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Specifying circular connectors: 6 factors to consider

Circular connectors are used in many automation technology applications, such as sensor signal transmission and low power supply, or for data communication in fieldbus technology.


Metric-sized circular connectors, like the M12 and M8, have been around for many years, but product evolution and technology advancement have provided performance enhancements and broadened their applications. {nomultithumb}

Although this is a standard connector that has been commoditized, there are still some features and new configurations available that should be considered when specifying such connectors for a particular equipment design.

1. Field-attachable versions. Field-attachable connectors allow for stripped wire to be attached to the connector in the field using a simple screwdriver tool. This facilitates a faster, less complicated installation. For example, some cables may be challenging to install, due to the need to be fed through holes as small as six mm.

Circular connectors that can be terminated in the field solve this problem, compared to buying double-ended, over-molded cable assemblies that require holes or spaces of 20 mm or more. Also, if the exact cable length is unknown, the cable length may be sized on the job, which avoids order errors.

Field-attachable connectors are available in axial construction as well as a 90-degree angled construction. This also provides a lower profile/clearance advantage for tight space installations. Finally, make sure the field-attachable connector that you specify maintains the IP67 (or greater) integrity of the whole system.

2. Over-molding. Over-molded metric type connectors can improve durability and streamline the size, as well as the appearance, of a cable connection. Over-molding can also reduce the cost of lifetime ownership of cable assemblies, making it an important consideration for harsh environment applications.

An extra strain relief around the wire terminations offers increased durability that results from the over-mold material bonding to the cable jacket. The overall assembly thus gives a high-reliability connector on each end, with customer-specified cable properties in between.

In addition to over-molding, the cable jackets need to be specified. Some performance parameters to consider include UV and sunlight resistance, low temperature flex rating for indoor-outdoor applications, burial, chemical/oil-resistance, weld slag and high-flex needs with millions of cycles possible.

Over-molded connectors are available in right angle and straight, shielded and unshielded versions. LEDs embedded in the over-mold material provide an easy indicator of signal integrity or power as an option. Additionally, over-molding allows for some customization, such as private labeling with company logos, custom lengths and colors.

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3. High temperature. The demands for higher temperature resistance continue to increase in industrial automation, so this may be one of the most important considerations for an equipment designer and installer. For these kinds of applications, some suppliers offer high-temperature connectors – some which can withstand 8000 h at a constant temperature of 125 C, with temporary peak values of up to 150 C over 2000 h.

Such connectors are a particularly good fit for food and beverage industry applications, as long as they also meet the requirements and industry standards for chemical and temperature resistance.

Today, circular connectors can be made of materials that meet those high hygienic needs and extended times at extreme temperatures. Be sure to recognize in your specs the need to tolerate harsh cleaning agents, in addition to high-pressure cleaning processes.

4. Industrial data bus protocols. The utilization of fieldbus technology in the industrial sector has increased rapidly over the last few years, and if paired with a cable assembly that uses a circular connector, the protocol types needed are important to define at the design stage. Data bus systems like Profibus, DeviceNet and Industrial Ethernet each have their own defined type of connector and, in some cases, color coding, contact arrangement and wiring code.

The construction and design of the connectors that are necessary for data communication are bus-specific and should be carefully selected. Circular versions are available for Profibus DP, industrial Ethernet and DeviceNet protocols in several specifications from a number of manufacturers.

5. Growing popularity of RJ45 and USB results in new products. While metric-type connectors have become the standard in industrial applications, RJ45 and USB circular connectors are expected to become more popular. Market demand has resulted in new families of RJ45 for Ethernet, and USB interfaces in ruggedized forms, and offer an IP67 rating or better.

In the industrial automation market, much of the upload and download activity that goes on in programming machines is done via Ethernet and/or laptop computer. Such connections can be plugged into a sealed RJ45 connected point-to-point, allowing for easy download of data without requiring machine shutdown. The ruggedized circular body of the RJ45’s housing is ideal for this, because it protects against exposure to any kind of abuse or ingress from dust, dirt or water.

For structured, industrial cabling in accordance with Realtime Ethernet/IP specifications, RJ45 connectors with bayonet coupling mechanism are now available that conform to IEC 61076-3-106 standards. The receptacle housing kits are available in front- or rear-panel-mount with different termination technologies.

Inside the device, connections can be made with inline couplers, IDC or solder termination options with appropriate strain relief to tolerate machine vibrations. This recent product development provides for reliable connections for heavy industrial environments. The mating cable applications can be specified for either indoor or outdoor use.

The same protection is true of the ruggedized circular USB housing. USB connector systems for harsh environments can be used for front or rear mounting into a panel with a thickness up to 3.2 mm. The integrated USB connector meets USB 2.0 specifications, and provides IP67 sealing performance when the connector halves are fully mated or the protection cap is applied.

The new addition of USB ruggedized connections now adds to the data and peripheral possibilities in applications for harsh environments, such as ”thumb-stick” loaded applications and data storage.

Using RJ45s and USBs in these types of industrial applications are examples of the connector industry pushing standard I/Os to the edge in terms of where they’re used. Previously only used in office-type, clean environments, today’s I/O connections are being tested by a growing need for instant online access by all kinds of machinery.

Many designers want to access their complex electronic and control systems via the Internet. These new ruggedized circular connectors enable that ability. Factory floor devices can now be equipped with these types of connectors. The need to troubleshoot from a remote location is driving this trend. Remote access is the key, and the Ethernet interface provides that.

6. Pricing and availability. Pricing and availability are significant considerations in specifying connectors for industrial applications. If a connector is needed for an installation on a factory floor, short lead-time is critical.

Even with the latest features and advancements, in the end, a design eng
ineer wants to work with the supplier that won’t delay the installation.

Fred Kozlof has been in the connector industry for more than 30 years. He is currently with Conec Corp. in Garner, NC, where he is heavily involved with several families of IP67 connectors for harsh environments. This article originally appeared in the June 2012 issue of Manufacturing AUTOMATION.