Circuit arrangements for controlling detector signals in surface inspection systems

A surface inspection system including a plurality of adjacent detectors each having photodetection means and responsive to light received from a different part of the surface to produce a detector signal having an amplitude related to the intensity of the light received, each detector having associated therewith an equalisation circuit arrangement comprising amplification means operable to amplify the associated detector signal, first signal level detection means responsive to an amplified detector signal appearing in the amplification means to control the level of the detector signal applied to the amplification means, second signal level detection means responsive to said amplified detector signal to compensate for components of the detector signal due to the reception of ambient light, and band-pass filter means responsive to said amplified detector signal to compensate for variations in said signal due to changes in the optical gain of the detector by controlling the gain of the amplification means in accordance with said variations, said equalisation circuit arrangements providing a composite output signal at a circuit node to which each equalisation circuit output is connected, and filter means connected to receive signals from said signal node and operable to pass signal variations at high frequencies due to disturbances and to block signal variations at low frequencies due to the combination of output signals of adjacent detectors.

A surface inspection system including a plurality of adjacent detectors each having photodetection means and responsive to light received from a different part of the surface to produce a detector signal having an amplitude related to the intensity of the light received, at least one equalisation circuit arrangement comprising amplification means operable to amplify the composition, or an individual detector, signal, first signal level detection means responsive to an amplified detector signal appearing in the amplification means to control the level of the detector signal applied to the amplification means, second signal level detection means responsive to said amplified detector signal to compensate for components of the detector signal due to the reception of ambient light, and band-pass filter means responsive to said amplified detector signal to compensate for variations in said signal due to changes in the optical gain of the detector by controlling the gain of the amplification means in accordance with said variations, and light diffusing means, through which light from the surface reaches each detector, having anisoptropic diffusing properties arranged to diffuse the light only in the direction of a line connecting adjacent detectors so as to cause light which would otherwise be incident upon the junction between adjacent detectors to be diffused and be incident upon either detector or both detectors.