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Every offset printing machine is equipped with a Ã¢€˜DOUBLE SHEET DETECTORÃ¢€™. In older machines, this device is an electro-mechanical device. This tries to check the difference between thickness of single sheet and multiple sheets. Whenever the thickness is more, the switch is activated and the impression of machine goes off. These devices have certain drawbacks:
So the dependability of these Double sheet detectors is very poor and occurrence of Double sheet is quite common.
This double sheet results into a presence of blank sheet in the delivery or in some cases such multiple double sheets jam the machine. The problem of blank sheet is extremely CRITICAL in case of Pharma leaflets. A presence of blank leaflet is considered as critical error
To eliminate this problem, we have Supersonic Double sheet sensors, which work on the principle of sound. These sensors are used in the offset machines manufactured currently in the most advanced countries like Germany and Japan. Ultrasonic double-sheet detectors distinguish between single and double sheets of paper and prevent double sheet or machine damage. A standard double sheet detector, with control unit suitable for the offset printing machine contains supersonic sensor along with a timing sensor and interlocking sensor. The interlocking sensor do not allow the operator to start the machine without removing the double sheet.