We report on the commissioning of a high count rate detector on a synchrotron-based reflectivity instrument on Station 2.3 at the SRS, Daresbury Laboratory. The device is a commercial system which has been electronically modified to give an upper count rate limit of about 3 MHz. The experimental set-up and the electronic hardware are described. Intense X-ray profiles of a good tungsten-carbon multilayer were measured by the modified system and a standard detector to compare their performance. Detection response was also characterised on another versatile diffraction instrument, Station 16.3 as a part of the commissioning. The results presented show that an improved performance from the modifications has been achieved.