To measure the opacity of sheet material, such as paper, a beam of light is directed against the material and the intensity of any light passing through the material is sensed and converted to a visual readout. A plurality of opacity measurements are made at different areas on the sheet material and, when a selected number of measurements have been made, a readout of the average value of the measurements is generated. The particular technique enables a large number of opacity measurements to be quickly and conveniently made and averaged, and is considerably less complicated and time consuming than opacity measurements which are conventionally made as a function of contrast ratios.
A method of detecting the feeding of doubles in a high speed document counter is disclosed. Also, a method of detecting the feeding of a chain of documents as a batch of documents are fed through a feed path is disclosed.
Holes, tears and missing portions in a sheet, such as a banknote, are detected. The sheet is irradiated with radiation so that the radiation passes through the sheet with a relatively low degree of attenuation in areas where holes, tears and missing portions do not exist and with a relatively high degree of attenuation in areas where holes, tears and missing portions exist. The attenuated radiation is retroreflective back through the sheet and is then received by appropriate photodetectors. Since the sheet is relatively opaque and the radiation passes through the same points in the sheet twice, the contrast between the received radiation having passed through the holes, tears and missing portions and the received radiation passing through the relatively opaque sheet is very high making it simple to differentiate between those areas and thereby to positively detect holes, tears and missing portions in the sheet.
A method and a device for monitoring the transparency of at least a portion of a preassembled laminated pane by analysis of the luminous intensity of the image of a test pattern viewed through the portion of the pane. The luminous intensity, picked up by a detector, of each point of the test pattern viewed through the pane is digitized to produce a number. The numbers obtained for the points of one same image are then averaged, the average obtained being compared with a previously determined theoretical value.
