Relays without relays

Changing the safety market forever is a safety relay that does not require relays. Replacing the electromechanical switching that we all know and love are FETs (Field Effect Transistors).

While FETs themselves are an established technology, introducing them into the highly critical safety arena is something of a taboo. The all electronic PNOZeleg was developed, designed and is manufactured by Pilz of Germany.

As Thomas Peter, a design engineer at Pilz explains, having the safety knowledge, experience, and access to modern technologies allowed Pilz to realise the many benefits of an all electronic ‘relay’.

‘We had to build up a lot of experience before using FET technology — the technique had to, in our experience, be mature. The FETs must also be the ‘state of the art’ before being used in safety applications.’

‘However the technique is well known from our experience with the PSS (programmable safety systems). PSS development was the base of PNOZelog design and provided the knowledge to design safety FET outputs. The main issue is the testing of the outputs to make the outputs safe. From there the development took us two years.’ In a sense bringing PLC technology into the realm of relays.

In the same footprint

‘The challenges were; to be competitive to the ‘standard’ PNOZ, to bring some new features and benefits, and to bring all this into small housing.’

Each device in the PNOZelog range combines the merits of the classic electromechanical PNOZ with those of modern electronics: wear and tear free, maintenance-free, long service life and high reliability.

The semiconductor technology enables, amongst other things, the universal integration of input devices that use contacts, for example, emergency stop relays and semiconductor sensors, e.g. light curtains.

The self-diagnostic output, together with the LEDs provides detailed information on the status of inputs and outputs. This means that wiring faults, shorts across the input contacts and incorrect input types can be determined. All of this is on an identical foot print to its electromechanical predecessor.

Application areas for the PNOZelog are similar to those of electromechanical safety relays. The respective selection is carried out according to the different, technical requirements of the application. For example, electromechanical safety relays are particularly suitable for switching large loads, while on the other hand, electronic relays are more suited for switching medium and small loads and for applications requiring frequent switching cycles.

The output is, however, limited to 2A. The PNOZelog range covers all safety applications from category 2 up to and including category 4 in accordance with EN 954-1. The PNOZe1p is the first relay in the range and its multi-functional features mean it can be used for all applications from emergency stopping to light curtain monitoring. Being multi-functional, logistics costs can be reduced to a minimum. PNOZelog will be the same price as the earlier PNOZ relays.

On the web