What is dynamic Instantiation

[Guruprasad K V]

This is regarding multiple or dynamic instantiation.

1.I a field device supports a multiple instantiation how i will come to know?
2. Whether my host system should be capable of showing it to me through DD files?

3. What you mean by capability level with respect to a fieldbus device?
please explain in detail

thanks in advance?

[smr]

Item 1:
Look at the CFF file for the device. If a function block has a BLOCK_INDEX parameter filled out, the host will automatically have space reserved for the block when the device is loaded (static instance). If the function block doesn’t have a BLOCK_INDEX then you will have to add it with the host system (dynamic instance).
For an example: SMAR LD302 is mostly dynamic blocks, Foxboro IDP10 is static


Item 2:
Check the literature for your DCS they should have a list of compatible devices. Just because a device is compatible, use custom blocks with caution as the host may not be able to instantiate them.

[Mike ONeill]

JBerge says Oct 5th 2005 (sorry, couldn't work out how to reference a previous thread!)

As far as blocks I think there are three kinds of devices in the market today:
1. A fixed set of a few blocks that cannot be changed at all
2. A small set of fixed blocks available as default plus a fixed set of additional blocks that can also be activated if a license code is loaded into each device
3. A large memory and a large library of different block types (say 17 kinds) to chose from until the memory is full (say 20 blocks).

I think that by definition only item 3 is actually true block insantiation/deletion (using action object) - it is clearly very "dynamic". Item 2 is perhaps kind of "static" in the sense that the number of each type of block is fixed.

Having a block library and instantiation in a device has some benefits.
1. The device can support both standard and enhanced blocks. For example, a standard PID as well as PID enhanced with additional functionality
2. The device can have blocks for additional functioality such as computation, linearization, selection, limiting, timers, logic, and alarms etc. allowing you to compute and control in the field to get local indication of inferred measurements etc.
3. The device can have multiple instances of a block type, for example if a device has 2, 3, or 8 channels it can have several PID blocks for control.

Obviously you never need 17 different types of blocks, each application may only use a few of those but these library contains many because across the many industries there are so many different kinds of applications. Similarly you will never need to load as many as 20 blocks, but some blocks require more memory than others.

The ability to select either standard and enhanced blocks has benefits for interchangeability. For example, for simple loops you can use the standard PID block and AI block. This makes it possible to replace that transmitter in the future with a device from just about any manufacturer since most support the standard PID and AI. If you use the enhanced PID, or enhanced AI, you can only replace with identical device because enhanced blocks are proprietary (meaning enhanced blocks from different suppliers are not the same - but it is still possible to see and configure all parameters thanks to EDDL). That is, using devices having (dynamically) instantiable function blocks you can use standard blocks in most applications, and use enhanced blocks only when the application really calls for such unique functionality.

All field devices from SMAR have instantiable function blocks since almost 10 years ago I believe. Initially there were some integration "challanges" becuase not all hosts support instantiation. However, all of that is now overcome as all leading hosts now support block instantiation and other hosts simply accept the devices with their default block sets (without being able to instantiate more or delete).

There are some differences in how hosts implement block instantiation. One other host I have worked with requires you to select the blocks you need when the device is first "created" in the tool. While the SMAR SYSTEM302 simply allows you to drag and drop block on the fly as you build your control strategy.

Instanitiable function blocks is of course also used in HSE devices such as the controller and flow computer etc. Here the library of different blocks is much bigger than for a field device, and the memory is of course also much bigger. When you buy DCS the block instantiation within the controllers themselves is a must.