Why does the IQ3 use an absolute encoder?

The IQ3 uses Rotork patented absolute encoder technology. This only has four active parts which reduces the fault probability. The absolute encoder includes built in redundancy. Position can still be determined (albeit at reduced resolution) even if one part fails. Power is not required to measure position, so any movement without power (mains and battery) will rotate the integral parts and transmit the correct position value once power is restored (mains or battery). Position measurement on older actuator designs used an incremental resolver that did not record position change without mains or 9V battery power.