These hollow-shaft resolvers for “smart” servo motors are accurate to within ±8 arc min, depending on product variants. They can remain fully operational even under extreme environmental conditions and have low sensitivity to electromagnetic interference. Because of their mechanical structure and automated coil incorporation, they have long lifetimes. The resolvers also offer resistance to humidity, many lubricants, shock and vibration. They incorporate one transformer for powering the rotor and a second transformer for determining angles. They have a maximum rotational speed of 20,000 rpm and provide absolute angular information throughout 360°. The operating temperature range is -55 to 150 °C.