CDL is also a Centre of Technical Excellence for Mitsubishi Automation. When Pilz launched the PNOZmulti software-configurable modular safety controller and the family of communications modules that go with it, CDL was understandably keen to try using the CC-Link module to connect a PNOZmulti safety controller with a Mitsubishi Q-series high-end modular PLC. The results were impressive.
A PNOZmulti m1p base unit with a PNOZ mc7p CC-Link communications module was connected with a Pilz PITestop emergency stop switch and a Pilz PSEN 1.1p-10 non-contact safety switch. Using a standard CC-Link cable plugged into the CC-Link module on the PNOZmulti, the safety equipment was connected to the Mitsubishi Q-series PLC via a Mitsubishi QJ61BT11 CC-Link network card. This CC-Link card was configured as a master; the module on the PNOZmulti operates as a slave.
Configuration of the PNOZmulti was performed using the PNOZmulti Configurator software running on a laptop PC, with the configuration data transferred to the PNOZmulti via a serial cable (no safety-related data can be transferred via the CC-Link cable). Mitsubishi's GX Developer software was used to write ladder code for the Q-series PLC and the QJ61BT11 CC-Link network card.
In addition to the hardware described above, a touchscreen HMI (human-machine interface) was connected to the Q-series PLC and configured with E Designer such that the safety data from the PNOZmulti could be monitored. In other words, the status of the safety circuit could be viewed on-screen in real-time.
Furthermore, the HMI was configured to incorporate a reset switch so that a reset signal could be initiated at the HMI and sent via the Q-series PLC and CC-Link fieldbus to the PNOZmulti. Alternatively, a conventional reset switch could have been connected directly to the PLC and its status monitored via the HMI concurrently with the safety-related data from the PNOZmulti.
This exercise clearly demonstrates how easy it is to incorporate a Pilz PNOZmulti safety controller within an automation system based on a Mitsubishi Q-series PLC and a CC-Link industrial fieldbus. Being able to monitor the safety functions so accurately on a machine's HMI would enable the causes of stoppages to be identified far more quickly so that downtime can be minimised. In addition, almost no extra wiring would be required, as the CC-Link cable would already be in place around the machine to serve the conventional I/O. Of course, once the data about the status of the safety components is available within the PLC, the machine builder is not limited to just displaying it on an HMI; almost anything could be done with it to help minimise downtime, log events, or feed into a machine availability analysis system, for example.
For those who are concerned about the apparent mixing of safety and non-safety data, they can rest assured that there is absolutely no way that the PNOZmulti configuration can be altered by data sent via the CC-Link cable, and the monitoring of safety status data is effectively no different from hard-wiring a PLC to the auxiliary contacts on conventional electromechanical safety relays.
Matt Wills, the Technical Applications Engineer at CDL who ran the trials, comments: "We wondered how easy it would be to link the PNOZmulti with the Q-series, and the answer was 'very'. In fact it worked first time and we were astonished at how simple it was to access data that can make such a big difference to a plant's uptime."
Lee Clarke, the Sales Manager at CDL, adds: "We believe there is a significant niche market for this type of arrangement. Anyone building a medium-complexity machine with a Mitsubishi Q-series PLC could save money anyway by using a PNOZmulti rather than safety relays, and then you effectively get the diagnostics for free! Of course the same result can also be achieved using an old A series PLC or a current FX PLC. But to try and get this level of monitoring using traditional hard-wiring would simply be unfeasible for most applications."
In addition to the CC-Link communications module, Pilz also offers versions for use with Profibus DP, DeviceNet, Interbus or CANopen. Similar remote monitoring of safety-related data can therefore be achieved with automation systems using these other fieldbus protocols.