ADVERTISEMENT FEATURE COVER STORY


REED RELAYS DELIVER MEASURABLE BENEFITS


Words by Keith Moore, CEO, Pickering Electronics F


or many switching applications, reed relays remain the superior solution,


thanks to their small size, high isolation resistance, hermetically sealed contact surfaces and high life expectancy. A reed relay designed with high quality in mind - with no compromise on methods or materials - delivers the greatest performance and reliability, which is crucial to end users. The benefits for the user are vast: a reduction in cost of ownership, longer component life, reduced downtime and full magnetic screening, enabling higher packing density which reduces system hardware and connectivity. Pickering Electronics was formed over


50 years ago to design and manufacture high quality reed relays, intended principally for use in instrumentation and test equipment. Today, Pickering’s Single-in-Line (SIL/SIP) range is well developed in the relay industry, with devices 25 per cent the size of many competitors. These small SIL/SIP reed relays are sold in high volumes to large ATE and semiconductor companies throughout the world.


REED RELAY DEVELOPMENT Pickering is responsible for a number of technological advancements that have enabled the company to deliver its range of high-performance, miniature relays, including the use of formerless coils and Mu metal shielding. All Pickering’s reed relays are constructed using the company’s SoftCenter technology, which employs a soft inner material to reduce stresses on the reed switch. In addition, contact life and more reliable contact resistance are achieved thanks to the company’s former-less, fully-automated coil winding process. By dispensing with the supporting bobbin, the available coil winding area is increased by up to 50 per cent, greatly increasing magnetic efficiency, and hence saving space. The switch contacts in a reed relay are operated by the magnetic field, generated by the coil that is wound around the hermetically sealed switch capsule. When these relays are stacked close together, the field from adjacent relays will partially oppose the magnetic field from the relay alongside, reducing


10 FEBRUARY 2020 | ELECTRONICS Figure 1:


USEFUL REED RELAY FACTS AND FIGURES • Fast operate and release times of 80µS - faster than many photoMOS optocouplers


• Insulation Resistance > 10TΩ • Low duty, high pulse overload handling without degradation


its sensitivity. This means that a higher coil voltage will be required to operate it. For very small relays, this increase could be as high as 40 per cent, meaning that it may not be possible to operate the relay at its normal coil voltage (see figure 1 for a graphical summary).


Pickering’s relays are fitted with a


Mu-metal magnetic screen, rather than one made of steel, because of its high permeability and very low magnetic remanence. This screen concentrates the


permeability and very low magnetic remanence. This screen concentrates the magnetic field, improving the device’s efficiency and reliability, and


allowing side-by- side stacking to


maximise density. The


maximise density. The high packing densities


that can be achieved when using Pickering’s reed relays is illustrated in figure 2, which shows a high density reed relay PXI


hat can be achieved when using Pickering’s reed relays is illustrated in figure 2, which shows a high density reed relay PXI Matrix Module from its sister company, Pickering Interfaces.


4MM2 SERIES


Pickering’s ultra-high density 4mm2 miniature reed relays offer high performance levels and a small footprint – 4mm x 4mm. Within the family, Series 120 devices have a switching rating of up to 1A at 20W and a height of 15.5mm; Series 122 relays measure 12.5mm in height and are rated with a switching current of 0.5A at 10W; Series 124 products, which feature a profile at 9.5mm, are rated at 0.5A at 5W. All members of the 4mm2


series


feature sputtered ruthenium contacts, suitable for hot and cold switching, and are 100 per cent tested for dynamic contact resistance for guaranteed performance (see figure 3).


Figure 2:


• Consistent contact performance – Quality switches provide well-defined contact resistance over specification and time


• Extended operational life to one billion operations


• Hermetically sealed: switches do not suffer from oxidisation or contamination


CONCLUSION


A range of factors needs to be considered when selecting the appropriate reed relay for a particular application. Contact plating and


sensitivity, measured in Ampere


Turns (AT), are the main factors that affect the performance, but ot factors such as temperature, hot and cold switching, and magnetic interaction also need addressing. Pickering provides


Turns (AT), are the main factors


that affect the performance, but other factors such as temperature, hot and cold switching, and magnetic interaction also need addressing. Pickering provides full explanations of all these in their Concise Technical Guide to Reed Relays, available for free download. If the


Figure 3:


considerations discussed are understood and implemented, a reed relay will be the best choice for higher performance applications, such as instrumentation, semiconductor test, ATE, high voltage, low capacitance/attenuation, low thermal and others. Pickering’s wide range of reed relays is also available in the UK through distributor Rapid Electronics.


Pickering Electronics www.pickeringrelay.com


“A range of factors needs to be considered when selecting the appropriate reed relay for a particular application... Pickering provides full explanations of all these in their Concise Technical Guide to Reed Relays...”


/ ELECTRONICS sensitivity, measured in Ampere


A range of factors needs to be considered when selecting the appropriate reed relay for a particular application. Contact plating and


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