Power Electronics
Bulk Metal® Foil Ultra-High-Precision COTS Resistors

Bulk Metal® Foil Ultra-High-Precision COTS Resistors

Vishay Precision Group, Inc. announced that its Vishay Foil Resistors brand (VFR) Bulk Metal® Foil commercial off-the-shelf (COTS) resistors are increasingly in demand to meet the needs for high reliability and long-term stability in control and monitoring applications. Including the surface-mount VSMP Series (0603-2512), hermetically sealed oil-filled VHP100, and leaded Z Series, VFR's comprehensive portfolio offers a variety of resistor configurations, case sizes, and ultra-high-precision specifications for optimized performance. All are based on proven foil resistor technologies with a 50-year track record of delivering ultra-precision performance while continuing to evolve and improve to serve the needs of the market.

Many monitoring and control applications utilize a 4 mA to 20 mA closed-loop circuit, consisting of a DC power supply to power the loop, a sensor/transducer/transmitter that inserts the sensor-related current, and a meter or control device at the other end of the loop. Generally, analog sensors with just microvolt-level outputs continuously detect changes in any significant stage in the process.

The sense resistors used in these circuits, typically 250 ohms, are critical for system operation and must offer high stability and reliability. Since voltage across the resistor is fed directly to the meter, any error could indicate that the sensor is reading a non-existent condition. The process control correction made on this reading would then cause the system to operate at less than optimal conditions and reduce its efficiency, which could result in increased operating costs, environmental pollution, hazardous spills, associated fines, and poor product quality.

VFR's Bulk Metal Foil resistors for control and monitoring applications provide the high reliability and long-term stability required for 4 mA to 20 mA circuits. The surface-mount VSMP Series and through-hole Z Series devices offer ultra-low TCR of ±0.05 ppm/°C typical (0°C to +60°C) and ±0.2 ppm/°C typical (-55°C to +125°C, +25°C ref.), while the secondary standard VHP100 resistor offers an essentially zero TCR and is available with tight tolerances down to ±0.005% (50 ppm). The devices feature exceptional load-life stability of ±0.005% at 70°C for 2,000 hours at rated power and ±0.01% at 70°C for 10,000 hours. The resistors are virtually immune to extraordinary incidents such as radiation exposure and withstand ESD spikes to at least 25 kV.

Featuring a non-inductive (<0.08 µH), non-capacitive design, Bulk Metal Foil devices offer a rise time of 1.0 ns, with effectively no ringing, a thermal stabilization time of <1 s (nominal value achieved within 10 ppm of steady state value), current noise below 0.010 µVrms per volt of applied voltage (<-40 dB), voltage coefficient of <0.1 ppm/V, and thermal EMF of 0.05 µV/°C typical. The devices provide wide resistance ranges, with any resistance value within their given range available at any tolerance with no additional cost or lead-time effect.

Samples and production quantities of the foil resistors are available now, with lead times of five days for prototype samples and from two days to five weeks for standard orders at the catalog houses, depending on their shelf availability. 

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