The High Luminosity upgrade of the Large Hadron Collider will increase the LHC luminosity and with it the density of particles on the detector by an order of magnitude. For protecting the inner silicon detectors of the ATLAS experiment and for monitoring the delivered luminosity, a radiation hard beam monitor has been developed. A set of detectors has been developed based on polycrystalline Chemical Vapor Deposition diamonds and a new dedicated radiation-hard front-end ASIC. To satisfy the requirements imposed by the HL-LHC, our solution is based on segmenting diamond sensors into devices of varying size and reading them out with new multichannel readout ASICs divided into two independent parts, each of them serving one of the tasks of the system. This document describes the system design including detectors, electronics and the ATLAS FPGA FELIX based readout. Additionally, it presents preliminary results of the readout with data from beam tests from 2023 at the SPS beam line at CERN.