Design engineers strive to boost the productivity of the systems and machines they create. By adding greater functionality into a standard sensor, it can be made more intelligent and provided with enhanced two-way communication channels to increase the flow of useful data.
Smart sensors help to manage fast processes or to speed up processes, increasing efficiency and productivity. They reduce the load on a PLC, replacing extensive PLC programming by setting and monitoring a few sensor parameters. Smart sensors also provide flexibility by remote parameter setting and parameter change through the PLC / HMI.
They do this without the need for special cabling and can be easily integrated into the PLC system via IO-Link. A wide selection of gateway cards is available from the major PLC manufacturers to integrate smart sensors into automation networks. By avoiding the need for bespoke cable systems, users can combine standard and smart sensors to create a network utilising high end sensors in critical areas of a plant or machine where they are needed.
Smart sensor functions include condition monitoring for predictive maintenance, flexible remote parameter setting, visualisation for application analysis and quick device replacement with automatic parameter upload/download.
In addition, smart sensors can be equipped with add-on Advanced Functions such as a high-speed counter, a timer, debouncing and false tripping suppression, a speed and acceleration monitor, or a time stamp for security and traceability.
Smart moves
With these functions – core and advanced – we can see that logical loops have been moved from the PLC into the sensor. Real time events can be detected and analysed near to where the action is happening, without waiting for the raw data to be uploaded to the PLC, processed and information extracted before being acted on.
This facility speeds up the management of fast processes, reduces data processing capability limitations on optimum process speeds and enables higher productivity and efficiency.
There are further benefits to the deployment of smart sensors. The computing load on a PLC can be reduced by replacing the central programming with local processing functions. The flexibility and time saving offered by remote parameter setting of the sensor device from the central PLC or HMI makes sense in terms of reduced downtime during process changes. Some costs can even be reduced on an application by application basis, for example an encoder could be economically replaced by a smart sensor such as speed measurement.
Applying intelligence
A guide to the power of smart sensors can best be achieved looking at the advantages of these powerful aids to more efficient and productive operation.
A common scenario in a plant is that the sensors at the heart of a mechanical process are subjected to extreme stress from a harsh industrial environment; vibration, high temperatures, contamination and mechanical shocks are common. As a result, the sensors that provide vital intelligence about the operation may fail and imperil the process.
The operatives have to pinpoint the failed sensor (it might be one of many, or in an inaccessible location), replace it and then configure the replacement using teach-in buttons. The find and replace procedure frequently results in hours of downtime which may be very costly.
On the other hand, a typical smart sensor can display its exact location on an HMI, allowing speedy location and replacement. No manual configuration is needed, as the automation system will recognise a new device and automatically download the application-specific, correct settings.
Personnel do not have to be specifically trained for teaching-in the process; all they have to do is remount and re-connect. Fitting a smart sensor with this capability is also advantageous for OEM machinery suppliers, who also operate a maintenance and spare parts supply service.
The replacement events are precisely recorded and the process is restarted once the new sensor is centrally checked as correct.
Flexible central sensor resetting
To maximise throughput and minimise manufacturing costs, many lines are run on three, eight hour shifts, with different products which may have a variety of shapes and configurations. While 'dumb' sensors can cope with this, they usually have to be manually reset with each change, a process that takes unproductive downtime and is subject to setting errors; the more complex and varied the changes, the more risk of errors and the more need for skilled personnel.
With smart sensors, all settings are centrally held and can be downloaded to the sensors from the PLC. Each product change has a suite of settings to take account of size, weight, colour, shape, material and a myriad other variations. In fact, the increased flexibility of the system allows a production line to be used for a much wider range of product types than would otherwise be possible, and even facilitate shorter runs and smaller batches than would have been possible or economical previously.
Smart monitoring and maintenance
By providing diagnostic data routinely and on interrogation, the smart sensor can transform the cost of condition monitoring and preventative maintenance on a busy production line. It allows production management to assess and tailor maintenance schedules on a plant-wide basis using real time updates of data from areas under most stress. Critical pinch points can be identified and their requirements balanced against plant segments where necessary but less urgent work can be deferred, all backed by full data.
Smart sensors condition monitoring can give unprecedented control of a preventative maintenance programme while permitting informed schedule flexibility.
Real time parts inventory
Allied to preventative maintenance, centralised control also enables centralised inventory and documentation of all sensors, settings and maintenance work. This capability facilitates detailed record keeping for parts lifetime and replacement costs monitoring, for process traceability that allows production history to be accurately recorded.
Each of these core functions can be monitored and controlled through the sensor visualisation software which is uploaded to the PLC via a USB link. The visualisation software can also be used for simple configuration and setting adjustment of advanced functions.
Fieldbus integration
To benefit from smart sensing, an IO-Link compatible with a wide range of fieldbus protocols is essential. While sensor manufacturers are rapidly building enhanced capability from the sensor end, major PLC manufacturers are also tackling the opportunity for more functionality, as are a number of third party suppliers.
The contribution from smart sensors to modern automated manufacturing is being realised more and more widely. Manufacturers like SICK are introducing "smart" variants into their ranges at a rapid rate, realising the potential, not only to simply detect any object, often at high-speeds but also to eliminate production headaches.
David Hannaby is product manager for presence detection at SICK UK
