Pickering Electronics have expanded their high voltage Single-in-line (SIL) Reed Relay range to include three new series, that all offer higher packing density. The Series 67 and 68 dry Reed Relay range for up to 10kV, and the Series 119 Micro-SIL range for up to 3kV, will all be showcased this January at Semicon Korea on stand 2509.

The recently released Series 67 and 68 Reed Relay range are available for up to 10kV stand-off, 7.5kV switching, with an option of either PCB or flying lead switch connections. These new relays are manufactured in a SIL format using former-less coils which dispense with the more usual coil supporting bobbin allowing a smaller package than similar rated devices.

The unusual package design presents some interesting packing possibilities for high density applications such as multiplexers and matrices in instrumentation and test systems. 5, 12 and 24 volt coils are available as standard, and other voltages can be supplied to special order, as can variations in the lead length of the Series 68 range. The relays are suitable for high voltage transformer and cable test and some electro-medical applications such as defibrillators.

The new Series 119 is the industry’s smallest high voltage SIL Reed Relay for up to 3kV stand-off. These can be stacked side-by-side for maximum packing density (all Pickering SIL Relays have full magnetic screening allowing side by side operation).

This new relay is intended for voltages considerably higher than standard small SIL relays, ideal for Cable and Backplane Testers and Mixed signal ATE. Pickering also offer other Single-in-Line High Voltage dry Reed Relays with the Series 104 for use up to 3kV stand-off, 25 Watts switching.

To find out more about the new Reed Relays visit Pickering on stand 2509 at Semicon Korea 2016, or alternatively go to the website.

The original article ican be seen here.

Reed relays contain a reed switch, a coil for creating a magnetic field, an optional diode for handling back EMF from the coil, and an encapsulating package with connection terminals. In many ways, a reed relay, if used correctly, is a near perfect device with a low-resistance metallic switch path and inherent isolation between the control voltage operating the coil and the signal being switched.

The Reed Switch Explained

The reed switch has two shaped metal blades made of a ferromagnetic material (roughly 50:50 nickel iron) and a glass envelope that holds the metal blades in place and provides a hermetic seal that prevents any contaminants from entering the critical contact area inside the glass envelope. Most (but not all) reed switches have open contacts in their normal state.

If a magnetic field is applied along the axis of the reed blades, the field is intensified in the reed blades because of their ferromagnetic nature, the open contacts of the reed blades are attracted to each other, and the blades deflect to close the gap. With enough applied field, the blades touch, and electrical contact is made (Figure 1).

The only movable part in the reed switch is the deflection of the blades; there are no pivot points or materials trying to slide past each other. The contact area is enclosed in a hermetically sealed envelope with inert gasses, or in the case of high-voltage switches a vacuum, so the switch area is sealed against external contamination. This gives the reed switch an exceptionally long mechanical life.

Another reed switch design variable is size. Longer switches do not have to deflect the blades as far (measured by angle of deflection) as short switches to close a given gap size between the blades. Short reeds often are made of thinner materials so they deflect more easily, but this clearly has an impact on their rating and contact area. Smaller reed switches allow smaller relays to be constructed—an important consideration where space is critical. The larger switches may be more mechanically robust and have greater contact area, improving their signal-carrying capability.

Various plating materials and methods are used for the switch contact areas: most commonly, rhodium, iridium, or ruthenium—all rare platinum group metals. These all provide hard, wear-resistant surfaces with good resistance stability for a long life, often into billions of operations. For very high voltages, 5 kV to 15 kV, tungsten tends to be the preferred material due to its very high melting point and resistance to welding through arcing across the contacts. Reed switch contacts can be coated by either electroplating or vacuum deposition (sputtering). Pickering Electronics’ relays intended for low-level instrumentation use sputtered ruthenium contacts.To operate a relay, a magnetic field needs to be created that is capable of closing the reed switch contacts. Reed switches can be used with permanent magnets (for example, to detect doors closing), but for the reed relays, the field is generated by a coil, which can have a current passed through in response to a control signal. The coil surrounds the reed switch and generates the axial magnetic field needed to close the reed contacts.

Generating the Magnetic Field

Different reed switches require different levels of magnetic field to close the contacts, and this usually is quoted in terms of the ampere turns (AT)—simply the product of the current flowing in the coil multiplied by the number of turns. Stiffer reed switches for higher power levels or high-voltage switches with larger contact gaps usually require higher AT numbers to operate, so the coils need more power.

Changing the wire gage for the coil and the number of turns creates relays with different drive-voltage requirements and coil powers. The resistance of the wire coil controls the amount of steady-state current flowing through the coil and therefore the power the coil consumes when the contacts are closed. Whenever fine wires are used in Pickering Electronics relays, the termination leads from the coils are skeined with several strands of wire twisted together to increase their physical strength.

While Figure 2 shows only a few turns of wire, in reality there can be hundreds, thousands, or even tens of thousands of turns.

Packaging Reed Relays

Most Pickering reed relays are constructed using former-less coils, which dispense with the usual supporting bobbin. This leaves more room for the coil winding, permitting smaller relays or higher coil resistance figures. Reed relays are available in many package styles such as dual-in-line, single-in-line, and surface-mount.

Often, reed relays are molded using very hard materials that can cause stresses on the delicate glass/metal seal of the reed switch capsule with the risk of damage. Pickering, instead, uses a soft inner encapsulation, which provides a buffer to protect the switch. Without this, stresses can distort the reed switch slightly, thereby changing the contact area and degrading performance and contact resistance stability. An internal mu-metal magnetic screen enables Pickering relays to be stacked closely together without the magnetic field from one relay affecting adjacent parts. This allows the highest level of packing density.

