Alpha USR-SF Series

The USR-SF series from Alpha Electronics is an ultra-stable primary standard resistor which is an enhanced version of the USR / ASR series. The ultra-stable resistive element utilises the new generation stress-free Bulk Metal® foil technology, which results in an extremely low temperature coefficient of ±0.05 ppm/°C at +23°C ±5°C. This performance is unique to Alpha Electronics throughout the world.

• Ultra-stable primary standard resistor
• Utilises new generation stress-free Bulk Metal® foil technology
• Long-term stability: 0.5 ppm/yr (0.2 ppm/yr typical)
• Temperature coefficient: less than ±0.05 ppm/°C at +23°C ±5°C
• Excellent humidity coefficient of resistance of less than 0.1 ppm/% RH
• Excellent pressure coefficient of resistance of less than 0.001 ppm/hPa
• Available in a wide range of resistances values (1Ω, 10Ω, 25Ω, 100Ω, 1KΩ and 10KΩ)
• Maximum power rating of 1W
• Temperature range of +18°C to +28°C
• Storage temperature range of 0 to +50°C
• 5 terminals

The stress-free resistance element eliminates stress factors by using a special treatment process, and is encapsulated in a specially-designed ceramic case to protect against humidity, oxidation and vibration during transportation. Alpha’s Bulk Metal® foil construction provides excellent AC characteristics, superior in performance compared to conventional wire-wound standard resistors.

The USR-SF, with its extreme long-term stability and low TCR, can be used in normal air environments, which eliminates the additional cost of operating and maintaining oil baths.

The USR-SF series has a weight of approximately 2.2kg and dimensions of 155mm x 97mm x 112mm.

The below table gives the full specifications for each model available of the Alpha USR-SF series:

* Rated power will be different for future additional lower resistance values