How Integral Time and Derivative Time Affect PCS 7 PIDConL Output
In PCS 7 PIDConL, reducing a positive integral time TI strengthens integral accumulation for the same error and effective gain; increasing TI weakens it. TI is a time parameter, so it must not be confused with repeats per minute. Derivative time TD governs a response to changing error under the configured controller structure. The explanation below uses the documented APL V9.0 algorithm and does not prescribe plant tuning values.
Table of Contents
- Integral Time Controls the Accumulation Rate
- Convert Minutes per Repeat and Repeats per Minute
- Derivative Time Acts on Changing Error
- Account for the Actual Controller Configuration
- Evaluate a Tuning Change Deliberately
- Verification
- Limitations and Operational Precautions
- Engineer FAQ
- Technical References
- Related Articles
- Related Tags
Integral Time Controls the Accumulation Rate
For PIDConL in APL V9.0, the documented standard controller equation includes the integral term GainEff / (TI × s). TI is an integral time in seconds, not an independent integral gain.
For a constant nonzero error, enabled integral action and no limiting or tracking intervention, the equation gives:
Rate of change of the integral contribution = GainEff × error / TI
This is an engineering derivation of the documented algorithm, not a measured plant response. A shorter positive TI increases the accumulation rate; a longer TI reduces it. The sign of the error and effective controller action determine the direction, so shortening TI does not mean that MV must increase.
Convert Minutes per Repeat and Repeats per Minute
These are reciprocal ways of expressing integral strength when they refer to the same controller convention:
- Minutes per repeat = TI in seconds / 60.
- Repeats per minute = 60 / TI in seconds, for positive TI.
These are calculated unit conversions. They are not recommended tuning values. Do not transfer a repeats-per-minute number directly into a seconds field or assume another controller uses the same algorithm and scaling.
Derivative Time Acts on Changing Error
The documented standard PIDConL equation has a delayed derivative term governed by TD and DiffGain. It is not a permanent output contribution for a constant error.
Increasing TD changes both the derivative weighting and, for the documented form, the associated delay TD / DiffGain. Therefore changing TD is not equivalent to increasing a constant output bias. Review the actual derivative configuration before predicting its response to a setpoint or measurement change.
Account for the Actual Controller Configuration
The manual's standard equation has explicit conditions, including enabled P, I and D components and particular feedback-path settings. Do not apply its simple constant-error interpretation while the controller is tracking, limited or using another structure.
For this documented version, TI = 0 disables integral action; it does not request infinitely strong integration. The manual also describes output-limit anti-windup behavior. A persistent error with no accumulating MV therefore needs a configuration and limit check before a tuning change.
Evaluate a Tuning Change Deliberately
Use this engineering approach rather than applying universal parameter values:
- Identify the installed block version, units, controller direction and active structure.
- Preserve current parameters and establish the permitted operating range and rollback values.
- Trend SP, PV, MV and relevant mode or limit indications under a stable, approved condition.
- Change one intended parameter at a time within the approved test plan.
- Compare disturbance or setpoint response with the agreed process criteria, including actuator movement and limits.
- Restore the baseline if the acceptance criteria are not met.
The choice of test stimulus and acceptable response is process-specific. No PID Tuner availability or exact tuning sequence for an unidentified release is assumed.
Verification
Confirm that the actual field is TI in seconds and that integral action is enabled before comparing settings. Evaluate the sign and rate of change under conditions where the simplified interpretation applies.
For derivative changes, compare response to an approved changing input; a steady error does not test the derivative contribution. Record the controller mode, limits and structure with the trend so observed behavior is not incorrectly attributed to one parameter.
Limitations and Operational Precautions
The explanation is scoped to PIDConL APL V9.0; another controller's integral-gain convention can differ. The conversions assume a positive finite TI. They do not describe TI = 0 handling in other products.
No process dynamics or safe tuning values are established by the general question. Review actuator limits, process constraints and rollback before changing live tuning. Faster integral accumulation is not a guarantee of a faster or less oscillatory process response.
Engineer FAQ
Does a larger TI produce stronger integral action?
For the stated positive-TI conditions, it produces a lower accumulation rate.
Does reducing TI always raise MV?
No. The error sign and controller action matter.
Is derivative action a constant boost?
No. The documented derivative term responds to changing error under its configured structure.
Technical References
- Siemens: Advanced Process Library V9.0, March 2017, A5E39147331-AA — section 5.7.3, pages 731–732, standard algorithm and component behavior; section 5.7.6, PIDConL I/Os and TI units. The manufacturer PDF was downloaded and read directly. The rate expression and unit table above are explicitly identified derivations.