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Murrelektronik is an internationally operating, family-owned company in the automation technology industry with over 2,700 employees. At the core of the business is the idea of decentralisation as Murrelektronik works to optimise connections between the control cabinet level and the sensor-actuator level in machines and systems.
Are relays still prevalent or are alternative technologies replacing them?
Baier: A relays is an old and cheap piece of technology which has had little innovation for a number of years. The relay market has therefore stagnated in recent times and it could even be said that there is a downward trend in the specification of relays for industrial applications. An increasing number of fieldbus modules are being used in the course of automation which are powerful enough in modern times to be able to switch larger currents themselves. This means that the classic relay switching element has moved from the control cabinet out into the field to the automation products. Nevertheless, there are still some applications for the control cabinet, but in the case of these, Murrelektronik recommends that customers use optocoupler modules. Optocouplers have a number of advantages compared to relays:
- Long life time
- Mechanically wear-free
- No contact bounce
- Short switching times
- Low inrush current
- Shock and vibration insensitive
Why is there such a variety in price for relays?
Baier: The price difference between relays mainly comes down to the quality of the products themselves. Murrelektronik is not a relay manufacturer and so it buys relays from manufacturers before building them into products and solutions for their customers. The current trend in the relay market – as it is in many other markets – is that customers want cheaper products in order to keep costs to a minimum for the job at hand. This therefore means that Murrelektronik needs to buy cheaper components in order to help its customers meet strict budget requirements. As a relay is a relatively cheap piece of technology, customers often choose relays as the switching component and so Murrelektronik offers a wide variety of differently priced relays.
On the other hand, if a customer has more room to manoeuvre in terms of budget, then Murrelektronik again recommends spending a little more and making use of an optocoupler. Optocouplers offer the advantages mentioned previously which result in an overall decrease in downtime in comparison to solutions that utilise relays.
What are some important points to consider when specifying relays?
Baier: When specifying a relay module, there are some crucial points that must be observed for professional use. These include the nominal voltage of the coil, contact material, contact load, switching times, and mechanical properties such as vibration shock load and ambient temperature. The contact material is particularly important for the lifetime of the relay. Depending on whether inductive, capacitive or resistive loads are to be switched, a customer must select a specific contact load for their relay.
The contact material of standard relays is cheap, usually consisting of silver alloys such as silver nickel, silver tin oxide or silver cadmium. Silver alloy is specified for applications with larger loads. Relays with hard gold plating must be selected for the switching of small loads. They are adapted to these applications and guarantee reliable signal transmission over a long period of time. Customers tend to know which contact material they need, but Murrelektronik is able to assist with any issues that a customer may face.
What are some key ways to prolong the life of a relay?
Baier: Relays are exposed to mechanical stress. The contacts wear with each switching operation and in the long run they will wear off. They have to be replaced before they stop switching completely. This can be a complicated job since there are usually large numbers of relays installed in a cabinet, placed side by side. Considering the limited space in a cabinet, disconnecting the wires, exchanging the relay modules and reconnecting the wires requires considerable installation time. Murrelektronik therefore offers its MIRO 6.2 Pluggable which features a snap-in and ejection mechanism that connects the relay module to the socket. If a relay module has to be replaced it can simply be ejected and a new relay module can be snapped in. These time savings add up to a considerable amount, even with smaller systems.
On the other hand, optocouplers operate without mechanical wearing components. Murrelektronik’s MIRO optocoupler combines a high switching current of up to 6A with a high switching frequency of up to 500 Hz, with no need for any secondary-side auxiliary power. If you already have a control cabinet with Murrelektronik modules, the relay modules connected to them can be easily replaced by the optocoupler module during regular maintenance work. The plug base wiring can remain the same. At a width of only 6.2 mm, plug bases can be arranged in a series; they don’t take up very much space in the control cabinet.
What does the future hold for relays?
Baier: A relay continues to be a simple, yet effective piece of technology. Despite being on the market for 20-25 years, there has been little innovation within the relay market. Murrelektronik believes that relays will continue to stay the same. One trend is that the switching element will leave cabinets for the field with fieldbus modules because they can now switch the current directly, making the switching element in the cabinet redundant. Overall, Murrelektronik recommends optocouplers in favour of conventional relays as they offer greater savings by reducing the amount of production downtime.
Bastian Baier is Senior Product Manager for Interfaces at Murrelektronik and has been with the company for over 15 years.
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