RWR81S2R70BPS70

FAQFrequently Asked Questions

• What are the key design considerations when integrating the RWR81S2R70BPS70 into a high-temperature industrial circuit? The RWR81S2R70BPS70 is rated for operation up to 250°C, which makes it suitable for downhole, aerospace, or automotive under-hood applications where ambient or component temperatures exceed standard limits. However, the 1W power rating must be derated when operating near the upper temperature range; Vishay Dale typically recommends applying a derating curve that reduces available power by approximately 50% at 250°C compared to room temperature operation. Additionally, the ±50ppm/°C temperature coefficient means that resistance value will shift by approximately ±0.135 ohms across the full -55°C to 250°C range, which may require compensation in precision current-sense or feedback circuits. Confirm that your circuit tolerance budget accommodates this drift before selecting the RWR81S2R70BPS70.
• Can the RWR81S2R70BPS70 replace lower-tolerance wirewound resistors in existing designs, and what are the upgrade implications? The RWR81S2R70BPS70 offers ±0.1% tolerance, which is significantly tighter than standard ±1% or ±5% wirewound options. When upgrading from a higher-tolerance 2.7-ohm resistor to the RWR81S2R70BPS70, you gain tighter initial tolerance and improved long-term stability; however, verify that your PCB layout and thermal management can accommodate the RWR81S2R70BPS70's axial form factor, which is 0.250" long and 0.085" in diameter. If the legacy design used a different case size, mechanical clearance or mounting density may be affected. Additionally, the RWR81S2R70BPS70 carries a military qualification (MIL-PRF-39007) and higher cost; use this upgrade only if your application requires the tighter tolerance, military-grade reliability, or extended temperature performance.
• How does moisture resistance in the RWR81S2R70BPS70 affect reliability in humid or sealed enclosure environments? The RWR81S2R70BPS70 is specified as moisture resistant, which means the wirewound element and coating are designed to withstand high humidity without significant degradation in resistance or insulation properties. In sealed enclosures or potted assemblies, the RWR81S2R70BPS70 will maintain its electrical characteristics even if condensation forms temporarily during thermal cycling. However, "moisture resistant" is not the same as hermetically sealed; if your application involves direct water immersion or extended exposure to salt spray, consider conformal coating or potting compound as an additional layer of protection. For marine or offshore applications, the combination of the RWR81S2R70BPS70's moisture-resistant construction with a protective coating will provide longer service life than an uncoated standard resistor.
• What is the failure rate specified for the RWR81S2R70BPS70, and how does it apply to reliability predictions? The RWR81S2R70BPS70 carries a failure rate of P (0.1%), which corresponds to MIL-HDBK-217F reliability modeling. A failure rate of 0.1% per 1000 hours means approximately 1 failure per million device-hours under specified conditions. This data point is useful for calculating mean time between failures (MTBF) in redundant or high-availability systems; for a single RWR81S2R70BPS70 in a non-critical application, the calculated MTBF exceeds 100,000 hours under nominal operating conditions. However, reliability predictions degrade with temperature stress, so verify that your thermal management strategy keeps the RWR81S2R70BPS70 below 150°C during normal operation to maintain the predicted failure rate.
• Is the RWR81S2R70BPS70 suitable for current-sense applications in power management circuits? Yes, the RWR81S2R70BPS70 is well-suited for current-sense networks because of its ±0.1% tolerance and low temperature coefficient (±50ppm/°C). In a typical high-side or low-side current-sense application, you would place the RWR81S2R70BPS70 in series with a load and measure the voltage drop across it using a precision ADC or analog front-end. The tight tolerance ensures minimal measurement error across different units, and the low temperature coefficient reduces zero-drift errors as the circuit warms up. However, confirm that the 2.7-ohm value matches your desired sensitivity; for a 1A load, the RWR81S2R70BPS70 will generate a 2.7V drop, which is suitable for analog inputs rated 0–5V or higher. If you need a lower voltage drop or higher current range, select a lower resistance value from the RWR81 series.
