Advanced control blocks > Fuzzy Logic Control (FLC) function block

Fuzzy Logic Control function block parameters

The following table lists the system parameters for the Fuzzy Logic Control function block:

Table: Fuzzy Logic Control function block parameters

Parameter

Units

Description

ABNORM_ACTIVE

None

The indication that a block error condition not selected in BAD_MASK (on the function block level) is True (Active), an error condition (at the module level) not selected in MERROR_MASK is True (Active), or a module status not selected in MSTATUS_MASK is True (Active).

ALARM_HYS

Percent

The amount that the alarm value must return within the alarm limit before the associated active alarm condition clears. ALARM_HYS is limited to 50% of scale.

BAD_ACTIVE

None

The indication that a block error condition selected in BAD_MASK (at the function block level) is True (Active), an error condition (at the module level) selected in MERROR_MASK is True (Active), or a module status selected in MSTATUS_MASK is True (Active).

BAD_MASK

None

The set of active error conditions that triggers a user-defined Bad condition. The user selects a subset of block error (BLOCK_ERR) conditions in the BAD_MASK parameter. When any of these conditions is True, the BAD_ACTIVE parameter becomes True. When any of the BLOCK_ERR conditions not included in BAD_MASK is True, ABNORM_ACTIVE becomes True.

BKCAL_IN

EU of OUT_SCALE

The analog input value and status from another block's BKCAL_OUT output that is used by an upstream block for bumpless transfer.

BKCAL_OUT

EU of PV_SCALE

The value and status required by the BKCAL_IN input of another block to prevent reset windup and to provide bumpless transfer to closed loop control.

BLOCK_ERR

None

The summary of active error conditions associated with the block. The possible block errors for the FLC function block are:

  • Out of Service

  • Readback Failed

  • Output Failure

  • Input Failure/Bad PV

  • Local Override

  • Simulate Active

  • Configuration Error

  • Other Error

BYPASS

None

The Bypass option is intended for slave PID blocks whose PV status is Bad.

When BYPASS is on and the block is in AUTO, CAS, or RCAS mode, the block bypasses the normal control algorithm by transferring the SP value (in percent) to OUT.

When BYPASS is on and the block is in MAN, ROUT, LO, or IMAN mode, SP is calculated from the value of OUT. The value of SP is not affected by any of the SP-PV track... control options. The value of BKCAL_OUT is not affected by the Use PV for BKCAL_OUT control option.

When BYPASS is off, the block operates normally.

To turn BYPASS on or off, select the CONTROL_OPTS Bypass Enable option and set the block to MAN or OOS mode, then change BYPASS to On or Off.

CAS_IN

EU of PV_SCALE

The remote setpoint value from another block.

CONTROL_OPTS

None

Control options allow you to specify control strategy options. The supported control options for the FLC function block are:

  • No OUT limits in Manual

  • Obey SP lim if Cas or RCas

  • Use PV for BKCAL_OUT

  • Track in Manual

  • Track Enable

  • Direct Acting

  • SP-PV Track in LO or IMan

  • SP-PV Track in ROut

  • SP-PV Track in Man

  • Bypass Enable.

DV_HI_ACT

None

The result of alarm detection associated with DV_HI_LIM. If DV_HI_ACT equals True, DV_HI_LIM has been exceeded.

DV_HI_LIM

EU of PV_SCALE

The amount by which PV can deviate above SP before the deviation high alarm is triggered. The magnitude of DV_HI_LIM cannot be greater than the range of PV_SCALE. When this limit is exceeded, DV_HI_ACT is set to True.

DV_LO_ACT

None

The result of alarm detection associated with DV_LO_LIM. If DV_LO_ACT equals True, DV_LO_LIM has been exceeded.

DV_LO_LIM

EU of PV_SCALE

The amount by which PV can deviate below SP before the deviation low alarm is triggered. The magnitude of DV_LO_LIM cannot be greater than the range of PV_SCALE. When this limit is exceeded, DV_LO_ACT is set to True. Note that DV_LO_LIM is a negative number and is compared against PV – SP.

ERROR

EU of PV_SCALE

The difference between SP (setpoint) and PV (process variable).

