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A flexible approach to small automation tasks

Written by Fraser Cowie, Product Manager- Interface

There are many industrial automation applications where the complexity of a Programmable Logic Controller, or PLC, is not necessary, and these applications lend themselves to the use of a ‘Smart Relay’ or ‘Smart Controller’ instead.

However, even smart relays have their limitations and drawbacks. These may be a lack of analogue options, difficult to use and costly software, or internal relays that have a poor switching capability or that when additional modules are required, they just take up too much space!

There are a huge variety of smart relays on the market today, but none that have really addressed these issues. That is until Phoenix Contact came up with a unique and slightly ‘outside of the box’ solution, known as PLC Logic.

Range examples at RS include these, plus additional interface modules (171-9689) (711-4715) .

The PLC Logic relay system is the first to combine logic, interface and field connection levels in a single solution. This means that you can switch and control your I/O using a single compact system. You can combine the PLC logic module with the corresponding relay and analogue modules as required. This modular structure opens up a multitude of applications.

So how does it all work?

First, you pick a suitable logic module – there are two different base logic modules: the SAM or Stand-Alone Module and the BM or Base Module. When using the SAM module, you are restricted to a maximum of 16 I/O, but with the BM module, you can extend the system to 48 I/O. Each logic module has eight 24V DC inputs, two of which can be configured as analogue (0 ... 10 V).

You then choose and connect a further eight channels, via the PLC interface side, and each of these channels can be configured as an input or an output, as digital or as analogue. They can even be used as a PT100 or PT1000 temperature transmitter.

This gives you 16 I/O and the flexibility to configure 10 of the channels. All of this in a product that is only 50mm wide!

As the system uses Phoenix Contact's PLC relay range you get all their associated benefits: such as their pluggability, for fast swap out, the choice of electro-mechanical or solid-state relays, bridging of the connections and screw or push-in connection technology.

How is the PLC logic programmed?

It is programmed using Phoenix Contact's LOGIC+ software.

This is an intuitive software which allows you to program your PLC Logic controller quickly and easily. Download the software for free, along with any specific function blocks that the application may require, from the Phoenix Contact web site.

You can program in Ladder or use the more flexible and powerful function block programming.

Logic+ software is intuitive and this easy handling helps when it comes to configuration and startup. Any programs created can be simulated offline via your PC and tested online during operation.

How do I connect to my PLC Logic controller?

Most smart relay applications tend to be stand-alone, but with the PLC logic, you have the choice to do that or integrate it into an upstream device. This is achieved via an optional Fieldbus gateway, which are available with all common bus networks.

This enables bi-directional communication with a higher-level controller, as well as diagnostics and visualisation. The base controller has Modbus RTU on board, so can be used directly with any PLC or HMI with this capability, to configure and view the application.

A third option of visualisation is achieved wirelessly via a Bluetooth adapter. This is used in conjunction with a free app (from the Apple app store) that can be installed on your smartphone or tablet.

Once the app is installed, you can use it to adjust the parameters of the logic modules. The app can be used for operation and monitoring, as it can access all program variables. The Bluetooth connection enables efficient monitoring of multiple logic modules, with just one visualisation device.

In summary, PLC Logic is easy to use, it's modular and has free software. It is unique in its construction and its flexibility and can be programmed and adapted via your laptop, tablet or mobile phone!

It truly is your ‘flexible friend’ when it comes to small automation tasks!

For more information, contact Fraser Cowie on 07584 514963 or email


Phoenix Contact is a world leader for electronic components, systems and solutions in the field of electrical engineering, electronics and automation. The family-owned company currently employs 17400 people worldwide and achieved a total revenue of 2.38 billion euro in 2018. The headquarters are in Blomberg, Germany. The Phoenix Contact Group consists of nine companies and 55 sales companies. The worldwide presence is also supported by 30 agencies in Europe and overseas.

29 Jun 2020, 14:20