The second article in this two-part series will look at the future of reed relays and compare them with other switching technologies.

The original article can be seen here.

About the author:

Graham Dale began his career in telecommunications with the U.K. Ministry of Defense. In the 1970s while working on a research project at The University of Essex sponsored by the British General Post Office (later to become British Telecom), he met John Moore, the founder of Pickering Electronics. This was in the early days of computer-controlled switching systems, and the project became a user of Pickering reed relays. Dale started working for Pickering at the beginning of 1975 and remains with the company today as a technical director and applications engineer.

Bei Pickering Electronics dreht sich alles um Reed-Relais, die eine Alternative zu HL-, MEMS- und elektromechanischen Relais sind.

Ein Reed-Relais bietet seinem Anwender, wenn es korrekt eingesetzt wird, höchste Zuverlässigkeit bei langer Lebensdauer. Auf dem Markt befinden sich zwar alternative Lösungen in anderen Technologien auf Basis von Halbleitern, MEMS und Elektromechanik, die einfache Einsetzbarkeit und die erreichten Fortschritte bei Baugröße und Leistungsdaten sind jedoch Garanten dafür, dass Reed-Relais noch viele Jahre im Markt vor sich haben.

Erfunden wurde das Reed-Relais 1936 von den Bell Telephone Laboratories. Seit dieser Zeit hat sich dieser Relais-Typ von ursprünglich sehr großen, relativ simplen Teilen kontinuierlich weiterentwickelt zu den kleinen, hochzuverlässigen Bauelementen, die wir heute kennen. Produktionsverfahren und Qualitätsmanagement-Systeme haben sich seither enorm verbessert, und die Kosten sind drastisch gefallen. Mehr als 30 Jahre nach der Erfindung des Reed-Relais wurde im Jahre 1968 die Firma Pickering Electronics gegründet, und selbst zu dieser Zeit gab es noch Stimmen, die diesen elektromechanischen Bauteilen eine nur sehr begrenzte Lebensdauer im Markt zubilligen wollten. Die Entwicklung verlief anders, und qualitativ hochwertige Reed-Relais haben Märkte erobert, die damals unvorstellbar waren.

Die Technik des Reed-Relais

Ein Reed-Relais besteht im Wesentlichen aus zwei ferromagnetischen Metallzungen (Nickel und Eisen im Verhältnis von ca. 50:50), die von einem Glasgehäuse umschlossen sind, das nicht nur die Position der Metallzungen fixiert, sondern diese Zungen auch hermetisch einschließt und so verhindert, dass der kritische Kontaktbereich im Innern des Gehäuses kontaminiert wird.

Wird ein magnetisches Feld in Richtung der Achse der Metallzungen angelegt, wird das Feld dort wegen des ferromagnetischen Charakters der Zungen verstärkt, und die offenen Kontakte der Metallzungen bewegen sich aufeinander zu, bis die Lücke zwischen ihnen geschlossen ist und der Strom fließt. Die hermetisch dichte Hülle um die Reed-Kontakte ist mit Inertgas gefüllt. Bei Hochspannungsausführungen ist im Glasgehäuse statt der Gasfüllung ein Vakuum. Diese Gas-/Vakuumfüllung verleiht dem Reedschalter seine außergewöhnlich hohe mechanische Lebensdauer.

The following interview explains what Reed Relays are, their unique features and what needs to be considered when using them within switching solutions. Graham Dale, Technical Director of Reed Relay manufacturer, Pickering Electronics, explains.

Why should engineers use Reed Relays in switching applications?

Reed Relays remain an attractive solution for switching applications. Having a metallic path, they do not suffer from a relatively high contact resistance and high off-state leakage current usually associated with solid state relays. Having hermetically sealed contacts, reed relays offer a better low level performance than conventional electro-mechanical relays as they do not suffer from oxidization or films building up on the contacts. They also have the advantage of faster operate and release times, critical in today’s instrumentation and test systems.

How do Reed Relays work?

A reed relay consists of two ferro-magnetic switch blades that exit the opposite ends of a hermetically sealed glass tube. This tube is filled with an inert gas, usually nitrogen. A vacuum is normally used instead in the case of high voltage reed switches. The overlapping blades are attracted to each other when they become magnetized by the field generated by a coil wound around the switch and the contacts will close. These contacts are plated using various methods and materials appropriate to the application. Pickering favour Sputtered Ruthenium plating for low level switching.

In general, the most common construction for a reed relay offers no magnetic screening, involves the use of a hard moulded package and an operating coil wound on a plastic bobbin surrounding the reed switch capsule. Pickering offer a technically superior solution including SoftCenter construction, mu-metal magnetic screens and former-less coil winding techniques.

What is SoftCenter technology?

Instead of the more usual hard moulded package, Pickering use our SoftCenter® technology, whereby a soft inner material is used to protect the delicate glass to metal seal of the reed switch capsule against expansion mismatches. This de-stresses the switch ensuring accurate alignment of the switch blades which in turn gives a longer and more reliable life.

What is former-less coil winding?

Relay operating coils are commonly wound on bobbins. The great majority of Pickering relays are manufactured with self-supporting coils, thus avoiding the space required for these bobbins. In the case of the smaller relays types, this gives around 50 percent more room for the coil winding, allowing the use of less sensitive reed switches with their inherent advantages of higher operating and restoring forces. In some ranges, this technique allows Pickering to achieve extremely high coil resistance figures.