C135 PCS 7 (PCS7)
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Add Reusable Motor-Speed Decision Logic to a PCS 7 CMT

Add Reusable Motor-Speed Decision Logic to a PCS 7 CMT

Put the speed comparison and mutually exclusive increase/decrease requests into a reusable CMT function, then connect it to the motor CM through technological I/Os. Siemens documents how to create and insert that function. The actual speed thresholds, drive input timing and permission behavior remain project-specific; define them before wiring. A decrease request for excessive speed is only one part of the required decision logic.

Table of Contents

Specify the Speed Decision

The requested action is to select an increase or decrease command according to motor speed, including a decrease command when speed is too high. Before implementing it, define the target or acceptable speed range and the drive's command semantics.

The following is a proposed engineering specification, not a manufacturer block configuration:

Established conditionIncrease requestDecrease requestSpeed above accepted rangeOffOnSpeed below accepted rangeOnOffSpeed within accepted rangeOffOffInvalid measurement or operation not permittedDefined by the reviewed safe behaviorDefined by the reviewed safe behavior

Do not implement the last row by guessing. Determine whether the real drive expects pulses, maintained levels or another interface.

Create the Documented CMT Function

Siemens documents this reusable function method:

  1. In Plant View, right-click the CMT storage folder and select Create New Object > Control Module Type.
  2. Name and open the type.
  3. Drag the required logic blocks into CFC, name them and establish their internal connections.
  4. Drag the required parameters and signals into Technological I/Os.
  5. Activate the Function option. It is selectable only when no SubCMs are used.

Engineering with CMT, section 5.4.

For this adaptation, expose the actual speed, decision thresholds, relevant permission and two resolved command outputs. Select real blocks and types from the installed library; no unverified comparator block name or API is prescribed here.

Insert and Connect the Function

  1. Open the intended CM instance's chart.
  2. In Templates, select the project library containing the function.
  3. Drag the function into the instance's Technological I/Os window; it is created in an empty CFC subplan.
  4. Position, connect and parameterize it.

This insertion sequence is documented. Engineering with CMT, section 5.4. Applying it to a drive's increase/decrease commands requires the actual drive interface and reviewed output behavior.

Verification

In an isolated test configuration, evaluate values below, inside and above the accepted range, including exact boundaries. Confirm that the two requests cannot unintentionally oppose each other.

Also test invalid measurement, operation permissions and any required pulse or maintained-command behavior against the drive specification. Compare the resulting speed response with the intended control action; a Boolean output changing does not prove the drive accepted it. No application test has been performed.

Limitations and Operational Precautions

The installed PCS 7/CFC/library versions, threshold definition, drive command interface and measurement-failure behavior are missing. The reusable-function construction is verified; the complete motor implementation remains unresolved.

Back up the project and assess affected instances before changes. Do not bypass existing drive interlocks or make production speed changes to test the logic. Confirm output timing and rollback in the approved commissioning plan.

Engineer FAQ

Must simple comparisons be encoded entirely as sequence steps? The documented CMT function method provides a reusable place for logic.

Can a function contain SubCMs in this method? The documented Function selection requires no SubCMs.

Is the proposed table sufficient to wire a drive? No; the drive's real input semantics and permissions remain necessary.

Technical References

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