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VPG rolls out Z-Foil power current sensing resistor line

19 Jun 2013

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Vishay Precision Group(VPG) recently unveiled that its Vishay Foil Resistors brand (VFR) has released new ultra-high-precision Z-Foil power current sensing resistors for applications where rapid ΔR stabilisation and resistance stability under transient power conditions are required.

Designed to provide optimal performance when mounted on a chassis or cooled heat sink, the VCS331Z, VCS332Z, VFP4Z, and CSNG Series feature low TCR of ±0.2 ppm/°C from -55°C to 125°C, 25°C ref., PCR (ΔR due to self-heating) of 4ppm/W typical, and tolerances to ±0.01 per cent. For high-power applications, the devices offer power ratings up to 10W (on heatsink) and a four-terminal Kelvin configuration in order to remove the unwanted influence of lead resistance and lead sensitivity to temperature.

The VCS331Z, VCS332Z, VFP4Z, and CSNG offer excellent load-life stability to ±0.005 per cent typical (50ppm) at 3 W (heat sink) and 25°C for 2,000 hours, a thermal stabilisation time of <1s (within 10ppm of steady state value), and a wide resistance range from 0.25Ω to 500Ω. (Lower and higher values are also available.) Any resistance value within this range is available at any tolerance with no additional cost or lead time effect. The resistors offer a rise time of 1.0ns with effectively no ringing, current noise of 0.010µVrms/V of applied voltage (<-40dB), and a voltage coefficient of <0.1ppm/V. The devices withstand ESD to at least 25kV for increased reliability, and they offer a non-inductive (<0.08 μH), non-capacitive design.

The Bulk Metal Foil resistor is based on the planar construction of a cold-rolled Ni-Cr foil bonded to a flat ceramic substrate. The monolithic foil, as opposed to the agglomeration of particles in thin film resistors, has a strength and substance independent of the substrate, which gives the metal foil its own specific thermal linear coefficient of expansion (LCE). The foil also has a known and repeatable independent positive temperature coefficient of resistance (TCR). When the foil is bonded to the substrate, it attempts to respond to temperature changes in accordance with its own LCE but is constrained to follow the lower LCE of the ceramic substrate. The resistance change due to the differential LCEs counterbalances the metal's positive TCR for a near-zero net TCR of the resistor. The composite formation with a planar foil structure makes it possible to very accurately etch a pattern into the resistor that is non-inductive and non-capacitive, with low noise and low thermal EMF.

The VCS331Z, VCS332Z, and VFP4Z are differentiated by power rating, thermal EMF, and configuration. The CSNG is a custom version of these resistors that can be uniquely designed and tailor-made to the customer's specific applications and which has already been used by several research institutes and test and measurement companies.




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