The Analog Input (AI) function block accesses a single analog measurement value and status from an I/O channel. You can configure the channel type for each I/O channel to be the transmitter's 4 to 20 mA signal or the digitally communicated primary or non-primary variable from a HART transmitter.
The AI function block supports block alarming, signal scaling, signal filtering, signal status calculation, mode control, and simulation.
In Automatic mode, the block's output parameter (OUT) reflects the process variable (PV) value and status. In Manual mode, OUT can be set manually.
To support testing, you can enable simulation. This allows the measurement value and status to be supplied manually or from another block through the SIMULATE_IN input.
AI Function Block With Simulation Enabled
SIMULATE_IN is the simulated value from another block that is used by the Analog Input function block when simulation is enabled.
OUT is the block output value and status.
The following diagram shows the internal components of the Analog Input function block. The parameters may vary slightly for extended blocks.
Analog Input Function Block Schematic Diagram
The following diagram shows the timed response of the Analog Input function block:
Analog Input Function Block Timing Diagram
You select the manner of processing the analog measurement value by configuring the I/O selection, signal conversion, and filtering parameters.
I/O Selection
When you configure the Analog Input function block, you select the I/O channel associated with an analog measurement by configuring the Device Signal Tag (DST) of the IO_IN parameter. You select the Device Tag and the parameter the AI block accesses on that channel.
When the channel type is configured as Analog Input Channel, the only selectable channel parameter for IO_IN is:
FIELD_VAL_PCT – the 4 to 20 mA signal, in percent of range. You should configure XD_SCALE as 0 – 100%.
When the channel type is configured as HART Analog Input Channel, you can select one of the following parameters:
HART_FIELD_VAL – the 4 to 20 mA signal of the HART transmitter, in the range and engineering units defined by XD_SCALE or OUT_SCALE, depending on L_TYPE. HART Status is applied. The range and units are automatically sent to the transmitter to set its range and units. The specified units must be supported by the transmitter.
HART_PV – the Primary Variable of a HART transmitter, in engineering units. This value is read digitally.
HART_SV – the Secondary Variable of a HART transmitter, in engineering units. This value is read digitally.
HART_TV – the Tertiary Variable of a HART transmitter, in engineering units. This value is read digitally.
HART_FV – the Fourth Variable of a HART transmitter, in engineering units. This value is read digitally.
For more information on the DeltaV implementation of HART communications, refer to the HART Devices and the DeltaV System topic.
You can configure anti-aliasing filtering, NAMUR limit detection, and overrange/underrange detection for the channel parameters. For information on these capabilities, refer to the I/O Configuration topic.
Simulation
To support testing, you can enable simulation. This allows the measurement value and status to be supplied manually or from another block.
During configuration, decide whether you want the simulated value/status to be entered manually during operation or you will use a value/status from another block for the simulated value/status.
When the value is entered manually:
Note Use the SIMULATE parameter to enter values manually and make sure SIMULATE_IN is not connected. If SIMULATE_IN is connected or a value is entered manually into SIMULATE_IN, the SIMULATE_IN value overrides the SIMULATE value.
When the value/status from another block is used:
Note Do not enter a value for the SIMULATE_IN parameter. If you do and the status of SIMULATE_IN is not Bad: NotConnected, the manually entered value for SIMULATE_IN overrides any value you enter in SIMULATE.
Signal Conversion
You choose direct, indirect, or indirect square root signal conversion with the linearization type parameter (L_TYPE). Refer to the HART Devices and the DeltaV System topic for information on signal conversion for HART devices.
Select one of the following signal conditioning options:
Direct signal conditioning – simply passes through the accessed channel input value (or the simulated value when simulation is enabled). For direct conversion, OUT_SCALE is written to XD_SCALE in controller-resident blocks.
Indirect signal conditioning – linearly converts the accessed channel input value (or the simulated value when simulation is enabled) from its specified range (XD_SCALE) to the range and units of the PV and OUT parameters (OUT_SCALE).
