This application note describes the use and limitations of DeltaV Simulate CHARMS I/O using MiMiC DeltaV CIOC/VCIOC SIO Driver.

Overview

The DeltaV simulation of a CHARMs I/O Card (CIOC) has a few requirements and limitations.  The first requirement is a DeltaV controller, SD+ or SX only.  Second requirement is either a real CIOC or a virtual CIOC.  The virtual CIOC provided by Emerson is a virtual machine emulating the function of the card and communicates with the physical controller on the DeltaV network.

If either of these requirements cannot be met, simulation must be performed by communicating directly with the DeltaV function blocks.  This direct block method can be used with real controllers or with the DeltaV Simulate/Simulate Pro solution using OPC directly to the block’s SIMULATE value. 

The exchange of data with the DeltaV simulated CIOC is performed via an OPC connection to the CHARM channel’s value.  The data representing the field value is passed to the DeltaV OPC Server where it is sent on to the simulation CIOC (real or virtual) and then brought in to the DeltaV function blocks as I/O_IN.  This value is then processed by the AI Block’s L_TYPE handling to provide the FIELD_VAL.

The following diagram illustrates this data flow.

Analog Input (AI) Function Block Schematic Diagram from DeltaV Books Online

To activate the simulate feature for a CIOC, the card’s property must be altered by checking the Simulate CHARMs option within DeltaV Explorer.  This must be done whether a virtual or real CIOC is commissioned.  The procedure for this can be found in DeltaV’s Book’s Online by searching for Simulating CHARM I/O.

Limitations

Using the DeltaV simulated CIOC available in DeltaV version 11.3 has two limitations in addition to the physical requirements listed above.  The first limitation (as stated in DeltaV Books Online) is that no HART values are simulated by the CIOC and the I/O referencing the digital items will always have bad status.  The second is that all PV data in the DeltaV simulated CIOC is treated as either 0-20mA signals or 4-20mA signals and as such the values passed into the simulated CIOC are limited to 0 to 125 for 0-20mA defined channels, or 0 to 131.25 for 4-20mA channels.  These two limitations in the DeltaV simulated CIOC prevent HART_FIELD_VAL, HART_PV, HART_SV, HART_TV, HART_FV, HART_DV_SLOT[0-3] mappings from receiving the appropriate data into the AI block in DeltaV. 

For example, configure a block in DeltaV (AI) with both OUT and XD scales set to 0-200°C, the L_TYPE set to Direct and the Device Signal Tag of the AI block to HART_FIELD_VAL.   The CHARMs channel is configured as an AI 4-20 mA HART Analog Input.  On the MiMiC configuration side, the CHARMS_INT_IODEF I/O Definition should list this particular channel and the SIOTAG_SUBVALUE should be EU.  The MiMiC model has an AI block with OUT and XD Scales set to 0-200 °C as well.  Once communications is started set the IN value of the MiMiC AI to 120°C and examine the Control Studio of DeltaV.  The value is transmitted perfectly and will continue to until you exceed 131.25.  There the value sent in from MiMiC is high limited by the DeltaV simulated CIOC.  This can also be examined at the DeltaV diagnostics level for the CHARM signal. 

In addition, the Discrete Input CHARM (Pulse Count Input Channel) which can be 16bit unsigned value or 32bit unsigned value which is typically provided to the channel by the MiMiC Simulation software. However, the CHARM Simulate application does not support writing to this channel type at this time. We are working with Emerson Engineering towards a solution that will make it possible to write into Pulse Count Input Channel. 

This procedure can also be examined without MiMiC involved using DeltaV’s CHARMS Simulate program.  Launch the CHARMS Simulate application found in the DeltaV->Engineering program group.   Click on the appropriate CIOC and then double-click on the specific channel.  Any value within the 0-131.25% range will pass through and the block in the DeltaV module will use it directly as 131.25°C.

Possible Workarounds

A work around for the DeltaV simulated CIOC I/O type restriction is intrusive but could be performed using a MiMiC Testbench script.  This would involve setting the online values for the DeltaV block modes to Out of Service, changing the L_TYPE to Indirect, setting the XD_SCALE to 0-100 and finally returning the mode to Auto. 

MiMiC Testbench changing the Analog Input block via OPC

For this method to work set all of the SIOTAG_SUBVALUES to Percent for the HART_FIELD_VAL SIOTags in the I/O Definition.  The MiMiC Testbench workaround would only apply to DeltaV AI blocks whose Device Signal is mapped to HART_FIELD_VAL. The other HART values cannot be simulated using the DeltaV Simulated CIOC.  This workaround is not recommended.  While it will work for the specific case mentioned it is also prone to DeltaV controller and module downloads which will re-enforce the configured settings.

The recommended procedure for simulating the CHARMS on a heavily HART based I/O system is to use the MiMiC CHARMS function block OPC I/O Definition.  This is identical to the standard MiMiC Deltav OPC I/O Definition but allows the simulation models to continue to reference the CHARM I/O locations.

To utilize this workaround, start the CHARMS simulation node with the CHARMS_DVOPC_IODEF (created by the MiMiC DeltaV FHX utility) instead of the CHARMS_INT_IODEF.  This will allow the MiMiC simulation blocks to talk directly to the DeltaV function blocks.