I/O Blocks > Fieldbus Multiplexed Analog Input (FFMAI_RMT) function block

Fieldbus Multiplexed Analog Input function block application information

Note

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

This function block is for fieldbus applications where the sensor types and functionality of each channel (that is, values for simulate, scaling, filtering, mode, and so on) are the same. The FFMAI_RMT block can optimize the communications on an H1 segment by providing all of the information for the 8 measurements in a single function block.

Use the FFMAI_RMT block when higher density fieldbus transmitters are being used. The Rosemount Model 848T device is a typical example of a higher density fieldbus transmitter. The Model 848T supports up to eight Thermocouples or RTDs. You can configure the eight signals using a combination of AI function blocks and the FFMAI_RMT function block.

The FFMAI_RMT block and AI blocks can both be used within one device. The FFMAI_RMT block can process the eight measurements in the device or be set to custom and have the measurements selected. The AI block can process an individually selected measurement, even one already being processed in the FFMAI_RMT block.

Note that the FFMAI_RMT block uses the same scaling parameters (L_TYPE, XD_SCALE, OUT_SCALE) for all eight inputs. This means that the RTD's or thermocouples must all have the same range in order to use the same FFMAI_RMT block. Also, the same simulation value and mode handling applies to all outputs.

The FFMAI_RMT block does not have built-in standard alarms. Use an alarm block to generate standard alarms for an individual channel from the FFMAI_RMT block. If separate tag names (module names) are required for each channel the Alarm Module Template (found in the DeltaV library Module Templates/Monitoring) can be used.

Alarms generated by a fieldbus device can be viewed in the Event Chronicle and the operator environment. The unit and area assignment for a fieldbus device is determined by the lowest object index in the device. This is typically the primary measurement or output of a fieldbus device. For the Model 848T, this means that the module assigned to the Analog Input function block object index 2400 is the module used to determine the area to which the alarms from the Model 848T will be assigned. If there is no module assigned to this function block, this device will be assigned to the same area as it's controller (which defaults to area A).

Example:

On the Model 848T, you have two temperature measurements with unique ranges and 6 with the same ranges. You could use two AI blocks for the unique ranges and 1 FFMAI_RMT block for the other 6 measurements.

In the above example, suppose each of the six measurements need separate tag indication (TI-1 through TI-6) along with each measurement having a HIHI and a LOLO alarm. This could be accomplished as follows:

  1. Create a module TI-0 using the FFMAI_RMT block. This module communicates with the Model 848T and contains the information from the FFMAI_RMT block.

  2. Create six additional modules named TI-1 through TI-6 using the module template (found in the DeltaV library Module Templates/Monitoring) ALARM. Each of these modules will provide alarming of one of the FFMAI_RMT outputs.

  3. Edit each of the six alarm modules, assigning the external reference parameter to one of the channels in the FFMAI_RMT block. Configure the HIHI and LOLO alarms.