The Project

The Palletiser machine at smiths flour mill had ran the original PLC control unit for 20+ years, the original PLC was a Siemens Simatic S5-135U (922 CPU) which included a high speed input card along with standard input and output cards the system used a basic HMI which included various push buttons and a non-colour LCD screen. The reason for the upgrade was that the original hardware was obsolete, the HMI was causing problems and no spares were available as it was such an old unit, if the HMI was to break down the machine would be rendered useless. Smiths originally wanted only the HMI to be replaced and the PLC to remain intact however the PLC and HMI used outdated multiplexing digital communication, this caused problems because no up to date HMIs still use this method of communication. This meant that the PLC and HMI had to be upgraded together. The new PLC was to be a Siemens S7-300 series and the HMI was to be upgraded to a SCADA system based on a 15" touch screen panel PC opposed to push buttons and and a small screen displaying minimal information.

This project was unique as most projects are usually enhancements to a machine however the machine functioned as it was required to from the word go. The task in hand was to upgrade the existing hardware to something more modern and supportable. The code from the original PLC needed to be implemented using the new PLC although this wasn't a straight forward job, Siemens provide an S5 to S7 code converter, this was a tremendous help to the project but there was areas that the converter couldn't work with which meant some portions of the software had to be re-written from scratch. Re-writing the original software wasn't a simple task as the S5 software is written in a DOS application and is close to machine code meaning the step between S5 and S7 software is very large, S7 uses ladder logic and function blocks, deciphering this old code and re-writing it in a new format can be a very difficult task without extended knowledge of both S5 and S7.

The new hardware was taken to site, the old hardware was powered down, the old wires (all 360 of them) were removed from the old and refitted to new I/O cards, the old S5 PLC was then removed, and the new S7 PLC was fitted and the I/O cards were plugged in, a 24v power supply was connected to the new PLC. The whole panel was then powered up for initial testing, a fault alarm was sounding however the machine was reset and everything seemed good, a pallet and bags were put into the machine for a dry run, the process was a success!

The SCADA was to be installed by smiths themselves at a later date although Vaalto provided the hardware and software. The upgraded control system should see the machine running smoothly for years to come, however if any support is required we will always be around to help out.