FF_ENABLE

None

Enables/disables feedforward control.

FF_GAIN

None

The feedfoward gain value. FF_VAL is multiplied by FF_GAIN before it is added to the calculated control output.

FF_SCALE

None

The high and low scale values, engineering units code, and number of digits to the right of the decimal point associated with the feedforward value (FF_VAL).

FF_VAL

EU of FF_SCALE

The feedforward control input value and status.

FIELD_VAL

Percent

The value and status from either the I/O card or the simulated input (if simulation is enabled).

HI_ACT

None

The result of alarm detection associated with HI_LIM. If HI_ACT equals True, HI_LIM has been exceeded.

HI_HI_ACT

None

The result of alarm detection associated with HI_HI_LIM. If HI_HI_ACT equals True, HI_HI_LIM has been exceeded.

HI_HI_LIM

EU of PV_SCALE

The setting for the alarm limit used to detect the high high alarm condition.

HI_LIM

EU of PV_SCALE

The setting for the alarm limit used to detect the high alarm condition.

IN

EU of PV_SCALE

The connection for the PV input from another block.

INSPECT_ACT

None

Indicates if Inspect is enabled and one or more of the limits for the block have been exceeded. The normal value is 0. This parameter is set to 1 if both of the following conditions are true:

  • The Write to Inspect Alarm context menu item was selected from Inspect for this block.

  • With the Current Hour filter selected, Inspect indicates that an abnormal condition exists for Mode, Control, Input, or Variability. (Note that an abnormal condition will only exist for Variability if both the Variability Index and the Standard Deviation have exceeded their defined limits.)

IO_IN

None

Defines the input DST for the I/O channel used for the PV.

IO_OPTS

None

I/O options allow you to select how I/O signals are processed. The available options are:

  • Low cutoff

  • Increase to close

IO_OUT

None

Defines the output DST for the block.

IO_READBACK

None

Defines the Device Signal Tag (DST) for the input channel that provides readback for the value written to the channel defined by IO_OUT.

L_TYPE

None

Linearization type. Determines whether the field value is used directly (Direct), is converted linearly (Indirect), or is converted with the square root (Indirect Square Root).

LO_ACT

None

The result of alarm detection associated with LO_LIM. If LO_ACT equals True, LO_LIM has been exceeded.

LO_LIM

EU of PV_SCALE

The setting for the alarm limit used to detect the low alarm condition.

LO_LO_ACT

None

The result of alarm detection associated with LO_LO_LIM. If LO_LO_ACT equals True, LO_LO_LIM has been exceeded.

LO_LO_LIM

EU of PV_SCALE

The setting for the alarm limit used to detect the low low alarm condition.

LOW_CUT

EU of PV_SCALE

Activated when the Low Cutoff I/O option is enabled (True). When the converted measurement is below the LOW_CUT value, the PV is set to 0.0.

MODE

None

Parameter used to show and set the block operating state.

OUT

EU of OUT_SCALE

The block output value and status.

OUT_HI_LIM

EU of OUT_SCALE

The maximum output value allowed.

OUT_LO_LIM

EU of OUT_SCALE

The minimum output value allowed.

OUT_READBACK

EU of OUT_SCALE

The value and status of the output channel referenced by IO_READBACK.

OUT_SCALE

None

The high and low scale values, engineering units code, and number of digits to the right of the decimal point associated with OUT.

PV

EU of PV_SCALE

The process variable used in block execution and alarm limit detection.

PV_FTIME

Seconds

The time constant of the first-order PV filter.

PV_SCALE

None

The high and low scale values, engineering units code, and number of digits to the right of the decimal point associated with PV.

RCAS_IN

EU of SP_SCALE

The remote analog setpoint value and status. Input provided by either a device or the output of another block.

RCAS_OUT

EU of PV_SCALE

The remote analog setpoint value and status after ramping. Output provided to a device for back calculation and to allow action to be taken under limiting conditions or mode change.

ROUT_IN

EU of OUT_SCALE

Remote output value and status. Input provided by a device to the control block for use as the output (ROut mode).

