Medium Large Transport
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 5
Confusion; Distraction
ATC Issue All Types; Conflict Airborne Conflict; Deviation - Speed All Types
Air Traffic Control Issued New Clearance
Aircraft; ATC Equipment / Nav Facility / Buildings
It was the 1st day that fusion multiple sensor radar was put in use. The perception of speed is skewed with constant updates as opposed to 8 second updates. Aircraft X was on a base leg to Runway 28L indicating 230 KTS. Reported the field in sight and was cleared for the visual approach. Aircraft Y was on vectors for the straight in indicating 210 KTS. Aircraft X slowed to 140 KTS once established on the final. By the time I noticed the overtake it was a little too late. I slowed Aircraft Y and turned him out; but still lost separation. This was my 1st session working final in fusion mode on the 1st day that fusion was activated. I was having a hard time with the perception of speed and Aircraft X's speed reduction was sudden and drastic compared to the normal operations with Aircraft X's type aircraft.In my belief fusion radar is not a reliable resource for working final control. The targets jump and in my opinion don't always give an accurate portrayal of the aircraft's position while the aircraft is in a turn. I recommend that single site radar should be allowed to be used for working final control.
In discussion with reporter; he stated that they do get a speed indication in the data block; but this is not updated as quick as the target moves while using Fusion Radar. On final now they are allowed to use one site radar to separate traffic.
TRACON Controller reports of operational error due to aircraft slowing more than he thought on final; causing the Controller to re-sequence the following aircraft.  Controller also attributes the loss of separation due to the use of Fusion Radar; which was his first time actually using it.