Try integrating solutions instead of just buying-in components

As is known, each device is more than the sum of all parts it consists from. And the performance level of an application is mainly the result of the engineer’s competence – plus the quality, reliability and applicability of its components. To put it in a nutshell: the entire chain is always as strong as its weakest link. 

As much as every engineer prefers to be free in his creation processhe still is bounded by a growing number of chainswhich all are claiming highest priority. Butwhether it is the safety chainthe functional chainthe process – or last but not least the value chain – even only one weak link would be out of place at all.

Thus – metaphorically speaking – product engineering is akin to juggling 10 balls at the same time: Only those that have the process under control and do not allow the grass to grow under their feet are able to compete with the pacemakers.

The best way to master this feat is to have the right partners that introduce the right balls at the right time. When taken in the context of product engineering: technological partners with high levels of applications and solutions competence who give the development engineer the security of being able to delegate a large number of the daily challenges that go hand-in-hand with designing devices. This gives him more room to manoeuvreallowing him to concentrate more of his energy on his core competencies. That is why design-in partnerships offer a decisive competitive advantage: synergies free up available resourcesreducing development and manufacturing costs as well as the time to market. The following declinations may illustrate this approach exemplarily.

To meet the countless requirementsand to master the well-known or almost unexpected challengesit is essential to continuously extend the own understanding of the interdependencies along the entire life cycleand the resulting influences to every step of the engineering process.

On the hardware sitethat includes at least three different interdependent fields of design: functional and safety design; electronics design; and mechanical design.

From the earliest stage of the design processa holistic view on all aspects of design-in is essential to avoid unnecessary design iterationsproject delaysand compromises at the approvals stage as well as excess costsinefficient production processcomplaintsreworking and many other problems. This holistic view implies to account each element as a part of the entire installation and embedded in its specific environments – whether it belongs to the component-application- or the system level (Fig. 1).

 

he technical requirements are determined top down from the system level to the components level. According to the above mentioned design fieldsplus economical feasibilityit is mainly four categories to differentiate the parameters: Functioninteractionconstruction and amortisation.

Finallythe degree of integration is one key to optimal resultsas well as reliabilityperformance and design is one factor of the diversification which is essential to attain – and continuously defence – a strong market position (Fig. 2).

For exampleit is one thing to meet the component standards and anotherto make it through the application approvals. Trends such as ongoing miniaturisation make high demands on electrical and thermal capabilitieseven while the performance is still increasing at the same time.Thus it is essential to ensure that the components still deliver its ratings as stated in the data sheet even when integrated to the device.

As the norms basically define the bottom line of a products or device capabilityit is preferable to extend these minimum requirements by in-house standardswhich observe the expertise of a design-in-partner regarding the real-life-conditionsthat such a product is dedicated to work under for decades.

For instancethe rated current. When determining the rated current in accordance with DINEN61984section 7.3.3due to the test setup under DINEN60512-5-2it is possible to include ‘artificial’ heat sinks. The defined test assembly allows not only wire loops at the field sideto simulate the cable conductor’s heat sink capabilitiesbut also at the bottom side of the PCBcorresponding to the circuit path’s on the board. As the test is done with the maximum nominal cross sectionthese loops finally deliver quite effective heat sinkstoo (Fig.3).

When it comes to real operating conditions of the applicationan engineer has to mind some further impacts – such as temperature rise through power electronics – to ensure that there is no weak link hidden to the functional or even the safety chain.

The higher the packaging densitythe stronger is the constraining interdependencies. That is why Weidmüller's in-house standards instruct the use of short links of the bottom side of the board (see picture above). The norm conditions may enable higher ratingsbut fundamentallyreliability and plant availability are given priority over marketing effects. And it goes without saying that basic physics should generally be considered by the design partner.

For examplethe relationship between the ambient temperaturethe insulation (moulding) material and the resulting current ratingsis displayed in the so-called ‘Derating Curve’.

The current-carrying capacity of a connection is determined by the maximum operational temperature of its insulating material. The sum of the ambient temperature plus the temperature rise which is caused by the loaded current is not allowed to overrun this limit.

