Configuring MotSpdCL PID Speed Control in SIMATIC PCS 7 APL

Overview

Speed-controlled pump motors in SIMATIC PCS 7 are implemented through the MotSpdCL block from the Advanced Process Library (APL). When the application requires closed-loop regulation of a process variable such as tank level, flow, or pressure, the MotSpdCL speed reference must be driven by a PID controller output rather than a fixed operator entry. The two blocks that drive this regulation are PIDConL (PID controller, enhanced) for the control loop and MotSpdCL for the variable-speed drive supervision.

This guide covers the recommended pattern for using an external setpoint (SP_Ext) on the MotSpdCL to receive the manipulated variable (MV) from a PID controller, the two-mode (manual then auto) start-up logic to prevent integral windup during discharge disturbances, and the CFC wiring required for the SIMATIC PCS 7 V9.0 / V9.1 APL library. The reference is the MotSpdCL function manual entry in the Siemens Industry Online Support entry ID 109794385.

Prerequisites

• SIMATIC PCS 7 V9.0 SPx or V9.1 with the Advanced Process Library installed in the master data library.
• PCS 7 APL block types: MotSpdCL, PIDConL, CtrlPid (alternative), AnScl (analog scaling), and DigDig (digital selector if required).
• A variable-frequency drive (VFD) such as SINAMICS G120, G120X, G150, or ET 200S FC that exposes a 4–20 mA or PROFIBUS/PROFINET speed reference channel wired to the MotSpdCL analog output V_NormOut.
• Level transmitter on Tank 4 (LT_4001) connected to an analog input module (AI 4xU/I 2-wire, 6ES7331-7RD02-0AB0 for example) and made available as a CFC signal.
• Discharge valve feedback (V211) wired through a digital input for interlock of the two control modes.
• Engineering station with SIMATIC Manager / PCS 7 Engineering Toolset, including the APL faceplate plug-in.

MotSpdCL Block Reference Summary

The MotSpdCL block is the APL type for a bi-directional variable-speed motor with two directions of rotation and speed setpoint handling. The signal interfaces that participate in closed-loop speed regulation are summarised below.

PIDConL Block Reference Summary

The PIDConL block is the APL enhanced PID controller. It implements the standard ISA form with separate gain, integral, and derivative terms, anti-windup, setpoint ramping, alarm limits, and bumpless transfer support.

Signal Scaling and Engineering Units

Tank level is measured by LT_4001 in litres. The PID controller expects both PV and SP in the same engineering units. The MotSpdCL expects SP_Int / SP_Ext in normalized speed (0–100 %). The recommended approach is to keep the PID loop in percent of full-scale tank volume so that the operator faceplate displays 0–100 %, with a scaling block converting to litres for trending if required.

Step-by-Step CFC Wiring

1. Drop MotSpdCL into the CFC chart of Tank 4's equipment phase. Set the block instance name to MOT_P401 and assign the APL faceplate.
2. Drop PIDConL into the same chart. Instance name PID_LT4001. Assign the APL PID faceplate.
3. Wire the level transmitter PV: LT_4001 → AnScl (LTR_to_Pct) → PIDConL.PV. Set scaling so 5 L equals 50 %.
4. Wire the setpoint source: create a constant block SP_5L with value 50 (%) and connect to PIDConL.SP_Ext. Alternatively wire the SFC-driven target variable.
5. Wire the controller output: PIDConL.MV → MotSpdCL.SP_Ext.
6. Set the selector: MotSpdCL.SP_LiOp = 1 (always external when the loop is in regulation). Drive this from a digital constant or an SFC transition so that the operator faceplate cannot accidentally switch to internal during automatic control.
7. Wire the bumpless transfer: MotSpdCL.V_Act (or MotSpdCL.V_NormOut when feedback is unavailable) → PIDConL.MV_Track. This prevents an MV step when the controller switches from manual to auto.
8. Wire the mode cross-coupling: PIDConL.ManAct → MotSpdCL.ManAct and PIDConL.AutoAct → MotSpdCL.AutoAct. This keeps the motor's manual/auto state in step with the controller's mode so that the operator view is consistent across faceplates.
9. Wire the VFD reference: MotSpdCL.V_NormOut → analog output channel (e.g. AO 4xU/I, 6ES7332-5HD01-0AB0) → VFD analog input 1 (terminal 3/4 on SINAMICS G120 CU240E-2).
10. Wire the speed feedback: VFD analog output 1 → AI channel → MotSpdCL.V_Act.
11. Compile the chart and download to the AS. Open the faceplate in WinCC and verify that the MotSpdCL displays SP_Ext as the active setpoint source.