Indirect square root signal conditioning – converts the accessed channel input value (or the simulated value when simulation is enabled) from its specified range (XD_SCALE) by taking the square root of the value and scaling it to the range and units of the PV and OUT parameters (OUT_SCALE). If the input value is less than zero, signal conditioning stops and the input value is passed directly to the output.
Direct Independent signal conditioning – simply passes through the accessed channel input values (or the simulated value when simulation is enabled). OUT_SCALE is independent of XD_SCALE.
You view the accessed value (in percent of XD_SCALE) through the FIELD_VAL parameter.
When the converted input value is below the limit specified by the LOW_CUT parameter and the Low Cutoff I/O option (IO_OPTS) is enabled (True), a value of zero is used for the converted value (PV). This option can be useful with zero-based measurement devices, such as flowmeters.
Note You can set the I/O option in Manual or Out of Service mode only.
Filtering
You apply filtering to the converted value (PV) by specifying the filter time constant (in seconds) in the PV_FTIME parameter. When you specify a value of zero, no filtering is applied.
Block Errors
The following conditions are reported in the BLOCK_ERR parameter:
Block configuration error – The block is wired to a HART channel and the HART device indicates that the function block's units are not compatible with the device. In this case, the Out of Service block error is also set.
Simulate active – Simulation is enabled and the block is using a simulated value in its execution.
Input failure/process variable has Bad status – The source of the block's process variable is bad. Indicates a hardware failure, a non-existent Device Signal Tag (DST), or a Bad status on the SIMULATE parameter.
Out of Service – The block is in Out of Service (OOS) mode.
The AI function block supports the following modes:
Initialization Manual (IMan)
Out of Service (OOS)
Manual (Man)
Automatic (Auto)
The OOS, Man and Auto modes can be selected by the user during configuration.
The target mode of a block can be restricted to one or more of the supported modes.
For complete descriptions of the supported modes, refer to the Function Block Modes topic.
Block alarm detection is based on the OUT value. You can configure the alarm limits of the following standard alarms:
This block supports conditional alarming. Enabling conditional alarming makes additional parameters available for this block. For more information about conditional alarming and for a description of the additional parameters, refer to the topic Conditional Alarming.
NAMUR Alarming
If the high high and low low alarm limits are changed to a value outside the range defined in OUT_SCALE and the PV exceeds the alarm limits, the PV status high and low limits, respectively, are set. In this case, the associated active alarm parameters indicate that the measurement is overrange/underrange. If these alarm limits are set more than 3% outside the span of OUT, the active alarm condition is set after the overrange condition elapsed time exceeds four seconds.
Normally, the status of the measurement value provided by the analog input card reflects the operating condition of the I/O card, and processing condition.
If you configure the block to use a HART Analog Input Channel, you can select which conditions associated with a HART channel impact the status of the block. Refer to the HART Devices and the DeltaV System topic for information on these selections.
The channel input status to the analog input block is set high- or low-limited by the input card if the channel value exceeds the overrange and underrange limits and if the IO_IN parameter is selected as HART_FIELD_VAL or FIELD_VAL_PCT. you may change the default overrange and underrange limits independently on each input channel. Refer to the Overrange and Underrange Detection topic for more information. If the channel value is outside a range of -20.12 to 116.6%, the channel input status is set to BAD by the input card.
The STATUS_OPTS parameter allows you to choose how the PV and OUT status are determined. There are three AI block status options:
Note You can set the status option in Out of Service mode only.
The analog input block PV status normally reflects the channel input status. However, if the channel status is limited, then PV status is set to Uncertain limited or Bad Limited if you choose the status option Uncertain if Limited and Bad if limited respectively
In Auto mode, OUT normally reflects the value and status quality of the PV. However, if the PV status is Good but the PV value is more than -10% to 110% outside the span defined by PV_SCALE, then the OUT status is change to Uncertain.
In Man mode, the OUT status limit indication is set to constant and the OUT status is Good unless you have selected the Uncertain in Man mode status option.
In Out of Service mode, the OUT status is set to BAD.
