The PushPull approach

Jan 23, 2013 | Cables & connectors

Kevin Canham from HARTING takes a look at the benefits offered by today’s PushPull connectors for industrial applications

The internationally standardised PushPull connector design combines ease of insertion with a simple and reliable locking mechanism and, in many cases, a protection to IP65 or IP67. In recent years, however, the concept has evolved to cover connectors that can integrate data, signal and power interfaces as well as fibre-optic transmission.

These benefits are embodied in the HARTING PushPull Signal connector, which ensures the reliable transmission of power, signals and data in all performance ranges via one uniform connector system. In its Han PushPull Variant 14, it is the preferred connector for decentralised automation in the field for data transmission and power supply according to the guidelines of the PROFIBUS User Organisation and the Automatisierungsinitiative deutscher Automobilhersteller (AIDA – Automation Initiative of German Automobile Manufacturers).

The connectors are finding application in the manufacturing robots used in highly automated automotive welding and assembly lines.

Because of the variety of sensing and imaging processes involved, there is a need for individual signal and data communication processes as well as the defined standards aimed at the data area. In addition to power and standard data communications, the transmission of analogue, digital, bus and low-voltage signals also has to be accommodated for control purposes.

The HARTING PushPull Signal connector transmits nominal currents of 5A on ten contacts with wire cross-sections up to 0.75mm². To ensure EMC interference immunity, the contact inserts are fully shielded as RJ45 data connectors, and it is possible to connect shielded cables. The PushPull locking ensures reliable and intuitive connector insertion, with an audible signal indicating proper locking.

PushPull Signal connectors can also handle hybrid applications – for example, part of the mating face can be used to transmit power while other contacts are available for communication. In addition to the Variant 14, these are also available in Variant 4 as defined by IEC 61076-6-107.

Simple wire termination in the field is key to these applications. The PushPull Signal connector is already pre-assembled when delivered, and it is installed by inserting individual crimp contacts into the pre-assembled insulation inserts. Simply pressing down on the insulation insert causes it to lock into its final position and fix the crimp contacts in place. Users can easily correct any mistakes that show up after the insulation insert has been installed.

The use of factory-prefabricated cable assemblies, available in different lengths, reduces the processing effort in the field.

Fibre-optic connectors

A wealth of industrial applications require large amounts of data to be transmitted safely and quickly over long distances. In many modern systems – including large-scale manufacturing facilities, conveyor-belt systems in luggage or parcel sorting operations, wind power plants with mast heights

of 120m or 140m, and tunnel control systems – the technically feasible limit of 100m when using copper cable is often reached. As a result, fibre-optic cable (FOC) is used for data transfer in these applications, while copper cables are used only for internal wiring.

Transceivers are used as the interface between fibre-optic cable and the copper world. However, to be able to reliably fulfil their task, these electro-optical converters are frequently encased to ensure a reliable connection process and prevent the use of unsuitable transceivers.

The disadvantages of current solutions include the high costs associated with the available electro-optical converters when operated in harsh environments, their painstaking processing and strong variability in contact reliability.

It is now possible to significantly reduce the costs of using fibre-optic transceivers via the PushPull solution’s direct plug-in feature. The necessary contact reliability and robust design – essential in view of the application scenarios in harsh environments – are ensured by a hermetically sealed housing. Processing is much easier, and the widely employed SFP (small form-factor pluggable) transceivers can be used, leading to further cost reductions.

As the mechanical dimensions of SFP transceivers are not standardised in total, there are significant variances which until now have had to be compensated for by specific connector solutions. The use of costly special solutions and the need for complex processing represent deter the use of these approaches.

A new solution is now available on the transceiver side, with compensation for plug variances being ensured via an adaptable circuit board that is anchored in the PushPull Fibre Box. Thanks to the secure sealing of the circuit board to the PushPull box, the box can be completely encased. This enables the use of connectors, which must be painstakingly sealed in alternative solutions.

The transfer of power and data is by way of connectors such as har-flex devices located on the side of the box. On the converter side, this permits the use of standard SFP transceivers of the type well-known in office IT applications, which also offer much lower costs than the special connectors and electro-optic converters employed to date. The encapsulation of the plug and secure fixing enable utilisation scenarios in harsh operating environments.


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