A focal plan array system of the bolometer type having means for determining the rate of non-uniformity which comprises: (a) an array of i×j pixel detectors of the bolometer type for sensing scenery radiation; (b) a case which accommodates said array of detectors, said case having a front window that provides exposure to the sensing element of all the i×j pixel detectors to radiation coming from the scenery; (c) at least a portion of column j+1 of blind detectors that are shielded from the scenery by a homogeneous reference surface; (d) reading circuitry for reading indication for the scenery radiation as sensed by each of the i×j detectors of the array, and for reading indication for the non uniformity as sensed by said detectors in column (j+1); (e) a register for recording the radiation values as read from all the detectors within column (j+1); and (f) a processing unit for finding the standard deviation σ of all the values in said register, and for comparing the same to a predetermined threshold Q, wherein a standard deviation above Q being an indication for a non uniformity above the allowed level.