Our aim is to produce a PLC program that is reliable and easy to understand which reports the state of the machine so that integration of the program via a laptop is not required. We would discuss with the customer at the design stage the operation of the machine and produce a sequence in the form of a spreadsheet. This would form the design documentation. The key features of our software are.

Step Sequence

The first step before writing any software is to meet with the customer and discuss the operation of the machine. From these discussions a spreadsheet is constructed where the machines function is broken down into steps with each action allocated a step number. Diagnostics and interlocks are included in the sheet and are allocated to every step. This makes the machine functions easier for all levels of personnel to understand and because of the use of diagnostic messages for every action and movement, there is no need for maintenance staff to look at or change the ladder logic.

Diagnostic Messages

We use interlocks in both automatic and manual, in automatic we monitor every sensor on the machine and if it changes state at the wrong time we display a Diagnostic message and drop the machine out of automatic. In manual we use the interlocks to tell the operator how to get the machine back into the correct state ready for automatic, so with operator having very little experience he can still re-sequence the machine. Also if the operator tries to operate an invalid or dangerous function the diagnostic message will tell why this function is not possible .When the machine stops there is always a message displaying the reason why. Typical diagnostic messages consist of a message number, description & I/O number.

Interlocks

Interlocks in both automatic and manual are generated. In automatic every sensor on the machine is monitored. If a sensor changes state at the wrong time we display a Diagnostic message and drop the machine out of automatic. In manual we use the interlocks to tell the operator how to get the machine back into the correct state ready for automatic This enables a very inexperienced operator to re-sequence the machine. Also if the operator tries to operate an invalid or dangerous function the diagnostic message will tell why this function is not possible. . • PLC Experience We have over 20 years experience in written PLC software for the following PLC’s ;- Siemens S5 and S7 series, Allen Bradley SLC, PLC5, MicroLogix and ControlLogix, Honeywell IPC 300 and 620, Modicon 984/Quantum, Mitsubishi Q/A series.

Bus Systems

Bus systems make building a system easy providing that the designer stays within the limit of the Bus systems capability. We have had many call outs from customers that have installed bus networks that are too large and the software issues they are experiencing are hardware issues caused by too many nodes or cable length.

At IRS we will consider using Bus systems but always check that it’s the most cost effective and suitable solution for the client first.