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
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
We are pleased to provide you with a range of videos, please see below for the latest content available:
VIDEOS
Resistor Stability Put to the Test (Demo Video)
In this video, our host Richard Zuratt puts the stability of the three major resistor technologies — foil, thin, and thick film — to the test. Each resistor type is subjected to an overload pulse and its change in resistance value is recorded. Due to the homogeneous nature of the VPG Bulk Metal® Foil resistor, it is the only of the three to experience no change from the high power pulse. This demonstrated performance makes foil resistors the technology of choice for critical applications where long-term stability and survivability are paramount.
Advantages of Using Bulk Metal® Foil Resistors in High-Humidity Environments
All resistors that are based on nichrome, which is a category that includes both thin film devices and Bulk Metal Foil resistors, are susceptible to electro-chemical corrosion or etching when placed in a high humidity environment and powered with a very low wattage. But since the nichrome element of a Bulk Metal Foil resistor is hundreds of times thicker than the element in a thin film device with the same value, it will last much longer under these conditions. This video shows the actual etching process and survival times for thin film and foil nichrome resistive elements as they are tested in 100% humidity conditions.
Comparison Testing of Chip Resistor Technologies Under High Vibration
Surface-mount resistors suffer physical stresses when exposed to high vibration or thermally unstable environments. Failure modes commonly occur in welds, solder joints, connectors, and terminations, ultimately resulting in circuit failure. In this demonstration, vibration-table-mounted boards are subjected to ±2° deflection 25 times per second and monitored for any ΔR > 0.1%. All the chip resistors failed in 2 to 12 minutes (8K to 16K cycles). But the Alpha MPP molded Bulk Metal® Z-Foil resistor with flexible terminations experienced over a million cycles with no change in resistance.
VIDEOS
Resistor Stability Put to the Test (Demo Video
In this video, our host Richard Zuratt puts the stability of the three major resistor technologies — foil, thin, and thick film — to the test. Each resistor type is subjected to an overload pulse and its change in resistance value is recorded. Due to the homogeneous nature of the VPG Bulk Metal® Foil resistor, it is the only of the three to experience no change from the high power pulse. This demonstrated performance makes foil resistors the technology of choice for critical applications where long-term stability and survivability are paramount.
Advantages of Using Bulk Metal® Foil Resistors in High-Humidity Environments
All resistors that are based on nichrome, which is a category that includes both thin film devices and Bulk Metal Foil resistors, are susceptible to electro-chemical corrosion or etching when placed in a high humidity environment and powered with a very low wattage. But since the nichrome element of a Bulk Metal Foil resistor is hundreds of times thicker than the element in a thin film device with the same value, it will last much longer under these conditions. This video shows the actual etching process and survival times for thin film and foil nichrome resistive elements as they are tested in 100% humidity conditions.
Surface-mount resistors suffer physical stresses when exposed to high vibration or thermally unstable environments. Failure modes commonly occur in welds, solder joints, connectors, and terminations, ultimately resulting in circuit failure. In this demonstration, vibration-table-mounted boards are subjected to ±2° deflection 25 times per second and monitored for any ΔR > 0.1%. All the chip resistors failed in 2 to 12 minutes (8K to 16K cycles). But the Alpha MPP molded Bulk Metal® Z-Foil resistor with flexible terminations experienced over a million cycles with no change in resistance.