NAMUR Limit Detection
If NAMUR limit detection is enabled for I/O channels (by setting the NAMUR_ENA parameter to True when configuring the AI card) and the IO_IN type is FIELD_VAL_PCT or HART_FIELD_VAL, the PV status of the input is set to Bad if the signal level is above 21 mA or below 3.6 mA for more than four seconds. The Bad status is cleared when the signal returns within these limits. You can use this feature when the transmitter is designed to flag a device failure by setting its current signal outside the normal 4-20 mA range.
Note The actual mode of a control block will automatically go to Man if the input has a Bad status. Thus, NAMUR limit detection should not be enabled if a measurement is used in control unless this behavior (control going to manual ) is an appropriate action on limit detection.
The following table lists the system parameters for the Analog Input function block:
Analog Input 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). |
| ACK_OPTION* | None | Enables or disables automatic acknowledgment of fieldbus device alarms associated with Fuji, Endress&Hauser, and Honeywell devices. The default value is 0 (disabled). Set the value of this parameter to 65535 to enable the parameter before downloading the AI block. (0 = disabled (the default); 65535 = enabled). |
| ALARM_HYS | Percent or Percent of PV_SCALE |
The amount the alarm value must return within the alarm limit before the associated active alarm condition clears. ALARM_HYS is limited to 50% of scale. |
| ALERT_KEY* | 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. |
| ALM_SEL | None | Used to select the process alarm conditions that cause the OUT_D parameter to be True (Active). |
| 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. |
| BLOCK_ERR | None | The
summary of active error
conditions associated
with the block. The
block errors for the
Analog Input function
block:
|
| CHANNEL* | 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. |
| FIELD_VAL | Percent | The value and status from the I/O card or from the simulated input when 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 | The setting for the alarm limit used to detect the high high alarm condition. |
| HI_HI_PRI* | None | To ensure proper operation, do not alter the default value unless instructed to do so by technical support. |
| HI_LIM | EU of PV | The setting for the alarm limit used to detect the high alarm condition. |
| HI_PRI* | None | To ensure proper operation, do not alter the default value unless instructed to do so by technical support. |
| 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 by Inspect and is
set to 1 only if the
following conditions are
true:
|
| IO_IN** | None | Defines the input DST for the I/O channel used for the PV. |
| IO_OPTS | None | The
supported I/O option for
the Analog Input
function block is:
Refer to I/O options for more information. |
| L_TYPE | None | Linearization type. Determines whether the field value is used directly (Direct or Direct Independent), 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 | 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 | The setting for the alarm limit used to detect the low low alarm condition. |
| LO_LO_PRI* | None | To ensure proper operation, do not alter the default value unless instructed to do so by technical support. |
| LO_PRI* | None | To ensure proper operation, do not alter the default value unless instructed to do so by technical support. |
| LOW_CUT | EU of PV | 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 request and show the source of the output used by the block. |
| OUT | EU of OUT_SCALE | The primary value and status calculated by the block in Auto mode. OUT can be set manually in Man mode. |
| OUT_D | None | The discrete output value and status. |
| 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 OUT | The process variable used in block execution and alarm limit detection. |
| PV_FTIME | Seconds | The time constant of the first-order PV filter. It is the time required for a 63% change in the FIELD_VAL to be reflected in the PV. |
| SIMULATE | EU of XD_SCALE | 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** | EU of XD_SCALE | 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 always
overrides SIMULATE.
Note When SIMULATE_IN is wired from an input source on the function block diagram, it always overrides a manually entered value. |
| ST_REV* | 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 | None | Use
status
options to set how
status is handled and
processed. When the
block is assigned to a
controller, the
available status options
are:
When the block is assigned to a fieldbus device, the available options are:
|
| STDEV | EU of OUT_SCALE or EU of PV_SCALE | The standard deviation of PV. For analog control blocks in AUTO, mean is assumed to be the SP. Refer to Loop Performance Calculations for more details on how this parameter is calculated. |
| 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. Refer to Loop Performance Calculations for more details on how this parameter is calculated. |
| STDEV_TIME** | Seconds
(reports in percent to Inspect) |
The
timeframe 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* | None | Used to identify groupings of blocks. This data is not checked or processed by the block. |
| SUBSTITUTE_IN* | Determined by source or EU of PV_SCALE | If there is a problem communicating with the field device and SUBSTITUTE_IN has a non-Bad status, the controller passes the SUBSTITUTE_IN value through to the output parameter(s) of the shadow 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. |
* These parameters are only visible in one or more of the extended versions of this block.
