SINAMICS p1120 Ramp Up Time with Motorized Potentiometer

This technical reference clarifies how the SINAMICS parameter p1120 (Ramp Function Generator ramp-up time) interacts with the Motorized Potentiometer (MOP) function block. A common engineering question is whether the configured ramp-up time applies to the full 0–p1082 (maximum speed) span or to a delta from the current speed. The answer is unambiguous: p1120 is the time to accelerate from 0 rpm to p1082 (or the configured maximum). When the MOP raises the setpoint from an intermediate speed, the elapsed time is proportional to the speed delta.

1. Overview of the Ramp Function Generator (RFG)

The Ramp Function Generator (RFG) sits between the main setpoint source (typically p1070) and the speed controller. It limits the rate of change of the setpoint to protect mechanics, avoid overcurrent trips, and shape process dynamics. Two parameters define the basic ramp shape:

2. Maximum Speed and Reference Parameters

Three related parameters govern the upper boundary of the setpoint range and the normalization of the RFG:

When p1120 is set, the drive internally calculates the ramp slope as dn/dt = p1082 / p1120 (in rpm/s). That slope remains constant regardless of the current setpoint value; it is applied as the active ramp limit.

3. Motorized Potentiometer (MOP) Parameter Set

The Motorized Potentiometer emulates a motor-driven setpoint potentiometer. It has its own internal ramp generator and a separate start value. This is the source of the most common confusion: which ramp limits the setpoint rise when the MOP raise key is held?

The MOP output (r1050) is the setpoint it produces. It is normally wired into the main setpoint via p1070[0] = 1050. From there it enters the RFG, which is governed by p1120 / p1121. This is the architecture in which two ramp times can be active simultaneously.

4. Ramp Time Calculation Theory

Because the RFG defines a slope, the time to traverse any speed delta is:

t_ramp = (|n_target - n_current| / p1082) × p1120

Where:

• t_ramp = actual ramp time in seconds
• n_target = target speed in rpm (the MOP setpoint after raise command)
• n_current = current speed in rpm at the instant the raise command is issued
• p1082 = maximum speed in rpm
• p1120 = configured ramp-up time in seconds

Worked Example 1 — 0 to 800 rpm

With p1082 = 1500 rpm and p1120 = 20 s, accelerating from 0 to 800 rpm:

t_ramp = (800 / 1500) × 20 = 10.67 s

Worked Example 2 — 800 to 1000 rpm

Continuing from the previous example, raising from 800 to 1000 rpm:

t_ramp = ((1000 - 800) / 1500) × 20 = 2.67 s

Worked Example 3 — Delta calculation directly

The slope in rpm/s is constant:

slope = 1500 / 20 = 75 rpm/s
t_ramp = 200 rpm / 75 rpm/s = 2.67 s

All three approaches yield the same result. The 20-second figure applies only to the full 0–1500 rpm span; any partial acceleration is shorter by the ratio of the delta to the maximum.

5. MOP Internal Ramp vs. RFG Ramp

The MOP has p1047 (ramp-up) and p1048 (ramp-down) controlling its internal rate of change of the MOP output. The RFG has p1120 and p1121. When the MOP output feeds the RFG main setpoint, both ramp generators can be active in series. The effective ramp is the slower of the two slopes.

The decision tree when the MOP raise command is issued:

1. MOP integrator accumulates the raise command at a rate set by p1047; the MOP setpoint climbs from its current value toward p1037 (MOP maximum).
2. The MOP output (r1050) is fed to the RFG via p1070.
3. The RFG compares the requested setpoint to the current RFG output and limits the rate of change to p1082 / p1120.
4. The motor follows the RFG output (after the speed controller and torque limits).

If the MOP setpoint rises faster than the RFG can pass through, the RFG simply caps the rate. If the MOP setpoint rises slowly, the MOP itself is the bottleneck. Setting p1047 = 0 effectively disables the MOP internal ramp (instantaneous change), leaving p1120 as the only ramp.

6. MOP Start Value (p1040) and Pre-loading

p1040 defines the value the MOP outputs immediately after power-up, after a fault reset, or after the MOP is re-enabled. If the drive is already running at 500 rpm when the MOP is engaged and p1040 = 0, the MOP output will be 0. The RFG will then ramp the setpoint from the MOP output (0) up to whatever the raise command produces (e.g. 1000 rpm), taking (1000 / p1082) × p1120 seconds.

To avoid an unintended deceleration when the MOP is engaged, pre-load the MOP to the current motor speed. This is done by routing the current speed (r0063 or r0021 after scaling) into p1043/p1044 latching, or simply by setting p1040 to the current operating speed before enabling the MOP. Field practice: set p1040 to the last commanded speed and accept the small transient, or use a parameter-driven initialization PLC sequence.

7. Configuration Procedure

Prerequisites

• SINAMICS G120 (CU240B/E-2 or similar) with IOP/BOP access or Starter / Startdrive commissioning software.
• Motor commissioned: p1300, p0310, p0311, p0335 set; motor identification (p1900) completed if required.
• Speed limits defined: p1080 (min), p1082 (max), p2000 (reference).
• Digital inputs available: DI4 = raise, DI5 = lower (typical convention).

