The remaining eccentricity is easily corrected using the combined output of two readheads. Renishaw’s new DSi (Dual SiGNUM™ Interface) blends the output of two readheads whilst providing a repeatable and customer programmable reference mark propoZ™ position. Once the DSi has eliminated eccentricity, the only other errors remaining are graduation and cyclic error (sub-divisional error - SDE) both of which are exceedingly small.
When REXM is used with the DSi, it is possible to achieve a total installed accuracy of better than ±1 arc second. Tests on a 183mm REXM 
ring have achieved an impressive total installed accuracy of ±0.22 arc seconds.
Furthermore, REXM maintains the dynamic performance advantages of SIGNUM™ encoders. As a non-contact system, REXM rings are directly locked to the rotor, eliminating coupling losses, oscillation, shaft torsion and other hysteresis errors that plague enclosed encoders.
The total installed accuracy of a typical REXM system is ±0.22 arc second, determined by analysis of sequentially rotated installations.
For applications that require the highest angular accuracy, the REXM angle encoder offers new levels of angular metrology - better than ±1 arc second total installed accuracy, zero coupling losses and exceptional repeatability.