** 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.
The method you use to configure an Analog Input function block and its associated input channel depends on whether the measurement is from a traditional 4 to 20 mA transmitter or a HART transmitter.
Traditional 4 to 20 mA Transmitter
When you are using a measurement from a traditional 4 to 20 mA transmitter, you configure the associated input channel and Analog Input function block as follows:
Channel Type: Analog Input Channel
Analog Input block IO_IN parameter: FIELD_VAL_PCT
Analog Input block L_TYPE parameter: Select Indirect when the measurement is linearly related to the 4 to 20 mA signal. Select Indirect Square Root when this is a flow measurement using differential pressure and when square root extraction is not performed in the transmitter.
Analog Input block XD_SCALE parameter: Set the range and engineering units to 0 – 100%.
Analog Input block OUT_SCALE parameter: Set the range and engineering units to the values that correspond to the transmitter's 4 to 20 mA signal.
HART Transmitter
Refer to the HART Devices and the DeltaV System topic for additional information. When you are using a measurement from a HART transmitter connected to an analog input channel, you configure the associated input channel and Analog Input function block as follows:
Channel Type: HART Analog Input Channel
Analog Input block IO_IN parameter: The analog input card passes the percent or engineering unit measurement of the primary variable (or the engineering unit value of a non-primary variable) based on the selection of IO_IN. The following table lists the IO_IN selections:
Analog Input Function Block IO_IN Parameter Selections for HART Transmitters
Variable |
Access |
IO_IN Selection |
|
Engineering Units |
Percent |
||
| Primary | 4 to 20 mA | HART_FIELD_VAL | FIELD_VAL_PCT |
| Primary | Digital | HART_PV | N/A |
| Secondary | Digital | HART_SV | N/A |
| Tertiary | Digital | HART_TV | N/A |
| 4th | Digital | HART_FV | N/A |
Note When
a channel value is accessed
digitally, the update rate of
the analog input channel value
depends on the number of
channels on the associated I/O
card that are configured as
HART Analog Input channels.
When all eight channels are
configured as HART channels,
each channel is updated every
six seconds. When there is
only one such channel on the
card, the channel is updated
approximately every 0.5
seconds.
Therefore, when you are using
the primary measurement in
closed loop control of a fast
or moderately fast process, we
recommend that you define
IO_IN to access the 4 to 20 mA
signal. You can use the
digital value when you require
the improved accuracy and
range of the digital value for
a monitoring application or
for a control application
involving a slow process.
Analog Input block L_TYPE parameter: Select Direct to use an I/O parameter that provides its signal in the engineering units that you want for the block output.
Select Indirect when you want to convert the I/O parameter value to engineering units based on the input and output ranges defined by XD_SCALE and OUT_SCALE.
Select Indirect Square Root when the block I/O parameter value represents a flow measurement made using differential pressure, and when square root extraction is not performed by the transmitter.
Select Direct Independent for RTD and Thermocouple inputs to allow OUT_SCALE to be set to a narrower range than XD_SCALE.
Analog Input block OUT_SCALE parameter: Set the desired ranges and engineering units for the PV and OUT parameters to correspond to the XD_SCALE range and the L_TYPE conversion.
Analog Input block XD_SCALE parameter: When the IO_IN channel type is FIELD_VALUE_PCT, configure XD_SCALE as 0 – 100%. When any other channel type is selected, configure XD_SCALE to match the range and units of the transmitter.
Note When
you select HART_FIELD_VAL as
the channel type, the range
and units defined by the
XD_SCALE or the OUT_SCALE
parameter are written to the
transmitter. This assumes that
the specified engineering
units are supported by the
transmitter. If the
transmitter units you specify
are not supported by the
transmitter, the channel
status is set to Bad.
