In considering options for the low end PLC there were numerous possible solutions. Following a competitive tender the PLC system chosen to meet the requirement was the Omron CJ1 series. This was a relatively new product to the market at the time and offered good functionality in a small modular form factor. The CPU43H and CPU12M processors were selected to meet Diamonds needs and a selection of preferred I/O module types were defined, these included Ethernet, temperature, isolated relay and digital I/O. this was expanded later to include 12 bit analogue.
Communication to EPICS was realized over a serial connection using the Omron specific protocol. This was implemented using the ORNL communications structure under EPICS and provides functions for writing and reading to single register or blocks of register, where registers can be data memory or I/O location, writing to direct I/O was disabled. Again the common EPICS records are supported.
The Diamond control system design means that the interface to the technical systems was defined by technical area and geographical location. Hence, the low end PLC applications on the Diamond Storage ring alone would require twenty four systems for vacuum valve control and protection, and twenty four systems for the storage ring vessel protection. This is lead to the decision behind the concept of the standard modular device design.
From the various applications sited for low-end PLCs three types of products were identified. These were; the Machine Protection Marshaling, the Four and Six Valve Vacuum Control Crates and the Universal Thermal Protection Crate.
The two types of valve control crates functionality cover the requirements for vacuum protection within the Linac, booster synchrotron, transfer lines, storage ring, photon front ends and photon beamlines. In the total 30 Four Valve vacuum Crates were used. The Machine Protection Crate capabilities match the requirement for critical temperature interlocking and water flows for the booster synchrotron and storage ring.