Tuesday, 22 July 2008

Omron PLC Dummy I/O

Using dummy IO modules on an Omron PLC with a 'virtual backplane' (i.e. a CJ1M for example) is a good way to keep addresses used for varying projects the same, and adding extra I/O when needed for extra functions, without upsetting the existing addressing structure.

For example, suppose you have a machine process that requires three 16 way input cards, and three 16 way output cards. These could of course occupy address space 000, 001, 002, 003, 004 and 005 without problem. But then suppose their is a need for a similar process with some limited functionality that only required two input and output modules. Once again, these could occupy addresses 000, 001, 002 and 003, but these now conflict with the earlier allocation and could cause confusion when wiring and producing documentation, because where 'Solenoid 1' connected to output 003.00 previously, it now connects to output 002.00.

A solution to this is to insert some 'dummy' I/O modules into the I/O table to act as placeholders and to allow the addressing to remain consistent between the two processes. ('Dummy' I/O modules are not actual physical modules, but rather they are virtual.)

The picture below show an I/O table with some dummy modules inserted:

Dummy I/O modules of varying sizes can be added by selecting them from the Basic IO menu of the 'Add unit' dropdown menu.


Anonymous said...

i am a plc newbie,thanks for you blog


Andy Patten said...

Thanks, I hope you found some of the information useful.