SIMODRIVE 611U Ramp Time Not Responding: P1256/P1257 Field Troubleshooting

This reference documents a recurring field issue on the SIMODRIVE 611 universal (611U) module order number 6SN1118-0NH01 when configured as a stand-alone frequency inverter (V/Hz open-loop speed control) for a spindle drive (0-10000 rpm). The reported symptom is that changes to the ramp-up time in P1256 and ramp-down time in P1257 produce no observable change in acceleration or deceleration behavior. The drive accelerates and decelerates as if the ramp values were at their default 0.4 s, regardless of the value entered (verified up to 5.0 s in the field). The fault is configuration-related, not a defective module. This article isolates the root causes and walks through the corrective sequence used in production environments, citing the official SIMODRIVE 611 universal / 611 universal E Function Manual.

Affected Hardware and Configuration

The 6SN1118-0NH01 closed-loop control board is a standard 611U module commonly used in machine-tool retrofits. The frequency-inverter operating mode (n-set mode without encoder) is selected via drive parameters, and the ramp function generator (RFG) is the sub-function responsible for shaping the velocity profile. Without a working RFG, setpoint changes are applied as a step and the motor follows the setpoint slew rate of the analog input, producing the "no ramp effect" symptom.

Symptom Description

The reported behavior is consistent across multiple commissioning attempts:

1. PLC issues PAR.Set 1 selection, then a 65A control word (drive ON + enable).
2. Drive runs the spindle motor correctly at the requested speed, in either direction.
3. Operator changes P1256:0 through P1256:7 (ramp-up time per parameter set) from the documented 0.4 s default to 2.0 s or 5.0 s. Save and reset where required.
4. Operator changes P1257:0 through P1257:7 (ramp-down time) identically.
5. On the next start command the drive still accelerates as if the ramp were 32 ms (the value visible in P1813 in some test runs) and decelerates without a controlled ramp.
6. Setting P1813 from 32 ms to 2000 ms likewise produces no observable change in ramp behavior.

Because the drive itself runs without faults and responds to start/stop and setpoint changes, the cause is not in the power section. The fault is in the parameter / control-word chain that should engage the RFG.

Root Cause Analysis

On the 611U there are five independent failure modes that all produce this exact symptom. They are listed below in the order they are most commonly encountered in the field.

1. RFG Not Enabled (Most Common)

The ramp function generator is an optional sub-function. On 611U modules that were originally parameterized for a synchronous servo motor (or were shipped with servo defaults), the RFG is internally disabled because servo drives do not need a velocity ramp when the position controller is the outer loop. When the module is then re-purposed as a frequency inverter, the RFG remains disabled until it is explicitly enabled either:

• by a digital input function assignment, or
• by setting the corresponding enable bit in the parameter set, or
• by an internal jumper in the parameter tool.

If the RFG is not enabled, P1256 and P1257 are written into the drive but are never connected to the active speed setpoint path. The drive therefore ignores them. The official function manual covers RFG activation under chapter 6.1 (closed-loop speed control) and chapter 6.19 (Ramp Function Generator).

2. Wrong Parameter Index

Both P1256 and P1257 are indexed parameters. The base parameter selects the parameter set index. The 611U supports up to 8 parameter sets (index 0-7). The active index is selected by the digital input function "parameter set changeover" or by the bit field in the control word. If the operator edits the wrong index (e.g. index 0 while the drive is actually running on index 2), the value is stored correctly but never used. The convention is:

Verify in the small operator panel or SIMO COM U which index is active when the PLC issues the start command, then edit that index.

3. Firmware Version Compatibility

On 611U control modules with firmware versions below SW 2.4, the ramp-up and ramp-down parameters are P0616:8 and P0617:8 respectively, not P1256 and P1257. P1256 / P1257 were introduced as part of the unified ramp function block at the SW 2.4 release. The reported firmware in the source case is SW 10.1, which uses the new parameter numbers, but a module flashed to an older firmware (or a repaired module that came back with downgraded firmware) will silently ignore the new parameters. Always check the firmware level on the type plate or read P0618 / P0619 (version identifier) before assuming the parameter is missing.

4. P1813 Not Set for RFG Operation

P1813 is the RFG ramp time used by the high-level RFG block. If P1813 is left at 0 or is very small (the field report shows 32 ms), the RFG time constant dominates the small values of P1256 / P1257 and the operator sees only the 32 ms behavior. P1813 must be set in the same units (seconds, ms) as the indexed parameters and must be greater than or equal to the longest P1256 / P1257 in any active parameter set.

