ABS problem

Hi guys,wondered if anyone can help on a problem i have,basically the abs light is on and the fault code is 00283 which says its the n/s/f and that it has an intermittent fault in the circuit and if you check the measuring blocks with vag com it shows that when you set off the other 3 sensors start to build up speed but the n/s/f one doesn't register any speed until around 8kmh but after that speed the signal is equal to the other sensors,the sensor head is clean as is the pick up ring too so would this be down to a faulty sensor? Thought it could possibly be down to the gap between the sensor and the ring too,if so is there a specific gap between the sensor and the ring?

cheers