Factory automation: closing the 'last metre'

Paul Boughton
Daniel Heining explains how a smart interface can close the 'last metre' gap in factory automation.

The IO-Link interface provides an 'intelligent' method for closing the 'last metre' in the IO (input-output) field level of factory automation and reduces costs as well as staff-hours for engineering, installation and maintenance.

In process and factory automation, tremendous progress has been made in the past decades, as can be seen when comparing today's sensors and actuators with those from the early days of automation.[Page Break]

Automating repetitive process

The original idea was to use electromagnetic, hydraulic or pneumatic devices to automate repetitive processes. Then came freely programmable logic controllers (PLCs), more electronic advances and the evolution of intelligent interfaces, resulting in development of a huge number of highly integrated and powerful sensors and actuators.

Today, simple binary switches have evolved into intelligent communicative sensors.

In this context, 'intelligent' describes sensor or actuator devices that have, on the one hand, the ability to recognise and report defined conditions, and on the other hand, the capability to be diagnosed during error conditions and configured in the field.

However, these bi-directionally communicating devices need simple interfaces to communicate with the PLCs. Moreover, communication for calibrating the sensor/actuator devices is needed in most cases. In the past, many device manufacturers developed their own propriety communication solutions for calibration.

This 'last meter' gap in factory automation can be closed with a smart interface based on the IO-Link specification, which is defined by the IO-Link Consortium. IO-Link provides a simple and easy-to-use interface for intelligent sensor or actuator devices, as well as for more simple analogue and digital sensors and actuators. They are connected via a master on a field bus to a PLC or a parameter server.

Here the IO-Link serves not as a bus system, but as a point-to-point connection with the objective of ensuring downward compatibility and integration into all bus systems in factory and process automation. That means standardised M12, M8 and M5 connectors with three-wire cables up to 20meters in length can be used. IO-Link uses the IEC 61131-2 standardised 24V DC signal.[Page Break]

Dispersed manufacturing locations

IO-Link is an international standard, which means it is likely to supersede most proprietary solutions in the future. In addition to the benefits in the actual application area within a fabric, a positive impact is that there will be a uniform 'sensor language' at locally dispersed manufacturing locations.

IO-Link communication between master and device uses a signal that can be processed with a standard UART (today's standard for many microcontrollers).

Because IO-Link is a point-to-point connection, communication via the IO-Link telegram is much easier compared to bus communication. Communication conflicts and the long cycle times needed to recover from conflicts do not occur with IO-Link.

IO-Link offers three communication rates: COM1, COM2 and COM3. The COM1 data rate is 4.8 kBaud. COM 2 has a data rate of 38.4 kBaud, which is the most common speed, and the COM3 rate is 230.4 kBaud.[Page Break]


With IO-Link, a world standard is already in place. It is system and field-bus independent and can be integrated into all types of sensors and actuators.

The installation of IO-Link devices is cost-neutral. Traditional (three-wire) cables, including typical connection methods, can be used.

Using IO-Link, devices can be parameterised during operation. Central data from a parameter storage server enable immediate parameterisation.

Complex local programming can be a thing of the past, which is especially advantageous for very small devices with difficult access. With IO-Link, the down times for programming are significantly reduced (up to 90 per cent) and the quality of the production equipment is much higher.

IO-Link also offers a wide range of diagnostics for the sensor or actuator device itself. For example, pollution, abrasion, temperature, pressure and voltage levels can be monitored and remote maintenance can be performed very easily. Previously for common devices, this was only possible with proprietary solutions and it typically required significant additional cabling work. With IO-Link, down times caused by preventive maintenance or sudden breakdown of the equipment can be reduced by 80 per cent and problems can be detected much faster.[Page Break]


Within recent years, a trend of smaller yet more powerful sensors and actuators can be seen in process and factory automation. With IO-Link technology, it is easy to miniaturize products based on these new devices using universally standardized and 'intelligent' methods.

When using common proprietary solutions, especially those with high requirements for field bus integrity, to design sensors with bi-directional communication and other 'intelligent' features, significantly more printed circuit board space is typically required and costs can be considerably higher. The first IO-Link devices were assembled primarily using discreet components.

Today highly integrated microchips (cable driver ICs and microcontrollers) in very small packages of 3x5mm or 4x4mm or in wafer-level chip-scale package solutions (WL-CSP; see Fig. 1), with dimensions as small as 2.5x2.5mm, enable powerful and cost-saving integration of IO-Link into the smallest intelligent sensors and actuators. IC product families with the same pin count and size but different functionality can support effective and easy platform designs for IO-Link applications.

The integration of IO-Link is relative easy, as demonstrated by the example of a block schematic for an IO-Link sensor in Fig. 2. The IO-Link chip manufacturer and software provider very often support the integration as well.

The standardised IO-Link interface enables the first production of intelligent, cost-saving and field-bus-independent sensors and actuators at the lowest field level. It completes the 'last metre' between the field bus and sensors/actuators, enabling direct bi-directional communication between the control station and the sensor or actuator devices.[Page Break]

Key summary

Cost effective miniaturization with ZIOL2401 and ZIOL2211 in WL-CSP - an IO-Link standard compliant high voltage line driver IC:

- Space Saving - the small QFN24 4x4 mm and the very small wafer-level chip scale package (WL-CSP) of 2.5x2.5 mm is perfect for the miniaturization of sensors and actuators

- Short Time-To-Market - ZMDI provides excellent application support and evaluation kits

- Flexible - ZMDI'S IO-LINK product family for master and device applications

- Excellent EMC Performance - integrated slew-rate control

- High Driver Capability - up to 820 mA (dual channel) and 410 mA (single channel)

- Specific - IO-Link specific WURQ detection.

Enter √ at www.engineerlive.com/ede

Daniel Heining is with Zentrum Mikroelektronik Dresden AG, Dresden Germany. www.zmdi.com

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