IO-Link: Fast-becoming a safety interface


David Dearden of Euchner – one of the world’s first machinery safety specialists to adopt the common IO-Link platform and launch a range of compatible devices – looks at its growing popularity, especially within the machinery safety industry, and how its adoption can help machine builders and end-users protect personnel and equipment, at the same time maintaining efficient processes and preventative maintenance programmes.

IO-Link is a standardised IO technology for transmitting point-to-point data to different fieldbus systems or PLCs. It readily lets you control and operate devices, communicate diagnostic data and present parameter settings to and from field devices, including safety interlocks, using vendor-agnostic communication standards.

Functional safety communications over fieldbus technology has been around for over 20 years, but it is only recently that the widespread adoption of safety over communications channels has become a go-to. The recent increased adoption rate has been supported by the growth in the popularity of the safety PLC and associated components. Generally, the safety fieldbus connects remote and decentralised safety I/O with the local(ish) devices then hard-wired into these local points. With IO-Link, this becomes even easier and creates a host of valuable data in the process.

Even for products that do not contain an embedded IO-Link connection, there are solutions for retrofitting. For example, Euchner’s IO-Link Gateways (the GWY-CB and ESM-CB) can be added to any of their BR-type devices and serve as the interface between the safety interlock and the IO-Link master on the PLC or Fieldbus.

An Euchner IO-Link Gateway and up to 20 safety devices using them can transmit both cyclical (process) data, which the system continuously supplies to the IO-Link master, and acyclical (device/event) data, which can be polled specifically as needed. Process data includes door position status, actuator limit range, safety outputs state, general error messages, guard locking state, locking element state, and escape release state, with device/event data including sensor version/order number, number of devices in a chain, current/stored diagnostic code, code of current/blocked/taught-in actuator, voltage, temperature, number of switching cycles and LOG files.

But with the push towards Industry 4.0, which both produces and requires significant amounts of data, one question being asked is what the retrieved data is being used for and how to analyse that data.

As mentioned above, by using IO-Link compatible devices or gateways, end users can learn exactly what every device on a processing line is doing at all times. But additionally, by using the device data, for example, users can see when parameters change or predict when a unit is coming towards the end of its useful life, therefore affording engineers the time to schedule planned maintenance or, with the version/order number to hand in the data, simply remove the ageing device and install in a new one.

Putting process efficiencies to one side, more importantly, there’s personnel safety to consider, especially as we see IO-Link technology being adopted into our safety solutions. In traditional safety systems, devices would often be wired in series, so when one switch was opened, it would drop out a safety relay at the end of the chain, and everything would appear acceptable. However, determining which safety switch was open or closed was more difficult and often resulted in additional wiring going back to individual inputs on the PLC. And while the safety relays would themselves do some monitoring and fault finding, it was very easy for faults to be masked or the systems to be manipulated, e.g. the removal of a device from a series chain or opening downstream devices to remove faults on upstream devices. By using Euchner’s BR series-wiring technology with an IO-Link interface, it becomes very easy to bring all this information back to the control system and give real-time alarms when issues do occur.

With manipulation in mind, data including the number of devices in the chain, the taught-in switch/actuator codes, the codes of blocked actuators, etc., can also be retrieved, all of which can, if using IO-Link, be incorporated in the machine control system to protect the operator.

Now, with standards such as EN ISO 14119:2013 being the driving force for minimising the defeating of safety interlocks, the prevention of fault masking is very much a priority. This means those still operating older-style, safety-related control systems on their machines or designing-in series-connected switches may want to reflect on the new technology and latest standards.


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