I/O Blocks > Analog Output (AO) function block

Analog Output function block parameters

The following table lists the system parameters for the Analog Output function block:

Table: Analog Output function block system 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) or the indication that 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).

ALERT_KEY(1)

None

A user-assigned identification number reported in alarm messages from the block that allows HMI applications to sort and filter alarms and events. Set this parameter for each function block to indicate the physical unit the function block is associated with. This information can be used in the host for sorting alarms, and so on.

BAD_ACTIVE

None

The indication that a block error condition selected in BAD_MASK (at the function block level) is True (Active) or the indication that 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 are True, the BAD_ACTIVE parameter becomes True. When any of the BLOCK_ERR conditions that are not included in BAD_MASK are True, ABNORM_ACTIVE becomes True.

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 block errors for the Analog Output block are:

  • Out of Service

  • Readback Failed

  • Output Failure

  • Input Failure/Bad PV

  • Simulate Active

  • Configuration Error

CAS_IN

EU of PV_SCALE

The remote SP value from another function block.

CHANNEL(1)

None

The number of the logical hardware channel that is connected to the I/O block. It defines the transducer to be used going to or from the physical world.

FSTATE_TIME(1)

Seconds

The time in seconds from detection of fault of the output block remote setpoint to the output action of the block output if the condition still exists.

FSTATE_VAL(1)

EU of PV

The preset analog SP value to use when fault occurs. Ignored if the I/O option Fault State to value is false.

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 only if both of the following conditions are true:

  • The Write To Inspect Alarm context menu item has been 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 exists for Variability only if both the Variability Index and the Standard Deviation have exceeded their defined limits.)

IO_OPTS

None

I/O options determine how the I/O signals are processed. If the block is assigned to a controller, the available options are:

  • Use PV for BKCAL_OUT

  • Increase to close

  • SP-PV Track in LO or IMan

  • SP-PV Track in Man

If the block is assigned to a fieldbus device, the available options are:

  • Use PV for BKCAL_OUT

  • Tgt to Man if Fault St Act

  • Use Fault st val on restart

  • Increase to close

  • SP-PV Track in LO or IMan

  • SP-PV Track in Man

IO_OUT(2)

None

Defines the output DST for the block.

IO_READBACK(2)

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.

MODE

None

Parameter used to request and show the source of the setpoint and/or output used by the block.

OUT

Percent

The primary value and status calculated by the block in Auto mode. OUT can be set manually in Man mode.

PV

EU of PV_SCALE

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

PV_SCALE

None

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

RCAS_IN

EU of SP_SCALE

The remote analog setpoint value and status. Input provided by 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.

READBACK

Percent

The percent value of the measured or implied actuator position associated with the OUT value.

SHED_OPT

None

Defines action to be taken on remote control device time out.

SHED_TIME(2)

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. When simulation is enabled, the block does not attempt to write to the hardware.

SP

EU of PV_SCALE

The block's setpoint value.

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, then the setpoint is used immediately. For control blocks, rate limiting applies only in Auto. 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, then the setpoint is used immediately. For control blocks, rate limiting applies only in Auto. For output blocks, rate limiting applies in Auto, Cas, and RCas modes.

SP_WRK(2)

EU of PV_SCALE

The working setpoint of the block. It is the result of setpoint rate-of-change limiting. The value is converted to percent to obtain the block's OUT value.

ST_REV(1)

None

The revision level of the static data associated with the function block. To support tracking changes in static parameter fields, the associated block's static revision parameter is incremented each time a static parameter field value is changed. Also, the associated block's static revision parameter is incremented if a static parameter field is written but the value is not changed.

STATUS_OPTS(1)

None

Status options determine how status is handled and processed. The only available option is:

  • Propagate Fault Backward

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 and STDEV_CAP. This parameter is functional in the FFAO_RMT block. In the standard block, the parameter is visible but only serves as a placeholder.

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. This parameter is functional in the FFAO_RMT block. In the standard block, the parameter is visible but only serves as a placeholder.

STDEV_TIME(2)

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.

STRATEGY(1)

None

Used to identify groupings of blocks. This data is not checked or processed by the block.

XD_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 channel input value.

(1) These parameters are only visible in one or more of the extended versions of this block.
(2) These parameters may not be visible in certain extended versions of the block.
Note

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

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