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MALVERN, PENNSYLVANIA — Feb. 9, 2011 — Vishay Precision Group, Inc. (NYSE: VPG) today announced that its Vishay Foil Resistors (VFR) division has released a new ultra-high-precision Bulk Metal® Foil surface-mount Power Metal Strip® current-sensing resistor with a load-life stability of ±0.2% at +70 °C for 2,000 hours at rated power—a significant improvement over the load-life stability of ≥1% offered by typical current sensing products. The new CSM3637Z also features an absolute TCR of ±5 ppm/°C maximum from -55 °C to +125 °C, +25 °C ref., and a tolerance of ±0.1%. The CSM3637Z utilizes proprietary processing techniques that result in extremely low resistance values of 3 mΩ to 50 mΩ.
The improved resistance stability of the CSM3637Z makes it an excellent choice for tightened-stability voltage division, precision current sensing, and pulse applications in switching and linear power supplies, power amplifiers, feedback circuits, measurement instrumentation, bridge networks, satellites and aerospace systems, and medical and test equipment. The device’s stability can be further enhanced by post-manufacturing operations (PMO) which are uniquely applicable to Bulk Metal Foil Technology, such as temperature cycling, short-term overload and accelerated load-life.
Traditional passive current sensors and shunts generate heat under power, which changes their resistance, and thus their voltage output. The CSM3637Z’s low absolute TCR reduces errors due to temperature changes, thus reducing a major source of uncertainty in current measurement. Consider a typical current sense resistor with a TCR of 20 ppm/°C. While dissipating a power level that raises its temperature by 100 °C, it exhibits a 2000 ppm (0.2%) resistance change. That’s a 0.2% error in the measured current flowing through the resistor. Moreover, the temperature rise is not linear with power dissipation, and the measured current has an additional non-linearity relative to the current flow through it. The only way to reduce this error is with a very low absolute TCR as in the CSM3637Z. Further, the CSM3637Z 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.
The CSM3637Z features a low thermal electromotive force (EMF) that is critical in many precision DC 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 minimizing temperature variations. The resistor element is designed to uniformly dissipate power without creating hot spots, thereby minimizing parasitic contact resistance and contact resistance variation for a low thermal EMF of <3 µV/°C.
Featuring a four-terminal (Kelvin) design for precise and accurate current measurement, the CSM3637Z offers a power rating of 3 W for a resistance range of 3 mΩ to 10 mΩ and 2 W for 10 mΩ up to 50 mΩ. VFR foil resistors are not restricted to standard resistance values, and can be supplied with “as required” values (e.g. 10.2345 mΩ vs. 10 mΩ) at no extra cost or delivery time. The device features a maximum current up to 31 A, very low inductance of 0.5 nH, excellent frequency response to 50 MHz, and short time overload of ±0.1% typical. The CSM3637Z’s specifications are based on tests performed in accordance with methods prescribed by appropriate MIL-PRF standards (MIL-PRF-55342 and MIL-PRF-49465). Available in waffle-pack or tape-and-reel packaging, the resistor is available with lead (Pb)-free and tin/lead alloy terminations.
Designers often unnecessarily 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 CSM3637Z 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. Additionally, the overall system cost is often reduced by eliminating the necessity of additional compensating circuitry or temperature-controlling systems.
Samples and production quantities of the CSM3637Z are available now, with lead times of five days for samples, and eight weeks for standard orders.
About Vishay Foil Resistors
Vishay Foil Resistors is a division of Vishay Precision Group, producing the most precise and stable type of resistors available. The portfolio comprises products in a variety of resistor configurations and package types to meet the needs of a wide range of applications: discrete resistors and resistor networks in surface mount and through-hole (leaded) configurations; customized chip resistor networks; precision trimming potentiometers; and discrete chips for use in hybrid circuits. The foil resistors and current sensors are used in applications requiring a high degree of precision and stability, such as in medical testing equipment, high performance audio equipment, precision measuring instruments and aerospace
About Vishay Precision Group
Vishay Precision Group (VPG) produces sensors based on precision resistive foil technology, and sensor-based systems. It provides vertically integrated products and solutions for multiple growing markets in the areas of stress, force, weight, pressure and current measurements. As a spin-off from Vishay Intertechnology, VPG’s decades-long track record encompasses innovations in foil precision resistors, current sensors, and strain gages, which have served as a foundation for VPG’s more recent expansion into strain gage instrumentation, load cells and transducers, weighing modules and complete systems for process control and on-board weighing. Vishay Precision Group may be found on the Internet at www.vishaypg.com