An optical signal detection module includes an optical measurement device (OMD) configured to detect an optical emission signal from an emission signal source placed in a signal-detecting position of the OMD. The optical signal detection module also includes a cover moveable between a closed position covering the signal-detecting position and an open position not covering the signal-detecting position. The cover includes an optical reference material that emits a reference emission detectable by the OMD. The cover is configured so that, when the cover is in the closed position, the inner surface is in the signal-detecting position of the OMD so that the OMD detects the reference emission. The optical signal detection module can also include a drive assembly coupled to the cover and configured to move the cover between the open position and the closed position. In some embodiments, the OMD can include a fluorometer.