FB_TrackingIntegrator (Function Block)

Integrates the input error signal with back-calculation anti-windup.

Extends FB_Integrator by accepting an external comparator input, typically the Residual of an FB_Clamp block, to unwind the integrator gradually when the output is saturated. The residual is scaled by 1 / Tt and subtracted from the integrator input each cycle.

A typical wiring pattern:

fbI.Input           := fbP.Output; // Standard form. Use fError for parallel form.
fbI.ComparatorInput := fbClamp.Residual;
fbI.Run();
fbClamp.Input := fbP.Output + fbI.Output + fbD.Output;
fbClamp.Run();

Note

Set Maximum before Minimum to ensure the clamp guard applies correctly.

Use FB_init to set tTn and tTt at declaration time.

Extends: FB_Integrator

Properties

ComparatorInput

Type: LREAL

Gets or sets the comparator input.

This is typically the Residual of an FB_Clamp block placed after the PID summation, passed directly without negation. The block subtracts the scaled residual from the integrator input internally to unwind the integrator when the output is saturated.

A positive value indicates the unsaturated sum exceeded the clamp maximum. A negative value indicates it fell below the clamp minimum.

Tt

Type: LTIME

Gets or sets the tracking time constant (Tt).

Controls how quickly the integrator unwinds after saturation. A typical starting value is SQRT(Tn \* Td). Setting it to LTIME#0 disables the back-calculation correction entirely.

Methods

FB_init

Inputs

Name	Type	Description
`bInitRetains`	`BOOL`	if TRUE, the retain variables are initialized (warm start / cold start)
`bInCopyCode`	`BOOL`	if TRUE, the instance afterwards gets moved into the copy code (online change)
`tTn`	`LTIME`	Integral action time. LTIME#0 disables integration.
`tTt`	`LTIME`	Tracking time constant (Tt). A typical starting value is SQRT(Tn * Td).

Run

Advances the tracking integrator by one time step.

Note

Must be called once per cycle on a single PLC task. If Tn is LTIME#0 the output is set to zero. If Tt is LTIME#0 the back-calculation correction is disabled.