5. PLC Control Word Does Not Enable RFG

When the drive is started from a PLC via the parallel control word interface, the RFG start/stop is gated by a bit in the control word. The 65A pattern reported in the source is a typical "ON + enable ramp" sequence, but if the bit that triggers the RFG is not asserted in the same write that releases the enable, the RFG stays off for the first start cycle. The control word sequencing must be aligned with the parameter set selection. Refer to chapter 6.4 of the SIMODRIVE 611 universal Function Manual for the exact bit map and timing requirements.

Parameter Reference Table

Step-by-Step Solution

Follow this sequence in the order shown. Each step is verified before moving to the next.

Step 1 - Verify Firmware Version

1. Connect SIMO COM U (expert mode: Ctrl+E) to the drive.
2. Read P0618 / P0619 or look at the SW field on the type plate.
3. If SW < 2.4, edit P0616:8 and P0617:8 instead of P1256 and P1257. Continue with the remaining steps using the legacy parameters.
4. If SW ≥ 2.4 (including the SW 10.1 reported in the source), use P1256 / P1257.

Step 2 - Enable the Ramp Function Generator

1. In SIMO COM U, navigate to the parameter list and search for "RFG" or "ramp function generator".
2. Locate the RFG enable parameter for the active axis (A-axis in the field case: drive A; the equivalent for a B-axis module would be b0660). The small operator panel shows it as A0660 or b0660 depending on the axis.
3. Set the RFG enable to 1 (enabled). In the source, the suggested quick test is to hard-wire digital input I 0.A to function 9 (RFG enable) and observe whether the ramp becomes active. If it does, the issue was the enable path and you can then refine the assignment in P0660 / P0661.
4. If the digital input is already used for another function in the project, move the RFG enable to a free input, e.g. I 1.A, and update P0661 accordingly.

Step 3 - Set the Correct Parameter Index

1. Determine which parameter set the PLC is selecting. In the source, the PLC issues "PAR.Set 1" before the 65A start. Confirm whether this is a logical parameter set selection (bit pattern on the control word) or a physical input-driven selection.
2. Open P1256 in SIMO COM U and verify the active index (the one with the highlight or "active" marker). The other indices remain editable but are not used until their parameter set is selected.
3. Edit the active index to 2.0 s (or the desired ramp-up time). Repeat for P1257.
4. Write the changes to the drive and perform a power-on reset only if the manual requires it for the parameter to take effect. On most SW versions a save and re-enable is sufficient.

Step 4 - Set P1813

1. Open P1813 in SIMO COM U.
2. Set the value to a number of milliseconds at least equal to the longest active P1256 or P1257 value. For 2.0 s ramps, set P1813 = 2000 ms. The field report shows that 2000 ms was tested but the RFG was not yet enabled, hence no change was observed.
3. Save and acknowledge any parameter-change messages.

Step 5 - Align the PLC Control Word

1. Review the PLC logic that builds the 65A control word. Identify the bit that engages the RFG (refer to chapter 6.4 of the SIMODRIVE 611 universal Function Manual).
2. Make sure the bit is asserted in the same PLC write cycle that asserts the ON and enable bits, otherwise the drive starts in a non-ramped state and the first start cycle ignores the ramp.
3. If the PLC uses a handshake, do not toggle the RFG bit on the falling edge of enable; hold it active for the entire run cycle.

Verification Procedure

1. Use the SIMO COM U test running function. If the drive is being controlled from the operator panel rather than the PLC, the test run will issue a warning "enable missing" when the RFG is set to 0. The warning disappears as soon as the RFG is enabled.
2. Issue a small step change in setpoint (e.g. 10% of full scale). Observe on the trace window in SIMO COM U that the velocity now follows a linear ramp with the time constant set in P1256 / P1257.
3. Issue a stop command. Observe the deceleration ramp on the trace.
4. Restore PLC control and repeat the same step / stop sequence from the PLC. Verify the trace shows the configured ramp.
5. Repeat the test for every active parameter set (index 0..7) that the PLC can select.

Common Pitfalls

Commissioning Tips for SIMO COM U

• Press Ctrl+E in SIMO COM U to enter expert mode and reveal the full parameter list. From there, right-click any line and select Find to search by parameter number or keyword such as "ramp" or "RFG".
• Always test-run the system locally from SIMO COM U first, then migrate the control to the PLC. This isolates whether the issue is in the drive configuration or in the PLC sequencing.
• For spindle applications, default ramp values of 10 s (factory) are common in correctly configured asynchronous setups. A default of 0.4 s is a strong indicator that the module retained synchronous-servo defaults.
• Save the parameter file (PAR file) at the end of every successful commissioning step. The PAR file is the only way to audit later whether the change in ramp behavior was caused by a parameter edit or by a control-word change.

Safety and Functional Notes

Frequently Asked Questions