In geometry|lang=en terms the difference between sector and diameter

is that sector is (geometry) part of a circle, extending to the center while diameter is (geometry) the maximum distance between any two points in a metric space.

As nouns the difference between sector and diameter

is that sector is section while diameter is (geometry) any straight line between two points on the circumference of a circle that passes through the centre/center of the circle.

is that sector is section while amount is the total, aggregate or sum of material (not applicable to discrete numbers or units or items in standard english).