the AQ integer.

Step-by-Step Commissioning

1. Hardware check. Verify CPU, signal board, and drive wiring against the table in the wiring section. Confirm shield is bonded at the drive end only.
2. Drive parameters. Load F07 = 0.1 s, F08 = 0.1 s, F01 = 1 (terminal [12] reference), F02 = 1 (terminal run), C30 = 50.0 Hz, C32 = 0.02 s. Save with the drive keypad PRG key.
3. PLC project. Add the CPU 12xx to the project, add the SB 1232 or SM 1232 analog module, paste the SCL source for FB_Ramp and FB_RampDrive, compile, and download to the PLC.
4. Online watch table. Add iAQRaw, rHzOutput, bRunFwdOut, and bRunRevOut to a watch table. Force rHzSetpoint = 0.0, bEnable = FALSE, bRunFwd = FALSE. Verify iAQRaw = 0 and the drive shows 0.00 Hz on the keypad.
5. Ramp test, no load. Set bEnable = TRUE, rHzSetpoint = 30.0 Hz, rRampUp = 10.0 s, rRampDown = 15.0 s. Click bRunFwd momentarily to latch. The HMI should show rHzOutput climbing from 0 → 30 Hz in 10 s linearly. Click bRunFwd OFF: rHzOutput should fall to 0 in 15 s.
6. Emergency stop test. Activate the Emergency_Stop input. Verify rHzOutput falls to 0 in 3 s (rRampStop) and that the drive stops without DC braking (F11 = 0).
7. Load test. Couple the motor to the load. Run the full setpoint profile 0 → 50 → 0 Hz three times. Capture the ramp profile on the HMI trend.
8. Fault injection. Pull the analog cable from terminal [12] with the drive running. The drive should detect the loss of signal only if C32 (analog filter) and C36 (signal loss detection) are configured. Add C36 = 1 (alarm) or C36 = 2 (forced stop) for production deployment.

Verification Checklist

Troubleshooting Matrix

Safety and Standards Notes

• For Safe Torque Off (STO) per IEC 61800-5-2, use the FRENIC-ACE option card or wire the drive's EN terminal (X3) to a 24 V output that is released by an emergency stop. Do not rely on the analog setpoint alone for safe stop.
• For applications requiring Safety Integrity Level 1 or higher (PL c/d), the ramp function is not a substitute for a safety-rated stop. Implement a separate, hardwired safety chain that removes drive power via a contactor or the STO input.
• For pump and fan curves, the ramp should follow the affinity laws: a linear frequency ramp produces a quadratic flow ramp, which is gentler on hydraulics. Use 30–60 s ramps for large centrifugal pumps.

Performance and Tuning

The cycle time of the cyclic interrupt OB is the dominant factor in ramp accuracy. A 100 ms OB30 yields a minimum step size of (setpoint × 0.1 / ramp_time). For a 50 Hz setpoint with a 10 s ramp, the increment is 0.5 Hz per cycle, which is well below the 12-bit analog resolution (0.012 V / 0.06 Hz). For very fast ramps (≤ 1 s), use a 10 ms OB30 cycle to keep the discretization error under 1%.

For closed-loop control where the PLC is the PID master and the drive is the actuator, wrap the ramp FB around the PID output. This prevents the PID from commanding a step change that would trip the drive on overcurrent:

// Sequence:
//   PID outputs Hz setpoint (raw) -> FB_RampDrive limits rate of change
//   FB_RampDrive outputs smoothed Hz -> AQ or PROFINET
//   Drive follows smoothed Hz internally with F08 = 0.1 s

FAQ