For 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 measurable: 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 by far the most developed in the relay industry with devices 25% 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.
Pioneering reed relay development
Pickering has pioneered a number of technological advancements which have enabled the company to deliver its range of high-performance, miniature relays, including the use of formerless cores 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%, 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 which 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 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% which means that it may not be possible to operate the relay at its normal coil voltage. See Figure 1.
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 magnetic field, greatly improving the device’s efficiency and reliability and allowing side by side stacking to maximize density. The high packing densities that can be achieved when using Pickering’s reed relays is illustrated in Figure 2 which shows a PXI high density reed relay PXI Matrix Module from its sister company Pickering Interfaces.
The current state-of-the-art in high-performance miniature reed relays is represented by Pickering’s ultra-high density 4mm2 series, which feature industry’s smallest 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, and Series 124 products which feature industry’s lowest profile - 9.5mm - are rated at 0.5A at 5W. All members of the 4mm2 series feature sputtered ruthenium contacts which is suitable for and cold switching, and devices are 100% tested for dynamic contact resistance for guaranteed performance. Figure 3.
Useful reed relay facts and figures
• Fast operate and release times of 80µS - faster than many photoMOS optocouplers
•Exceptional Insulation Resistance > 10 T?
•Low duty, high pulse overload handling without degradation
•Consistent Contact Performance – Quality switches provide well-defined contact resistance over specification and time.
•Extended operational life to 1 billion operations
•Hermetically sealed: switches do not suffer from oxidization or contamination
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 other factors such as temperature, hot and cold switching and magnetic interaction also need addressing. Pickering provides full explanations of all these issues and more in its Concise Technical Guide to Reed Relays, available for free download. If the 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.