Method for examining sheet-like objects

Claim 1

Method of examining sheet material for multiple transport, comprising the following steps: a) in a preliminary calibrating operation, a number of samples of one type (10) are successively irradiated by radiation of a current-operated radiation source (12) along at least one predetermined scanning section (62), b) depending on the radiation transparency of the respective sample, a sequence of scanning signals (S) is generated along the scanning/measuring section (20, 64), c) a mean value (SM) is formed from the scanning signals (S) (66), d) from the mean values (SM) for the individual samples of this type, an arithmetic overall mean value or set value (M) is produced (68), e) by repeated entering of these samples, the current (I) for the radiation source is changed until the overall mean value or set value (M) lies within a predetermined value range (M1, M2) (70), f) this current (I) is made up of a basic current (Io) and a differential current (ΔI), which is determined in accordance with a predetermined control function ΔI = f(M), wherein M is the overall mean value or set value, g) in a subsequent testing operation, instead of the samples a sheet material of this type (10) to be tested is irradiated by radiation of the radiation source, fed by the abovementioned current (I), along the predetermined scanning section (84), h) depending on the radiation transparency of the sheet material (10) to be tested, a sequence of testing/scanning signals is generated, i) from the testing/scanning signals, a mean value of the testing/scanning signals of a kind similar to the mean value (SM) is formed (86), j) depending on the comparison of the mean value (SM) of the testing/scanning signals with tolerance limits (61, 62) of the overall mean value or set value (M) for samples of this kind, a detection signal is generated.