• What are the compliance and supply-chain implications of selecting the RWR81S2R70BPS70? The RWR81S2R70BPS70 is RoHS non-compliant, which means it may contain lead solder or other restricted substances; verify that your end application and target markets allow RoHS exemptions or that you have a compliant alternative available. The RWR81S2R70BPS70 is also REACH Affected, so if your supply chain or customers operate under REACH regulations, confirm that Vishay Dale's SVHC (Substances of Very High Concern) declarations are current and acceptable. For military, aerospace, or medical applications, the RWR81S2R70BPS70's MIL-PRF-39007 qualification provides traceability and quality assurance; however, lead times may be longer and unit costs higher than commercial-grade alternatives. Plan your procurement timeline accordingly, especially if the RWR81S2R70BPS70 is a critical component or if supply is limited.
• How should the RWR81S2R70BPS70 be mounted and soldered to minimize thermal stress? The RWR81S2R70BPS70 is an axial through-hole component, so it mounts vertically or horizontally on a PCB with leads inserted into plated holes and soldered on the opposite side. To minimize thermal stress during reflow or wave soldering, keep the solder joint dwell time under 4 seconds and avoid peak temperatures above 260°C; the RWR81S2R70BPS70's wirewound construction is more sensitive to rapid heating than thin-film resistors. If hand-soldering, use a temperature-controlled iron at 350–380°C and limit contact time to 3 seconds per lead to prevent solder from wicking up the lead and embrittling the wirewound element. After soldering, allow the assembly to cool naturally; do not subject the RWR81S2R70BPS70 to mechanical stress or vibration until the solder joint is fully solidified, as wirewound resistors are more susceptible to lead fracture than other types if stressed while warm.
• Can the RWR81S2R70BPS70 be used in AC circuits, or is it limited to DC applications? The RWR81S2R70BPS70 is suitable for both DC and AC circuits. In DC applications, the resistor acts as a simple ohmic load with resistance of 2.7 ohms at any current level within the 1W rating. In AC circuits, the wirewound construction introduces parasitic inductance and distributed capacitance; the RWR81S2R70BPS70 will exhibit slightly higher impedance at radio frequencies compared to its DC resistance, and resonances may occur at frequencies above 1 MHz depending on the exact construction. For precision AC measurements or RF applications, verify the frequency-dependent behavior of the RWR81S2R70BPS70 using impedance measurements or simulation; if the application requires flat response across a wide frequency range, consider a non-inductive thin-film resistor as an alternative.
• What derating and thermal management practices should be applied to the RWR81S2R70BPS70 in continuous operation? The RWR81S2R70BPS70 is rated for 1W at 25°C ambient; to determine the maximum safe power dissipation at higher ambient temperatures, apply a linear derating factor that reduces power capacity by approximately 5–10 mW per degree Celsius above 25°C. For example, at 85°C ambient, the RWR81S2R70BPS70 should be derated to approximately 0.4–0.5W to maintain component temperature below 150°C and ensure long-term reliability. In a sealed or poorly ventilated enclosure, the RWR81S2R70BPS70's temperature will rise faster than in free air; use thermal modeling or testing to validate that the resistor temperature remains within acceptable limits. If the RWR81S2R70BPS70 dissipates near its full 1W rating continuously, consider mounting it away from sensitive components and ensure adequate board-level thermal relief or airflow to prevent localized hot spots that could degrade nearby capacitors or ICs.
• How does the RWR81S2R70BPS70 compare to film or thick-film resistors for precision applications, and when should you choose one over the other? The RWR81S2R70BPS70 is a wirewound resistor with ±0.1% tolerance and ±50ppm/°C temperature coefficient, which places it in the mid-to-high precision category. Compared to thin-film resistors (typical ±0.1% tolerance and ±25ppm/°C), the RWR81S2R70BPS70 offers lower precision and higher temperature drift, but superior power handling and extended operating temperature range (-55°C to 250°C versus typically -55°C to 125°C for thin-film). Thick-film resistors offer lower cost and similar temperature range but wider tolerance (±1–5%) and higher temperature coefficient (±100–500ppm/°C). Choose the RWR81S2R70BPS70 when your application requires 1W power dissipation in a low resistance value (under 10 ohms) with tight tolerance and extended temperature range; for lower power precision networks at room temperature, thin-film resistors are often more cost-effective. For industrial or automotive applications requiring both power handling and reliability, the RWR81S2R70BPS70's military qualification and moisture resistance justify the higher cost.