Two-Mode Control Logic for Discharge Disturbance

When the discharge valve V211 opens, the level in Tank 4 drops faster than the pump can compensate under normal PID action. A pure PID loop with default tuning will exhibit a large initial deviation that may swing the VFD to its maximum speed and trip on overcurrent. The recommended pattern splits the regulator behaviour into two states that an SFC manages.

Mode 1 - Discharge Valve Closed

• Operator runs the equipment phase in automatic.
• If the level drops below a lower threshold (for example 4.7 L = 47 %), the SFC enables the VFD at a minimum speed of 60 % until the level returns to the target.
• PID remains in automatic and slowly corrects residual error.

Mode 2 - Discharge Valve Open

1. On V211 = OPEN rising edge, the SFC forces PIDConL into manual mode (ManAct = 1, MV_Track = 1) and writes a fixed MV equal to the minimum speed (e.g. 60 %) into MotSpdCL.SP_Ext for a settling time A seconds (typically 3–10 s depending on line length).
2. After timer A expires, the SFC ramps the MV over time B from 60 % to 100 % (the high-pump-speed setpoint) using the Rmp (Ramp) APL block, so the pump brings the level back toward 5 L without a step disturbance.
3. Once level reaches the target band (for example 4.95–5.05 L), the SFC switches PIDConL to automatic (AutoAct = 1, MV_Track = 0) and disconnects the ramped MV so that the PID becomes the active driver of MotSpdCL.SP_Ext.
4. PID tuning parameters Gain, TI, TD are tuned for steady-state level control only — the disturbance handling is done by the SFC.

Commissioning and Verification

1. Open the MotSpdCL faceplate in WinCC and confirm that SP_Ext is shown as the active source (the faceplate highlights the active setpoint input).
2. Force PIDConL to manual and verify that MV tracks MotSpdCL.V_NormOut with no step.
3. Step the manual MV to 30 % and confirm the VFD accelerates and V_Act reads back the expected speed.
4. Place PIDConL in automatic with a setpoint of 50 % (5 L). Introduce a small level disturbance by momentarily opening a manual drain valve.
5. Trend PV, SP, and MV simultaneously in the WinCC online trend control. Verify that the MV moves toward the new speed, the PV converges to SP within the allowed settling time, and that there is no oscillation beyond three cycles.
6. Trigger Mode 2 by opening V211 from the faceplate. Confirm the SFC executes steps 1–3 above and that the PID takes over cleanly without a step in MV.
7. Verify all PIDConL alarm limits (AH, AL, WH, WL) are configured against the scaled PV (0–100 %).

Parameter Tuning Guidance

Troubleshooting Matrix

Related Equipment Module Templates

Siemens ships an application example titled Equipment Modules for SIMATIC PCS 7 using the example of the Chemical Industry which contains a fully engineered level-control scenario in chapter 5.1. The example includes a SFC that demonstrates the two-mode pattern above with simulated instrumentation, so all PID tuning can be performed offline before connecting to the live plant. The example is published on the Siemens Industry Online Support portal under entry ID 109794385 and the related APL documentation set.

Safety and Operational Notes

• Ensure that MotSpdCL is configured with the correct rotation direction; the VFD must be parameterised to accept a positive reference for forward pump operation.
• The minimum speed of the VFD must be above the pump's thermal minimum flow to prevent dry-running. The block's V_LoLim should match the VFD parameter P1080 (minimum speed).
• If the tank can run empty (level below the probe's low-cutoff), implement a permissive interlock that forces MotSpdCL to stop rather than continue at minimum speed.
• Always connect the VFD fault contact to MotSpdCL.FbkRun or the appropriate fault input so that the block enters a safe state on drive trip.

FAQ