ROUT_OUT

EU of OUT_SCALE

Remote output value and status. Output provided to a device for back calculation in ROut mode and to allow action to be taken under limiting conditions or mode change.

SF_DELTERR

None

The change-in-error scaling factor. A tuning parameter that converts the change in error (from previous scan) to a normalized value used by the fuzzy logic algorithm.

SF_ERROR

None

The error scaling factor. A tuning parameter that converts the error (PV-SP) to a normalized value used by the fuzzy logic algorithm.

SF_OUTPUT

None

The change-in-output scaling factor. A tuning parameter that converts the normalized output of the fuzzy logic algorithm to an increment of change for OUT.

SHED_OPT

None

Defines action to be taken on remote control device timeout.

SHED_TIME

Seconds

The maximum allowable time between RCAS_IN and ROUT_IN updates. If exceeded, mode shedding takes place.

SIMULATE

Percent

Enables simulation and allows you to enter an input value and status. The SIMULATE value is used by the block only when SIMULATE_IN is not connected.

SIMULATE_IN

Percent

The input connector value and status used by the block instead of the analog measurement when simulation is enabled. If SIMULATE_IN is connected or has a manually entered value, SIMULATE_IN will always override SIMULATE.

Note

When SIMULATE_IN is wired from an input source on the function block diagram, it will always override a manually entered value.

SP

EU of PV_SCALE

The block's setpoint value.

SP_FACTOR

Percent

The minimum setpoint change between scans required to initiate scaling factor adaptation.

SP_FTIME

Seconds

Time constant of the first order SP filter.

SP_HI_LIM

EU of PV_SCALE

The highest SP value allowed.

SP_LO_LIM

EU of PV_SCALE

The lowest SP value allowed.

SP_RATE_DN

EU of PV_SCALE per second

Ramp rate at which downward setpoint changes are acted on in Auto mode (in PV units per second). If the ramp rate is set to 0.0, the setpoint will be used immediately. For control blocks, rate limiting applies only in Auto mode. For output blocks, rate limiting applies in Auto, Cas, and RCas modes.

SP_RATE_UP

EU of PV_SCALE per second

Ramp rate at which upward setpoint changes are acted on in Auto mode (in PV units per second). If the ramp rate is set to 0.0, the setpoint will be used immediately. For control blocks, rate limiting applies only in Auto mode. For output blocks, rate limiting applies in Auto, Cas, and RCas modes.

SP_WRK

EU of PV_SCALE

The working setpoint of the block. It is the result of setpoint limiting and/or setpoint rate-of-change limiting.

STATUS_OPTS

None

Status options allow you to select options for status handling and processing. The supported status options for the FLC function block are:

  • Bad if Limited

  • Uncertain if Limited

  • Target to Manual if Bad IN

  • Use Uncertain as Good

STDEV

EU of OUT_SCALE or EU of PV_SCALE

(reports in percent to Inspect)

The standard deviation of PV. For analog control blocks in AUTO, mean is assumed to be the SP.

STDEV_CAP

EU of OUT_SCALE or EU of PV_SCALE

(reports in percent to Inspect)

The estimated capability standard deviation  (measurement of short term variation). An estimate of the least standard deviation the process could achieve ideally.

STDEV_TIME

Seconds

The time frame over which STDEV and STDEV_CAP are performed. The default value of zero is good for most processes where the scan rate is no more than approximately 10 times faster than the time to steady state.

If the process is relatively much slower, it is recommended that you enter the approximate time it takes for the process to return to steady state after a change. This ensures that the STDEV and STDEV_CAP calculations accurately consider the actual time constant of the process.

TRACK_OPT

None

Allows for a choice for behaviors when the status of TRK_IN_D is Bad. The three options are:

  • Always use value

  • Use last Good value

  • Track if Bad

TRK_IN_D

None

Discrete input that initiates external tracking.

TRK_SCALE

None

The high and low scale values, engineering units code, and number of digits to the right of the decimal point associated with the external tracking value (TRK_VAL).

TRK_VAL

EU of TRK_SCALE

The analog input used in the external tracking function.

Note

Default values and data type information for the parameters are available by expanding the Parameter View window.