Dynamic signals in machine safety means cost savings to machine builders 
(19/05/2008)
It has been common practice in the machine building industry to use a two channel switching method in order to achieve a high safety performance. This means that two different supply sources are generated from a control unit such as a safety relay and these sources are connected to a field device and fed back to the control unit for monitoring.
The control unit will monitor for symptoms such as short circuit or if one supply source is removed i.e. an open circuit as well as the safety device itself.
In order to enable the machine builder to ensure the highest level of safety is applied to, each safety device must be connected to its own monitoring control unit.
Therefore if a machine has four Emergency Stop Buttons and four Safety Switches fitted to the doors, the machine would need eight safety relays in order to meet the safety level of Category 4/ SIL3. As a result, this is an expensive method, not just because the amount of safety devices being used but because of the wiring and installation time involved.
Jokab Safety designed a system, which means that the machine builder can enjoy the benefit of series connecting all safety devices and being able to meet the highest safety requirement.
The unique safety system, called the Vital Solution, consists of a control unit the Vital 1 which is the same size as a standard safety relay. This control device has two functions; one is to provide two safety outputs in the form of two, twin channel, volt free contacts to switch the main power circuit when a safety device in the field has been activated.
The second is to produce a coded signal from a monitoring circuit. This coded signal is sent to the field safety device and is reassigned using a tiny interface. At the same time the signal is distributed out again. When the coded signal is sent to a second safety device it is converted back to the original form sent from the Vital 1. The interface circuit is incorporated in to safety devices such as the Eden non contact sensors, Spot Safety Light Beams and Smile Emergency Stop Buttons, however in order to assist engineers when they need to include other manufacturers safety devices on to the system there is a whole range of external interfaces which are able to monitor volt free contacts from components such as mechanical switches and Emergency Stop units together with interfaces for safety mats and bumpers.
These interfaces are called Tina units and can used in conjunction with safety devices which already exist on the machine. By giving engineers the advantage of not having to change the existing field devices means they can still be familiar with the safety system.
Vital 1 can support up to 30 field devices connect in series, within a 500m cable run.
The Vital system means that manufacturers can enjoy a cost reducing functional safety system without the compromise of reducing the safety level. At component level, machine manufacturers can enjoy a saving of up to 30%. The added benefit of an increase of productivity during installation means that the cost savings can go even higher.
An added feature of the Vital system is when a single channel fault occurs on a conventional system, the normal action is to replace the safety relay or power it off and on. The single channel fault is still there and appears when the device which is in the circuit is activated. This is not possible with the Vital system because of the unique use of coded signal monitoring and therefore no loss of safety at all.
There is no programming or addressing involved during installation therefore no Plc experience is necessary when designing a safety system.
Related categories: Building management system Enclosures Industrial Industrial circuit protection Machine Safety Monitoring equipment Panelboards and consumer units Relays and Timers
