Passive Components


Current sensing resistors

26 May 2010 Passive Components

Vishay has enhanced its CSM series of ultra-precision, surface-mount, current-sensing resistors in the compact 2512 and 3637 case sizes.

The improved devices offer a standard TCR of ±15 ppm/°C (-55°C to +125°C, +25°C ref.), with ±10 ppm/°C available on request, and an extended resistance range down to 1 mΩ.

The CSM series features a low thermal electromotive force (EMF) that is critical in many precision applications. The device’s all-welded construction is composed of a Bulk Metal resistive element with welded copper terminations, plated for soldering. The terminations make true ohmic contact with the resistive layer along the entire side of the resistive element, thereby minimising temperature variations. The resistor element is designed to uniformly dissipate power, thereby minimising parasitic contact resistance and contact resistance variation for a low thermal EMF of 3 μV/°C.

Traditional passive current sensors and shunts generate heat under power, which changes their resistance, and thus their voltage output. The CSM’s low absolute TCR reduces errors due to temperature gradients, thus reducing a major source of uncertainty in current measurement. The CSM can withstand unconventional environmental conditions, including the extremely high temperatures and radiation-rich environments of down-hole oil exploration and well logging, or the deep-sea underwater repeaters in cross-ocean communications.

Featuring a four-terminal (Kelvin) design, load-life stability to ±0,2% at 70°C for 2000 hours at rated power and available with screening in accordance to EEE-INST002 (MIL-PRF 55342 and MIL-PRF 49465), the devices provide high stability and performance in precision current-sensing applications. Designers often pay for tighter tolerances than required simply to accommodate the resistance stability shifts they know to be imminent in an application due to the large application-related changes in the components they selected. Selection of a high-stability component like the CSM in these applications eliminates the need for shift allowance due to ‘planned instability,’ and allows initial tolerances to be looser than would be necessary with current-sensing resistors based on other technologies.

The CSM2512 features a 1 W power rating over its entire resistance range from 1 mΩ to 200 mΩ, while the CSM3637 is rated for 3 W from 1 mΩ to 10 mΩ and for 2 W from 10 mΩ up to 200 mΩ. Vishay Foil resistors are not restricted to standard resistance values, and can be supplied with ‘as required’ values (eg, 2,3456 mΩ vs. 2 mΩ) at no extra cost or delivery time. The devices feature a maximum current up to 54 A, low inductance of <5 nH, and thermal EMF of 3 μV/ °C. The CSM2512 and CSM3637 offer compact dimensions of just 6,35 by 3,175 mm and 9,14 by 9,4 mm, respectively, with a height profile of 0,635 mm.

Available in waffle-pack or tape-and-reel packaging, the CSM2512 and CSM3637 are available with lead-free and tin/lead alloy terminations.

For more information contact Marian Ledgerwood, Future Electronics, +27 (0)21 421 8292, marian.ledgerwood@futureelectronics.com, www.futureelectronics.com



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