PULSE-ECHO TECHNOLOGY. THE NEXT GENERATION OF NON-CONTACT SAFETY COMPONENTS
With an established range of magnetic, non-contact safety guarding components, machine safety manufacturer Schmersal could be forgiven for resting on its corporate laurels. However, its R&D department has already developed the next generation based on pulse-echo technology. Managing director Terry Hayward explains.
Ultrasonic pulse-echo technology isn’t new. It is widely used in areas of industry such as Non Destructive Testing for maintenance and inspection. However, when Schmersal applied the principles of pulse-echo technology in the machine safety field, it was not pulse echo technology as we know it.
Schmersal’s "pulse echo" is an inductive coupling between the sensor and the target. A pulse transports electrical energy to the target and the target itself sends a frequency back to the sensor. The frequency is the code and its intensity gives detailed information about the distance between sensor and target and its position in relation to the sensor.
While today’s technology needs a controller relay to monitor a series of connected sensors, Schmersal has integrated the self-monitoring of each sensor, making it possible to connect a series of sensors without the need for a controller relay.
And while many safety products will meet current regulations, Schmersal’s innovative interpretation of pulse echo technology provides a real advantage for customers – the facility to meet regulation and increase the productivity of their machines.
This is also the reason for integrating a powerful and greatly enhanced diagnostic function that identifies faults, but doesn’t necessarily stop the machine immediately.
Electronic diagnostic output is used to indicate an actuated sensor which, if operated close to the limit of its switching distance (for example due to the sagging of a guard door) is detected even before the safety outputs are disabled. The result is in an intermittent pulse on the electronic diagnostic output and visual diagnostic LED.
In a similar way, faults that do not immediately compromise the safe operation of the sensor, for example a crosswire short, are signaled as an advance warning and the machine can, in this case, be run down in a controlled manner. In fact, the function allows the machine to perform a controlled stop that is adjustable by the customer, via the sensor.
With this level of sophistication available it is very easy to define faults that don’t require the machine to stop immediately. And just one uncontrolled stop of an expensive production machine will cost more than the price of the sensors!
One obvious application for this technology is in the type of non-contact, electronic safety circuits used to monitor the position of movable safety guards, where the safety sensor monitors the closed position of hinged, sliding or removable guards with the aid of a coded actuator.
Whilst magnetic sensors provide high levels of safety they can be affected by misalignment caused by frequent access and abuse, and by a build-up of waste material on the magnetic surfaces in applications such as food machinery.
Pulse-echo technology overcomes both shortcomings and offers a wide range of other benefits.
In operation this latest generation of sensor and actuator are an accurately matched pair. As the actuator approaches the sensor, the sensor excites the actuator at a predetermined resonant frequency, and then reads back the actuator oscillation. The sensor evaluates the actuator frequency and its distance to the actuator. Identification of the actuator is interpreted as a closed guard by the safety sensor, and the safety outputs are enabled.
Another key feature that comes with the practical application of pulse-echo technology is that a number of safety sensors can be wired together in series to form a’ daisy chain’ over two hundred metres long. To achieve this, the redundant outputs of the first sensor are wired to the inputs of the second sensor, and so on.
Due to continuous internal function tests and the monitoring of the safety outputs, wiring the safety sensors in series does not affect the control category. Sensors in the chain are self monitoring and the last sensor provides two short-circuit proof PNP outputs for further connection to the safety control circuit. Faults within the chain, including any in the wiring to the safety control monitor, are automatically detected, and the complete chain therefore fulfills Category 4 safety requirements.
This latest generation of pulse-echo sensors fulfill the requirements of EN 60947-5-3 with the classification PDF-M (self-monitoring. Of dual-channel design, they have two short-circuit proof, safe PNP outputs, each of which can switch up to 500 mA.
In addition, as the components are manufactured and approved according to IEC 61508 customers have the added benefit that the tested fault immunities are twice as high in the previous standards.
In summary, Schmersal’s innovative interpretation of pulse-echo technology is already realising its potential in machine safety applications. Superior diagnostics, self-monitoring and advanced fault warning enables controlled machine shut-downs, which in turn produce significant increases in machine efficiency and plant productivity.
Ends
Home | About Us | Portfolio | Approach | Contact Us | Sitemap
16 The Cornhill, Stroud, Gloucestershire GL5 2JT | Tel: +44 (0) 1453 755 551 | Fax: +44 (0) 1453 751 525
Copyright © 2011 Cantillion King Advertising