Product category:
Machine Safety Components
News Release from: Pilz Automation Technology | Subject: PSEN range
Edited by the Engineeringtalk Editorial
Team on 16 July 2004
A safe way to help increase machinery
availability
Components used in safety-related control systems must be designed to be fail-safe in order to perform their proper function, but machine builders must also avoid jeopardising machine availability.
Components used within safety-related control systems for machinery, ranging from emergency stop switches to guard switches, light curtains and safety relays or controllers, must be designed to be fail-safe in order to perform their proper function However, machine builders need to take care when specifying safety components to avoid jeopardising machine availability
This article was originally published on Engineeringtalk on 14 Mar 2003 at 8.00am (UK)
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Wear-free machinery safety from magnetic switches
New from Pilz is the PSEN range of noncontact safety switches for gate monitoring applications.
Safety systems are put to the test
Pilz has developed a structured method for inspecting the safety-critical elements of plant and machinery to enable the suitability of the safety measures to be validated.
For example, consider a machine where a guard needs to be opened frequently and an electrosensitive protection device would be inappropriate.
Depending on the design of the control system, each time the guard is opened, the guard switch is activated and the safety relay is tripped.
If the guard switch is of the tongue-operated type, mechanical wear is inevitable.
Similarly, traditional electromechanical safety relays will also wear, though the life expectancy is typically greater than that of the guard switch.
Eventually one of these components will wear so that it ceases to function, though its final act should usually be to render the machine inoperable but safe.
Further reading
Courses cover safety standards and products
Having sold out many of its training courses during the first half of the year, Pilz Automation Technology has now published its course timetable for July to December 2008.
Monitoring relays allow easy setup
Menu-driven parameter setting is easy, quick and error-proof thanks to the plain text display and a turn-and-click encoder.
Configurator upgrade provides new control options
Status is indicated via LEDs on the front of the analogue input module and, if installed, via the PVIS intelligent diagnostics system and a suitable Pilz display.
One way to extend the time before this occurs or to avoid it altogether is to specify noncontact gate switches, such as those from the Pilz PSEN range, and a solid-state safety controller that is not subject to electromechanical wear in the same way as conventional safety relays.
The Pilz PNOZmulti software-configurable modular safety controller uses dual redundant transistors to perform the switching function, with an electromechanical relay monitoring the transistor output and only operating in the event of one or both of the transistors not switching as they should.
Electromechanical wear of these backup relays is therefore virtually nonexistent due to the small number of times they are required to operate, and solid-state transistors do not wear at all, so the safety controller can be considered to be nonwearing.
Because the PSEN guard switches are magnetically operated, they are effectively wear-free as well.
Furthermore, the IP67 housings are designed to withstand wet or dusty environments, and the PBT (polybutylene terephthalate) casing material has low water absorption, is resistant to temperature extremes, and has extremely stable electrical properties.
If conditions are particularly harsh, the switching part of the sensor (with its M12 electrical connector) can be protected by polycarbonate or another non-magnetic material, leaving only the actuator part of the switch exposed.
Should the switch be damaged, perhaps through accidental impact, it can be quickly changed thanks to the use of an M12 Brad Harrison connector - with no need to disturb the wiring unless that has also been damaged.
Pilz offers the PSEN sensors in two compact styles: rectangular units for use where space is at a premium, and cylindrical versions with threaded bodies.
The switching range and tolerated misalignment depend on the model selected, but the maximum switching range is 8mm.
They are also certified as evasion-proof in accordance with VDE0660.
A further advantage of the PSEN switches is that a single device can be used on a guard to meet the requirements of BS EN954-1 Category 4.
If traditional switches were used, two would be required to provide the necessary redundancy; the PSEN switches have dual internal contacts that meet this need.
And for BS EN954-1 Category 4 applications, it should be noted that the combination of a PNOZmulti safety controller and a PSEN switch has BG approval in accordance with EN60 947-5-3.
For Category 2 or Category 3 applications, users have a further option of using a Pilz interface unit to link multiple PSEN switches in series, thereby reducing the number of inputs used on the PNOZmulti controller.
Almost any application requiring more than a handful of safety relays can benefit from a PNOZmulti safety controller, particularly if the safety control system is likely to need to be upgraded or if series machines are being built.
Recent additions to the range of PNOZmulti modules include communications interfaces for linking to Profibus DP, DeviceNet, Interbus, CANopen - and now CC-Link as well.
But most importantly, when a PNOZmulti is used in combination with PSEN noncontact switches, the result is a safety control system that is highly unlikely to ever impair the machine's availability.
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