Step-by-Step

1. Set p1082 to the maximum allowed speed (rpm). Example: 1500.
2. Set p2000 = p1082 (1500) so that 100 % of any scaled setpoint equals 1500 rpm.
3. Set p1120 (RFG ramp-up) and p1121 (RFG ramp-down) to the required times. Example: 20 s each.
4. Configure MOP raise source: p1035 = 722.4 (digital input 4 status).
5. Configure MOP lower source: p1036 = 722.5 (digital input 5 status).
6. Set p1037 = p1082 (MOP max = drive max) and p1038 = 0 (or p1080 if reverse is enabled).
7. Set MOP internal ramp times: p1047 = 20, p1048 = 20 (match RFG for predictability).
8. Set MOP start value: p1040 = 0 (default) or pre-load to expected operating speed.
9. Wire MOP output to main setpoint: p1070[0] = 1050.
10. Set command source: p0700 = 2 (terminals) or p0700 = 6 (fieldbus), and ON/OFF1 to p0840 as required.
11. Save parameters: copy RAM to ROM (p0971 = 1).
12. Run commissioning: with drive stopped, command ON; close DI4; observe r0021 climbing; verify ramp duration on the trace matches the calculation in Section 4.

8. Verification Procedure

1. Use the Starter / Startdrive trace function to record r0062 (setpoint after RFG) and r0021 (actual speed smoothed) simultaneously.
2. Command ON with MOP raise active. Measure the time from 0 rpm to p1082; confirm it matches p1120 within ±5 % (allowing for rounding, controller saturation, and torque limits).
3. Stop the drive at an intermediate speed by releasing the raise key. Re-engage raise. Measure the time from current speed to new target. Confirm it equals (delta / p1082) × p1120.
4. Check r1050 (MOP setpoint) and r0062 (RFG output) in the trace; verify that the MOP internal ramp (p1047) is not the limiting factor unless intentionally set that way.
5. Validate that no fault (F) or warning (A) appears during the ramp, particularly F07901, F07902, F07801, A07901, A07902.
6. For reverse operation, test n_target < 0; ramp time uses the same slope — polarity does not enter the formula.

9. Edge Cases and Field-Proven Caveats

9.1 Load Inertia / Torque Limiting

If the mechanical load is heavy and the torque limit (p1520/p1521) is reached, the motor will not track the RFG output exactly. The ramp time measured at the shaft will be longer than the RFG ramp time because the controller saturates. Verify with r0067 (torque utilization) and r0080 (torque actual).

9.2 Field Weakening Range

Above base speed (p0311), the drive enters field-weakening. The available torque drops; acceleration capability decreases; ramp may be longer in this range.

9.3 Pre-charge and DC Bus Stabilization

On power-up, line-side pre-charge takes 1–3 seconds before the drive can produce torque. The first few hundred milliseconds of the ramp may show no motor movement. Do not adjust p1120 to compensate for this; it is a pre-charge effect.

9.4 Extended RFG Rounding (p1130/p1131)

With p1115 = 1, the rounding times add effective delay at the start and end of the ramp. The total ramp time from 0 to p1082 becomes p1120 + (p1130 + p1131) / 2. Adjust expectations accordingly.

9.5 Brake Control

If the motor has a holding brake (p1215), the brake release/apply times (p1216, p1217) modify the apparent ramp. The RFG continues internally while the brake is closed; this can produce setpoint vs. speed divergence.

9.6 Multiple Setpoint Sources

If a PLC or HMI forces the MOP via p1050 override or fieldbus setpoint, the MOP ramp and the RFG ramp both still apply. Always confirm the final main setpoint path with r1078 (active main setpoint).

9.7 Reversal via MOP

If p1038 < 0, the MOP can ramp through zero to a negative setpoint. The ramp time formula uses absolute value of delta: |n_target - n_current| / p1082 × p1120. The polarity transition through 0 incurs the full ramp up to p1082 magnitude.

10. Diagnostic Fault and Warning Codes

11. Troubleshooting Matrix

12. Quick-Reference Formulas

Slope (rpm/s)   = p1082 / p1120
Ramp time (s)   = (|n_target - n_current| / p1082) × p1120
Ramp time (s)   = (|n_target - n_current|) / slope
Effective slope = MIN(p1082 / p1120, p1082 / p1047)   // when MOP feeds RFG
Extended RFG    = p1120 + (p1130 + p1131) / 2

13. Summary

The p1120 ramp-up time in SINAMICS is the time to traverse the full speed range from 0 to p1082, not the time for any individual speed step. The Motorized Potentiometer (MOP) has its own internal ramp (p1047) and a start value (p1040). When the MOP output is wired into the RFG, the slower of the two ramps dominates. To compute the actual ramp duration for any speed change, divide the speed delta by p1082 and multiply by p1120. Always pre-load the MOP to the current operating speed if you engage the MOP while the motor is already running to avoid an unintended deceleration to p1040.