Thorough purging of all four bearing seals on each universal joint can help alleviate the possibility of mixing incompatible greases. U-joint cross, broken at a bearing surface. U-joints seldom break off at the bearing surface. It takes a very large shock load to cause this type of failure. It is also very difficult to inspect for this type of failure because they, many times, start as a small crack and progress into a complete failure some time further âdown the roadâ.
A quantity called the slew rate, which is the rate of change of gradient amplitude is usually quoted in evaluating gradient performance and potential physiological effects (e.g. a maximum slew rate of 200 Tm-1s-1).
What is important is not the absolute value of rise time, but rise time scaled according to the maximum achievable gradient strength. This is encapsulated in the slew rate, defined as. Slew Rate = Peak Gradient Strength Ã· Rise Time. Slew rates are measured in units of Tesla per meter per second (T/m/s).Thus a gradient that ramps from 0 to peak amplitude of 30 mT/m in 0.5 msec would have a slew rate of 60 T/m/s.aveat emptor: The typical gradient strengths and slew rates quoted above are per axis (i.e. values for the x-, y-and z-gradients individually). Some vendors, often those with somewhat inferior gradient performance, will instead quote effective gradient strengths and slew rates.