When the range or units of the
transmitter's primary variable
for your application is
different than that defined in
OUT_SCALE, set L_TYPE to
Indirect and define the input
and output ranges in XD_SCALE
and OUT_SCALE.
Application Example: Traditional Temperature Transmitter
Assume a temperature transmitter is calibrated for a range of 200 to 400°F and is used in a monitor (non-control) application in which accuracy is important. You configure the associated input channel and Analog Input function block as follows.
Analog Input Function Block Configuration Example for a Traditional Temperature Transmitter
Configuration Setting |
Traditional 4 to 20 mA Transmitter |
HART Transmitter |
| Channel Type | Analog Input | HART Analog Input |
| AI Block IO_IN Parameter | FIELD_VAL_PCT | HART_PV |
| L_TYPE | Indirect | Direct |
| XD_SCALE | 0 to 100% | 200 to 400°F |
| OUT_SCALE | 200 to 400°F | 200 to 400°F |
The following figure is the function block diagram for this example.
Analog Input Function Block Diagram Example for a Traditional Temperature Transmitter
Application Example: Traditional Pressure Transmitter
Assume the level of a small open tank is to be measured using a pressure tap near the bottom of the tank. Based on the tap location and the density of the material in the tank, the pressure transmitter is calibrated at 0 to 200 in. H2O for a tank level of 0 to 10 ft. The level measurement is used to control the tank level. You configure the associated input channel and Analog Input function block as follows.
Analog Input Function Block Configuration Example for a Traditional Pressure Transmitter
Configuration Setting |
Traditional 4 to 20 mA Transmitter |
HART Transmitter |
| Channel Type | Analog Input | HART Analog Input |
| AI Block IO_IN Parameter | FIELD_VAL_PCT | HART_FIELD_VAL |
| L_TYPE | Indirect | Indirect |
| XD_SCALE | 0 to 100% | 0 to 200 in.H20 |
| OUT_SCALE | 0 to 10 ft. | 0 to 10 ft. |
The following figure is the function block diagram for this example.
Analog Input Function Block Diagram Example for a Traditional Pressure Transmitter
Application Example: Traditional Differential Pressure Transmitter
Assume the liquid flow in a line is to be measured using the differential pressure across an orifice plate in the line. Based on the orifice specification sheet, the differential pressure transmitter was calibrated for 0 to 20 in. H20 for a flow of 0 to 800 gal/min. The flow measurement is used in a flow control loop. If the transmitter was not set up to take the square root of the differential pressure, you configure the associated input channel and Analog Input function block as follows.
Analog Input Function Block Configuration Example for a Traditional Differential Pressure Transmitter
Configuration Setting |
Traditional 4 to 20 mA Transmitter |
HART Transmitter |
| Channel Type | Analog Input | HART Analog Input |
| AI Block IO_IN Parameter | FIELD_VAL_PCT | HART_FIELD_VAL |
| L_TYPE | Indirect Square Root | Indirect Square Root |
| XD_SCALE | 0 to 100% | 0 to 20 in.H20 |
| OUT_SCALE | 0 to 800 gal/min | 0 to 800 gal/min |
The function block diagram for this example is identical to the diagram for the previous example.
The analog input card contains hardware filtering that limits the frequency of the input signal seen by the digital-to-analog (D/A) converter to about 3 Hz. In addition, you can define software filtering to be applied at the analog card when you configure the analog input channel properties (FILTER channel parameter). This feature prevents aliasing of the signal if the module execution rate is set slower than twice the highest frequency component of the input signal.
The default setting for the software filter is Filter Disabled. If an input signal is relatively free of process noise and is contained in a module executing at fast to moderate rates, you might not need to apply additional software filtering at the card.
If you choose to modify the filter, you see a selection of filter time constants in the Named State list. If you follow the module execution rate guideline (period of control) that is shown in parentheses next to the filter time constant you select, no aliasing occurs, even if the signal has significant noise.
Note If you modify the filter on an input channel, you might need to retune any control block that uses the channel for its controller variable.