i didnot closed the system yet
it is still open loop

i just give a speed command of 1 V for example to servo drive - motor turns ,say 200 rpm
and also feedback tacho signal from LM2917

if i run he motor without tacho it runs smooth
with tacho it stop and go

also i turned encoder with my hand left and right
and watched the tacho signal in oscilloscope
i felt it has a delay

i used the simple circuit in National's handbook of LM2917
i didnot add anything

i just wanna know if there's another tacho IC on the market