A module for an additive manufacturing system includes a frame, a dispenser configured to deliver a layer of particles over a platen, an energy source to generate a beam to fuse the particles, and a metrology system having a first sensor to measure a property of the surface of layer before being fused and a second sensor to measure a property of the layer after being fused. The dispenser, first sensor, energy source and second sensor are positioned on the frame in order along a first axis, and the dispenser, first sensor, energy source and second sensor are fixed to the frame such that the frame, dispenser, first sensor, energy source and second sensor can be mounted and dismounted as a single unit from a movable support.