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Finder 38.51 interface relays showing DIN rail mounting |
Processes, machine control and automation are becoming ever more complex, driven by the insatiable demand for more and more at ever lower cost, and by the increasing demands of world-wide legislation on safety, the environment, and similar issues. As the price of silicon has fallen, industrial controllers have now become commodity items that offer more than enough computing and logic processing power for most applications. One considerable drawback, however, is that they generally come with fixed, and inflexible, interface devices.
Limitations
The inflexibility of standardised industrial controller outputs exist simply because it would be far too costly for an industrial controller to be universally fitted with oversized interface devices in order to handle just the few cases when that might be needed. The same would apply to the universal provision of the highest levels of isolation, or of socket replaceable switching elements as standard. But it is equally unviable for the industrial controller manufacturer to customise an interface package to suit a specific application.
So, cost pressure and standardisation almost always dictates that the output configuration is limited to a single pole Normally Open contact, open collector transistor or triac - usually of limited current handling capability and often offering only a low degree of isolation. This may well be incompatible with the circuit or load requirements of a number of the outputs.
Interface relay modules
To address this challenge, Finder has developed a range of interface relay modules to provide a bridge between the controller and the real world. If required, different versions can be selected channel by channel to match the particular load requirements, without over- or under-specification.
All the modules feature a replaceable relay element – offering quick and easy maintenance for those applications where exceptional longevity would have otherwise posed a problem for the non-replaceable output of a conventional controller – and an identification label facility to aid commissioning and maintenance.
Multi-way jumper links provide for easy and cost saving common circuit inter-connection between adjacent interface relay modules. Interface relays are characteristically fully-featured, ready-built assemblies comprising the relay, the socket and appropriate coil indication and coil suppression – either built into the socket or provided through the deployment of one of Finder’s wide range of plug-in modules.
By identifying a relatively limited number of relay/socket/module combinations, and by giving the combination a single part number, Finder has provided the design engineer with access to a range of ideally matched components that are ready assembled, ready to accept wiring, and frequently with the additional benefits of savings in inventory and purchasing time and costs.
The range
The Finder range of interface relay modules comprises seven series of products, each with their own characteristic key features. The following factors need to be taken into account when specifying a part:
Popular choice
The 38 series is Finder’s most contemporary, and arguably its most versatile, line of interface relay modules, and continuous development results in the regular addition of new versions with more features and options that are able to address a wider range of applications. The 38 series offers both electromechanical (EMR) and solid state relays (SSR), and most versions are available in a choice of either screw or screwless termination styles.
Essentially this series addresses the mainstream market for single- and two-pole devices, with the overriding aim of keeping the module width to a minimum to achieve the highest mounting density on industry standard 35mm rail.
The single-pole devices in general are just 6.2mm wide, whilst the two-pole and higher rated solid state relay versions occupy a 14mm width. Both versions set the standard for compactness in products of this type.
SSR devices have been introduced where much faster switching and virtual limitless life is an imperative. Single pole SSR versions are available in both the 6.2mm and the 14mm sizes, with options for switching AC or DC loads at current levels between 0.1A and 5A.
Targeting problematic applications are both EMR and SSR versions with “suppressed coil/input leakage current” circuitry. Certain industries and applications suffer from high leakage current level in the coil circuits when the circuit is supposed to be Off – which can cause real problems. In particular long cable runs can give rise to these induced currents or older style triac outputs of PLCs can permit troublesome leakage current: these special “suppressed current” types provide an effective countermeasure.
Another innovation is the super slim 6.2mm with an inbuilt multifunction timer, available in both EMR and SSR form. This can be particularly appreciated when the local adjustment of a time delay might be required, or where a delay is later found to be necessary and reprogramming the PLC is not a short or long term option.
Conclusion
Interface relay modules such as the Finder 38 series offer a flexible means of meeting the often conflicting needs of today’s demanding industrial automation environment – providing a simple ready-assembled solution for popular relay/socket combinations, with a comprehensive range of advanced operational features.