While selecting the suitable components in order to ensure reliable connections that cover all thermal and load profilesit is helpful to understand that a derating curve already displays only 80 per cent of the really evaluated current. The norm requires the reduction as a security buffer in case of abbreviations to the test conditions while operationsuch as lower nominal torques of a screw connectionor even quality fluctuations of the line voltage. Furthermorewhen it comes to overload capacityit is up to the temperature-distributing ability of the connector constructionas well as to the thermal stability and ageing characteristics at temperature cycling due to load profile or peaks (Fig. 4).

The applicable rule of thumb (in accordance with the so called ‘Arrhenius-equation’. A reduction in relation to the maximum continuous operating temperature by 10°C doubles the operational lifetime of the component group – and converselythe operational lifetime is halved by an increase in temperature of 10°C. That is why the insulation material of a PCB terminal or connector makes such a difference regarding the long-term-reliability or the short-term overload capability.

For examplethe following derating curve shows the difference between the same terminal block made from different insulation materials: The maximum current of 24Amps is limited by the conductor cross section due to IEC60947-7-1. Butdepending on the maximum continuous temperature of each molding materialthe terminal block is able to permanently carry its nominal current at about 53°C or even at 73°C (Fig. 5).

A material that applies to these high requirements is WEMID – a halogen- and phosphor-free special thermoplastic from Weidmüller that allows an enhanced continuous operating temperature of 120°C orif glass-fibre-reinforcedof even 125° (by comparison:
PA 66 = 100°C). This material also delivers improved fire resistance characteristics (Flammability in accordance with UL 94 class = V0 (PA 66 = V2).

The advantage for the application: A higher ambient temperature (20 Kelvin) at the same load current. Or to put it in another waythe same physical size of connector offers a greater power spectrum and a higher safety buffer. That means in practical applications that smaller and more economic PCB terminals can be used for the same power spectrum.

 

ndon the other handwith a given ambient temperatureit enables the utilisation of higher currents. That means more compact electronics modules and in turn more compact devices can be realised. It goes without sayingthat WEMID fulfils the RoHS Directive specifications (Reduction of Hazardous Substances). WEMID is furthermore qualified for use in railway applications in accordance with NFF16-101 specifications. Thusas electronic and mechatronic devices are becoming smaller and more complexthis trend leads to an extremely high assembly density of the integrated PCBs and to correspondingly high temperatures to match.

Buttemperature it is not for this reason alone that it is so important to take a much wider viewas discussed above. For exampleit is only thanks to this ‘lateral thinking ability’ that the HP (High Performance) connectors in Weidmüller's power connectors today already fulfil a voluntary clearance distance of >3mm to the test finger. According to the IEC DIN EN 61800-5-1 this is a requirement that ‘Adjustable speed electrical power drive systems’ (for examplefrequency converters) have to fulfil since the latest update in 2007.

That also applies when the connector is plugged and is as such a part of the device. Design features such as a higher screw dome and a longer wire entry funnel mean that the device does not need an additional shroud (Fig.6).

Although it is not possible here to cover the subject of design-in with regard to connection technology in all its aspects or with any sense of finality. it is true that generally applicable design-in rules can be structured and made availablebut it is not possible to fully replace individual design-in support.

 

In saying thatat no time does any form of dependency on the partner enter into the equation. The development engineer can return to his familiar product procurement arrangements at any time. Howeverprofiting from the optimum means moving forward and away from the suboptimum level forever. And finally: it is quite natural that the process of 'competence sharing' will enhance the personal experience and expertise of the development engineer.

Experience tells us that electromechanical components more are closely linked to conventional problems such as EMCthermal managementapprovals and production processes than the electronics development engineer is aware. They have far more influence on reliabilityperformancedesign and cost effectiveness than the product manager would care to admit. Connection technology is initially often neglected and then integrated into the development process at a date later than the design engineerthe purchasing manager andleast of allthe inspector would prefer.
To achieve the best possible resultsdesign-partners should accompany the development process from the very beginning.  Able to call on more than 60 years of experience in the world of electrical connection technology managementWeidmuller's development engineers provide support to all users worldwode in the form of innovative solutions and competent phase and inwards.
A design-in partnership is in favour for much more than simply supplying a reliable components at a competitive price.  Being ablse to reliably master and juggle the 'balls' throughout the product creation process is the core task of such a partnership.  The result is a win-win situation for all sides.

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